fix(compiler): use span-overlap check for signal mutation ranges (#2785)#3019
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viniciusdacal merged 2 commits intomainfrom Apr 28, 2026
Merged
fix(compiler): use span-overlap check for signal mutation ranges (#2785)#3019viniciusdacal merged 2 commits intomainfrom
viniciusdacal merged 2 commits intomainfrom
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Replace the point-membership check in `is_in_mutation_range` with a half-open span-overlap check (`ident.start < range.end && ident.end > range.start`), and rename the predicate to `overlaps_mutation_range`. The previous check only tested whether the identifier's first character sat inside a recorded mutation range. That happened to work because `mutation_analyzer` always records a span starting at the identifier's start, but any future tightening (e.g., the operator-only span for `+=`, or a span recorded on an inner sub-expression) would silently misclassify the identifier as outside the range and double-handle it by appending `.value` on top of the mutation rewrite. Applied the new predicate at all three call sites: identifier reads, assignment-expression LHS, and update-expression targets. Added three regression tests that inject a mutation range whose start is greater than the identifier's start and assert `.value` is suppressed at each site. Closes #2785 Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
…2785] Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Summary
Closes #2785.
is_in_mutation_rangeinsignal_transformer.rsused a point-membership check onident.span.start(pos >= start && pos < end). The contract relied onmutation_analyzeralways recording a span that begins exactly at the identifier's first character — robust today, but silently broken by any future tightening (e.g., the operator-only span for+=, or a span recorded on an inner sub-expression).Replaced the predicate with a half-open span-overlap check (
ident_start < range.end && ident_end > range.start), renamed it tooverlaps_mutation_range, and applied it at all three call sites:visit_identifier_reference(signal reads)visit_assignment_expression(LHS of=,+=, etc.)visit_update_expression(++,--)Today this is observationally equivalent to the old check — every recorded range happens to start at the identifier's start, so both predicates agree. The change makes the predicate robust to future analyzer changes.
Public API Changes
None — internal compiler logic only.
Test plan
signal_transformer::testsinject a custom mutation range whose start is greater than the identifier's start and assert.valueis suppressed at each call site.signal_transformertests still pass.cargo test --all,cargo clippy --all-targets -- -D warnings,cargo fmt --all -- --checkall green.🤖 Generated with Claude Code