Fix code coverage collection.

.bazelci/presubmit.yml

@@ -35,11 +35,19 @@ crate_universe_vendor_example_targets: &crate_universe_vendor_example_targets
 crate_universe_unnamed_vendor_example_targets: &crate_universe_unnamed_vendor_example_targets
   - "//vendor_remote_manifests:crates_vendor"
   - "//vendor_remote_pkgs:crates_vendor"
+coverage_validation_post_shell_commands: &coverage_validation_post_shell_commands
+  - |
+    grep -q '^SF:.*\.rs$' bazel-out/_coverage/_coverage_report.dat \
+    || { 1>&2 echo "Failed to find any Rust coverage" \
+      ; 1>&2 cat bazel-out/_coverage/_coverage_report.dat \
+      ; exit 1 \
+      ; }
 tasks:
   ubuntu2004:
     build_targets: *default_linux_targets
     test_targets: *default_linux_targets
     coverage_targets: *default_linux_targets
+    post_shell_commands: *coverage_validation_post_shell_commands
   rbe_ubuntu1604:
     shell_commands:
       - sed -i 's/^# load("@bazelci_rules/load("@bazelci_rules/' WORKSPACE.bazel
@@ -57,6 +65,7 @@ tasks:
     build_targets: *default_macos_targets
     test_targets: *default_macos_targets
     coverage_targets: *default_macos_targets
+    post_shell_commands: *coverage_validation_post_shell_commands
   windows:
     build_targets: *default_windows_targets
     test_targets: *default_windows_targets
@@ -90,9 +99,11 @@ tasks:
   ubuntu2004_with_aspects:
     name: With Aspects
     platform: ubuntu2004
+    build_flags: *aspects_flags
     build_targets: *default_linux_targets
     test_targets: *default_linux_targets
-    build_flags: *aspects_flags
+    coverage_targets: *default_linux_targets
+    post_shell_commands: *coverage_validation_post_shell_commands
   rbe_ubuntu1604_with_aspects:
     name: With Aspects
     platform: rbe_ubuntu1604
@@ -126,15 +137,19 @@ tasks:
   macos_with_aspects:
     name: With Aspects
     platform: macos
+    build_flags: *aspects_flags
     build_targets: *default_macos_targets
     test_targets: *default_macos_targets
-    build_flags: *aspects_flags
+    coverage_targets: *default_macos_targets
+    post_shell_commands: *coverage_validation_post_shell_commands
   macos_rolling_with_aspects:
     name: "Macos Rolling Bazel Version With Aspects"
     platform: macos
+    build_flags: *aspects_flags
     build_targets: *default_macos_targets
     test_targets: *default_macos_targets
-    build_flags: *aspects_flags
+    coverage_targets: *default_macos_targets
+    post_shell_commands: *coverage_validation_post_shell_commands
     soft_fail: yes
     bazel: "rolling"
   windows_with_aspects:
@@ -190,17 +205,21 @@ tasks:
   ubuntu1804:
     name: "Min Bazel Version"
     # If updating the minimum bazel version, please also update /docs/index.md
-    bazel: "5.0.0"
+    bazel: "5.2.0"
     platform: ubuntu1804
     build_targets: *default_linux_targets
     test_targets: *default_linux_targets
+    coverage_targets: *default_linux_targets
+    post_shell_commands: *coverage_validation_post_shell_commands
   ubuntu1804_with_aspects:
     name: "Min Bazel Version With Aspects"
-    bazel: "5.0.0"
+    bazel: "5.2.0"
     platform: ubuntu1804
     build_targets: *default_linux_targets
     test_targets: *default_linux_targets
     build_flags: *aspects_flags
+    coverage_targets: *default_linux_targets
+    post_shell_commands: *coverage_validation_post_shell_commands
   ubuntu2004_min_rust_version:
     name: "Min Rust Version"
     platform: ubuntu2004
@@ -257,10 +276,12 @@ tasks:
     name: "Rolling Bazel Version With Aspects"
     bazel: "rolling"
     platform: ubuntu2004
+    build_flags: *aspects_flags
     soft_fail: yes
     build_targets: *default_linux_targets
     test_targets: *default_linux_targets
-    build_flags: *aspects_flags
+    coverage_targets: *default_linux_targets
+    post_shell_commands: *coverage_validation_post_shell_commands
   linux_docs:
     name: Docs
     platform: ubuntu2004

.bazelrc

@@ -5,14 +5,17 @@
 ## https://bazel.build/docs/best-practices#bazelrc-file
 ###############################################################################
 
+# https://bazel.build/reference/command-line-reference#flag--enable_platform_specific_config
+common --enable_platform_specific_config
+
 # https://bazel.build/docs/windows#symlink
 startup --windows_enable_symlinks
-
-# Required on windows
-common --enable_platform_specific_config
-startup:windows --windows_enable_symlinks
 build:windows --enable_runfiles
 
+# Enable the only currently supported report type
+# https://bazel.build/reference/command-line-reference#flag--combined_report
+coverage --combined_report=lcov
+
 ###############################################################################
 ## Unique configuration groups
 ###############################################################################

docs/index.md

@@ -93,7 +93,7 @@ Failure to do so will result in rules attempting to match a `stable` toolchain w
 
 ## Supported bazel versions
 
-The oldest version of Bazel the `main` branch is tested against is `5.0.0`. Previous versions may still be functional in certain environments, but this is the minimum version we strive to fully support.
+The oldest version of Bazel the `main` branch is tested against is `5.2.0`. Previous versions may still be functional in certain environments, but this is the minimum version we strive to fully support.
 
 We test these rules against the latest rolling releases of Bazel, and aim for compatibility with them, but prioritise stable releases over rolling releases where necessary.
 

rust/private/rust.bzl

@@ -474,8 +474,16 @@ def _rust_test_impl(ctx):
         if not toolchain.llvm_profdata:
             fail("toolchain.llvm_profdata is required if toolchain.llvm_cov is set.")
 
-        env["RUST_LLVM_COV"] = toolchain.llvm_cov.path
-        env["RUST_LLVM_PROFDATA"] = toolchain.llvm_profdata.path
+        llvm_cov_path = toolchain.llvm_cov.short_path
+        if llvm_cov_path.startswith("../"):
+            llvm_cov_path = llvm_cov_path[len("../"):]
+
+        llvm_profdata_path = toolchain.llvm_profdata.short_path
+        if llvm_profdata_path.startswith("../"):
+            llvm_profdata_path = llvm_profdata_path[len("../"):]
+
+        env["RUST_LLVM_COV"] = llvm_cov_path
+        env["RUST_LLVM_PROFDATA"] = llvm_profdata_path
     components = "{}/{}".format(ctx.label.workspace_root, ctx.label.package).split("/")
     env["CARGO_MANIFEST_DIR"] = "/".join([c for c in components if c])
     providers.append(testing.TestEnvironment(env))
@@ -652,11 +660,6 @@ _common_attrs = {
         ),
         default = Label("@bazel_tools//tools/cpp:current_cc_toolchain"),
     ),
-    "_collect_cc_coverage": attr.label(
-        default = Label("//util:collect_coverage"),
-        executable = True,
-        cfg = "exec",
-    ),
     "_error_format": attr.label(
         default = Label("//:error_format"),
     ),
@@ -698,6 +701,28 @@ _common_attrs = {
     ),
 }
 
+_coverage_attrs = {
+    "_collect_cc_coverage": attr.label(
+        default = Label("//util:collect_coverage"),
+        executable = True,
+        cfg = "exec",
+    ),
+    # Bazel’s coverage runner
+    # (https://github.com/bazelbuild/bazel/blob/6.0.0/tools/test/collect_coverage.sh)
+    # needs a binary called “lcov_merge.”  Its location is passed in the
+    # LCOV_MERGER environmental variable.  For builtin rules, this variable
+    # is set automatically based on a magic “$lcov_merger” or
+    # “:lcov_merger” attribute, but it’s not possible to create such
+    # attributes in Starlark.  Therefore we specify the variable ourselves.
+    # Note that the coverage runner runs in the runfiles root instead of
+    # the execution root, therefore we use “path” instead of “short_path.”
+    "_lcov_merger": attr.label(
+        default = configuration_field(fragment = "coverage", name = "output_generator"),
+        executable = True,
+        cfg = "exec",
+    ),
+}
+
 _experimental_use_cc_common_link_attrs = {
     "experimental_use_cc_common_link": attr.int(
         doc = (
@@ -765,7 +790,7 @@ _rust_test_attrs = dict({
         default = Label("@bazel_tools//tools/cpp:grep-includes"),
         executable = True,
     ),
-}.items() + _experimental_use_cc_common_link_attrs.items())
+}.items() + _coverage_attrs.items() + _experimental_use_cc_common_link_attrs.items())
 
 _common_providers = [
     rust_common.crate_info,

util/collect_coverage.sh

@@ -6,14 +6,20 @@ if [[ -n "${VERBOSE_COVERAGE:-}" ]]; then
   set -x
 fi
 
+if [[ "${RUNFILES_DIR:0:1}" != "/" ]]; then
+  if [[ -n "${ROOT}" ]]; then
+    RUNFILES_DIR="${ROOT}/${RUNFILES_DIR}"
+  fi
+fi
+
 readonly profdata_file=$COVERAGE_DIR/coverage.profdata
 
-"$RUNFILES_DIR/$TEST_WORKSPACE/$RUST_LLVM_PROFDATA" \
+"$RUNFILES_DIR/$RUST_LLVM_PROFDATA" \
   merge \
   --sparse "$COVERAGE_DIR"/*.profraw \
   -output "$profdata_file"
 
-"$RUNFILES_DIR/$TEST_WORKSPACE/$RUST_LLVM_COV" \
+"$RUNFILES_DIR/$RUST_LLVM_COV" \
   export \
   -format=lcov \
   -instr-profile "$profdata_file" \
@@ -22,4 +28,7 @@ readonly profdata_file=$COVERAGE_DIR/coverage.profdata
   -path-equivalence=.,"$ROOT" \
   "$RUNFILES_DIR/$TEST_WORKSPACE/$TEST_BINARY" \
   @"$COVERAGE_MANIFEST" \
-  | sed 's#/proc/self/cwd/##' > "$COVERAGE_OUTPUT_FILE"
+  | sed 's#/proc/self/cwd/##' > "$COVERAGE_DIR/rust_coverage.dat"
+
+# Bazel doesn't support LLVM profdata coverage amongst other coverage formats.
+rm "$profdata_file"