refactor: invoke git via argv in coverage diff helpers

2026-05-04T01:11:49+00:00

`coverage-core.el` was running git through `shell-command-to-string`, which has two practical problems for central tooling: shell parsing surfaces (especially the `$(git merge-base ...)` substitution), and silent failure modes when git exits non-zero (the bad output just becomes empty parse results). I extracted three small helpers. `cj/--coverage-git-string` runs git via `process-file` against a temp buffer and signals `user-error` on non-zero exit, with the argv, status, and trimmed output included. `cj/--coverage-git-merge-base` does its own `git merge-base HEAD ` invocation. `cj/--coverage-git-diff` is the diff wrapper that always appends `--unified=0`. `cj/--coverage-changed-lines` now uses `pcase` over the scope symbol and composes the helpers. Branch-vs-main and branch-vs-parent compute the merge-base in a separate call before running `git diff ..HEAD`, with no shell substitution involved. One behavior change is worth flagging. A git failure used to disappear into an empty hash table. It now signals a `user-error` with the failing command, exit status, and git's stderr output. Tests: I added two argv-boundary cases (working-tree and branch-vs-parent both assert the exact argv list seen) plus a non-zero-exit case that asserts the user-error path. The existing `test-coverage-core--command.el` smoke test gets its `shell-command-to-string` stub upgraded to a `process-file` stub.

feat(coverage): add changed-lines helper and diff parser

2026-04-22T22:07:07+00:00

Second of three pure helpers for the coverage-report command. cj/--coverage-parse-diff-output is pure. It takes a git unified-diff string and returns a hash table of file to set of added or modified line numbers (based on the +new_start,new_count hunk headers). Files with deletion-only hunks appear in the result with an empty set, so reporters can distinguish "coverage not tracked" from "no changes touched this file." cj/--coverage-changed-lines wraps that parser with scope dispatch. Scopes are working-tree, staged, branch-vs-main, and branch-vs-parent. Branch-vs-parent takes an optional BASE arg; if omitted, falls back to @{upstream}. Unknown scopes signal user-error. Tests cover Normal (single hunk, multiple files), Boundary (new file via @@ -0,0, deletion-only, binary markers, single-line hunks without a count, empty input), and Error (malformed hunk headers skipped; unknown scope). Git invocation is stubbed via cl-letf in the smoke test so the parser logic is exercised without shelling out. Part of the coverage-core work per docs/design/coverage.org.

dotemacs/tests/test-coverage-core--changed-lines.el, branch main

refactor: invoke git via argv in coverage diff helpers

feat(coverage): add changed-lines helper and diff parser