GHC should be able to warn on unsafe CPP usage

GCC has a warning -Wundef that catches unsafe CPP usage like:

#if variable_does_not_exist
// something
#endif

The GCC man page says about -Wundef:

  -Wundef
    Warn if an undefined identifier is evaluated in an "#if" directive.

Following GCC's lead, GHC should have a similar warning flag to detect and warn about this problem in Haskell code that uses CPP.

Trac metadata

Trac field	Value
Version	8.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
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Blocking
CC
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changed weight to 5

added Tfeature request Trac import labels

assigned to @trac-erikd

I suspect this is just a matter of adding a GHC warning flag named something like -Dcpp-undef and then if that is set, passing -Wundef to the C pre-processor.

changed title from GHC should be able to warn on usafe CPP usage to GHC should be able to warn on unsafe CPP usage

mentioned in commit 3cb32d8b

closed

changed milestone to %8.2.1

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

Well okay, but you could also just use -optP -Wundef since forever.

added Pnormal label