Merging and matching paths

How poly-crap merges several reports, lines up report entries with source files, and treats functions no report covers.

Merging reports

Pass --coverage more than once to merge reports, for example one per language. Where two reports cover the same line, a hit in either counts.

Matching paths

Coverage tools write paths relative to their own roots, so poly-crap matches a source file to a report entry in three steps:

1. The same path, as written.
2. The same file after resolving symlinks, when both paths are absolute.
3. The longest path suffix shared with exactly one report entry. A suffix must cover at least the file name and its directory, unless the report names the file with no directory at all, as SF:app.py does. Without that rule a file the tests never ran, such as pkg_a/util.py, could borrow the coverage of pkg_b/util.py.

A suffix shared by two report entries matches neither. Poly-crap warns on stderr when source files and report entries do not line up, and the Coverage scope line at the end of the report counts both sides. A report entry for a file the excludes dropped, such as a test file the coverage tool instrumented, is spoken for and does not count as coverage-only.

Poly-crap does not read JavaScript source maps. For TypeScript, the coverage tool must report the original .ts paths, which c8 and Vitest do by default.

Functions without coverage

A function has no coverage when its file is not in any report, or when the report has no executable lines inside the function. --missing decides what happens:

• pessimistic, the default, scores it as 0% covered.
• optimistic scores it as 100% covered.
• skip leaves it out of the report and the gates.

In every case the function’s coverage is null in JSON and N/A in the table, so you can tell a measured 0% from a missing one.