troubleshoot: Detect Nix builds and show LOCALE_ARCHIVE

app/utf8-troubleshoot/Main.hs

@@ -4,6 +4,8 @@
 
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE TypeApplications #-}
 
 #include <HsBaseConfig.h>
 
@@ -12,13 +14,15 @@ module Main (main) where
 import Prelude hiding (print, putStr, putStrLn)
 
 import Control.Exception.Safe (catchIO, tryIO)
-import Control.Monad (filterM, forM_)
+import Control.Monad (filterM, forM_, when)
 import Data.List (sort)
+import Data.Maybe (isJust)
 import Data.Version (showVersion)
 import Foreign.C.String (CString, peekCAString)
 import GHC.IO.Encoding (getLocaleEncoding, initLocaleEncoding)
 import GHC.IO.Encoding.Iconv (localeEncodingName)
 import GHC.Show (showLitString)
+import Language.Haskell.TH.Env (envQ)
 import System.Directory (doesDirectoryExist, doesPathExist, listDirectory)
 import System.Environment (lookupEnv)
 import System.FilePath ((</>))
@@ -57,6 +61,21 @@ showSystem = do
             <> compilerName <> " " <> showVersion compilerVersion
     showEnvVar "TERM"
 
+    -- Nix stuff
+    let builtNix = isJust ($$(envQ @String "NIX_BUILD_TOP"))
+    when builtNix $ do
+      putStrLn "  * Built with Nix"
+    let builtNixShell = isJust ($$(envQ @String "IN_NIX_SHELL"))
+    when builtNixShell $ do
+      putStrLn "  * Built in nix-shell"
+    inNixShell <- isJust <$> lookupEnv "IN_NIX_SHELL"
+    when inNixShell $ do
+      putStrLn "  * Running in nix-shell"
+
+    when (builtNix || builtNixShell) $ do
+      showEnvVar "LOCALE_ARCHIVE"
+
+
 showGhc :: IO ()
 showGhc = do
     putStrLn "# GHC"

package.yaml

@@ -57,6 +57,7 @@ executables:
       - filepath
       - process
       - safe-exceptions
+      - th-env
 
 tests:
   with-utf8-test:

stack.yaml

@@ -4,3 +4,6 @@
 
 resolver: lts-14.25
 packages: [.]
+
+extra-deps:
+  - th-env-0.1.0.1

stack.yaml.lock

@@ -3,7 +3,14 @@
 # For more information, please see the documentation at:
 #   https://docs.haskellstack.org/en/stable/lock_files
 
-packages: []
+packages:
+- completed:
+    hackage: th-env-0.1.0.1@sha256:960423c1951e3c36ba62d5286c7fa859095d41a309c4ea13c2d90abfe5d35bca,1171
+    pantry-tree:
+      size: 370
+      sha256: bfbb41d856bdb5c678f678a4af9ee4a96ad9aa73460444f12d952e9901df2940
+  original:
+    hackage: th-env-0.1.0.1
 snapshots:
 - completed:
     size: 524163