---
title: Merging and matching paths
description: 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.