Merge branch 'main' into wasp-ai

2024-12-26 10:35:04 +03:00 · 2023-06-21 11:06:45 +02:00 · 2023-06-21 11:06:45 +02:00 · cfa09771e1
commit cfa09771e1
parent 98fa699011 802e0c5e5d
43 changed files with 948 additions and 458 deletions
--- a/waspc/cli/src/Wasp/Cli/Command.hs
+++ b/waspc/cli/src/Wasp/Cli/Command.hs
@ -1,24 +1,35 @@
+{-# LANGUAGE GADTs #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}

 module Wasp.Cli.Command
  ( Command,
    runCommand,
    CommandError (..),
+
+    -- * Requirements
+
+    -- See "Wasp.Cli.Command.Requires" for documentation.
+    require,
+    Requirable (checkRequirement),
  )
 where

-import Control.Monad.Except (ExceptT, MonadError, runExceptT)
+import Control.Monad.Error.Class (MonadError)
+import Control.Monad.Except (ExceptT, runExceptT)
 import Control.Monad.IO.Class (MonadIO)
+import Control.Monad.State.Strict (StateT, evalStateT, gets, modify)
+import Data.Data (Typeable, cast)
+import Data.Maybe (mapMaybe)
 import System.Exit (exitFailure)
 import Wasp.Cli.Message (cliSendMessage)
 import qualified Wasp.Message as Msg

-newtype Command a = Command {_runCommand :: ExceptT CommandError IO a}
+newtype Command a = Command {_runCommand :: StateT [Requirement] (ExceptT CommandError IO) a}
  deriving (Functor, Applicative, Monad, MonadIO, MonadError CommandError)

 runCommand :: Command a -> IO ()
 runCommand cmd = do
-  runExceptT (_runCommand cmd) >>= \case
+  runExceptT (flip evalStateT [] $ _runCommand cmd) >>= \case
    Left cmdError -> do
      cliSendMessage $ Msg.Failure (_errorTitle cmdError) (_errorMsg cmdError)
      exitFailure
@ -27,3 +38,33 @@ runCommand cmd = do
 -- TODO: What if we want to recognize errors in order to handle them?
 --   Should we add _commandErrorType? Should CommandError be parametrized by it, is that even possible?
 data CommandError = CommandError {_errorTitle :: !String, _errorMsg :: !String}
+
+data Requirement where
+  Requirement :: Requirable r => r -> Requirement
+
+class Typeable r => Requirable r where
+  -- | Check if the requirement is met and return a value representing that
+  -- requirement.
+  --
+  -- This function must always return a value: if the requirement is not met,
+  -- throw a 'CommandError'.
+  checkRequirement :: Command r
+
+-- | Assert that a requirement is met and receive information about that
+-- requirement, if any is offered.
+--
+-- To use, pattern match on the result, e.g.
+--
+-- @
+-- do
+--   HasDbConnection <- require
+-- @
+require :: Requirable r => Command r
+require =
+  Command (gets (mapMaybe cast)) >>= \case
+    (req : _) -> return req
+    [] -> do
+      -- Requirement hasn't been met, so run the check
+      req <- checkRequirement
+      Command $ modify (Requirement req :)
+      return req
--- a/waspc/cli/src/Wasp/Cli/Command/Build.hs
+++ b/waspc/cli/src/Wasp/Cli/Command/Build.hs
@ -13,11 +13,9 @@ import System.Directory
    removeDirectoryRecursive,
  )
 import Wasp.Cli.Command (Command, CommandError (..))
-import Wasp.Cli.Command.Common
-  ( findWaspProjectRootDirFromCwd,
-  )
 import Wasp.Cli.Command.Compile (compileIOWithOptions, printCompilationResult)
 import Wasp.Cli.Command.Message (cliSendMessageC)
+import Wasp.Cli.Command.Require (InWaspProject (InWaspProject), require)
 import qualified Wasp.Cli.Common as Common
 import Wasp.Cli.Message (cliSendMessage)
 import Wasp.CompileOptions (CompileOptions (..))
@ -35,7 +33,7 @@ import Wasp.Project (CompileError, CompileWarning)
 -- Very similar to 'compile'.
 build :: Command ()
 build = do
-  waspProjectDir <- findWaspProjectRootDirFromCwd
+  InWaspProject waspProjectDir <- require
  let buildDir =
        waspProjectDir </> Common.dotWaspDirInWaspProjectDir
          </> Common.buildDirInDotWaspDir
--- a/waspc/cli/src/Wasp/Cli/Command/Clean.hs
+++ b/waspc/cli/src/Wasp/Cli/Command/Clean.hs
@ -10,14 +10,14 @@ import System.Directory
    removeDirectoryRecursive,
  )
 import Wasp.Cli.Command (Command)
-import Wasp.Cli.Command.Common (findWaspProjectRootDirFromCwd)
 import Wasp.Cli.Command.Message (cliSendMessageC)
+import Wasp.Cli.Command.Require (InWaspProject (InWaspProject), require)
 import qualified Wasp.Cli.Common as Common
 import qualified Wasp.Message as Msg

 clean :: Command ()
 clean = do
-  waspProjectDir <- findWaspProjectRootDirFromCwd
+  InWaspProject waspProjectDir <- require
  let dotWaspDirFp = SP.toFilePath $ waspProjectDir SP.</> Common.dotWaspDirInWaspProjectDir
  cliSendMessageC $ Msg.Start "Deleting .wasp/ directory..."
  doesDotWaspDirExist <- liftIO $ doesDirectoryExist dotWaspDirFp
--- a/waspc/cli/src/Wasp/Cli/Command/Common.hs
+++ b/waspc/cli/src/Wasp/Cli/Command/Common.hs
@ -1,52 +1,20 @@
 module Wasp.Cli.Command.Common
-  ( findWaspProjectRootDirFromCwd,
-    findWaspProjectRoot,
-    readWaspCompileInfo,
+  ( readWaspCompileInfo,
    throwIfExeIsNotAvailable,
  )
 where

 import Control.Monad.Except
 import qualified Control.Monad.Except as E
-import Data.Maybe (fromJust)
 import StrongPath (Abs, Dir, Path')
-import qualified StrongPath as SP
 import StrongPath.Operations
-import System.Directory (doesFileExist, doesPathExist, findExecutable, getCurrentDirectory)
-import qualified System.FilePath as FP
+import System.Directory (findExecutable)
 import Wasp.Cli.Command (Command, CommandError (..))
-import Wasp.Cli.Common (dotWaspRootFileInWaspProjectDir)
 import qualified Wasp.Cli.Common as Cli.Common
 import Wasp.Project (WaspProjectDir)
 import Wasp.Util (ifM)
 import qualified Wasp.Util.IO as IOUtil

-findWaspProjectRoot :: Path' Abs (Dir ()) -> Command (Path' Abs (Dir WaspProjectDir))
-findWaspProjectRoot currentDir = do
-  let absCurrentDirFp = SP.fromAbsDir currentDir
-  doesCurrentDirExist <- liftIO $ doesPathExist absCurrentDirFp
-  unless doesCurrentDirExist (throwError notFoundError)
-  let dotWaspRootFilePath = absCurrentDirFp FP.</> SP.fromRelFile dotWaspRootFileInWaspProjectDir
-  isCurrentDirRoot <- liftIO $ doesFileExist dotWaspRootFilePath
-  if isCurrentDirRoot
-    then return $ SP.castDir currentDir
-    else do
-      let parentDir = SP.parent currentDir
-      when (parentDir == currentDir) (throwError notFoundError)
-      findWaspProjectRoot parentDir
-  where
-    notFoundError =
-      CommandError
-        "Wasp command failed"
-        ( "Couldn't find wasp project root - make sure"
-            ++ " you are running this command from a Wasp project."
-        )
-
-findWaspProjectRootDirFromCwd :: Command (Path' Abs (Dir WaspProjectDir))
-findWaspProjectRootDirFromCwd = do
-  absCurrentDir <- liftIO getCurrentDirectory
-  findWaspProjectRoot (fromJust $ SP.parseAbsDir absCurrentDir)
-
 readWaspCompileInfo :: Path' Abs (Dir WaspProjectDir) -> IO String
 readWaspCompileInfo waspDir =
  ifM
--- a/waspc/cli/src/Wasp/Cli/Command/Compile.hs
+++ b/waspc/cli/src/Wasp/Cli/Command/Compile.hs
@ -18,10 +18,8 @@ import Data.List (intercalate)
 import StrongPath (Abs, Dir, Path', (</>))
 import qualified Wasp.AppSpec as AS
 import Wasp.Cli.Command (Command, CommandError (..))
-import Wasp.Cli.Command.Common
-  ( findWaspProjectRootDirFromCwd,
-  )
 import Wasp.Cli.Command.Message (cliSendMessageC)
+import Wasp.Cli.Command.Require (InWaspProject (InWaspProject), require)
 import qualified Wasp.Cli.Common as Common
 import Wasp.Cli.Message (cliSendMessage)
 import Wasp.CompileOptions (CompileOptions (..))
@ -36,7 +34,7 @@ compile = do
  -- TODO: Consider a way to remove the redundancy of finding the project root
  -- here and in compileWithOptions. One option could be to add this to defaultCompileOptions
  -- add make externalCodeDirPath a helper function, along with any others we typically need.
-  waspProjectDir <- findWaspProjectRootDirFromCwd
+  InWaspProject waspProjectDir <- require
  compileWithOptions $ defaultCompileOptions waspProjectDir

 -- | Compiles Wasp project that the current working directory is part of.
@ -47,7 +45,7 @@ compile = do
 -- Finally, throws if there was a compile error, otherwise returns any compile warnings.
 compileWithOptions :: CompileOptions -> Command [CompileWarning]
 compileWithOptions options = do
-  waspProjectDir <- findWaspProjectRootDirFromCwd
+  InWaspProject waspProjectDir <- require
  let outDir =
        waspProjectDir </> Common.dotWaspDirInWaspProjectDir
          </> Common.generatedCodeDirInDotWaspDir
--- a/waspc/cli/src/Wasp/Cli/Command/Db.hs
+++ b/waspc/cli/src/Wasp/Cli/Command/Db.hs
@ -4,8 +4,8 @@ module Wasp.Cli.Command.Db
 where

 import Wasp.Cli.Command (Command, runCommand)
-import Wasp.Cli.Command.Common (findWaspProjectRootDirFromCwd)
 import Wasp.Cli.Command.Compile (compileWithOptions, defaultCompileOptions)
+import Wasp.Cli.Command.Require (DbConnectionEstablished (DbConnectionEstablished), InWaspProject (InWaspProject), require)
 import Wasp.CompileOptions (CompileOptions (generatorWarningsFilter))
 import Wasp.Generator.Monad (GeneratorWarning (GeneratorNeedsMigrationWarning))

@ -19,8 +19,9 @@ runDbCommand = runCommand . makeDbCommand
 makeDbCommand :: Command a -> Command a
 makeDbCommand cmd = do
  -- Ensure code is generated and npm dependencies are installed.
-  waspProjectDir <- findWaspProjectRootDirFromCwd
+  InWaspProject waspProjectDir <- require
  _ <- compileWithOptions $ compileOptions waspProjectDir
+  DbConnectionEstablished <- require
  cmd
  where
    compileOptions waspProjectDir =
--- a/waspc/cli/src/Wasp/Cli/Command/Db/Migrate.hs
+++ b/waspc/cli/src/Wasp/Cli/Command/Db/Migrate.hs
@ -8,10 +8,8 @@ import Control.Monad.Except (ExceptT (ExceptT), liftEither, runExceptT, throwErr
 import Control.Monad.IO.Class (liftIO)
 import StrongPath (Abs, Dir, Path', (</>))
 import Wasp.Cli.Command (Command, CommandError (..))
-import Wasp.Cli.Command.Common
-  ( findWaspProjectRootDirFromCwd,
-  )
 import Wasp.Cli.Command.Message (cliSendMessageC)
+import Wasp.Cli.Command.Require (InWaspProject (InWaspProject), require)
 import qualified Wasp.Cli.Common as Cli.Common
 import Wasp.Generator.Common (ProjectRootDir)
 import Wasp.Generator.DbGenerator.Common (MigrateArgs (..), defaultMigrateArgs)
@ -24,7 +22,7 @@ import Wasp.Project.Db.Migrations (DbMigrationsDir, dbMigrationsDirInWaspProject
 -- The migrate function takes care of copying migrations from the generated project back to the source code.
 migrateDev :: [String] -> Command ()
 migrateDev optionalMigrateArgs = do
-  waspProjectDir <- findWaspProjectRootDirFromCwd
+  InWaspProject waspProjectDir <- require
  let waspDbMigrationsDir = waspProjectDir </> dbMigrationsDirInWaspProjectDir
  let projectRootDir =
        waspProjectDir
--- a/waspc/cli/src/Wasp/Cli/Command/Db/Reset.hs
+++ b/waspc/cli/src/Wasp/Cli/Command/Db/Reset.hs
@ -6,15 +6,15 @@ where
 import Control.Monad.IO.Class (liftIO)
 import StrongPath ((</>))
 import Wasp.Cli.Command (Command)
-import Wasp.Cli.Command.Common (findWaspProjectRootDirFromCwd)
 import Wasp.Cli.Command.Message (cliSendMessageC)
+import Wasp.Cli.Command.Require (InWaspProject (InWaspProject), require)
 import qualified Wasp.Cli.Common as Common
 import Wasp.Generator.DbGenerator.Operations (dbReset)
 import qualified Wasp.Message as Msg

 reset :: Command ()
 reset = do
-  waspProjectDir <- findWaspProjectRootDirFromCwd
+  InWaspProject waspProjectDir <- require
  let genProjectDir =
        waspProjectDir </> Common.dotWaspDirInWaspProjectDir </> Common.generatedCodeDirInDotWaspDir

--- a/waspc/cli/src/Wasp/Cli/Command/Db/Seed.hs
+++ b/waspc/cli/src/Wasp/Cli/Command/Db/Seed.hs
@ -16,16 +16,16 @@ import qualified Wasp.AppSpec.App.Db as AS.Db
 import qualified Wasp.AppSpec.ExtImport as AS.ExtImport
 import qualified Wasp.AppSpec.Valid as ASV
 import Wasp.Cli.Command (Command, CommandError (CommandError))
-import Wasp.Cli.Command.Common (findWaspProjectRootDirFromCwd)
 import Wasp.Cli.Command.Compile (analyze)
 import Wasp.Cli.Command.Message (cliSendMessageC)
+import Wasp.Cli.Command.Require (InWaspProject (InWaspProject), require)
 import qualified Wasp.Cli.Common as Common
 import Wasp.Generator.DbGenerator.Operations (dbSeed)
 import qualified Wasp.Message as Msg

 seed :: Maybe String -> Command ()
 seed maybeUserProvidedSeedName = do
-  waspProjectDir <- findWaspProjectRootDirFromCwd
+  InWaspProject waspProjectDir <- require
  let genProjectDir =
        waspProjectDir </> Common.dotWaspDirInWaspProjectDir </> Common.generatedCodeDirInDotWaspDir

--- a/waspc/cli/src/Wasp/Cli/Command/Db/Studio.hs
+++ b/waspc/cli/src/Wasp/Cli/Command/Db/Studio.hs
@ -8,8 +8,8 @@ import Control.Concurrent.Async (concurrently)
 import Control.Monad.IO.Class (liftIO)
 import StrongPath ((</>))
 import Wasp.Cli.Command (Command)
-import Wasp.Cli.Command.Common (findWaspProjectRootDirFromCwd)
 import Wasp.Cli.Command.Message (cliSendMessageC)
+import Wasp.Cli.Command.Require (InWaspProject (InWaspProject), require)
 import qualified Wasp.Cli.Common as Common
 import Wasp.Generator.DbGenerator.Jobs (runStudio)
 import Wasp.Generator.Job.IO (readJobMessagesAndPrintThemPrefixed)
@ -17,7 +17,7 @@ import qualified Wasp.Message as Msg

 studio :: Command ()
 studio = do
-  waspProjectDir <- findWaspProjectRootDirFromCwd
+  InWaspProject waspProjectDir <- require
  let genProjectDir =
        waspProjectDir </> Common.dotWaspDirInWaspProjectDir </> Common.generatedCodeDirInDotWaspDir

--- a/waspc/cli/src/Wasp/Cli/Command/Deploy.hs
+++ b/waspc/cli/src/Wasp/Cli/Command/Deploy.hs
@ -7,12 +7,12 @@ import Control.Monad.Except (throwError)
 import Control.Monad.IO.Class (liftIO)
 import System.Environment (getExecutablePath)
 import Wasp.Cli.Command (Command, CommandError (CommandError))
-import Wasp.Cli.Command.Common (findWaspProjectRootDirFromCwd)
+import Wasp.Cli.Command.Require (InWaspProject (InWaspProject), require)
 import qualified Wasp.Project.Deployment

 deploy :: [String] -> Command ()
 deploy cmdArgs = do
-  waspProjectDir <- findWaspProjectRootDirFromCwd
+  InWaspProject waspProjectDir <- require
  deployResult <- liftIO $ do
    -- `getExecutablePath` has some caveats:
    --   https://frasertweedale.github.io/blog-fp/posts/2022-05-10-improved-executable-path-queries.html
--- a/waspc/cli/src/Wasp/Cli/Command/Deps.hs
+++ b/waspc/cli/src/Wasp/Cli/Command/Deps.hs
@ -8,8 +8,8 @@ import Control.Monad.IO.Class (liftIO)
 import Wasp.AppSpec (AppSpec)
 import qualified Wasp.AppSpec.App.Dependency as AS.Dependency
 import Wasp.Cli.Command (Command, CommandError (..))
-import Wasp.Cli.Command.Common (findWaspProjectRootDirFromCwd)
 import Wasp.Cli.Command.Compile (defaultCompileOptions)
+import Wasp.Cli.Command.Require (InWaspProject (InWaspProject), require)
 import Wasp.Cli.Terminal (title)
 import qualified Wasp.Generator.NpmDependencies as N
 import qualified Wasp.Generator.ServerGenerator as ServerGenerator
@ -19,7 +19,7 @@ import qualified Wasp.Util.Terminal as Term

 deps :: Command ()
 deps = do
-  waspProjectDir <- findWaspProjectRootDirFromCwd
+  InWaspProject waspProjectDir <- require
  appSpecOrAnalyzerErrors <- liftIO $ analyzeWaspProject waspProjectDir (defaultCompileOptions waspProjectDir)
  appSpec <-
    either
--- a/waspc/cli/src/Wasp/Cli/Command/Dockerfile.hs
+++ b/waspc/cli/src/Wasp/Cli/Command/Dockerfile.hs
@ -7,13 +7,13 @@ import Control.Monad.Except (throwError)
 import Control.Monad.IO.Class (liftIO)
 import qualified Data.Text.IO as T.IO
 import Wasp.Cli.Command (Command, CommandError (..))
-import Wasp.Cli.Command.Common (findWaspProjectRootDirFromCwd)
 import Wasp.Cli.Command.Compile (defaultCompileOptions)
+import Wasp.Cli.Command.Require (InWaspProject (InWaspProject), require)
 import Wasp.Project (compileAndRenderDockerfile)

 printDockerfile :: Command ()
 printDockerfile = do
-  waspProjectDir <- findWaspProjectRootDirFromCwd
+  InWaspProject waspProjectDir <- require
  dockerfileContentOrCompileErrors <- liftIO $ compileAndRenderDockerfile waspProjectDir (defaultCompileOptions waspProjectDir)
  either
    (throwError . CommandError "Displaying Dockerfile failed due to a compilation error in your Wasp project" . unwords)
--- a/waspc/cli/src/Wasp/Cli/Command/Info.hs
+++ b/waspc/cli/src/Wasp/Cli/Command/Info.hs
@ -1,5 +1,3 @@
-{-# LANGUAGE TypeApplications #-}
-
 module Wasp.Cli.Command.Info
  ( info,
  )
@ -12,9 +10,10 @@ import StrongPath.Operations ()
 import System.Directory (getFileSize)
 import qualified Wasp.AppSpec.Valid as ASV
 import Wasp.Cli.Command (Command)
-import Wasp.Cli.Command.Common (findWaspProjectRootDirFromCwd, readWaspCompileInfo)
+import Wasp.Cli.Command.Common (readWaspCompileInfo)
 import Wasp.Cli.Command.Compile (analyze)
 import Wasp.Cli.Command.Message (cliSendMessageC)
+import Wasp.Cli.Command.Require (InWaspProject (InWaspProject), require)
 import Wasp.Cli.Command.Start.Db (getDbSystem)
 import Wasp.Cli.Terminal (title)
 import qualified Wasp.Message as Msg
@ -24,7 +23,7 @@ import qualified Wasp.Util.Terminal as Term

 info :: Command ()
 info = do
-  waspDir <- findWaspProjectRootDirFromCwd
+  InWaspProject waspDir <- require

  compileInfo <- liftIO $ readWaspCompileInfo waspDir
  projectSize <- liftIO $ readDirectorySizeMB waspDir
--- a/waspc/cli/src/Wasp/Cli/Command/Require.hs
+++ b/waspc/cli/src/Wasp/Cli/Command/Require.hs
@ -0,0 +1,98 @@
+module Wasp.Cli.Command.Require
+  ( -- * Asserting Requirements
+
+    -- There are some requirements we want to assert in command code, such as
+    -- ensuring the command is being run inside a wasp project directory. We
+    -- might end up wanting to check each requirement multiple times, especially
+    -- if we want the value from it (like getting the wasp project directory),
+    -- but we also want to avoid duplicating work. Using 'require' results in
+    -- checked requirements being stored so they can be immediately retrieved
+    -- when checking the same requirements additional times.
+    --
+    -- For example, you can check if you are in a wasp project by doing
+    --
+    -- @
+    -- do
+    --   InWaspProject waspProjectDir <- require
+    -- @
+    --
+    -- See instances of 'Requirable' for what kinds of requirements are
+    -- supported. To implement a new requirable type, give your type an instance
+    -- of 'Requirable'.
+    require,
+
+    -- * Requirables
+    Requirable (checkRequirement),
+    DbConnectionEstablished (DbConnectionEstablished),
+    InWaspProject (InWaspProject),
+  )
+where
+
+import Control.Monad (unless, when)
+import Control.Monad.Error.Class (throwError)
+import Control.Monad.IO.Class (liftIO)
+import Data.Data (Typeable)
+import Data.Maybe (fromJust)
+import qualified StrongPath as SP
+import System.Directory (doesFileExist, doesPathExist, getCurrentDirectory)
+import qualified System.FilePath as FP
+import Wasp.Cli.Command (CommandError (CommandError), Requirable (checkRequirement), require)
+import Wasp.Cli.Common (WaspProjectDir)
+import qualified Wasp.Cli.Common as Cli.Common
+import Wasp.Generator.DbGenerator.Operations (isDbRunning)
+
+data DbConnectionEstablished = DbConnectionEstablished deriving (Typeable)
+
+instance Requirable DbConnectionEstablished where
+  checkRequirement = do
+    -- NOTE: 'InWaspProject' does not depend on this requirement, so this
+    -- call to 'require' will not result in an infinite loop.
+    InWaspProject waspProjectDir <- require
+    let outDir = waspProjectDir SP.</> Cli.Common.dotWaspDirInWaspProjectDir SP.</> Cli.Common.generatedCodeDirInDotWaspDir
+    dbIsRunning <- liftIO $ isDbRunning outDir
+    if dbIsRunning
+      then return DbConnectionEstablished
+      else throwError noDbError
+    where
+      noDbError =
+        CommandError
+          "Can not connect to database"
+          ( "The database needs to be running in order to execute this command."
+              ++ " You can easily start a managed dev database with `wasp start db`."
+          )
+
+-- | Require a Wasp project to exist near the current directory. Get the
+-- project directory by pattern matching on the result of 'require':
+--
+-- @
+-- do
+--   InWaspProject waspProjectDir <- require
+-- @
+newtype InWaspProject = InWaspProject (SP.Path' SP.Abs (SP.Dir WaspProjectDir)) deriving (Typeable)
+
+instance Requirable InWaspProject where
+  checkRequirement = do
+    -- Recursively searches up from CWD until @.wasproot@ file is found, or
+    -- throw an error if it is never found.
+    currentDir <- fromJust . SP.parseAbsDir <$> liftIO getCurrentDirectory
+    findWaspProjectRoot currentDir
+    where
+      findWaspProjectRoot currentDir = do
+        let absCurrentDirFp = SP.fromAbsDir currentDir
+        doesCurrentDirExist <- liftIO $ doesPathExist absCurrentDirFp
+        unless doesCurrentDirExist (throwError notFoundError)
+        let dotWaspRootFilePath = absCurrentDirFp FP.</> SP.fromRelFile Cli.Common.dotWaspRootFileInWaspProjectDir
+        isCurrentDirRoot <- liftIO $ doesFileExist dotWaspRootFilePath
+        if isCurrentDirRoot
+          then return $ InWaspProject $ SP.castDir currentDir
+          else do
+            let parentDir = SP.parent currentDir
+            when (parentDir == currentDir) (throwError notFoundError)
+            findWaspProjectRoot parentDir
+
+      notFoundError =
+        CommandError
+          "Wasp command failed"
+          ( "Couldn't find wasp project root - make sure"
+              ++ " you are running this command from a Wasp project."
+          )
--- a/waspc/cli/src/Wasp/Cli/Command/Start.hs
+++ b/waspc/cli/src/Wasp/Cli/Command/Start.hs
@ -10,9 +10,9 @@ import Control.Monad.Except (throwError)
 import Control.Monad.IO.Class (liftIO)
 import StrongPath ((</>))
 import Wasp.Cli.Command (Command, CommandError (..))
-import Wasp.Cli.Command.Common (findWaspProjectRootDirFromCwd)
 import Wasp.Cli.Command.Compile (compile, printWarningsAndErrorsIfAny)
 import Wasp.Cli.Command.Message (cliSendMessageC)
+import Wasp.Cli.Command.Require (DbConnectionEstablished (DbConnectionEstablished), InWaspProject (InWaspProject), require)
 import Wasp.Cli.Command.Watch (watch)
 import qualified Wasp.Cli.Common as Common
 import qualified Wasp.Generator
@ -23,13 +23,15 @@ import Wasp.Project (CompileError, CompileWarning)
 -- It also listens for any file changes and recompiles and restarts generated project accordingly.
 start :: Command ()
 start = do
-  waspRoot <- findWaspProjectRootDirFromCwd
+  InWaspProject waspRoot <- require
  let outDir = waspRoot </> Common.dotWaspDirInWaspProjectDir </> Common.generatedCodeDirInDotWaspDir

  cliSendMessageC $ Msg.Start "Starting compilation and setup phase. Hold tight..."

  warnings <- compile

+  DbConnectionEstablished <- require
+
  cliSendMessageC $ Msg.Start "Listening for file changes..."
  cliSendMessageC $ Msg.Start "Starting up generated project..."

--- a/waspc/cli/src/Wasp/Cli/Command/Start/Db.hs
+++ b/waspc/cli/src/Wasp/Cli/Command/Start/Db.hs
@ -18,9 +18,10 @@ import qualified Wasp.AppSpec.App as AS.App
 import qualified Wasp.AppSpec.App.Db as AS.App.Db
 import qualified Wasp.AppSpec.Valid as ASV
 import Wasp.Cli.Command (Command, CommandError (CommandError))
-import Wasp.Cli.Command.Common (findWaspProjectRootDirFromCwd, throwIfExeIsNotAvailable)
+import Wasp.Cli.Command.Common (throwIfExeIsNotAvailable)
 import Wasp.Cli.Command.Compile (analyze)
 import Wasp.Cli.Command.Message (cliSendMessageC)
+import Wasp.Cli.Command.Require (InWaspProject (InWaspProject), require)
 import Wasp.Cli.Common (WaspProjectDir)
 import qualified Wasp.Message as Msg
 import Wasp.Project.Db (databaseUrlEnvVarName)
@ -36,7 +37,7 @@ import qualified Wasp.Util.Network.Socket as Socket
 -- in Wasp configuration and spins up a database of appropriate type.
 start :: Command ()
 start = do
-  waspProjectDir <- findWaspProjectRootDirFromCwd
+  InWaspProject waspProjectDir <- require
  appSpec <- analyze waspProjectDir

  throwIfCustomDbAlreadyInUse appSpec
--- a/waspc/cli/src/Wasp/Cli/Command/Telemetry/Project.hs
+++ b/waspc/cli/src/Wasp/Cli/Command/Telemetry/Project.hs
@ -31,7 +31,7 @@ import qualified System.Environment as ENV
 import qualified System.Info
 import Wasp.Cli.Command (Command)
 import qualified Wasp.Cli.Command.Call as Command.Call
-import Wasp.Cli.Command.Common (findWaspProjectRootDirFromCwd)
+import Wasp.Cli.Command.Require (InWaspProject (InWaspProject), require)
 import Wasp.Cli.Command.Telemetry.Common (TelemetryCacheDir)
 import Wasp.Cli.Command.Telemetry.User (UserSignature (..))
 import Wasp.Util (ifM)
@ -100,7 +100,9 @@ checkIfEnvValueIsTruthy (Just v)
 newtype ProjectHash = ProjectHash {_projectHashValue :: String} deriving (Show)

 getWaspProjectPathHash :: Command ProjectHash
-getWaspProjectPathHash = ProjectHash . take 16 . sha256 . SP.toFilePath <$> findWaspProjectRootDirFromCwd
+getWaspProjectPathHash = do
+  InWaspProject waspRoot <- require
+  return . ProjectHash . take 16 . sha256 . SP.toFilePath $ waspRoot
  where
    sha256 :: String -> String
    sha256 = show . hashWith SHA256 . ByteStringUTF8.fromString
--- a/waspc/cli/src/Wasp/Cli/Command/Test.hs
+++ b/waspc/cli/src/Wasp/Cli/Command/Test.hs
@ -10,9 +10,9 @@ import Control.Monad.IO.Class (liftIO)
 import StrongPath (Abs, Dir, (</>))
 import StrongPath.Types (Path')
 import Wasp.Cli.Command (Command, CommandError (..))
-import Wasp.Cli.Command.Common (findWaspProjectRootDirFromCwd)
 import Wasp.Cli.Command.Compile (compile)
 import Wasp.Cli.Command.Message (cliSendMessageC)
+import Wasp.Cli.Command.Require (InWaspProject (InWaspProject), require)
 import Wasp.Cli.Command.Watch (watch)
 import qualified Wasp.Cli.Common as Common
 import qualified Wasp.Generator
@ -27,7 +27,7 @@ test _ = throwError $ CommandError "Invalid arguments" "Expected: wasp test clie

 watchAndTest :: (Path' Abs (Dir ProjectRootDir) -> IO (Either String ())) -> Command ()
 watchAndTest testRunner = do
-  waspRoot <- findWaspProjectRootDirFromCwd
+  InWaspProject waspRoot <- require
  let outDir = waspRoot </> Common.dotWaspDirInWaspProjectDir </> Common.generatedCodeDirInDotWaspDir

  cliSendMessageC $ Msg.Start "Starting compilation and setup phase. Hold tight..."
--- a/waspc/examples/todoApp/todoApp.wasp
+++ b/waspc/examples/todoApp/todoApp.wasp
@ -46,7 +46,7 @@ app todoApp {
  },
  server: {
    setupFn: import setup from "@server/serverSetup.js",
-    middlewareConfigFn: import { serverMiddlewareFn } from "@server/serverSetup.js"
+    middlewareConfigFn: import { serverMiddlewareFn } from "@server/serverSetup.js",
  },
  client: {
    rootComponent: import { App } from "@client/App.tsx",
--- a/waspc/headless-test/README.md
+++ b/waspc/headless-test/README.md
@ -23,4 +23,4 @@ npm run example-app:start

 ### How to run in CI

-We set up a GitHub Action to run the test in CI. See `.github/workflows/ci.yml` for details.
+We set up a GitHub Action to run the test in CI. See `.github/workflows/ci.yml` for details.
--- a/waspc/headless-test/package-lock.json
+++ b/waspc/headless-test/package-lock.json
@ -9,27 +9,15 @@
      "version": "1.0.0",
      "license": "ISC",
      "dependencies": {
-        "@prisma/client": "^4.12.0"
+        "@prisma/client": "^4.12.0",
+        "linebyline": "^1.3.0"
      },
      "devDependencies": {
        "@playwright/test": "^1.33.0",
-        "concurrently": "^8.0.1",
        "prisma": "^4.12.0",
        "wait-port": "^1.0.4"
      }
    },
-    "node_modules/@babel/runtime": {
-      "version": "7.21.5",
-      "resolved": "https://registry.npmjs.org/@babel/runtime/-/runtime-7.21.5.tgz",
-      "integrity": "sha512-8jI69toZqqcsnqGGqwGS4Qb1VwLOEp4hz+CXPywcvjs60u3B4Pom/U/7rm4W8tMOYEB+E9wgD0mW1l3r8qlI9Q==",
-      "dev": true,
-      "dependencies": {
-        "regenerator-runtime": "^0.13.11"
-      },
-      "engines": {
-        "node": ">=6.9.0"
-      }
-    },
    "node_modules/@playwright/test": {
      "version": "1.33.0",
      "resolved": "https://registry.npmjs.org/@playwright/test/-/test-1.33.0.tgz",
@ -87,15 +75,6 @@
      "integrity": "sha512-OPs5WnnT1xkCBiuQrZA4+YAV4HEJejmHneyraIaxsbev5yCEr6KMwINNFP9wQeFIw8FWcoTqF3vQsa5CDaI+8Q==",
      "dev": true
    },
-    "node_modules/ansi-regex": {
-      "version": "5.0.1",
-      "resolved": "https://registry.npmjs.org/ansi-regex/-/ansi-regex-5.0.1.tgz",
-      "integrity": "sha512-quJQXlTSUGL2LH9SUXo8VwsY4soanhgo6LNSm84E1LBcE8s3O0wpdiRzyR9z/ZZJMlMWv37qOOb9pdJlMUEKFQ==",
-      "dev": true,
-      "engines": {
-        "node": ">=8"
-      }
-    },
    "node_modules/ansi-styles": {
      "version": "4.3.0",
      "resolved": "https://registry.npmjs.org/ansi-styles/-/ansi-styles-4.3.0.tgz",
@ -139,20 +118,6 @@
        "node": ">=8"
      }
    },
-    "node_modules/cliui": {
-      "version": "8.0.1",
-      "resolved": "https://registry.npmjs.org/cliui/-/cliui-8.0.1.tgz",
-      "integrity": "sha512-BSeNnyus75C4//NQ9gQt1/csTXyo/8Sb+afLAkzAptFuMsod9HFokGNudZpi/oQV73hnVK+sR+5PVRMd+Dr7YQ==",
-      "dev": true,
-      "dependencies": {
-        "string-width": "^4.2.0",
-        "strip-ansi": "^6.0.1",
-        "wrap-ansi": "^7.0.0"
-      },
-      "engines": {
-        "node": ">=12"
-      }
-    },
    "node_modules/color-convert": {
      "version": "2.0.1",
      "resolved": "https://registry.npmjs.org/color-convert/-/color-convert-2.0.1.tgz",
@ -180,49 +145,6 @@
        "node": "^12.20.0 || >=14"
      }
    },
-    "node_modules/concurrently": {
-      "version": "8.0.1",
-      "resolved": "https://registry.npmjs.org/concurrently/-/concurrently-8.0.1.tgz",
-      "integrity": "sha512-Sh8bGQMEL0TAmAm2meAXMjcASHZa7V0xXQVDBLknCPa9TPtkY9yYs+0cnGGgfdkW0SV1Mlg+hVGfXcoI8d3MJA==",
-      "dev": true,
-      "dependencies": {
-        "chalk": "^4.1.2",
-        "date-fns": "^2.29.3",
-        "lodash": "^4.17.21",
-        "rxjs": "^7.8.0",
-        "shell-quote": "^1.8.0",
-        "spawn-command": "0.0.2-1",
-        "supports-color": "^8.1.1",
-        "tree-kill": "^1.2.2",
-        "yargs": "^17.7.1"
-      },
-      "bin": {
-        "conc": "dist/bin/concurrently.js",
-        "concurrently": "dist/bin/concurrently.js"
-      },
-      "engines": {
-        "node": "^14.13.0 || >=16.0.0"
-      },
-      "funding": {
-        "url": "https://github.com/open-cli-tools/concurrently?sponsor=1"
-      }
-    },
-    "node_modules/date-fns": {
-      "version": "2.30.0",
-      "resolved": "https://registry.npmjs.org/date-fns/-/date-fns-2.30.0.tgz",
-      "integrity": "sha512-fnULvOpxnC5/Vg3NCiWelDsLiUc9bRwAPs/+LfTLNvetFCtCTN+yQz15C/fs4AwX1R9K5GLtLfn8QW+dWisaAw==",
-      "dev": true,
-      "dependencies": {
-        "@babel/runtime": "^7.21.0"
-      },
-      "engines": {
-        "node": ">=0.11"
-      },
-      "funding": {
-        "type": "opencollective",
-        "url": "https://opencollective.com/date-fns"
-      }
-    },
    "node_modules/debug": {
      "version": "4.3.4",
      "resolved": "https://registry.npmjs.org/debug/-/debug-4.3.4.tgz",
@ -240,21 +162,6 @@
        }
      }
    },
-    "node_modules/emoji-regex": {
-      "version": "8.0.0",
-      "resolved": "https://registry.npmjs.org/emoji-regex/-/emoji-regex-8.0.0.tgz",
-      "integrity": "sha512-MSjYzcWNOA0ewAHpz0MxpYFvwg6yjy1NG3xteoqz644VCo/RPgnr1/GGt+ic3iJTzQ8Eu3TdM14SawnVUmGE6A==",
-      "dev": true
-    },
-    "node_modules/escalade": {
-      "version": "3.1.1",
-      "resolved": "https://registry.npmjs.org/escalade/-/escalade-3.1.1.tgz",
-      "integrity": "sha512-k0er2gUkLf8O0zKJiAhmkTnJlTvINGv7ygDNPbeIsX/TJjGJZHuh9B2UxbsaEkmlEo9MfhrSzmhIlhRlI2GXnw==",
-      "dev": true,
-      "engines": {
-        "node": ">=6"
-      }
-    },
    "node_modules/fsevents": {
      "version": "2.3.2",
      "resolved": "https://registry.npmjs.org/fsevents/-/fsevents-2.3.2.tgz",
@ -269,15 +176,6 @@
        "node": "^8.16.0 || ^10.6.0 || >=11.0.0"
      }
    },
-    "node_modules/get-caller-file": {
-      "version": "2.0.5",
-      "resolved": "https://registry.npmjs.org/get-caller-file/-/get-caller-file-2.0.5.tgz",
-      "integrity": "sha512-DyFP3BM/3YHTQOCUL/w0OZHR0lpKeGrxotcHWcqNEdnltqFwXVfhEBQ94eIo34AfQpo0rGki4cyIiftY06h2Fg==",
-      "dev": true,
-      "engines": {
-        "node": "6.* || 8.* || >= 10.*"
-      }
-    },
    "node_modules/has-flag": {
      "version": "4.0.0",
      "resolved": "https://registry.npmjs.org/has-flag/-/has-flag-4.0.0.tgz",
@ -287,20 +185,10 @@
        "node": ">=8"
      }
    },
-    "node_modules/is-fullwidth-code-point": {
-      "version": "3.0.0",
-      "resolved": "https://registry.npmjs.org/is-fullwidth-code-point/-/is-fullwidth-code-point-3.0.0.tgz",
-      "integrity": "sha512-zymm5+u+sCsSWyD9qNaejV3DFvhCKclKdizYaJUuHA83RLjb7nSuGnddCHGv0hk+KY7BMAlsWeK4Ueg6EV6XQg==",
-      "dev": true,
-      "engines": {
-        "node": ">=8"
-      }
-    },
-    "node_modules/lodash": {
-      "version": "4.17.21",
-      "resolved": "https://registry.npmjs.org/lodash/-/lodash-4.17.21.tgz",
-      "integrity": "sha512-v2kDEe57lecTulaDIuNTPy3Ry4gLGJ6Z1O3vE1krgXZNrsQ+LFTGHVxVjcXPs17LhbZVGedAJv8XZ1tvj5FvSg==",
-      "dev": true
+    "node_modules/linebyline": {
+      "version": "1.3.0",
+      "resolved": "https://registry.npmjs.org/linebyline/-/linebyline-1.3.0.tgz",
+      "integrity": "sha512-3fpIYMrSU77OCf89hjXKuCx6vGwgWEu4N5DDCGqgZ1BF0HYy9V8IbQb/3+VWIU17iBQ83qQoUokH0AhPMOTi7w=="
    },
    "node_modules/ms": {
      "version": "2.1.2",
@ -337,101 +225,6 @@
        "node": ">=14.17"
      }
    },
-    "node_modules/regenerator-runtime": {
-      "version": "0.13.11",
-      "resolved": "https://registry.npmjs.org/regenerator-runtime/-/regenerator-runtime-0.13.11.tgz",
-      "integrity": "sha512-kY1AZVr2Ra+t+piVaJ4gxaFaReZVH40AKNo7UCX6W+dEwBo/2oZJzqfuN1qLq1oL45o56cPaTXELwrTh8Fpggg==",
-      "dev": true
-    },
-    "node_modules/require-directory": {
-      "version": "2.1.1",
-      "resolved": "https://registry.npmjs.org/require-directory/-/require-directory-2.1.1.tgz",
-      "integrity": "sha512-fGxEI7+wsG9xrvdjsrlmL22OMTTiHRwAMroiEeMgq8gzoLC/PQr7RsRDSTLUg/bZAZtF+TVIkHc6/4RIKrui+Q==",
-      "dev": true,
-      "engines": {
-        "node": ">=0.10.0"
-      }
-    },
-    "node_modules/rxjs": {
-      "version": "7.8.1",
-      "resolved": "https://registry.npmjs.org/rxjs/-/rxjs-7.8.1.tgz",
-      "integrity": "sha512-AA3TVj+0A2iuIoQkWEK/tqFjBq2j+6PO6Y0zJcvzLAFhEFIO3HL0vls9hWLncZbAAbK0mar7oZ4V079I/qPMxg==",
-      "dev": true,
-      "dependencies": {
-        "tslib": "^2.1.0"
-      }
-    },
-    "node_modules/shell-quote": {
-      "version": "1.8.1",
-      "resolved": "https://registry.npmjs.org/shell-quote/-/shell-quote-1.8.1.tgz",
-      "integrity": "sha512-6j1W9l1iAs/4xYBI1SYOVZyFcCis9b4KCLQ8fgAGG07QvzaRLVVRQvAy85yNmmZSjYjg4MWh4gNvlPujU/5LpA==",
-      "dev": true,
-      "funding": {
-        "url": "https://github.com/sponsors/ljharb"
-      }
-    },
-    "node_modules/spawn-command": {
-      "version": "0.0.2-1",
-      "resolved": "https://registry.npmjs.org/spawn-command/-/spawn-command-0.0.2-1.tgz",
-      "integrity": "sha512-n98l9E2RMSJ9ON1AKisHzz7V42VDiBQGY6PB1BwRglz99wpVsSuGzQ+jOi6lFXBGVTCrRpltvjm+/XA+tpeJrg==",
-      "dev": true
-    },
-    "node_modules/string-width": {
-      "version": "4.2.3",
-      "resolved": "https://registry.npmjs.org/string-width/-/string-width-4.2.3.tgz",
-      "integrity": "sha512-wKyQRQpjJ0sIp62ErSZdGsjMJWsap5oRNihHhu6G7JVO/9jIB6UyevL+tXuOqrng8j/cxKTWyWUwvSTriiZz/g==",
-      "dev": true,
-      "dependencies": {
-        "emoji-regex": "^8.0.0",
-        "is-fullwidth-code-point": "^3.0.0",
-        "strip-ansi": "^6.0.1"
-      },
-      "engines": {
-        "node": ">=8"
-      }
-    },
-    "node_modules/strip-ansi": {
-      "version": "6.0.1",
-      "resolved": "https://registry.npmjs.org/strip-ansi/-/strip-ansi-6.0.1.tgz",
-      "integrity": "sha512-Y38VPSHcqkFrCpFnQ9vuSXmquuv5oXOKpGeT6aGrr3o3Gc9AlVa6JBfUSOCnbxGGZF+/0ooI7KrPuUSztUdU5A==",
-      "dev": true,
-      "dependencies": {
-        "ansi-regex": "^5.0.1"
-      },
-      "engines": {
-        "node": ">=8"
-      }
-    },
-    "node_modules/supports-color": {
-      "version": "8.1.1",
-      "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-8.1.1.tgz",
-      "integrity": "sha512-MpUEN2OodtUzxvKQl72cUF7RQ5EiHsGvSsVG0ia9c5RbWGL2CI4C7EpPS8UTBIplnlzZiNuV56w+FuNxy3ty2Q==",
-      "dev": true,
-      "dependencies": {
-        "has-flag": "^4.0.0"
-      },
-      "engines": {
-        "node": ">=10"
-      },
-      "funding": {
-        "url": "https://github.com/chalk/supports-color?sponsor=1"
-      }
-    },
-    "node_modules/tree-kill": {
-      "version": "1.2.2",
-      "resolved": "https://registry.npmjs.org/tree-kill/-/tree-kill-1.2.2.tgz",
-      "integrity": "sha512-L0Orpi8qGpRG//Nd+H90vFB+3iHnue1zSSGmNOOCh1GLJ7rUKVwV2HvijphGQS2UmhUZewS9VgvxYIdgr+fG1A==",
-      "dev": true,
-      "bin": {
-        "tree-kill": "cli.js"
-      }
-    },
-    "node_modules/tslib": {
-      "version": "2.5.0",
-      "resolved": "https://registry.npmjs.org/tslib/-/tslib-2.5.0.tgz",
-      "integrity": "sha512-336iVw3rtn2BUK7ORdIAHTyxHGRIHVReokCR3XjbckJMK7ms8FysBfhLR8IXnAgy7T0PTPNBWKiH514FOW/WSg==",
-      "dev": true
-    },
    "node_modules/wait-port": {
      "version": "1.0.4",
      "resolved": "https://registry.npmjs.org/wait-port/-/wait-port-1.0.4.tgz",
@ -448,59 +241,6 @@
      "engines": {
        "node": ">=10"
      }
-    },
-    "node_modules/wrap-ansi": {
-      "version": "7.0.0",
-      "resolved": "https://registry.npmjs.org/wrap-ansi/-/wrap-ansi-7.0.0.tgz",
-      "integrity": "sha512-YVGIj2kamLSTxw6NsZjoBxfSwsn0ycdesmc4p+Q21c5zPuZ1pl+NfxVdxPtdHvmNVOQ6XSYG4AUtyt/Fi7D16Q==",
-      "dev": true,
-      "dependencies": {
-        "ansi-styles": "^4.0.0",
-        "string-width": "^4.1.0",
-        "strip-ansi": "^6.0.0"
-      },
-      "engines": {
-        "node": ">=10"
-      },
-      "funding": {
-        "url": "https://github.com/chalk/wrap-ansi?sponsor=1"
-      }
-    },
-    "node_modules/y18n": {
-      "version": "5.0.8",
-      "resolved": "https://registry.npmjs.org/y18n/-/y18n-5.0.8.tgz",
-      "integrity": "sha512-0pfFzegeDWJHJIAmTLRP2DwHjdF5s7jo9tuztdQxAhINCdvS+3nGINqPd00AphqJR/0LhANUS6/+7SCb98YOfA==",
-      "dev": true,
-      "engines": {
-        "node": ">=10"
-      }
-    },
-    "node_modules/yargs": {
-      "version": "17.7.2",
-      "resolved": "https://registry.npmjs.org/yargs/-/yargs-17.7.2.tgz",
-      "integrity": "sha512-7dSzzRQ++CKnNI/krKnYRV7JKKPUXMEh61soaHKg9mrWEhzFWhFnxPxGl+69cD1Ou63C13NUPCnmIcrvqCuM6w==",
-      "dev": true,
-      "dependencies": {
-        "cliui": "^8.0.1",
-        "escalade": "^3.1.1",
-        "get-caller-file": "^2.0.5",
-        "require-directory": "^2.1.1",
-        "string-width": "^4.2.3",
-        "y18n": "^5.0.5",
-        "yargs-parser": "^21.1.1"
-      },
-      "engines": {
-        "node": ">=12"
-      }
-    },
-    "node_modules/yargs-parser": {
-      "version": "21.1.1",
-      "resolved": "https://registry.npmjs.org/yargs-parser/-/yargs-parser-21.1.1.tgz",
-      "integrity": "sha512-tVpsJW7DdjecAiFpbIB1e3qxIQsE6NoPc5/eTdrbbIC4h0LVsWhnoa3g+m2HclBIujHzsxZ4VJVA+GUuc2/LBw==",
-      "dev": true,
-      "engines": {
-        "node": ">=12"
-      }
    }
  }
 }
--- a/waspc/headless-test/package.json
+++ b/waspc/headless-test/package.json
@ -4,7 +4,7 @@
  "description": "",
  "main": "index.js",
  "scripts": {
-    "example-app:start": "concurrently \"npm:example-app:start-db\" \"npm:example-app:start-app\" --kill-others-on-fail",
+    "example-app:start": "node start.js",
    "example-app:start-db": "npm run example-app:cleanup-db && cd ./examples/todoApp && cabal run wasp-cli start db",
    "example-app:start-app": "npm run example-app:wait-for-db && cd ./examples/todoApp && cabal run wasp-cli db migrate-dev && cabal run wasp-cli start",
    "example-app:wait-for-db": "sleep 5 && ./node_modules/.bin/wait-port 5432",
@ -15,9 +15,9 @@
  "license": "ISC",
  "devDependencies": {
    "@playwright/test": "^1.33.0",
-    "concurrently": "^8.0.1",
    "prisma": "^4.12.0",
-    "wait-port": "^1.0.4"
+    "wait-port": "^1.0.4",
+    "linebyline": "^1.3.0"
  },
  "dependencies": {
    "@prisma/client": "^4.12.0"
--- a/waspc/headless-test/start.js
+++ b/waspc/headless-test/start.js
@ -0,0 +1,31 @@
+const cp = require('child_process');
+const readline = require('linebyline');
+
+function spawn(name, cmd, args, done) {
+  const spawnOptions = {
+    detached: true,
+  };
+  const proc = cp.spawn(cmd, args, spawnOptions);
+
+  // We close stdin stream on the new process because otherwise the start-app
+  // process hangs.
+  // See https://github.com/wasp-lang/wasp/pull/1218#issuecomment-1599098272.
+  proc.stdin.destroy();
+
+  readline(proc.stdout).on('line', data => {
+    console.log(`\x1b[0m\x1b[33m[${name}][out]\x1b[0m ${data}`);
+  });
+  readline(proc.stderr).on('line', data => {
+    console.log(`\x1b[0m\x1b[33m[${name}][err]\x1b[0m ${data}`);
+  });
+  proc.on('exit', done);
+}
+
+// Exit if either child fails
+const cb = (code) => {
+  if (code !== 0) {
+    process.exit(code);
+  }
+}
+spawn('app', 'npm', ['run', 'example-app:start-app'], cb);
+spawn('db', 'npm', ['run', 'example-app:start-db'], cb)
--- a/waspc/src/Wasp/Generator/DbGenerator/Jobs.hs
+++ b/waspc/src/Wasp/Generator/DbGenerator/Jobs.hs
@ -7,6 +7,7 @@ module Wasp.Generator.DbGenerator.Jobs
    runStudio,
    reset,
    seed,
+    dbExecuteTest,
    migrateStatus,
    asPrismaCliArgs,
  )
@ -113,6 +114,19 @@ seed projectDir seedName =
    projectDir
    (const ["db", "seed"])

+-- | Checks if the DB is running and connectable by running
+-- `prisma db execute --stdin --schema <path to db schema>`.
+--  Runs the command in the generated server code directory so it has access to the database URL.
+--
+-- Since nothing is passed to stdin, `prisma db execute` just runs an empty
+-- SQL command, which works perfectly for checking if the database is running.
+dbExecuteTest :: Path' Abs (Dir ProjectRootDir) -> J.Job
+dbExecuteTest projectDir =
+  let absSchemaPath = projectDir </> dbSchemaFileInProjectRootDir
+   in runPrismaCommandAsDbJob
+        projectDir
+        (const ["db", "execute", "--stdin", "--schema", SP.fromAbsFile absSchemaPath])
+
 -- | Runs `prisma studio` - Prisma's db inspector.
 runStudio :: Path' Abs (Dir ProjectRootDir) -> J.Job
 runStudio projectDir = runPrismaCommandAsDbJob projectDir $ \schema ->
--- a/waspc/src/Wasp/Generator/DbGenerator/Operations.hs
+++ b/waspc/src/Wasp/Generator/DbGenerator/Operations.hs
@ -6,6 +6,7 @@ module Wasp.Generator.DbGenerator.Operations
    areAllMigrationsAppliedToDb,
    dbReset,
    dbSeed,
+    isDbRunning,
  )
 where

@ -134,6 +135,16 @@ dbSeed genProjectDir seedName = do
    ExitSuccess -> Right ()
    ExitFailure c -> Left $ "Failed with exit code " <> show c

+isDbRunning ::
+  Path' Abs (Dir ProjectRootDir) ->
+  IO Bool
+isDbRunning genProjectDir = do
+  chan <- newChan
+  exitCode <- DbJobs.dbExecuteTest genProjectDir chan
+  -- NOTE: We only care if the command succeeds or fails, so we don't look at
+  -- the exit code or stdout/stderr for the process.
+  return $ exitCode == ExitSuccess
+
 generatePrismaClients :: Path' Abs (Dir ProjectRootDir) -> IO (Either String ())
 generatePrismaClients projectRootDir = do
  generateResult <- liftA2 (>>) generatePrismaClientForServer generatePrismaClientForWebApp projectRootDir
--- a/waspc/waspc.cabal
+++ b/waspc/waspc.cabal
@ -354,8 +354,13 @@ library waspls
    Wasp.LSP.Handlers
    Wasp.LSP.Diagnostic
    Wasp.LSP.Completion
-    Wasp.LSP.Util
+    Wasp.LSP.Completions.Common
+    Wasp.LSP.Completions.DictKeyCompletion
+    Wasp.LSP.Completions.ExprCompletion
+    Wasp.LSP.SignatureHelp
    Wasp.LSP.Syntax
+    Wasp.LSP.TypeInference
+    Wasp.LSP.Util
  build-depends:
      base
    , aeson
@ -370,6 +375,7 @@ library waspls
    , text
    , transformers ^>=0.5.6.2
    , utf8-string
+    , unordered-containers
    , waspc

 library cli-lib
@ -434,6 +440,7 @@ library cli-lib
    Wasp.Cli.Command.Deploy
    Wasp.Cli.Command.Dockerfile
    Wasp.Cli.Command.Info
+    Wasp.Cli.Command.Require
    Wasp.Cli.Command.Start
    Wasp.Cli.Command.Start.Db
    Wasp.Cli.Command.Telemetry
--- a/waspc/waspls/src/Wasp/LSP/Completion.hs
+++ b/waspc/waspls/src/Wasp/LSP/Completion.hs
@ -3,18 +3,18 @@ module Wasp.LSP.Completion
  )
 where

-import Control.Lens ((?~), (^.))
+import Control.Lens ((^.))
 import Control.Monad.Log.Class (MonadLog (logM))
 import Control.Monad.State.Class (MonadState, gets)
-import Data.Maybe (maybeToList)
-import qualified Data.Text as Text
+import Data.List (sortOn)
 import qualified Language.LSP.Types as LSP
 import qualified Language.LSP.Types.Lens as LSP
-import Wasp.Analyzer.Parser.CST (SyntaxNode)
-import qualified Wasp.Analyzer.Parser.CST as S
-import Wasp.Analyzer.Parser.CST.Traverse
-import Wasp.LSP.ServerState
-import Wasp.LSP.Syntax (findChild, isAtExprPlace, lexemeAt, lspPositionToOffset, showNeighborhood, toOffset)
+import Wasp.Analyzer.Parser.CST.Traverse (fromSyntaxForest)
+import Wasp.LSP.Completions.Common (CompletionContext (..), CompletionProvider)
+import qualified Wasp.LSP.Completions.DictKeyCompletion as DictKeyCompletion
+import qualified Wasp.LSP.Completions.ExprCompletion as ExprCompletion
+import Wasp.LSP.ServerState (ServerState, cst, currentWaspSource)
+import Wasp.LSP.Syntax (locationAtOffset, lspPositionToOffset, showNeighborhood)

 -- | Get the list of completions at a (line, column) position in the source.
 getCompletionsAtPosition ::
@ -30,76 +30,18 @@ getCompletionsAtPosition position = do
    Just syntax -> do
      let offset = lspPositionToOffset src position
      -- 'location' is a traversal through the syntax tree that points to 'position'
-      let location = toOffset offset (fromSyntaxForest syntax)
+      let location = locationAtOffset offset (fromSyntaxForest syntax)
+      logM $ "[getCompletionsAtPosition] position=" ++ show position ++ " offset=" ++ show offset
      logM $ "[getCompletionsAtPosition] neighborhood=\n" ++ showNeighborhood location
-      exprCompletions <-
-        if isAtExprPlace location
-          then do
-            logM $ "[getCompletionsAtPosition] offset=" ++ show offset ++ " position=" ++ show position ++ " atExpr=True"
-            getExprCompletions src syntax
-          else do
-            logM $ "[getCompletionsAtPosition] offset=" ++ show offset ++ " position=" ++ show position ++ " atExpr=False"
-            return []
-      let completions = exprCompletions
-      return completions
+      let completionContext = CompletionContext {_src = src, _cst = syntax}
+      let runCompletionProvider = \cp -> cp completionContext location
+      completionItems <- concat <$> mapM runCompletionProvider completionProviders
+      return $ sortOn (^. LSP.label) completionItems

-- | If the location is at an expression, find declaration names in the file
-- and return them as autocomplete suggestions
--
-- TODO: include completions for enum variants (use standard type defs from waspc)
-getExprCompletions ::
-  (MonadLog m) =>
-  String ->
-  [SyntaxNode] ->
-  m [LSP.CompletionItem]
-getExprCompletions src syntax = do
-  let declNames = findDeclNames src syntax
-  logM $ "[getExprCompletions] declnames=" ++ show declNames
-  return $
-    map
-      ( \(name, typ) ->
-          makeBasicCompletionItem (Text.pack name)
-            & (LSP.kind ?~ LSP.CiVariable)
-            & (LSP.detail ?~ Text.pack (":: " ++ typ ++ " (declaration type)"))
-      )
-      declNames
-
-- | Search through the CST and collect all @(declName, declType)@ pairs.
-findDeclNames :: String -> [SyntaxNode] -> [(String, String)]
-findDeclNames src syntax = traverseForDeclNames $ fromSyntaxForest syntax
-  where
-    traverseForDeclNames :: Traversal -> [(String, String)]
-    traverseForDeclNames t = case kindAt t of
-      S.Program -> maybe [] traverseForDeclNames $ down t
-      S.Decl ->
-        let declNameAndType = maybeToList $ getDeclNameAndType t
-         in declNameAndType ++ maybe [] traverseForDeclNames (right t)
-      _ -> maybe [] traverseForDeclNames $ right t
-    getDeclNameAndType :: Traversal -> Maybe (String, String)
-    getDeclNameAndType t = do
-      nameT <- findChild S.DeclName t
-      typeT <- findChild S.DeclType t
-      return (lexemeAt src nameT, lexemeAt src typeT)
-
-- | Create a completion item containing only a label.
-makeBasicCompletionItem :: Text.Text -> LSP.CompletionItem
-makeBasicCompletionItem name =
-  LSP.CompletionItem
-    { _label = name,
-      _kind = Nothing,
-      _tags = Nothing,
-      _detail = Nothing,
-      _documentation = Nothing,
-      _deprecated = Nothing,
-      _preselect = Nothing,
-      _sortText = Nothing,
-      _filterText = Nothing,
-      _insertText = Nothing,
-      _insertTextFormat = Nothing,
-      _insertTextMode = Nothing,
-      _textEdit = Nothing,
-      _additionalTextEdits = Nothing,
-      _commitCharacters = Nothing,
-      _command = Nothing,
-      _xdata = Nothing
-    }
+-- | List of all 'CompletionProvider's to use. We break this up into separate
+-- modules because the code for each can be pretty unrelated.
+completionProviders :: (MonadLog m) => [CompletionProvider m]
+completionProviders =
+  [ ExprCompletion.getCompletions,
+    DictKeyCompletion.getCompletions
+  ]
--- a/waspc/waspls/src/Wasp/LSP/Completions/Common.hs
+++ b/waspc/waspls/src/Wasp/LSP/Completions/Common.hs
@ -0,0 +1,51 @@
+{-# LANGUAGE TemplateHaskell #-}
+
+module Wasp.LSP.Completions.Common
+  ( CompletionProvider,
+    CompletionContext (..),
+    src,
+    cst,
+    makeBasicCompletionItem,
+  )
+where
+
+import Control.Lens (makeClassy)
+import qualified Data.Text as Text
+import qualified Language.LSP.Types as LSP
+import Wasp.Analyzer.Parser.CST (SyntaxNode)
+import Wasp.Analyzer.Parser.CST.Traverse (Traversal)
+
+-- | A function that providers 'LSP.CompletionItems' at a location.
+type CompletionProvider m = CompletionContext -> Traversal -> m [LSP.CompletionItem]
+
+data CompletionContext = CompletionContext
+  { _src :: String,
+    _cst :: [SyntaxNode]
+  }
+  deriving (Eq, Show)
+
+makeClassy 'CompletionContext
+
+-- | Create a completion item containing only a label. Use lenses and 'Control.Lens.(?~)'
+-- to set more fields, if desired.
+makeBasicCompletionItem :: Text.Text -> LSP.CompletionItem
+makeBasicCompletionItem name =
+  LSP.CompletionItem
+    { _label = name,
+      _kind = Nothing,
+      _tags = Nothing,
+      _detail = Nothing,
+      _documentation = Nothing,
+      _deprecated = Nothing,
+      _preselect = Nothing,
+      _sortText = Nothing,
+      _filterText = Nothing,
+      _insertText = Nothing,
+      _insertTextFormat = Nothing,
+      _insertTextMode = Nothing,
+      _textEdit = Nothing,
+      _additionalTextEdits = Nothing,
+      _commitCharacters = Nothing,
+      _command = Nothing,
+      _xdata = Nothing
+    }
--- a/waspc/waspls/src/Wasp/LSP/Completions/DictKeyCompletion.hs
+++ b/waspc/waspls/src/Wasp/LSP/Completions/DictKeyCompletion.hs
@ -0,0 +1,74 @@
+module Wasp.LSP.Completions.DictKeyCompletion
+  ( getCompletions,
+  )
+where
+
+import Control.Lens ((?~), (^.))
+import Control.Monad.Log.Class (MonadLog (logM))
+import Data.Bifunctor (Bifunctor (second))
+import qualified Data.HashMap.Strict as M
+import qualified Data.Text as Text
+import qualified Language.LSP.Types as LSP
+import qualified Language.LSP.Types.Lens as LSP
+import qualified Wasp.Analyzer.Parser.CST as S
+import Wasp.Analyzer.Parser.CST.Traverse (Traversal)
+import qualified Wasp.Analyzer.Parser.CST.Traverse as T
+import Wasp.Analyzer.Type (Type)
+import qualified Wasp.Analyzer.Type as Type
+import Wasp.LSP.Completions.Common (CompletionProvider, makeBasicCompletionItem)
+import qualified Wasp.LSP.Completions.Common as Ctx
+import Wasp.LSP.Syntax (hasLeft, parentIs)
+import Wasp.LSP.TypeInference (inferTypeAtLocation)
+import Wasp.LSP.Util (allP, anyP)
+
+-- | If the location is at a place where a dictionary key is expected, find
+-- the list of keys that are allowed in the dictionary around the location and
+-- return them as completion items.
+--
+-- The allowed keys are found by determining the expected type for the
+-- dictionary and getting the keys from that, assuming it is a 'Type.DictType'.
+-- No completions are made if there is no expected type or if the expected type
+-- is not a 'Type.DictType'.
+--
+-- See 'Wasp.LSP.TypeHint' for how the expected type for the dictionary is
+-- determined.
+getCompletions :: (MonadLog m) => CompletionProvider m
+getCompletions context location =
+  if not $ isDictKeyExpectedAtLocation location
+    then do
+      logM "[DictKeyCompletion] not at dict key"
+      return []
+    else do
+      logM "[DictKeyCompletion] at dict key"
+      getCompletionsAtDictKey
+  where
+    getCompletionsAtDictKey = case inferTypeAtLocation (context ^. Ctx.src) location of
+      Nothing -> do
+        logM "[DictKeyCompletion] no type hint, can not suggest keys"
+        return []
+      Just (Type.DictType fieldMap) -> do
+        logM "[DictKeyCompletion] found dict type hint"
+        return $ map completionItemFromDictField $ listDictFields fieldMap
+      Just _ -> do
+        logM "[DictKeyCompletion] found non-dict type hint, no keys to suggest"
+        return []
+
+    completionItemFromDictField (key, keyType) =
+      -- The user sees "key", but when they accept the completion "key: " is
+      -- inserted, via the @insertText@ field.
+      makeBasicCompletionItem (Text.pack key)
+        T.& (LSP.kind ?~ LSP.CiField)
+        T.& (LSP.detail ?~ Text.pack (":: " ++ show keyType))
+        T.& (LSP.insertText ?~ Text.pack (key ++ ": "))
+
+isDictKeyExpectedAtLocation :: Traversal -> Bool
+isDictKeyExpectedAtLocation =
+  anyP
+    [ parentIs S.Dict,
+      allP [parentIs S.DictEntry, not . hasLeft S.DictKey]
+    ]
+
+-- | List the (key, valuetype) pairs for a type. Returns an empty list for
+-- everything except a 'Type.DictType'.
+listDictFields :: M.HashMap String Type.DictEntryType -> [(String, Type)]
+listDictFields fieldMap = map (second Type.dictEntryType) $ M.toList fieldMap
--- a/waspc/waspls/src/Wasp/LSP/Completions/ExprCompletion.hs
+++ b/waspc/waspls/src/Wasp/LSP/Completions/ExprCompletion.hs
@ -0,0 +1,60 @@
+module Wasp.LSP.Completions.ExprCompletion
+  ( getCompletions,
+  )
+where
+
+import Control.Lens ((?~), (^.))
+import Control.Monad.Log.Class (MonadLog (logM))
+import Data.Maybe (maybeToList)
+import qualified Data.Text as Text
+import qualified Language.LSP.Types as LSP
+import qualified Language.LSP.Types.Lens as LSP
+import Wasp.Analyzer.Parser.CST (SyntaxNode)
+import qualified Wasp.Analyzer.Parser.CST as S
+import Wasp.Analyzer.Parser.CST.Traverse
+import Wasp.LSP.Completions.Common (CompletionProvider, makeBasicCompletionItem)
+import qualified Wasp.LSP.Completions.Common as Ctx
+import Wasp.LSP.Syntax (findChild, isAtExprPlace, lexemeAt)
+
+-- | If the location is at an expression, find declaration names in the file
+-- and return them as completion items.
+--
+-- TODO: include completions for enum variants (use standard type defs from waspc)
+getCompletions :: (MonadLog m) => CompletionProvider m
+getCompletions context location =
+  if not (isAtExprPlace location)
+    then do
+      logM "[ExprCompletion] not at expression"
+      return []
+    else do
+      logM "[ExprCompletion] at expression"
+      let declNames = getDeclNamesAndTypes (context ^. Ctx.src) (context ^. Ctx.cst)
+      logM $ "[ExprCompletion] declnames=" ++ show declNames
+      return $
+        map
+          ( \(name, typ) ->
+              makeBasicCompletionItem (Text.pack name)
+                & (LSP.kind ?~ LSP.CiVariable)
+                & (LSP.detail ?~ Text.pack (":: " ++ typ ++ " (declaration type)"))
+          )
+          declNames
+
+-- | Search through the CST and collect all @(declName, declType)@ pairs.
+getDeclNamesAndTypes :: String -> [SyntaxNode] -> [(String, String)]
+getDeclNamesAndTypes src syntax = traverseForDeclNames $ fromSyntaxForest syntax
+  where
+    traverseForDeclNames :: Traversal -> [(String, String)]
+    traverseForDeclNames t = case kindAt t of
+      S.Program -> maybe [] traverseForDeclNames $ down t
+      S.Decl ->
+        let declNameAndType = maybeToList $ getDeclNameAndType t
+         in declNameAndType ++ maybe [] traverseForDeclNames (right t)
+      _ -> maybe [] traverseForDeclNames $ right t
+
+    -- @getDeclNameAndType t@ expects 't' to be at a 'S.Decl' node. It finds the
+    -- lexemes for the 'S.DeclName' and 'S.DeclType'.
+    getDeclNameAndType :: Traversal -> Maybe (String, String)
+    getDeclNameAndType t = do
+      nameT <- findChild S.DeclName t
+      typeT <- findChild S.DeclType t
+      return (lexemeAt src nameT, lexemeAt src typeT)
--- a/waspc/waspls/src/Wasp/LSP/Handlers.hs
+++ b/waspc/waspls/src/Wasp/LSP/Handlers.hs
@ -4,6 +4,7 @@ module Wasp.LSP.Handlers
    didChangeHandler,
    didSaveHandler,
    completionHandler,
+    signatureHelpHandler,
  )
 where

@ -22,6 +23,7 @@ import Wasp.LSP.Completion (getCompletionsAtPosition)
 import Wasp.LSP.Diagnostic (concreteParseErrorToDiagnostic, waspErrorToDiagnostic)
 import Wasp.LSP.ServerM (ServerError (..), ServerM, Severity (..), gets, liftLSP, modify, throwError)
 import Wasp.LSP.ServerState (cst, currentWaspSource, latestDiagnostics)
+import Wasp.LSP.SignatureHelp (getSignatureHelpAtPosition)

 -- LSP notification and request handlers

@ -65,6 +67,15 @@ completionHandler =
    completions <- getCompletionsAtPosition $ request ^. LSP.params . LSP.position
    respond $ Right $ LSP.InL $ LSP.List completions

+signatureHelpHandler :: Handlers ServerM
+signatureHelpHandler =
+  LSP.requestHandler LSP.STextDocumentSignatureHelp $ \request respond -> do
+    -- NOTE: lsp-types 1.4.0.1 forgot to add lenses for SignatureHelpParams so
+    -- we have to get the position out the painful way.
+    let LSP.SignatureHelpParams {_position = position} = request ^. LSP.params
+    signatureHelp <- getSignatureHelpAtPosition position
+    respond $ Right signatureHelp
+
 -- | Does not directly handle a notification or event, but should be run when
 -- text document content changes.
 --
--- a/waspc/waspls/src/Wasp/LSP/Server.hs
+++ b/waspc/waspls/src/Wasp/LSP/Server.hs
@ -20,6 +20,7 @@ import Wasp.LSP.Handlers
 import Wasp.LSP.ServerConfig (ServerConfig)
 import Wasp.LSP.ServerM (ServerError (..), ServerM, Severity (..), runServerM)
 import Wasp.LSP.ServerState (ServerState)
+import Wasp.LSP.SignatureHelp (signatureHelpRetriggerCharacters, signatureHelpTriggerCharacters)

 lspServerHandlers :: LSP.Handlers ServerM
 lspServerHandlers =
@ -28,7 +29,8 @@ lspServerHandlers =
      didOpenHandler,
      didSaveHandler,
      didChangeHandler,
-      completionHandler
+      completionHandler,
+      signatureHelpHandler
    ]

 serve :: Maybe FilePath -> IO ()
@ -100,7 +102,9 @@ lspServerOptions :: LSP.Options
 lspServerOptions =
  (def :: LSP.Options)
    { LSP.textDocumentSync = Just syncOptions,
-      LSP.completionTriggerCharacters = Just [':']
+      LSP.completionTriggerCharacters = Just [':', ' '],
+      LSP.signatureHelpTriggerCharacters = signatureHelpTriggerCharacters,
+      LSP.signatureHelpRetriggerCharacters = signatureHelpRetriggerCharacters
    }

 -- | Options to tell the client how to update the server about the state of text
--- a/waspc/waspls/src/Wasp/LSP/SignatureHelp.hs
+++ b/waspc/waspls/src/Wasp/LSP/SignatureHelp.hs
@ -0,0 +1,257 @@
+module Wasp.LSP.SignatureHelp
+  ( getSignatureHelpAtPosition,
+    signatureHelpTriggerCharacters,
+    signatureHelpRetriggerCharacters,
+  )
+where
+
+import Control.Applicative ((<|>))
+import Control.Lens ((^.))
+import Control.Monad (guard)
+import Control.Monad.Log.Class (MonadLog, logM)
+import Control.Monad.State.Class (MonadState, gets)
+import Control.Monad.Trans.Class (lift)
+import Control.Monad.Trans.Maybe (MaybeT (runMaybeT))
+import qualified Data.HashMap.Strict as M
+import Data.List (elemIndex, foldl', intersperse)
+import Data.Maybe (mapMaybe)
+import Data.String (IsString (fromString))
+import qualified Data.Text as Text
+import qualified Language.LSP.Types as LSP
+import Text.Printf (printf)
+import Wasp.Analyzer.Parser.CST.Traverse (Traversal, fromSyntaxForest)
+import Wasp.Analyzer.Type (Type)
+import qualified Wasp.Analyzer.Type as Type
+import Wasp.LSP.ServerState (ServerState, cst, currentWaspSource)
+import Wasp.LSP.Syntax (locationAtOffset, lspPositionToOffset)
+import Wasp.LSP.TypeInference (ExprPathStep (DictKey, List, Tuple), findExprPathToLocation, findTypeForPath)
+import Wasp.LSP.Util (hoistMaybe)
+
+-- | Configuration for 'LSP.Options', used in "Wasp.LSP.Server".
+--
+-- When the client types one of these characters, it will send a SignatureHelp
+-- request. It is configured so that signatures will display when starting a
+-- dictionary, list, tuple, or starting a new field/value in the container.
+signatureHelpTriggerCharacters :: Maybe [Char]
+signatureHelpTriggerCharacters = Just "{[(:,"
+
+-- | Configuration for 'LSP.Options', used in "Wasp.LSP.Server".
+--
+-- When a client is already displaying signature help, typing one of these
+-- characters will cause it to update the displayed signature by sending a new
+-- SignatureHelp request. It is configured so that signatures will update when
+-- ending a dictionary, list, or  tuple.
+--
+-- NOTE: 'signatureHelpTriggerCharacters' are also counted as retrigger characters.
+signatureHelpRetriggerCharacters :: Maybe [Char]
+signatureHelpRetriggerCharacters = Just "}])"
+
+-- | Get 'LSP.SignatureHelp' at a position in the wasp file. The signature
+-- displays the type of the "container" that the position is in, if any.
+--
+-- SignatureHelp is usually displayed as a popup near the text you are typing,
+-- and highlights the part of the signature you are writing.
+--
+-- A container is an expression that holds other values, such as dictionaries
+-- and lists.
+--
+-- The parameter field of the signature is used for which part of the container
+-- the position is within, such as a key for a dictionary.
+getSignatureHelpAtPosition ::
+  (MonadState ServerState m, MonadLog m) =>
+  LSP.Position ->
+  m LSP.SignatureHelp
+getSignatureHelpAtPosition position = do
+  src <- gets (^. currentWaspSource)
+  gets (^. cst) >>= \case
+    Nothing ->
+      -- No CST in the server state, can't create a signature.
+      return emptyHelp
+    Just syntax ->
+      let offset = lspPositionToOffset src position
+          location = locationAtOffset offset (fromSyntaxForest syntax)
+       in getSignatureHelpAtLocation src location
+  where
+    getSignatureHelpAtLocation src location =
+      findSignatureAtLocation src location >>= \case
+        Nothing -> do
+          logM "[getSignatureHelpAtPosition] no signature found"
+          return emptyHelp
+        Just signature -> do
+          logM "[getSignatureHelpAtPosition] found a signature"
+          getLspSignatureFromSignature signature
+
+    getLspSignatureFromSignature signature = do
+      let signatureFragments = signatureToFragments signature
+      let params = getLspParamsInfoFromFragments signatureFragments
+      let activeParam = signatureParam signature >>= findActiveParameterIndex signatureFragments
+      logM $ "[getSignatureHelpAtPosition] at param idx = " ++ show activeParam ++ " params = " ++ show params
+      let signatureInformation =
+            LSP.SignatureInformation
+              { _label = Text.pack $ showFragments signatureFragments,
+                _parameters = Just $ LSP.List params,
+                -- NOTE: VSCode highlights the 0th parameter if activeParameter, so
+                -- it's set to -1 when we don't want any parameter highlighted.
+                _activeParameter = activeParam <|> Just (-1),
+                _documentation = Nothing
+              }
+      return $
+        LSP.SignatureHelp
+          { _signatures = LSP.List [signatureInformation],
+            _activeSignature = Just 0,
+            _activeParameter = Nothing
+          }
+
+    emptyHelp =
+      LSP.SignatureHelp
+        { _signatures = LSP.List [],
+          _activeSignature = Nothing,
+          _activeParameter = Nothing
+        }
+
+-- | 'Signature' describes the expected type at a specific location inside of
+-- a container in a wasp file. Every signature includes the type of the container
+-- surrounding the location. For example, the container type for a cursor
+-- positioned inside of a dictionary would be the type of the dictionary.
+--
+-- When the location is at a more specific place inside of the container--for
+-- example, immediately after @key: @ in a dictionary--then we say the location
+-- is at a parameter, and the parameter is described in relation to the container
+-- with an 'ExprPathStep'.
+data Signature = Signature
+  { signatureType :: !Type,
+    signatureParam :: !(Maybe ExprPathStep)
+  }
+  deriving (Eq, Show)
+
+-- | @'findSignatureAtLocation' sourceCode location@ runs type inference at the
+-- given location to try to find a 'Signature'.
+--
+-- To do this, two types are inferred: the /location type/ and the
+-- /container type/. The location type is the type expected exactly at the given
+-- location and the container type is the type of that contains the location
+-- type. For example, if the cursor is at the 2nd entry of a tuple with type
+-- @(string, number)@, then the tip type is @number@ and the parent type is
+-- that tuple type.
+--
+-- Then we check if the cursor is just inside a container or at a parameter
+-- inside a container. It's in a container when the location type is a container
+-- or if there is no container type.
+findSignatureAtLocation ::
+  (MonadLog m) =>
+  String ->
+  Traversal ->
+  m (Maybe Signature)
+findSignatureAtLocation src location = runMaybeT $ do
+  exprPath <- hoistMaybe $ findExprPathToLocation src location
+  lift $ logM $ "[SignatureHelp] at expr path " ++ show exprPath
+  guard $ not $ null exprPath
+  case exprPath of
+    [path] -> do
+      containerType <- hoistMaybe (findTypeForPath [path])
+      return $ Signature containerType Nothing
+    path -> do
+      -- Using init/last here is OK since we know @path@ has at least 2 elements.
+      locationType <- hoistMaybe $ findTypeForPath path
+      if isContainerType locationType
+        then return $ Signature locationType Nothing
+        else do
+          containerType <- hoistMaybe $ findTypeForPath $ init path
+          return $ Signature containerType (Just $ last path)
+  where
+    isContainerType :: Type -> Bool
+    isContainerType (Type.DictType _) = True
+    isContainerType (Type.ListType _) = True
+    isContainerType Type.TupleType {} = True
+    isContainerType _ = False
+
+-- | A fragment of the text representation of a signature, with information
+-- for finding the spans of parameters inside of the text representation.
+--
+-- This is used as an intermediate form between 'Signature' and the response
+-- format that the LSP specifies.
+data SignatureFragment
+  = -- | A plaintext fragment of a signature.
+    PlaintextFragment !String
+  | -- | A fragment that contains the text for a parameter of the signature. The
+    -- parameter is identified by the 'ExprPathStep'.
+    ParamFragment !ExprPathStep !String
+  deriving (Eq, Show)
+
+fragmentText :: SignatureFragment -> String
+fragmentText (PlaintextFragment text) = text
+fragmentText (ParamFragment _ text) = text
+
+fragmentParam :: SignatureFragment -> Maybe ExprPathStep
+fragmentParam (PlaintextFragment _) = Nothing
+fragmentParam (ParamFragment key _) = Just key
+
+instance IsString SignatureFragment where
+  fromString string = PlaintextFragment string
+
+-- | Convert the container type of a signature to a list of fragments.
+--
+-- To avoid unreadably long signatures, dictionary types inside of the container
+-- type are written as @{ ... }@.
+signatureToFragments :: Signature -> [SignatureFragment]
+signatureToFragments signature = case signatureType signature of
+  Type.DictType fieldMap
+    | M.null fieldMap -> ["{}"]
+    | otherwise ->
+        let fields = intersperse ",\n  " (map fieldToFragment (M.toList fieldMap))
+         in concat [["{\n  "], fields, ["\n}"]]
+  Type.ListType inner -> ["[", ParamFragment List (showInnerType inner), "]"]
+  Type.TupleType (a, b, cs) ->
+    let fieldTypes = a : b : cs
+        fields = intersperse ", " (zipWith (\n -> ParamFragment (Tuple n) . showInnerType) [0 ..] fieldTypes)
+     in concat [["("], fields, [")"]]
+  typ -> [fromString (show typ)]
+  where
+    showInnerType :: IsString s => Type -> s
+    showInnerType (Type.DictType _) = "{ ... }"
+    showInnerType typ = fromString (show typ)
+
+    fieldToFragment :: (String, Type.DictEntryType) -> SignatureFragment
+    fieldToFragment (key, Type.DictRequired typ) =
+      ParamFragment (DictKey key) $ printf "%s: %s" key (showInnerType typ :: String)
+    fieldToFragment (key, Type.DictOptional typ) =
+      ParamFragment (DictKey key) $ printf "%s?: %s" key (showInnerType typ :: String)
+
+-- | Convert a list of fragments to a string by concatenating the text of each
+-- fragment.
+showFragments :: [SignatureFragment] -> String
+showFragments = concatMap fragmentText
+
+-- | Search through a list of fragments to find the parameters.
+--
+-- The LSP wants the starting and ending offset of each parameter in the signature
+-- help text (computed in 'showFragments'), so this function also has to keep
+-- track of the 0-based offset into the final text.
+getLspParamsInfoFromFragments :: [SignatureFragment] -> [LSP.ParameterInformation]
+getLspParamsInfoFromFragments fragments =
+  reverse $ map labelToInfo $ snd $ foldl' go (0, []) fragments
+  where
+    -- A left fold is used because offset needs to increase as you go right across
+    -- the list. This means the parameter list needs to be reversed after the fold
+    -- so that they are in the same order as the parameters in the fragments.
+    go :: (LSP.UInt, [LSP.ParameterLabel]) -> SignatureFragment -> (LSP.UInt, [LSP.ParameterLabel])
+    go (offset, labels) (PlaintextFragment text) = (offset + fromIntegral (length text), labels)
+    go (offset, labels) (ParamFragment _ text) =
+      let end = offset + fromIntegral (length text)
+       in (end, LSP.ParameterLabelOffset offset end : labels)
+
+    labelToInfo :: LSP.ParameterLabel -> LSP.ParameterInformation
+    labelToInfo label =
+      LSP.ParameterInformation
+        { _label = label,
+          _documentation = Nothing
+        }
+
+-- | Find the index of the active parameter in a list of fragments.
+--
+-- NOTE: This function computes the index into the parameter list, not the
+-- fragment list. This is why 'PlaintextFragment's are filtered out of the
+-- list before indexing (via @mapMaybe fragmentParam@).
+findActiveParameterIndex :: [SignatureFragment] -> ExprPathStep -> Maybe LSP.UInt
+findActiveParameterIndex fragments key =
+  fromIntegral <$> elemIndex key (mapMaybe fragmentParam fragments)
--- a/waspc/waspls/src/Wasp/LSP/Syntax.hs
+++ b/waspc/waspls/src/Wasp/LSP/Syntax.hs
@ -3,7 +3,9 @@ module Wasp.LSP.Syntax

    -- | Module with utilities for working with/looking for patterns in CSTs
    lspPositionToOffset,
-    toOffset,
+    locationAtOffset,
+    parentIs,
+    hasLeft,
    isAtExprPlace,
    lexemeAt,
    findChild,
@ -16,6 +18,7 @@ import Data.List (find, intercalate)
 import qualified Language.LSP.Types as J
 import qualified Wasp.Analyzer.Parser.CST as S
 import Wasp.Analyzer.Parser.CST.Traverse
+import Wasp.LSP.Util (allP, anyP)

 -- | @lspPositionToOffset srcString position@ returns 0-based offset from the
 -- start of @srcString@ to the specified line and column.
@ -27,21 +30,31 @@ lspPositionToOffset srcString (J.Position l c) =

 -- | Move to the node containing the offset.
 --
-- This tries to prefer non-trivia tokens where possible. If the offset falls
-- exactly between two tokens, it choses the left-most non-trivia token.
-toOffset :: Int -> Traversal -> Traversal
-toOffset targetOffset start = go $ bottom start
+-- If the offset falls on the border between two nodes, it tries to first choose
+-- the leftmost non-trivia token, and then the leftmost token.
+locationAtOffset :: Int -> Traversal -> Traversal
+locationAtOffset targetOffset start = go $ bottom start
  where
    go :: Traversal -> Traversal
    go at
      | offsetAt at == targetOffset = at
      | offsetAfter at > targetOffset = at
-      | offsetAfter at == targetOffset && not (S.syntaxKindIsTrivia (kindAt at)) =
-          at
+      | offsetAfter at == targetOffset =
+          if not $ S.syntaxKindIsTrivia $ kindAt at
+            then at
+            else case at & next of
+              Just at' | not (S.syntaxKindIsTrivia (kindAt at')) -> at'
+              _ -> at
      -- If @at & next@ fails, the input doesn't contain the offset, so just
      -- return the last node instead.
      | otherwise = maybe at go $ at & next

+parentIs :: S.SyntaxKind -> Traversal -> Bool
+parentIs k t = Just k == parentKind t
+
+hasLeft :: S.SyntaxKind -> Traversal -> Bool
+hasLeft k t = k `elem` map kindAt (leftSiblings t)
+
 -- | Check whether a position in a CST is somewhere an expression belongs. These
 -- locations (as of now) are:
 --
@ -50,14 +63,13 @@ toOffset targetOffset start = go $ bottom start
 -- - Parent is a List
 -- - Parent is a Tuple
 isAtExprPlace :: Traversal -> Bool
-isAtExprPlace t =
-  (parentIs S.DictEntry && hasLeft S.DictKey)
-    || parentIs S.List
-    || (parentIs S.Decl && hasLeft S.DeclType && hasLeft S.DeclName)
-    || parentIs S.Tuple
-  where
-    parentIs k = Just k == parentKind t
-    hasLeft k = k `elem` map kindAt (leftSiblings t)
+isAtExprPlace =
+  anyP
+    [ allP [parentIs S.DictEntry, hasLeft S.DictKey],
+      allP [parentIs S.Decl, hasLeft S.DeclType, hasLeft S.DeclName],
+      parentIs S.List,
+      parentIs S.Tuple
+    ]

 -- | Show the nodes around the current position
 --
--- a/waspc/waspls/src/Wasp/LSP/TypeInference.hs
+++ b/waspc/waspls/src/Wasp/LSP/TypeInference.hs
@ -0,0 +1,124 @@
+module Wasp.LSP.TypeInference
+  ( -- * Inferred types for CST locations
+    inferTypeAtLocation,
+
+    -- * Lower level pieces
+    ExprPath,
+    ExprPathStep (..),
+    findExprPathToLocation,
+    findTypeForPath,
+  )
+where
+
+import Control.Monad (guard)
+import Data.Foldable (find)
+import qualified Data.HashMap.Strict as M
+import qualified Wasp.Analyzer.Parser.CST as S
+import Wasp.Analyzer.Parser.CST.Traverse (Traversal)
+import qualified Wasp.Analyzer.Parser.CST.Traverse as T
+import Wasp.Analyzer.StdTypeDefinitions (stdTypes)
+import Wasp.Analyzer.Type (Type)
+import qualified Wasp.Analyzer.Type as Type
+import Wasp.Analyzer.TypeDefinitions (DeclType (dtBodyType), getDeclType)
+import Wasp.LSP.Syntax (lexemeAt)
+
+inferTypeAtLocation :: String -> Traversal -> Maybe Type
+inferTypeAtLocation src location = findExprPathToLocation src location >>= findTypeForPath
+
+-- | A "path" through wasp expressions to a certain location.
+--
+-- === __Example__
+-- For the code
+--
+-- @
+-- app todoApp {
+--   auth: {
+--     usernameAndPassword: |
+--                          ^
+--   }
+-- }
+-- @
+--
+-- The path to the cursor would be @[Decl "app", DictKey "auth", DictKey "usernameAndPassword"]@.
+type ExprPath = [ExprPathStep]
+
+data ExprPathStep
+  = -- | @Decl declType@. Enter a declaration of type @declType@.
+    Decl !String
+  | -- | @DictKey key@. Enter a dictionary *and* its key @key@.
+    DictKey !String
+  | -- | Enter a value inside a list.
+    List
+  | -- | @Tuple idx@. Enter the @idx@-th value inside of a tuple.
+    Tuple !Int
+  deriving (Eq, Show)
+
+-- | This function only depends on the syntax to the left of the location, and
+-- tries to be as lenient as possible in finding paths.
+findExprPathToLocation :: String -> Traversal -> Maybe ExprPath
+findExprPathToLocation src location = reverse <$> go location
+  where
+    -- Recursively travel up the syntax tree, accumlating a path in reverse
+    -- order. Each recursion adds at most one new path component.
+    go :: Traversal -> Maybe ExprPath
+    go t = case T.up t of
+      Nothing -> Just [] -- Top level of the syntax reached.
+      Just t' -> case T.kindAt t' of
+        S.Program -> Just []
+        S.Decl -> do
+          typLoc <- find ((== S.DeclType) . T.kindAt) $ T.leftSiblings t
+          let typ = lexemeAt src typLoc
+          -- Stop recursion after finding a Decl
+          return [Decl typ]
+        S.DictEntry -> case find ((== S.DictKey) . T.kindAt) $ T.leftSiblings t of
+          Just keyLoc -> do
+            -- There is a key to the left, so @t@ is the value for that key.
+            let key = lexemeAt src keyLoc
+            t'' <- T.up t'
+            guard $ T.kindAt t'' == S.Dict
+            (DictKey key :) <$> go t''
+          Nothing -> go t'
+        S.List -> (List :) <$> go t' -- Inside a list.
+        S.Tuple -> do
+          -- Inside a tuple, number of expression nodes to the left is the tuple
+          -- index that @t@ is part of.
+          let nExprsBefore = length $ filter (S.syntaxKindIsExpr . T.kindAt) $ T.leftSiblings t
+          (Tuple nExprsBefore :) <$> go t'
+        _ -> go t' -- Found some other node, just ignore it and continue the tree.
+
+-- | Get the type in 'stdTypes' for the expression path. The path must start
+-- with a 'Decl', otherwise 'Nothing' is returned. If the path's decl does not
+-- exist in 'stdTypes', 'Nothing' is returned.
+--
+-- === __Example__
+-- >>> findTypeForPath [Dict "app", Key "auth", Key "methods", Key "usernameAndPassword"]
+-- Just (Type.DictType { fields = M.fromList [("configFn", Type.DictOptional { dictEntryType = Type.ExtImportType })] })
+findTypeForPath :: ExprPath -> Maybe Type
+findTypeForPath (Decl declType : originalPath) = do
+  topType <- getDeclType declType stdTypes
+  go (dtBodyType topType) originalPath
+  where
+    -- @go parentType path@ returns the result of following @path@ starting at
+    -- @parentType@.
+    go :: Type -> ExprPath -> Maybe Type
+    go typ [] = Just typ
+    go _ (Decl _ : _) = Nothing -- Can't follow a decl in the middle of a path.
+    go typ (DictKey key : path) =
+      case typ of
+        Type.DictType fields -> do
+          -- Get the type of the field corresponding to the key.
+          typ' <- Type.dictEntryType <$> fields M.!? key
+          go typ' path
+        _ -> Nothing -- Not a dict type, can't use Key here.
+    go typ (List : path) = case typ of
+      Type.ListType typ' -> go typ' path -- Use the inner type of the list.
+      _ -> Nothing -- Not a list type, can't use List here.
+    go typ (Tuple idx : path) = case typ of
+      Type.TupleType (a, b, cs) -> case idx of
+        -- Follow the current type (by index) of the tuple.
+        0 -> go a path
+        1 -> go b path
+        n | n < length cs + 2 -> go (cs !! (n - 2)) path
+        _ -> Nothing -- Index is too large for the tuple type.
+      _ -> Nothing -- Not a tuple type, can't use Tuple here.
+findTypeForPath _ = Nothing -- Doesn't start with a Decl.
--- a/waspc/waspls/src/Wasp/LSP/Util.hs
+++ b/waspc/waspls/src/Wasp/LSP/Util.hs
@ -1,6 +1,14 @@
-module Wasp.LSP.Util (waspSourceRegionToLspRange, waspPositionToLspPosition) where
+module Wasp.LSP.Util
+  ( allP,
+    anyP,
+    hoistMaybe,
+    waspSourceRegionToLspRange,
+    waspPositionToLspPosition,
+  )
+where

 import Control.Lens ((+~))
+import Control.Monad.Trans.Maybe (MaybeT (MaybeT))
 import Data.Function ((&))
 import qualified Language.LSP.Types as LSP
 import qualified Language.LSP.Types.Lens as LSP
@ -20,3 +28,15 @@ waspPositionToLspPosition (W.SourcePosition ln col) =
    { _line = fromIntegral ln - 1,
      _character = fromIntegral col - 1
    }
+
+-- | Check if all the supplied predicates are true.
+allP :: Foldable f => f (a -> Bool) -> a -> Bool
+allP preds x = all ($ x) preds
+
+-- | Check if any of the supplied predicates are true.
+anyP :: Foldable f => f (a -> Bool) -> a -> Bool
+anyP preds x = any ($ x) preds
+
+-- | Lift a 'Maybe' into a 'MaybeT' monad transformer.
+hoistMaybe :: Applicative m => Maybe a -> MaybeT m a
+hoistMaybe = MaybeT . pure
--- a/waspc/waspls/test/Wasp/LSP/CompletionTest.hs
+++ b/waspc/waspls/test/Wasp/LSP/CompletionTest.hs
@ -106,12 +106,19 @@ runCompletionTest testInput =
      fmtedCompletionItems = map fmtCompletionItem completionItems

      fmtCompletionItem :: LSP.CompletionItem -> String
-      fmtCompletionItem item =
-        unwords
-          [ printf "label={%s}" (show $ item ^. LSP.label),
-            printf "kind={%s}" (show $ item ^. LSP.kind),
-            printf "detail={%s}" (show $ item ^. LSP.detail)
-          ]
+      fmtCompletionItem item = unwords fields
+        where
+          fields =
+            concat
+              [ field "label" LSP.label,
+                optionalField "kind" LSP.kind,
+                optionalField "detail" LSP.detail,
+                optionalField "insertText" LSP.insertText
+              ]
+          field label getter = [printf "%s={%s}" (label :: String) (show $ item ^. getter)]
+          optionalField label getter = case item ^. getter of
+            Nothing -> []
+            Just v -> [printf "%s={%s}" (label :: String) (show v)]
   in "Completion items:\n" ++ unlines (map ("  " <>) fmtedCompletionItems)

 -- | Parses a completion test case into a pair of the wasp source code to
--- a/waspc/waspls/test/Wasp/LSP/completionTests/at_dict_key.golden
+++ b/waspc/waspls/test/Wasp/LSP/completionTests/at_dict_key.golden
@ -1 +1,3 @@
 Completion items:
+  label={"path"} kind={CiField} detail={":: string"} insertText={"path: "}
+  label={"to"} kind={CiField} detail={":: page (declaration type)"} insertText={"to: "}
--- a/waspc/waspls/test/Wasp/LSP/completionTests/at_dict_key.wasp
+++ b/waspc/waspls/test/Wasp/LSP/completionTests/at_dict_key.wasp
@ -6,8 +6,8 @@ app todoApp {
  title: "todo!",
 }

-route MainRoute { path: "/", | }
-                             ^
+route MainRoute { | }
+                  ^
 page MainPage {
  component: import { MainPage } from "@client/MainPage.jsx",
 }
--- a/waspc/waspls/test/Wasp/LSP/completionTests/dict_key_duplicate.golden
+++ b/waspc/waspls/test/Wasp/LSP/completionTests/dict_key_duplicate.golden
@ -0,0 +1,3 @@
+Completion items:
+  label={"path"} kind={CiField} detail={":: string"} insertText={"path: "}
+  label={"to"} kind={CiField} detail={":: page (declaration type)"} insertText={"to: "}
--- a/waspc/waspls/test/Wasp/LSP/completionTests/dict_key_duplicate.wasp
+++ b/waspc/waspls/test/Wasp/LSP/completionTests/dict_key_duplicate.wasp
@ -0,0 +1,14 @@
+//! test/completion
+app todoApp {
+  wasp: {
+    version: "^0.10.5", 
+  },
+  title: "todo!",
+}
+
+// we suggest all keys of a dictionary, even when some are already used  
+route MainRoute { path: "/", | }
+                             ^
+page MainPage {
+  component: import { MainPage } from "@client/MainPage.jsx",
+}
--- a/waspc/waspls/test/Wasp/LSP/completionTests/route_to.golden
+++ b/waspc/waspls/test/Wasp/LSP/completionTests/route_to.golden
@ -1,4 +1,4 @@
 Completion items:
-  label={"todoApp"} kind={Just CiVariable} detail={Just ":: app (declaration type)"}
-  label={"MainRoute"} kind={Just CiVariable} detail={Just ":: route (declaration type)"}
-  label={"MainPage"} kind={Just CiVariable} detail={Just ":: page (declaration type)"}
+  label={"MainPage"} kind={CiVariable} detail={":: page (declaration type)"}
+  label={"MainRoute"} kind={CiVariable} detail={":: route (declaration type)"}
+  label={"todoApp"} kind={CiVariable} detail={":: app (declaration type)"}