0b774cd7

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

Skip parsed-stage splice-span walk for DisableMutations modules

When a module carries {-# ANN module ("DisableMutations" :: String) #-},
the typecheck-stage plugin already short-circuits.  But the parser-stage
hook was still doing the full Data-generics walk to collect splice spans
for the --skip-th-splices feature, even though the spans would never be
consulted.

Look for the module-level ANN in the parsed AST (mirroring the
typecheck-stage check that uses tcg_ann_env) and skip the walk when it
is present.  The runtime-import injection still happens — it is cheap
and needed for -Wunused-packages on the sydtest-mutation-plugin dep.

Timeline