Respect --instrumentation_filter for Rust coverage#3998
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tamasvajk wants to merge 6 commits intobazelbuild:mainfrom
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Respect --instrumentation_filter for Rust coverage#3998tamasvajk wants to merge 6 commits intobazelbuild:mainfrom
--instrumentation_filter for Rust coverage#3998tamasvajk wants to merge 6 commits intobazelbuild:mainfrom
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Previously, all Rust targets were instrumented with -Cinstrument-coverage when running `bazel coverage`, regardless of --instrumentation_filter. This differs from how coverage works for Java and C++ targets, where only targets matching the filter are instrumented. Add ctx.coverage_instrumented() check so that Rust coverage respects the same filter, reducing unnecessary recompilation and keeping coverage reports focused on the code under test.
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Without an explicit --instrumentation_filter, Bazel's default filter may not match workspace targets, causing ctx.coverage_instrumented() to return False and producing empty Rust coverage reports. Add coverage --instrumentation_filter=^// to both .bazelrc and all CI coverage tasks. Projects with vendored dependencies should narrow this, e.g.: coverage --instrumentation_filter=^//,-^//third_party
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added 4 commits
April 28, 2026 18:19
ctx.coverage_instrumented() returns False for test targets by design (Bazel considers test sources not worth instrumenting). But Rust test binaries statically link their dependencies, and the coverage runtime only initializes if the binary itself is compiled with -Cinstrument-coverage. Without this, test binaries produce no profraw files and coverage collection fails with "no input files specified". Always add -Cinstrument-coverage for test crates (crate_info.is_test) when coverage is enabled, while still respecting the instrumentation filter for library targets.
This reverts commit d21e160.
When a test target is not instrumented (e.g. due to --instrumentation_filter), no .profraw files are produced. Previously llvm-profdata merge would fail with "no input files specified". Write an empty coverage file and exit successfully instead, so that uninstrumented test targets don't break coverage collection.
The .bazelrc is inherited by sub-workspace CI tasks (cc_common_link, bzlmod_repo_mapping, sys, pyo3) causing build/test failures. The flag is already passed via coverage_flags in presubmit.yml for coverage tasks.
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Summary
Respect
--instrumentation_filterwhen instrumenting Rust targets for coverage, consistent with Bazel's recommended approach for rules.Problem
Previously, all Rust targets were instrumented with
-Cinstrument-coveragewhen runningbazel coverage, regardless of--instrumentation_filter. This causes:Changes
rustc.bzl: Addctx.coverage_instrumented()check, the standard Bazel API for respecting--instrumentation_filter. Only targets matching the filter get-Cinstrument-coverage.collect_coverage.rs: Handle zero.profrawfiles gracefully. When a test target is not instrumented (because it doesn't match the filter), no profraw files are produced. Previously this causedllvm-profdata mergeto fail with "no input files specified". Now it writes an empty coverage file and exits successfully..bazelrc: Addcoverage --instrumentation_filter=^//so that all workspace targets are instrumented by default..bazelci/presubmit.yml: Add--instrumentation_filter=^//to all CI coverage tasks.Usage
The default
--instrumentation_filter=^//instruments all workspace targets. Projects with vendored dependencies should narrow this: