Support scoped Rust coverage workspaces (#351)

.github/actions/generate-coverage/CHANGELOG.md

@@ -2,6 +2,14 @@
 
 ## Unreleased
 
+- Add an optional `extra-cargo-args` input whose shell-parsed tokens are
+  appended to every `cargo llvm-cov` invocation. This allows callers to pass
+  workspace selection flags such as `--exclude <crate>`, including for the
+  optional cucumber-rs coverage run. Omitting the input preserves the existing
+  command unchanged. Package selection flags (`-p` or `--package`) suppress the
+  default `--workspace`, so they narrow coverage rather than being overridden by
+  it; `--exclude` keeps `--workspace` because it refines that selection.
+
 - Stop masking coverage failures with an empty-artefact-name error. The
   "Archive coverage" step runs with `if: always()`, but the step that computes
   its artefact name previously did not, so any earlier failure (for example a

.github/actions/generate-coverage/README.md

@@ -147,6 +147,7 @@ Known limitations:
 | with-cucumber-rs | Run cucumber-rs scenarios under coverage | no | `false` |
 | cucumber-rs-features | Path to cucumber feature files | no | |
 | cucumber-rs-args | Extra arguments for cucumber | no | |
+| extra-cargo-args | Extra arguments appended to `cargo llvm-cov`, parsed with shell quoting rules. Package selection flags suppress the default `--workspace`. | no | |
 | pytest-workers | Value passed to pytest-xdist's `-n` flag. Accepts a positive integer, `auto`, `logical`, or `""` (empty) to disable parallelism. | no | `auto` |
 <!-- markdownlint-enable MD013 -->
 
@@ -274,6 +275,42 @@ Disable cargo-nextest:
     use-cargo-nextest: false
 ```
 
+Exclude crates from Rust workspace coverage:
+
+```yaml
+- uses: ./.github/actions/generate-coverage
+  with:
+    output-path: coverage.xml
+    extra-cargo-args: >-
+      --exclude rustc-proxy
+      --exclude dylint-ui-fixture
+```
+
+```yaml
+- uses: leynos/shared-actions/.github/actions/generate-coverage@v1
+  with:
+    output-path: coverage.xml
+    extra-cargo-args: >-
+      --exclude rustc-proxy
+      --exclude dylint-ui-fixture
+```
+
+Measure a single crate instead of the whole workspace:
+
+```yaml
+- uses: leynos/shared-actions/.github/actions/generate-coverage@v1
+  with:
+    output-path: coverage.xml
+    extra-cargo-args: --package coverage-helper
+```
+
+The action passes `--workspace` by default so that `--exclude` has a package
+set to refine. When `extra-cargo-args` contains a package selection flag
+(`-p`, `--package`, or either spelling with an inline value), the default
+`--workspace` is omitted so the selection actually narrows the run — Cargo
+treats `--workspace` as "all members" and would otherwise build and report the
+whole workspace regardless of `--package`.
+
 Run pytest serially (disable pytest-xdist):
 
 ```yaml

.github/actions/generate-coverage/action.yml

@@ -58,6 +58,9 @@ inputs:
   cucumber-rs-args:
     description: Extra arguments for cucumber
     required: false
+  extra-cargo-args:
+    description: Extra arguments appended to cargo llvm-cov, e.g. --exclude <crate>
+    required: false
   pytest-workers:
     description: |
       Value passed to pytest-xdist's `-n` flag for the Python coverage run.
@@ -226,6 +229,7 @@ runs:
         INPUT_WITH_CUCUMBER_RS: ${{ inputs.with-cucumber-rs }}
         INPUT_CUCUMBER_RS_FEATURES: ${{ inputs.cucumber-rs-features }}
         INPUT_CUCUMBER_RS_ARGS: ${{ inputs.cucumber-rs-args }}
+        INPUT_EXTRA_CARGO_ARGS: ${{ inputs.extra-cargo-args }}
         BASELINE_RUST_FILE: ${{ inputs.baseline-rust-file }}
       shell: bash