CPP #includes may result in nonsensical SrcSpans

Consider the following code in compiler/prelude/PrimOp.hs

primOpInfo :: PrimOp -> PrimOpInfo
#include "primop-primop-info.hs-incl"
primOpInfo _ = error "primOpInfo: unknown primop" -- line 175 in PrimOp.hs

The MatchGroup for primOpInfo includes the SrcSpan

compiler/stage2/build/primop-primop-info.hs-incl:(1,1)-(175,49)

Here is line 175 in primop-primop-info.hs-incl

primOpInfo IndexSmallArrayOp = mkGenPrimOp (fsLit "indexSmallArray#") [alphaTyVar] [mkSmallArrayPrimTy alphaTy, intPrimTy] ((mkTupleTy Unboxed [alphaTy]))

The SrcSpans end is somewhere in the middle of that line.

I guess this occurs because combineSrcSpans doesn't take the file into account.

I can think of multiple ways to fix this:

1. Make combineSrcSpans output an UnhelpfulSrcSpan if the files don't match(quick and easy)
2. Extend SrcSpan to properly support things spanning multiple files
3. Don't fix: People who use CPP get what they deserve.

Option 3 is not unreasonable as options 1 and 2 will incur some performance penalty.

Trac metadata

Trac field	Value
Version	8.4.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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