fix(internal/librarian): tidy to skip duplicate API path check for hardcoded list in java (#5707)

Add logic in tidy to skip duplicate API path checks for this hardcoded
list when language is Java.

These API paths are duplicated in java's librarian.yaml config because
java geneates proto and grpc modules from these into
[java-iam](https://github.com/googleapis/google-cloud-java/tree/main/java-iam)
and gapic modules separately into
[java-iam-policy](https://github.com/googleapis/google-cloud-java/tree/main/java-iam-policy).

Fix #5706

Author: zhumin8

internal/librarian/tidy.go

@@ -36,6 +36,18 @@ var (
 	errDuplicateLibraryName  = errors.New("duplicate library name")
 	errDuplicateAPIPath      = errors.New("duplicate api path")
 	errNoGoogleapiSourceInfo = errors.New("googleapis source not configured in librarian.yaml")
+
+	// javaSkipDuplicatePaths lists special API paths that are allowed to appear in multiple
+	// libraries in Java without triggering the duplicate API path error.
+	// These are paths are duplicated in java because their generated code splits
+	// between java-iam and java-iam-policy.
+	javaSkipDuplicatePaths = map[string]bool{
+		"google/iam/v1":     true,
+		"google/iam/v2":     true,
+		"google/iam/v2beta": true,
+		"google/iam/v3":     true,
+		"google/iam/v3beta": true,
+	}
 )
 
 func tidyCommand() *cli.Command {
@@ -139,6 +151,9 @@ func validateLibraries(cfg *config.Config) error {
 		}
 		for _, ch := range lib.APIs {
 			if ch.Path != "" {
+				if cfg.Language == config.LanguageJava && javaSkipDuplicatePaths[ch.Path] {
+					continue
+				}
 				pathCount[ch.Path]++
 			}
 		}

internal/librarian/tidy_test.go

@@ -64,6 +64,35 @@ func TestValidateLibraries(t *testing.T) {
 			language: config.LanguageJava,
 			wantErr:  java.ErrInvalidDistributionName,
 		},
+		{
+			name: "skipped duplicate api paths",
+			libraries: []*config.Library{
+				{
+					Name: "lib1",
+					APIs: []*config.API{{Path: "google/iam/v1"}},
+				},
+				{
+					Name: "lib2",
+					APIs: []*config.API{{Path: "google/iam/v1"}},
+				},
+			},
+			language: config.LanguageJava,
+		},
+		{
+			name: "duplicate api paths not skipped for non-java",
+			libraries: []*config.Library{
+				{
+					Name: "lib1",
+					APIs: []*config.API{{Path: "google/iam/v1"}},
+				},
+				{
+					Name: "lib2",
+					APIs: []*config.API{{Path: "google/iam/v1"}},
+				},
+			},
+			language: config.LanguagePython,
+			wantErr:  errDuplicateAPIPath,
+		},
 	} {
 		t.Run(test.name, func(t *testing.T) {
 			cfg := &config.Config{