pantsbuild / pants / 33265103538

93%

push

github

Infer dependencies across local `replace` directives in the Go backend (#23431)

## Problem

A `go.mod` can `replace` a required module with a path to a local
directory holding another first-party module:

```
// context/app/go.mod
require example.com/shared v0.0.0
replace example.com/shared => ../shared
```

Module analysis skips these, since they are not third-party packages,
and nothing folded the replaced module's packages into the referencing
module's import-path map. An import of `example.com/shared/pkg/field`
from `context/app` was therefore never resolved by dependency inference,
and every cross-module dependency had to be listed by hand in BUILD
metadata. In a repo whose first-party graph is wired together with
directory replaces, that is most of the dependency edges.

## Fix

`determine_go_mod_info` records each `replace` whose target is a local
directory, mapping the replaced module path to that directory relative
to the build root. It reads this from the `go mod` JSON metadata Pants
already fetches, so no extra process runs.

`map_import_paths_to_packages` merges the replaced module's own
packages, import paths at or under its module path, into the referencing
module's mapping. Its third-party dependencies are deliberately not
merged: the referencing module resolves those through its own `go.mod`,
and merging them would make shared third-party imports ambiguous and
silently suppress inference. Replace directives are not transitive in
Go, so the merge is one level deep. A module without a directory replace
takes the unchanged path.

Closes #22097, and the matching TODO in `third_party_pkg.py`.

## Verification

Two new tests in `target_type_rules_test.py` cover inference across a
locally-replaced sibling module, and a third-party import shared by both
modules staying unambiguous. The `util_rules/::` and `target_type_rules`
suites pass. Validated end to end on a real 24-module monorepo: every
cross-module import that previously needed an exp... (continued)

49 of 54 new or added lines in 3 files covered. (90.74%)

95539 of 102848 relevant lines covered (92.89%)

3.66 hits per line