Set --instrumentation_filter for coverage in .bazelrc and CI

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

Author: Tamas Vajk

.bazelci/presubmit.yml

@@ -98,14 +98,18 @@ split_coverage_postprocessing_shell_commands: &split_coverage_postprocessing_she
   - echo "coverage --experimental_fetch_all_coverage_outputs" >> user.bazelrc
   - echo "coverage --experimental_split_coverage_postprocessing" >> user.bazelrc
   - echo "build --//rust/settings:experimental_use_coverage_metadata_files" >> user.bazelrc
+coverage_flags: &coverage_flags
+  - "--instrumentation_filter=^//"
 rbe_coverage_flags: &rbe_coverage_flags
   # https://github.com/bazelbuild/bazel/issues/20578
   - "--strategy=CoverageReport=local"
+  - "--instrumentation_filter=^//"
 tasks:
   ubuntu2204:
     build_targets: *default_linux_targets
     test_targets: *default_linux_targets
     coverage_targets: *default_linux_targets
+    coverage_flags: *coverage_flags
     post_shell_commands: *coverage_validation_post_shell_commands
     run_targets:
       - //test:query_test_binary
@@ -123,6 +127,7 @@ tasks:
     build_targets: *default_macos_targets
     test_targets: *default_macos_targets
     coverage_targets: *default_macos_targets
+    coverage_flags: *coverage_flags
     post_shell_commands: *coverage_validation_post_shell_commands
   windows:
     build_targets: *default_windows_targets
@@ -135,6 +140,7 @@ tasks:
     build_targets: *default_linux_targets
     test_targets: *default_linux_targets
     coverage_targets: *default_linux_targets
+    coverage_flags: *coverage_flags
     post_shell_commands: *coverage_validation_post_shell_commands
     run_targets:
       - //test:query_test_binary
@@ -156,6 +162,7 @@ tasks:
     build_targets: *default_macos_targets
     test_targets: *default_macos_targets
     coverage_targets: *default_macos_targets
+    coverage_flags: *coverage_flags
     post_shell_commands: *coverage_validation_post_shell_commands
   windows_no_bzlmod:
     name: No Bzlmod
@@ -177,12 +184,14 @@ tasks:
     platform: ubuntu2204
     shell_commands: *split_coverage_postprocessing_shell_commands
     coverage_targets: *default_linux_targets
+    coverage_flags: *coverage_flags
     post_shell_commands: *coverage_validation_post_shell_commands
   macos_split_coverage_postprocessing:
     name: Split Coverage Postprocessing
     platform: macos_arm64
     shell_commands: *split_coverage_postprocessing_shell_commands
     coverage_targets: *default_macos_targets
+    coverage_flags: *coverage_flags
     post_shell_commands: *coverage_validation_post_shell_commands
   ubuntu2204_opt:
     name: Opt Mode
@@ -218,6 +227,7 @@ tasks:
     build_targets: *default_linux_targets
     test_targets: *default_linux_targets
     coverage_targets: *default_linux_targets
+    coverage_flags: *coverage_flags
     post_shell_commands: *coverage_validation_post_shell_commands
   rbe_ubuntu2204_with_aspects:
     name: With Aspects
@@ -252,6 +262,7 @@ tasks:
     build_targets: *default_macos_targets
     test_targets: *default_macos_targets
     coverage_targets: *default_macos_targets
+    coverage_flags: *coverage_flags
     post_shell_commands: *coverage_validation_post_shell_commands
   macos_rolling_with_aspects:
     name: "Macos Rolling Bazel Version With Aspects"
@@ -260,6 +271,7 @@ tasks:
     build_targets: *default_macos_targets
     test_targets: *default_macos_targets
     coverage_targets: *default_macos_targets
+    coverage_flags: *coverage_flags
     post_shell_commands: *coverage_validation_post_shell_commands
     soft_fail: yes
     bazel: "rolling"
@@ -356,6 +368,7 @@ tasks:
     build_targets: *default_linux_targets
     test_targets: *default_linux_targets
     coverage_targets: *default_linux_targets
+    coverage_flags: *coverage_flags
     post_shell_commands: *coverage_validation_post_shell_commands
   ubuntu1804_with_aspects:
     name: "Min Bazel Version With Aspects"
@@ -366,6 +379,7 @@ tasks:
     test_targets: *default_linux_targets
     build_flags: *aspects_flags
     coverage_targets: *default_linux_targets
+    coverage_flags: *coverage_flags
     post_shell_commands: *coverage_validation_post_shell_commands
   ubuntu2204_min_rust_version:
     name: "Min Rust Version"
@@ -432,6 +446,7 @@ tasks:
     build_targets: *default_linux_targets
     test_targets: *default_linux_targets
     coverage_targets: *default_linux_targets
+    coverage_flags: *coverage_flags
     post_shell_commands: *coverage_validation_post_shell_commands
   linux_docs:
     name: Docs

.bazelrc

@@ -20,6 +20,12 @@ coverage --combined_report=lcov
 coverage --experimental_fetch_all_coverage_outputs
 coverage --experimental_split_coverage_postprocessing
 
+# Instrument all workspace targets for coverage. Without this, the default
+# --instrumentation_filter may not match workspace targets, resulting in
+# empty coverage reports. Projects should adjust this to exclude vendored
+# dependencies, e.g.: coverage --instrumentation_filter=^//,-^//third_party
+coverage --instrumentation_filter=^//
+
 # Required for some of the tests
 # https://bazel.build/reference/command-line-reference#flag--experimental_cc_shared_library
 common --experimental_cc_shared_library