Add support for split_coverage_post_processing (#2000)

This change introduces `experimental_use_coverage_metadata_files`
(#2082) which is required
to support
[--experimental_split_coverage_postprocessing](https://bazel.build/reference/command-line-reference#flag--experimental_split_coverage_postprocessing)'

Changes:
- Implemented coverage collection logic in Rust.
- Added a flag
`--@rules_rust//rust/settings:experimental_use_coverage_metadata_files`
to toggle the changes necessary for supporting
`--experimental_split_coverage_postprocessing`.
- Added regression testing in CI to test
`--experimental_split_coverage_postprocessing`.

.bazelci/presubmit.yml

@@ -42,6 +42,10 @@ coverage_validation_post_shell_commands: &coverage_validation_post_shell_command
  ; 1>&2 cat bazel-out/_coverage/_coverage_report.dat \
  ; exit 1 \
  ; }
+split_coverage_postprocessing_shell_commands: &split_coverage_postprocessing_shell_commands
+ - 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
 tasks:
  ubuntu2004:
  build_targets: *default_linux_targets
@@ -69,6 +73,18 @@ tasks:
  windows:
  build_targets: *default_windows_targets
  test_targets: *default_windows_targets
+ ubuntu2004_split_coverage_postprocessing:
+ name: Split Coverage Postprocessing
+ platform: ubuntu2004
+ shell_commands: *split_coverage_postprocessing_shell_commands
+ coverage_targets: *default_linux_targets
+ post_shell_commands: *coverage_validation_post_shell_commands
+ macos_split_coverage_postprocessing:
+ name: Split Coverage Postprocessing
+ platform: macos
+ shell_commands: *split_coverage_postprocessing_shell_commands
+ coverage_targets: *default_macos_targets
+ post_shell_commands: *coverage_validation_post_shell_commands
  ubuntu2004_opt:
  name: Opt Mode
  platform: ubuntu2004

rust/private/rust.bzl

@@ -480,13 +480,17 @@ def _rust_test_impl(ctx):
  if not toolchain.llvm_profdata:
  fail("toolchain.llvm_profdata is required if toolchain.llvm_cov is set.")
 
- llvm_cov_path = toolchain.llvm_cov.short_path
- if llvm_cov_path.startswith("../"):
- llvm_cov_path = llvm_cov_path[len("../"):]
+ if toolchain._experimental_use_coverage_metadata_files:
+ llvm_cov_path = toolchain.llvm_cov.path
+ llvm_profdata_path = toolchain.llvm_profdata.path
+ else:
+ 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("../"):]
+  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
@@ -742,7 +746,7 @@ _common_attrs = {
 
 _coverage_attrs = {
  "_collect_cc_coverage": attr.label(
- default = Label("//util:collect_coverage"),
+ default = Label("//util/collect_coverage"),
  executable = True,
  cfg = "exec",
  ),

rust/private/rustc.bzl

@@ -997,6 +997,7 @@ def construct_arguments(
  rustc_flags.add("proc_macro")
 
  if toolchain.llvm_cov and ctx.configuration.coverage_enabled:
+ # https://doc.rust-lang.org/rustc/instrument-coverage.html
  rustc_flags.add("--codegen=instrument-coverage")
 
  # Make bin crate data deps available to tests.
@@ -1364,8 +1365,10 @@ def rustc_compile_action(
  if toolchain.llvm_cov and ctx.configuration.coverage_enabled and crate_info.is_test:
  coverage_runfiles = [toolchain.llvm_cov, toolchain.llvm_profdata]
 
+ experimental_use_coverage_metadata_files = toolchain._experimental_use_coverage_metadata_files
+
  runfiles = ctx.runfiles(
- files = getattr(ctx.files, "data", []) + coverage_runfiles,
+ files = getattr(ctx.files, "data", []) + ([] if experimental_use_coverage_metadata_files else coverage_runfiles),
  collect_data = True,
  )
  if getattr(ctx.attr, "crate", None):
@@ -1376,18 +1379,29 @@ def rustc_compile_action(
  # https:/bazelbuild/rules_rust/issues/771
  out_binary = getattr(attr, "out_binary", False)
 
+ executable = crate_info.output if crate_info.type == "bin" or crate_info.is_test or out_binary else None
+
+ instrumented_files_kwargs = {
+ "dependency_attributes": ["deps", "crate"],
+ "extensions": ["rs"],
+ "source_attributes": ["srcs"],
+ }
+
+ if experimental_use_coverage_metadata_files:
+ instrumented_files_kwargs.update({
+ "metadata_files": coverage_runfiles + [executable] if executable else [],
+ })
+
  providers = [
  DefaultInfo(
  # nb. This field is required for cc_library to depend on our output.
  files = depset(outputs),
  runfiles = runfiles,
- executable = crate_info.output if crate_info.type == "bin" or crate_info.is_test or out_binary else None,
+ executable = executable,
  ),
  coverage_common.instrumented_files_info(
  ctx,
- dependency_attributes = ["deps", "crate"],
- extensions = ["rs"],
- source_attributes = ["srcs"],
+ **instrumented_files_kwargs
  ),
  ]
 

rust/repositories.bzl

@@ -67,11 +67,11 @@ def rules_rust_dependencies():
  maybe(
  http_archive,
  name = "bazel_skylib",
+ sha256 = "66ffd9315665bfaafc96b52278f57c7e2dd09f5ede279ea6d39b2be471e7e3aa",
  urls = [
- "https:/bazelbuild/bazel-skylib/releases/download/1.2.0/bazel-skylib-1.2.0.tar.gz",
- "https://mirror.bazel.build/github.com/bazelbuild/bazel-skylib/releases/download/1.2.0/bazel-skylib-1.2.0.tar.gz",
+ "https://mirror.bazel.build/github.com/bazelbuild/bazel-skylib/releases/download/1.4.2/bazel-skylib-1.4.2.tar.gz",
+ "https:/bazelbuild/bazel-skylib/releases/download/1.4.2/bazel-skylib-1.4.2.tar.gz",
  ],
- sha256 = "af87959afe497dc8dfd4c6cb66e1279cb98ccc84284619ebfec27d9c09a903de",
  )
 
  # Make the iOS simulator constraint available, which is referenced in abi_to_constraints()

rust/settings/BUILD.bazel

@@ -52,6 +52,13 @@ bool_flag(
  build_setting_default = False,
 )
 
+# A flag to have coverage tooling added as `coverage_common.instrumented_files_info.metadata_files` instead of
+# reporting tools like `llvm-cov` and `llvm-profdata` as runfiles to each test.
+bool_flag(
+ name = "experimental_use_coverage_metadata_files",
+ build_setting_default = False,
+)
+
 bzl_library(
  name = "bzl_lib",
  srcs = glob(["**/*.bzl"]),

rust/toolchain.bzl

@@ -640,6 +640,7 @@ def _rust_toolchain_impl(ctx):
  _pipelined_compilation = pipelined_compilation,
  _experimental_use_cc_common_link = experimental_use_cc_common_link,
  _experimental_use_global_allocator = experimental_use_global_allocator,
+ _experimental_use_coverage_metadata_files = ctx.attr._experimental_use_coverage_metadata_files[BuildSettingInfo].value,
  _no_std = no_std,
  )
  return [
@@ -784,6 +785,9 @@ rust_toolchain = rule(
  "_cc_toolchain": attr.label(
  default = Label("@bazel_tools//tools/cpp:current_cc_toolchain"),
  ),
+ "_experimental_use_coverage_metadata_files": attr.label(
+ default = Label("//rust/settings:experimental_use_coverage_metadata_files"),
+ ),
  "_experimental_use_global_allocator": attr.label(
  default = Label("//rust/settings:experimental_use_global_allocator"),
  doc = (

util/BUILD.bazel

@@ -4,8 +4,8 @@ sh_binary(
  tags = ["manual"],
 )
 
-filegroup(
+alias(
  name = "collect_coverage",
- srcs = ["collect_coverage.sh"],
+ actual = "//util/collect_coverage",
  visibility = ["//visibility:public"],
 )

util/collect_coverage/BUILD.bazel

@@ -0,0 +1,8 @@
+load("//rust:defs.bzl", "rust_binary")
+
+rust_binary(
+ name = "collect_coverage",
+ srcs = ["collect_coverage.rs"],
+ edition = "2018",
+ visibility = ["//visibility:public"],
+)