Implement -coverage-prefix-map feature

swift/internal/compiling.bzl

@@ -32,6 +32,7 @@ load(
     "SWIFT_FEATURE_CACHEABLE_SWIFTMODULES",
     "SWIFT_FEATURE_COMPILE_STATS",
     "SWIFT_FEATURE_COVERAGE",
+    "SWIFT_FEATURE_COVERAGE_PREFIX_MAP",
     "SWIFT_FEATURE_DBG",
     "SWIFT_FEATURE_DEBUG_PREFIX_MAP",
     "SWIFT_FEATURE_EMIT_C_MODULE",
@@ -293,6 +294,19 @@ def compile_action_configs():
                 [SWIFT_FEATURE_DEBUG_PREFIX_MAP, SWIFT_FEATURE_FULL_DEBUG_INFO],
             ],
         ),
+
+        # Make paths written into coverage info workspace-relative.
+        swift_toolchain_config.action_config(
+            actions = [swift_action_names.COMPILE],
+            configurators = [
+                swift_toolchain_config.add_arg(
+                    "-Xwrapped-swift=-coverage-prefix-pwd-is-dot",
+                ),
+            ],
+            features = [
+                [SWIFT_FEATURE_COVERAGE_PREFIX_MAP, SWIFT_FEATURE_COVERAGE],
+            ],
+        ),
     ]
 
     #### Coverage and sanitizer instrumentation flags

swift/internal/feature_names.bzl

@@ -61,6 +61,11 @@ SWIFT_FEATURE_COMPILE_STATS = "swift.compile_stats"
 # builds.
 SWIFT_FEATURE_DEBUG_PREFIX_MAP = "swift.debug_prefix_map"
 
+# If enabled, coverage builds will use the `-coverage-prefix-map` feature to
+# remap the current working directory to `.`, which increases reproducibility
+# of remote builds.
+SWIFT_FEATURE_COVERAGE_PREFIX_MAP = "swift.coverage_prefix_map"
+
 # If enabled, C and Objective-C libraries that are direct or transitive
 # dependencies of a Swift library will emit explicit precompiled modules that
 # are compatible with Swift's ClangImporter and propagate them up the build

test/BUILD

@@ -1,5 +1,6 @@
 load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
 load(":debug_settings_tests.bzl", "debug_settings_test_suite")
+load(":coverage_settings_tests.bzl", "coverage_settings_test_suite")
 load(":generated_header_tests.bzl", "generated_header_test_suite")
 load(":private_deps_tests.bzl", "private_deps_test_suite")
 load(":swift_through_non_swift_tests.bzl", "swift_through_non_swift_test_suite")
@@ -8,6 +9,8 @@ licenses(["notice"])
 
 debug_settings_test_suite()
 
+coverage_settings_test_suite()
+
 generated_header_test_suite()
 
 private_deps_test_suite()

test/coverage_settings_tests.bzl

@@ -0,0 +1,53 @@
+"""Tests for coverage-related command line flags under various configs."""
+
+load(
+    "@build_bazel_rules_swift//test/rules:action_command_line_test.bzl",
+    "make_action_command_line_test_rule",
+)
+
+default_coverage_test = make_action_command_line_test_rule(
+    config_settings = {
+        "//command_line_option:collect_code_coverage": "true",
+    },
+)
+
+coverage_prefix_map_test = make_action_command_line_test_rule(
+    config_settings = {
+        "//command_line_option:collect_code_coverage": "true",
+        "//command_line_option:features": [
+            "swift.coverage_prefix_map",
+        ],
+    },
+)
+
+def coverage_settings_test_suite(name = "coverage_settings"):
+    """Test suite for coverage options.
+
+    Args:
+        name: The name prefix for all the nested tests
+    """
+    default_coverage_test(
+        name = "{}_default_coverage".format(name),
+        tags = [name],
+        expected_argv = [
+            "-profile-generate",
+            "-profile-coverage-mapping",
+        ],
+        not_expected_argv = [
+            "-Xwrapped-swift=-coverage-prefix-pwd-is-dot",
+        ],
+        mnemonic = "SwiftCompile",
+        target_under_test = "@build_bazel_rules_swift//test/fixtures/debug_settings:simple",
+    )
+
+    coverage_prefix_map_test(
+        name = "{}_prefix_map".format(name),
+        tags = [name],
+        expected_argv = [
+            "-profile-generate",
+            "-profile-coverage-mapping",
+            "-Xwrapped-swift=-coverage-prefix-pwd-is-dot",
+        ],
+        mnemonic = "SwiftCompile",
+        target_under_test = "@build_bazel_rules_swift//test/fixtures/debug_settings:simple",
+    )

tools/worker/swift_runner.cc

@@ -187,6 +187,12 @@ bool SwiftRunner::ProcessArgument(
     consumer("-debug-prefix-map");
     consumer(GetCurrentDirectory() + "=.");
     changed = true;
+  } else if (arg == "-Xwrapped-swift=-coverage-prefix-pwd-is-dot") {
+    // Get the actual current working directory (the workspace root), which we
+    // didn't know at analysis time.
+    consumer("-coverage-prefix-map");
+    consumer(GetCurrentDirectory() + "=.");
+    changed = true;
   } else if (arg == "-Xwrapped-swift=-ephemeral-module-cache") {
     // Create a temporary directory to hold the module cache, which will be
     // deleted after compilation is finished.