nogo ignore generated source code

Implements a map that track usages of:
- Generated source code by rules_go
- Rewritten source code by rules_go

In case of generated source code, nogo will ignore those files by
default.  In case of rewritten source code (i.e. coverage tests), nogo
should only be run over the original source file.

go/tools/builders/compilepkg.go

@@ -184,6 +184,15 @@ func compileArchive(
 	}
 	defer cleanup()
 
+	// As part of compilation process, rules_go does generate and/or rewrite code
+	// based on the original source files.  We should only run static analysis
+	// over original source files and not the generated source as end users have
+	// little control over the generated source.
+	//
+	// nogoSrcsTranslate maps generated/rewritten source files back to original source.
+	// If the original source path is an empty string, exclude generated source from nogo run.
+	nogoSrcsTranslate := make(map[string]string)
+
 	if len(srcs.goSrcs) == 0 {
 		// We need to run the compiler to create a valid archive, even if there's
 		// nothing in it. GoPack will complain if we try to add assembly or cgo
@@ -194,13 +203,13 @@ func compileArchive(
 		// otherwise platforms without sandbox support may race to create/remove
 		// the file during parallel compilation.
 		emptyDir := filepath.Join(filepath.Dir(outPath), sanitizePathForIdentifier(importPath))
-		if err := os.Mkdir(emptyDir, 0700); err != nil {
+		if err := os.Mkdir(emptyDir, 0o700); err != nil {
 			return fmt.Errorf("could not create directory for _empty.go: %v", err)
 		}
 		defer os.RemoveAll(emptyDir)
 
 		emptyPath := filepath.Join(emptyDir, "_empty.go")
-		if err := os.WriteFile(emptyPath, []byte("package empty\n"), 0666); err != nil {
+		if err := os.WriteFile(emptyPath, []byte("package empty\n"), 0o666); err != nil {
 			return err
 		}
 
@@ -210,6 +219,8 @@ func compileArchive(
 			matched:  true,
 			pkg:      "empty",
 		})
+
+		nogoSrcsTranslate[emptyPath] = ""
 	}
 	packageName := srcs.goSrcs[0].pkg
 	var goSrcs, cgoSrcs []string
@@ -290,6 +301,7 @@ func compileArchive(
 
 			if i < len(goSrcs) {
 				goSrcs[i] = coverSrc
+				nogoSrcsTranslate[coverSrc] = origSrc
 			} else {
 				cgoSrcs[i-len(goSrcs)] = coverSrc
 			}
@@ -312,7 +324,7 @@ func compileArchive(
 		gcFlags = append(gcFlags, createTrimPath(gcFlags, srcDir))
 	} else {
 		if cgoExportHPath != "" {
-			if err := ioutil.WriteFile(cgoExportHPath, nil, 0666); err != nil {
+			if err := ioutil.WriteFile(cgoExportHPath, nil, 0o666); err != nil {
 				return err
 			}
 		}
@@ -390,11 +402,20 @@ func compileArchive(
 	// Run nogo concurrently.
 	var nogoChan chan error
 	outFactsPath := filepath.Join(workDir, nogoFact)
-	if nogoPath != "" {
+	nogoSrcs := make([]string, 0, len(goSrcs))
+	for _, goSrc := range goSrcs {
+		if originSrc, ok := nogoSrcsTranslate[goSrc]; ok && originSrc != "" {
+			nogoSrcs = append(nogoSrcs, originSrc)
+			continue
+		}
+
+		nogoSrcs = append(nogoSrcs, goSrc)
+	}
+	if nogoPath != "" && len(nogoSrcs) > 0 {
 		ctx, cancel := context.WithCancel(context.Background())
 		nogoChan = make(chan error)
 		go func() {
-			nogoChan <- runNogo(ctx, workDir, nogoPath, goSrcs, deps, packagePath, importcfgPath, outFactsPath)
+			nogoChan <- runNogo(ctx, workDir, nogoPath, nogoSrcs, deps, packagePath, importcfgPath, outFactsPath)
 		}()
 		defer func() {
 			if nogoChan != nil {