Generate coverage reports in LCOV format (#3117)

The generated TestMain now converts the go cover coverage reports to
LCOV. When combined with Bazel's --combined_report=lcov, this makes Go
coverage show up in cross-language, cross-target coverage reports by
default.

The combined report can be converted to HTML via e.g.

genhtml bazel-out/_coverage/_coverage_report.dat

If the old behavior of generating cover reports is still desired, it
can be enabled via:

--@io_bazel_rules_go//go/config:cover_format="go_cover"

Co-authored-by: Abhinav Gupta <[email protected]>

BUILD.bazel

@@ -105,6 +105,7 @@ cgo_context_data_proxy(
 # to depend on all build settings directly.
 go_config(
     name = "go_config",
+    cover_format = "//go/config:cover_format",
     # Always include debug symbols with -c dbg.
     debug = select({
         "//go/private:is_compilation_mode_dbg": "//go/private:always_true",

go/config/BUILD.bazel

@@ -58,6 +58,16 @@ string_list_flag(
     visibility = ["//visibility:public"],
 )
 
+string_flag(
+    name = "cover_format",
+    build_setting_default = "lcov",
+    values = [
+        "go_cover",
+        "lcov",
+    ],
+    visibility = ["//visibility:public"],
+)
+
 filegroup(
     name = "all_files",
     testonly = True,

go/private/actions/compilepkg.bzl

@@ -73,6 +73,7 @@ def emit_compilepkg(
             args.add("-cover_mode", "atomic")
         else:
             args.add("-cover_mode", "set")
+        args.add("-cover_format", go.cover_format)
         args.add_all(cover, before_each = "-cover")
     args.add_all(archives, before_each = "-arc", map_each = _archive)
     if importpath:

go/private/context.bzl

@@ -477,6 +477,7 @@ def go_context(ctx, attr = None):
         tags = tags,
         stamp = mode.stamp,
         label = ctx.label,
+        cover_format = mode.cover_format,
 
         # Action generators
         archive = toolchain.actions.archive,
@@ -780,6 +781,7 @@ def _go_config_impl(ctx):
         linkmode = ctx.attr.linkmode[BuildSettingInfo].value,
         tags = ctx.attr.gotags[BuildSettingInfo].value,
         stamp = ctx.attr.stamp,
+        cover_format = ctx.attr.cover_format[BuildSettingInfo].value,
     )]
 
 go_config = rule(
@@ -818,6 +820,10 @@ go_config = rule(
             providers = [BuildSettingInfo],
         ),
         "stamp": attr.bool(mandatory = True),
+        "cover_format": attr.label(
+            mandatory = True,
+            providers = [BuildSettingInfo],
+        ),
     },
     provides = [GoConfigInfo],
     doc = """Collects information about build settings in the current

go/private/mode.bzl

@@ -76,6 +76,7 @@ def get_mode(ctx, go_toolchain, cgo_context_info, go_config_info):
     stamp = go_config_info.stamp if go_config_info else False
     debug = go_config_info.debug if go_config_info else False
     linkmode = go_config_info.linkmode if go_config_info else LINKMODE_NORMAL
+    cover_format = go_config_info and go_config_info.cover_format
     goos = go_toolchain.default_goos
     goarch = go_toolchain.default_goarch
 
@@ -107,6 +108,7 @@ def get_mode(ctx, go_toolchain, cgo_context_info, go_config_info):
         goos = goos,
         goarch = goarch,
         tags = tags,
+        cover_format = cover_format,
     )
 
 def installsuffix(mode):

go/private/rules/test.bzl

@@ -101,6 +101,7 @@ def _go_test_impl(ctx):
             arguments.add("-cover_mode", "atomic")
         else:
             arguments.add("-cover_mode", "set")
+        arguments.add("-cover_format", go.cover_format)
     arguments.add(
         # the l is the alias for the package under test, the l_test must be the
         # same with the test suffix

go/tools/builders/compilepkg.go

@@ -46,6 +46,7 @@ func compilePkg(args []string) error {
 	var outPath, outFactsPath, cgoExportHPath string
 	var testFilter string
 	var gcFlags, asmFlags, cppFlags, cFlags, cxxFlags, objcFlags, objcxxFlags, ldFlags quoteMultiFlag
+	var coverFormat string
 	fs.Var(&unfilteredSrcs, "src", ".go, .c, .cc, .m, .mm, .s, or .S file to be filtered and compiled")
 	fs.Var(&coverSrcs, "cover", ".go file that should be instrumented for coverage (must also be a -src)")
 	fs.Var(&embedSrcs, "embedsrc", "file that may be compiled into the package with a //go:embed directive")
@@ -67,6 +68,7 @@ func compilePkg(args []string) error {
 	fs.StringVar(&outFactsPath, "x", "", "The output archive file to write export data and nogo facts")
 	fs.StringVar(&cgoExportHPath, "cgoexport", "", "The _cgo_exports.h file to write")
 	fs.StringVar(&testFilter, "testfilter", "off", "Controls test package filtering")
+	fs.StringVar(&coverFormat, "cover_format", "", "Emit source file paths in coverage instrumentation suitable for the specified coverage format")
 	if err := fs.Parse(args); err != nil {
 		return err
 	}
@@ -85,9 +87,6 @@ func compilePkg(args []string) error {
 	for i := range embedSrcs {
 		embedSrcs[i] = abs(embedSrcs[i])
 	}
-	for i := range coverSrcs {
-		coverSrcs[i] = abs(coverSrcs[i])
-	}
 
 	// Filter sources.
 	srcs, err := filterAndSplitFiles(unfilteredSrcs)
@@ -143,7 +142,8 @@ func compilePkg(args []string) error {
 		packageListPath,
 		outPath,
 		outFactsPath,
-		cgoExportHPath)
+		cgoExportHPath,
+		coverFormat)
 }
 
 func compileArchive(
@@ -169,7 +169,8 @@ func compileArchive(
 	packageListPath string,
 	outPath string,
 	outXPath string,
-	cgoExportHPath string) error {
+	cgoExportHPath string,
+	coverFormat string) error {
 
 	workDir, cleanup, err := goenv.workDir()
 	if err != nil {
@@ -232,23 +233,33 @@ func compileArchive(
 
 	// Instrument source files for coverage.
 	if coverMode != "" {
-		shouldCover := make(map[string]bool)
+		relCoverPath := make(map[string]string)
 		for _, s := range coverSrcs {
-			shouldCover[s] = true
+			relCoverPath[abs(s)] = s
 		}
 
 		combined := append([]string{}, goSrcs...)
 		if cgoEnabled {
 			combined = append(combined, cgoSrcs...)
 		}
 		for i, origSrc := range combined {
-			if !shouldCover[origSrc] {
+			if _, ok := relCoverPath[origSrc]; !ok {
 				continue
 			}
 
-			srcName := origSrc
-			if importPath != "" {
-				srcName = path.Join(importPath, filepath.Base(origSrc))
+			var srcName string
+			switch coverFormat {
+			case "go_cover":
+				srcName = origSrc
+				if importPath != "" {
+					srcName = path.Join(importPath, filepath.Base(origSrc))
+				}
+			case "lcov":
+				// Bazel merges lcov reports across languages and thus assumes
+				// that the source file paths are relative to the exec root.
+				srcName = relCoverPath[origSrc]
+			default:
+				return fmt.Errorf("invalid value for -cover_format: %q", coverFormat)
 			}
 
 			stem := filepath.Base(origSrc)

go/tools/builders/generate_test_main.go

@@ -70,6 +70,7 @@ type Cases struct {
 	Examples    []Example
 	TestMain    string
 	CoverMode   string
+	CoverFormat string
 	Pkgname     string
 }
 
@@ -171,10 +172,16 @@ func main() {
 		}
 	}
 
+	testDeps :=
+  {{if eq .CoverFormat "lcov"}}
+		bzltestutil.LcovTestDeps{TestDeps: testdeps.TestDeps{}}
+  {{else}}
+		testdeps.TestDeps{}
+  {{end}}
   {{if .Version "go1.18"}}
-	m := testing.MainStart(testdeps.TestDeps{}, testsInShard(), benchmarks, fuzzTargets, examples)
+	m := testing.MainStart(testDeps, testsInShard(), benchmarks, fuzzTargets, examples)
   {{else}}
-	m := testing.MainStart(testdeps.TestDeps{}, testsInShard(), benchmarks, examples)
+	m := testing.MainStart(testDeps, testsInShard(), benchmarks, examples)
   {{end}}
 
 	if filter := os.Getenv("TESTBRIDGE_TEST_ONLY"); filter != "" {
@@ -185,6 +192,12 @@ func main() {
 		flag.Lookup("test.failfast").Value.Set("true")
 	}
 
+	// Setting this flag serves two purposes:
+	// 1. It attains parity with "go test", which enables this feature by default.
+	//    https://cs.opensource.google/go/go/+/refs/tags/go1.18.1:src/cmd/go/internal/test/test.go;l=1331-1337
+	// 2. It provides a way to run hooks right before testing.M.Run() returns.
+	flag.Lookup("test.paniconexit0").Value.Set("true")
+
 	{{if ne .CoverMode ""}}
 	if len(coverdata.Counters) > 0 {
 		testing.RegisterCover(testing.Cover{
@@ -194,18 +207,23 @@ func main() {
 		})
 
 		if coverageDat, ok := os.LookupEnv("COVERAGE_OUTPUT_FILE"); ok {
+			{{if eq .CoverFormat "lcov"}}
+			flag.Lookup("test.coverprofile").Value.Set(coverageDat+".cover")
+			{{else}}
 			flag.Lookup("test.coverprofile").Value.Set(coverageDat)
+			{{end}}
 		}
 	}
 	{{end}}
 
 	{{if not .TestMain}}
-	os.Exit(m.Run())
+	res := m.Run()
 	{{else}}
 	{{.TestMain}}(m)
 	{{/* See golang.org/issue/34129 and golang.org/cl/219639 */}}
-	os.Exit(int(reflect.ValueOf(m).Elem().FieldByName("exitCode").Int()))
+	res := int(reflect.ValueOf(m).Elem().FieldByName("exitCode").Int())
 	{{end}}
+	os.Exit(res)
 }
 `
 
@@ -221,6 +239,7 @@ func genTestMain(args []string) error {
 	goenv := envFlags(flags)
 	out := flags.String("output", "", "output file to write. Defaults to stdout.")
 	coverMode := flags.String("cover_mode", "", "the coverage mode to use")
+	coverFormat := flags.String("cover_format", "", "the coverage report type to generate (go_cover or lcov)")
 	pkgname := flags.String("pkgname", "", "package name of test")
 	flags.Var(&imports, "import", "Packages to import")
 	flags.Var(&sources, "src", "Sources to process for tests")
@@ -270,8 +289,9 @@ func genTestMain(args []string) error {
 	}
 
 	cases := Cases{
-		CoverMode: *coverMode,
-		Pkgname:   *pkgname,
+		CoverFormat: *coverFormat,
+		CoverMode:   *coverMode,
+		Pkgname:     *pkgname,
 	}
 
 	testFileSet := token.NewFileSet()

go/tools/bzltestutil/BUILD.bazel

@@ -4,6 +4,7 @@ go_tool_library(
     name = "bzltestutil",
     srcs = [
         "init.go",
+        "lcov.go",
         "test2json.go",
         "wrap.go",
         "xml.go",
@@ -15,6 +16,7 @@ go_tool_library(
 go_test(
     name = "bzltestutil_test",
     srcs = [
+        "lcov_test.go",
         "wrap_test.go",
         "xml_test.go",
     ],