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Matthew Pickering pushed to branch wip/t26087 at Glasgow Haskell Compiler / GHC

Commits:

1ad84037

by Matthew Pickering at 2025-07-08T10:17:54+01:00

level imports: Fix infinite loop with cyclic module imports

I didn't anticipate that downsweep would run before we checked for
cyclic imports. Therefore we need to use the reachability function which
handles cyclic graphs.

Fixes #26087

5 changed files:

compiler/GHC/Unit/Module/Graph.hs
+ testsuite/tests/splice-imports/T26087.stderr
+ testsuite/tests/splice-imports/T26087A.hs
+ testsuite/tests/splice-imports/T26087B.hs
testsuite/tests/splice-imports/all.T

Changes:

compiler/GHC/Unit/Module/Graph.hs

@@ -866,7 +866,7 @@ mkTransZeroDeps = first graphReachability {- module graph is acyclic -} . module
  -- | Transitive dependencies, but with the stage that each module is required at.
  mkStageDeps :: [ModuleGraphNode] -> (ReachabilityIndex StageSummaryNode, (NodeKey, ModuleStage) -> Maybe StageSummaryNode)
 -mkStageDeps = first graphReachability . moduleGraphNodesStages
 +mkStageDeps = first cyclicGraphReachability . moduleGraphNodesStages
  type ZeroSummaryNode = Node Int ZeroScopeKey

testsuite/tests/splice-imports/T26087.stderr

 +./T26087B.hs: error: [GHC-92213]
 +    Module graph contains a cycle:
 +                    module ‘main:T26087B’ (./T26087B.hs)
 +            imports module ‘main:T26087A’ (T26087A.hs)
 +      which imports module ‘main:T26087B’ (./T26087B.hs)
++

testsuite/tests/splice-imports/T26087A.hs

 +{-# LANGUAGE ExplicitLevelImports #-}
 +module T26087A where
++
 +import quote T26087B

testsuite/tests/splice-imports/T26087B.hs

 +{-# LANGUAGE ExplicitLevelImports, TemplateHaskell #-}
 +module T26087B where
++
 +import T26087A

testsuite/tests/splice-imports/all.T

@@ -46,3 +46,4 @@ test('SI35',
       compile_and_run,
       ['-package ghc'])
  test('SI36', [extra_files(["SI36_A.hs", "SI36_B1.hs", "SI36_B2.hs", "SI36_B3.hs", "SI36_C1.hs", "SI36_C2.hs", "SI36_C3.hs"])], multimod_compile_fail, ['SI36', '-v0'])
 +test('T26087', [], multimod_compile_fail, ['T26087A', ''])