ea6f1381

By: Tom Sydney Kerckhove <syd@cs-syd.eu>

Detect TH splices by span containment, not just AST wrappers

The previous --skip-th-splices implementation only matched
XExpr (ExpandedThingTc orig expanded) where orig was a splice node.
That covers operator-style expansions, but most splices in
Yesod/Persistent codebases (mkYesodData, mkPersist [persistLowerCase|...|],
$(widgetFile ...)) are evaluated during renaming and the typechecked
AST sees the result as if it were original code, with no wrapper.

Collect splice spans from the parsed AST instead (HsUntypedSplice,
HsTypedSplice, SpliceD), store them per-module in a process-global IORef,
and in recordMutation drop any mutation whose RealSrcSpan is contained
in a splice span.

Walking the parsed AST uses Data generics so we don't have to enumerate
every AST constructor.

Timeline