PrelRules: Ensure that string unpack/append rule fires with source notes
Previously the presence of source notes could hide nested applications
of unpackFoldrCString# from our constant folding logic. For instance,
consider the expression:
unpackFoldrCString# "foo" c (unpackFoldrCString# "baz" c n)Specifically, ticks appearing in two places can defeat the rule:
- Surrounding the inner application of
unpackFoldrCString# - Surrounding the fold function,
c
The latter caused the str_rules testcase to fail when base was built
with -g3.
Fixes #16740 (closed).