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Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC

Commits:

9284a1f7

by Simon Hengel at 2026-06-23T05:55:33-04:00

Don't use global variables to address concurrency bugs! (fixes #27234)

This was originally introduce with
88f38b03025386f0f1e8f5861eed67d80495168a to address #17922.

In this specific case a better fix would have been to synchronize on
stderr:

    withHandle_ "stderrSupportsAnsiColors" stderr $ \ _ -> do
      ...

But apparently the dependency on `terminfo` was removed in
32ab07bf3d6ce45e8ea5b55e8095174a6b42a7f0, preventing #17922 in the first
place.

2 changed files:

compiler/GHC/Driver/DynFlags.hs
compiler/GHC/SysTools/Terminal.hs

Changes:

compiler/GHC/Driver/DynFlags.hs

@@ -546,6 +546,7 @@ initDynFlags dflags = do
                           `catchIOError` \_ -> return False
   ghcNoUnicodeEnv <- lookupEnv "GHC_NO_UNICODE"
   let useUnicode' = isNothing ghcNoUnicodeEnv && canUseUnicode
 + canUseColor <- stderrSupportsAnsiColors
   maybeGhcColorsEnv  <- lookupEnv "GHC_COLORS"
   maybeGhcColoursEnv <- lookupEnv "GHC_COLOURS"
   let adjustCols (Just env) = Col.parseScheme env
@@ -557,9 +558,9 @@ initDynFlags dflags = do
   return dflags{
          useUnicode    = useUnicode',
          useColor      = useColor',
 -        canUseColor   = stderrSupportsAnsiColors,
 +        canUseColor   = canUseColor,
          -- if the terminal supports color, we assume it supports links as well
 -        canUseErrorLinks = stderrSupportsAnsiColors,
 +        canUseErrorLinks = canUseColor,
          colScheme     = colScheme',
          tmpDir        = TempDir tmp_dir
+         }

compiler/GHC/SysTools/Terminal.hs

@@ -14,17 +14,9 @@ import qualified Graphics.Win32 as Win32
  import qualified System.Win32 as Win32
  #endif
 -import System.IO.Unsafe
+-
 --- | Does the controlling terminal support ANSI color sequences?
 --- This memoized to avoid thread-safety issues in ncurses (see #17922).
 -stderrSupportsAnsiColors :: Bool
 -stderrSupportsAnsiColors = unsafePerformIO stderrSupportsAnsiColors'
 -{-# NOINLINE stderrSupportsAnsiColors #-}
+-
  -- | Check if ANSI escape sequences can be used to control color in stderr.
 -stderrSupportsAnsiColors' :: IO Bool
 -stderrSupportsAnsiColors' = do
 +stderrSupportsAnsiColors :: IO Bool
 +stderrSupportsAnsiColors = do
  #if !defined(mingw32_HOST_OS)
    -- Equivalent of https://hackage.haskell.org/package/ansi-terminal/docs/System-Console-ANSI.html#v:hSupportsANSI
    isTerminal <- hIsTerminalDevice stderr