Module patch_coverage 

Patch (changed-line) coverage (Python — #132; TypeScript — #135; parent #46).

Enforces the README Coverage rule’s changed-line guarantee: every line a diff touches must be covered by the unit suite. Where crate::coverage measures the whole suite against a floor (#26), this measures only the lines <base>...HEAD added or modified — failing when any changed, executable line is left uncovered.

Two inputs are combined:

• the diff — changed_lines runs git diff --unified=0 <base>...HEAD and returns the new-side line numbers each file gained. This diff machinery is language-agnostic, shared by both arms (and the forthcoming Rust twin).
• the coverage — per the language. Python (check) reads coverage.py’s per-file missing_lines / missing_branches (crate::coverage::measure_patch_report); a changed line is uncovered when it is a missing line or the source of a branch the suite never took (uncovered_changed_lines). TypeScript (check_typescript) reads vitest’s per-file v8 coverage reduced to one uncovered-line set per file (crate::coverage::measure_patch_typescript) and intersects it directly (uncovered_changed_lines_ts). Either way, non-executable changed lines (comments, blanks) and coverage-exempt files have nothing to cover and are skipped.

Relationship to the commit-scoped co-change rule (crate::co_change, #33): co-change enforces that a changed source and its colocated test move together; patch coverage enforces that the changed lines are actually exercised. They are complementary, not overlapping — co-change can pass (the test file changed) while patch coverage fails (the change isn’t covered), and vice versa.

Structs

Uncovered

A changed source line the unit suite doesn’t cover — a root-relative path and the 1-based new-side line number.

Functions

changed_lines

The new-side lines each file gained in repo’s <base>...HEAD diff, keyed by repo-relative path. The diff machinery shared by the TS / Rust twins.

check

Every line added or modified in root’s <base>...HEAD diff that the unit suite doesn’t cover, sorted for deterministic output. omit is the coverage-rule exemptions (as in crate::coverage::measure) — an exempt file is omitted from the run, so its changed lines are lifted.

check_typescript

Every line added or modified in root’s <base>...HEAD diff that the TypeScript unit suite (vitest) doesn’t cover, sorted for deterministic output. exclude is the coverage-rule exemptions (as in crate::coverage::measure_typescript) — an excluded file is left out of the run, so its changed lines are lifted.

uncovered_changed_lines

Pure: every changed line the coverage report marks uncovered — a missing_line, or the source of a missing_branch (a branch out of the line the suite never took). A changed file absent from files was not measured (a test file, or a coverage-exempt file omitted from the run) and contributes nothing; a changed line that is neither missing nor a branch source (a comment or blank) has nothing to cover. files is keyed by root-relative path, as changed is.

uncovered_changed_lines_ts

Pure: every changed line a TypeScript coverage report marks uncovered. uncovered is the per-file set of uncovered lines (crate::coverage::measure_patch_typescript) — statements the suite never ran and the source lines of branches a path of which it never took — keyed by root-relative path, as changed is. A changed file absent from uncovered was not measured (a test file, a declaration file, or a coverage-exempt file excluded from the run) and contributes nothing; a changed line not in its set (a comment or blank) has nothing to cover.