#8914 Warn about untagged payload patterns shadowed by literal cases

A payload pattern whose values are all literal-case values can never match (warning 11/12), and a literal case covers the equal bool payload value in the exhaustiveness check. Fixes #8806.

• Changelog fragment changes/untagged-literal-overlap-warnings.fix.md
• No Tests trailer
• Marshaled AST, typed tree or Lambda type changes with no magic number bump

The check for untagged payload patterns shadowed by literal cases ran only when warning 11 was active, so with -w -11+12 or @warning("-11") a dead or-pattern alternative got no warning 12. It now runs when either warning is active; the usefulness analysis is still gated on warning 11.

Example ReScript

@unboxed type t = | @as("a") A | S(string)@warning("-11")let g = x => switch x { | S("a") => 1 | S("a" | "c") => 2 | S(_) | A => 3 }

Diagnostic output

Before: no warnings
After: Warning 12 on the "a" in S("a" | "c"); the dead S("a") case stays
silent because warning 11 is off.

No effect

Output: unchangedFormats: nonePPX: unchangedEditor: unchanged

Tests

super_errors tests/build_tests/~ super_errors/fixtures/warning_12_untagged_literal_shadows_or_pattern.res

• No committed generated JS changes