Remove recursive uses of `pprParendHsExpr` from `HsExpr.ppr_expr`

An HsExpr should look exactly as a user wrote some Haskell code. Its pretty printer should therefore be quite dumb. Just print out the code! But a few places in GHC create HsExprs and aren't scrupulous with regard to adding HsPar nodes where source syntax would need them. Thus, well-meaning souls have added pprParendExpr calls to the HsExpr pretty-printer to try to cover these cases.

Simon and I think that we should remove all recursive uses of pprParendExpr from the HsExpr pretty-printer and instead add the HsPars where necessary.

It was recently reported that the following test cases break when simply removing pprParendExpr:

Unexpected failures:
   deriving/should_fail          T4846 [stderr mismatch] (normal)
   generics                      GenDerivOutput [stderr mismatch] (normal)
   generics                      GenDerivOutput1_0 [stderr mismatch] (normal)
   generics                      GenDerivOutput1_1 [stderr mismatch] (normal)
   ghci/scripts                  T10248 [bad stderr] (ghci)
   indexed-types/should_compile  PushedInAsGivens [stderr mismatch] (normal)
   safeHaskell/safeLanguage      SafeLang10 [stderr mismatch] (normal)
   safeHaskell/safeLanguage      SafeLang17 [stderr mismatch] (normal)
   typecheck/should_fail         T8603 [stderr mismatch] (normal)
   typecheck/should_fail         tcfail177 [stderr mismatch] (normal)

See also considerable commentary on D1114.

Trac metadata

Trac field	Value
Version	7.10.2
Type	Task
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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