From b9f4bfe19815b3741cf455c2aa9238718da432ab Mon Sep 17 00:00:00 2001
From: Chris Penner <christopher.penner@gmail.com>
Date: Fri, 5 Jul 2024 12:09:00 -0700
Subject: [PATCH] Add unused binding detection to LSP

---
 unison-cli/src/Unison/LSP/FileAnalysis.hs     |  5 ++-
 .../Unison/LSP/FileAnalysis/UnusedBindings.hs | 32 +++++++++++++++++++
 unison-cli/unison-cli.cabal                   |  1 +
 3 files changed, 37 insertions(+), 1 deletion(-)
 create mode 100644 unison-cli/src/Unison/LSP/FileAnalysis/UnusedBindings.hs

diff --git a/unison-cli/src/Unison/LSP/FileAnalysis.hs b/unison-cli/src/Unison/LSP/FileAnalysis.hs
index f5f29b5e2..32a51af4a 100644
--- a/unison-cli/src/Unison/LSP/FileAnalysis.hs
+++ b/unison-cli/src/Unison/LSP/FileAnalysis.hs
@@ -35,6 +35,7 @@ import Unison.KindInference.Error qualified as KindInference
 import Unison.LSP.Conversions
 import Unison.LSP.Conversions qualified as Cv
 import Unison.LSP.Diagnostics (DiagnosticSeverity (..), mkDiagnostic, reportDiagnostics)
+import Unison.LSP.FileAnalysis.UnusedBindings qualified as UnusedBindings
 import Unison.LSP.Orphans ()
 import Unison.LSP.Types
 import Unison.LSP.VFS qualified as VFS
@@ -111,12 +112,14 @@ checkFile doc = runMaybeT do
           & toRangeMap
   let typeSignatureHints = fromMaybe mempty (mkTypeSignatureHints <$> parsedFile <*> typecheckedFile)
   let fileSummary = FileSummary.mkFileSummary parsedFile typecheckedFile
+  let unusedBindingDiagnostics = fileSummary ^.. _Just . to termsBySymbol . folded . _3 . folding (UnusedBindings.analyseTerm fileUri)
+  Debug.debugM Debug.Temp "Unused binding diagnostics" unusedBindingDiagnostics
   let tokenMap = getTokenMap tokens
   conflictWarningDiagnostics <-
     fold <$> for fileSummary \fs ->
       lift $ computeConflictWarningDiagnostics fileUri fs
   let diagnosticRanges =
-        (errDiagnostics <> conflictWarningDiagnostics)
+        (errDiagnostics <> conflictWarningDiagnostics <> unusedBindingDiagnostics)
           & fmap (\d -> (d ^. range, d))
           & toRangeMap
   let fileAnalysis = FileAnalysis {diagnostics = diagnosticRanges, codeActions = codeActionRanges, fileSummary, typeSignatureHints, ..}
diff --git a/unison-cli/src/Unison/LSP/FileAnalysis/UnusedBindings.hs b/unison-cli/src/Unison/LSP/FileAnalysis/UnusedBindings.hs
new file mode 100644
index 000000000..0a9e231c5
--- /dev/null
+++ b/unison-cli/src/Unison/LSP/FileAnalysis/UnusedBindings.hs
@@ -0,0 +1,32 @@
+module Unison.LSP.FileAnalysis.UnusedBindings (analyseTerm) where
+
+import Data.Foldable qualified as Foldable
+import Data.Map qualified as Map
+import Data.Set qualified as Set
+import Language.LSP.Protocol.Types (Diagnostic)
+import Language.LSP.Protocol.Types qualified as Lsp
+import U.Core.ABT (ABT (..))
+import U.Core.ABT qualified as ABT
+import Unison.LSP.Conversions qualified as Cv
+import Unison.LSP.Diagnostics qualified as Diagnostic
+import Unison.Parser.Ann (Ann)
+import Unison.Prelude
+import Unison.Symbol (Symbol)
+import Unison.Term (Term)
+
+analyseTerm :: Lsp.Uri -> Term Symbol Ann -> [Diagnostic]
+analyseTerm fileUri tm =
+  let (unusedVars, _) = ABT.cata alg tm
+   in Map.toList unusedVars & mapMaybe \(v, ann) -> do
+        range <- Cv.annToRange ann
+        pure $ Diagnostic.mkDiagnostic fileUri range Diagnostic.DiagnosticSeverity_Warning ("Unused binding " <> tShow v) []
+  where
+    alg :: (Foldable f, Ord v) => Ann -> ABT f v (Map v Ann, Set v) -> (Map v Ann, Set v)
+    alg ann abt = case abt of
+      Var v -> (mempty, Set.singleton v)
+      Cycle x -> x
+      Abs v (unusedBindings, usedVars) ->
+        if v `Set.member` usedVars
+          then (unusedBindings, Set.delete v usedVars)
+          else (Map.insert v ann unusedBindings, usedVars)
+      Tm fx -> Foldable.fold fx
diff --git a/unison-cli/unison-cli.cabal b/unison-cli/unison-cli.cabal
index a8b820276..94a05b1ea 100644
--- a/unison-cli/unison-cli.cabal
+++ b/unison-cli/unison-cli.cabal
@@ -128,6 +128,7 @@ library
       Unison.LSP.Conversions
       Unison.LSP.Diagnostics
       Unison.LSP.FileAnalysis
+      Unison.LSP.FileAnalysis.UnusedBindings
       Unison.LSP.FoldingRange
       Unison.LSP.Formatting
       Unison.LSP.HandlerUtils