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

Commits:

5cdcfaed

by Ben Gamari at 2025-11-06T09:01:36-05:00

compiler: Exclude units with no exposed modules from unused package check

Such packages cannot be "used" in the Haskell sense of the word yet
are nevertheless necessary as they may provide, e.g., C object code or
link flags.

Fixes #24120.

3 changed files:

compiler/GHC/Driver/Make.hs
+ testsuite/tests/driver/T24120.hs
testsuite/tests/driver/all.T

Changes:

compiler/GHC/Driver/Make.hs

@@ -474,6 +474,10 @@ warnUnusedPackages us dflags mod_graph =
                    ui <- lookupUnit us u
                    -- Which are not explicitly used
                    guard (Set.notMember (unitId ui) used_args)
 +                  -- Exclude units with no exposed modules. This covers packages which only
 +                  -- provide C object code or link flags (e.g. system-cxx-std-lib).
 +                  -- See #24120.
 +                  guard (not $ null $ unitExposedModules ui)
                    return (unitId ui, unitPackageName ui, unitPackageVersion ui, flag)
          unusedArgs = sortOn (\(u,_,_,_) -> u) $ mapMaybe resolve (explicitUnits us)

testsuite/tests/driver/T24120.hs

 +-- | This should not issue an @-Wunused-packages@ warning for @system-cxx-std-lib@.
 +module Main where
++
 +main :: IO ()
 +main = putStrLn "hello world"

testsuite/tests/driver/all.T

@@ -331,3 +331,4 @@ test('T24839', [unless(arch('x86_64') or arch('aarch64'), skip), extra_files(["t
  test('t25150', [extra_files(["t25150"])], multimod_compile, ['Main.hs', '-v0 -working-dir t25150/dir a.c'])
  test('T25382', normal, makefile_test, [])
  test('T26018', req_c, makefile_test, [])
 +test('T24120', normal, compile, ['-Wunused-packages -hide-all-packages -package base -package system-cxx-std-lib'])