fix(devtools/cmd/migrate-sidekick): fix mismatch in newline handling for documentationoverrides (#3341)

Add on a temp fix on top of the previous fix #3284. This fix tries to
align the expected format for `documentation_overrides` for
`google-cloud-orgpolicy-v1`. This is a brittle change, but as we don't
expect new `documentation_overrides` in the next few days and this is a
one time migration, it should be acceptable.


Verified locally after this change, `librarian generate
google-cloud-orgpolicy-v1` produces no diff. And the only diff it
produced for librarian.yaml is the following:

```
--- a/librarian.yaml
+++ b/librarian.yaml
@@ -1084,14 +1084,16 @@ libraries:
       title_override: Organization Policy Types
       documentation_overrides:
         - id: .google.cloud.orgpolicy.v1.Policy.ListPolicy
-          match: 'Ancestry subtrees must be in one of the following formats:'
+          match: |
+            Ancestry subtrees must be in one of the following formats:
           replace: |
-            
+
             Ancestry subtrees must be in one of the following formats:
         - id: .google.cloud.orgpolicy.v1.Policy.ListPolicy
-          match: The `supports_under` field of the associated `Constraint`  defines whether
+          match: |
+            The `supports_under` field of the associated `Constraint`  defines whether
           replace: |
-            
+
             The `supports_under` field of the associated `Constraint`  defines whether
```

Additional context about this fix:
#3330 (comment)

Fix #3330

Author: zhumin8

devtools/cmd/migrate-sidekick/main.go

@@ -807,9 +807,9 @@ func fixDocumentOverrideNewLines(yamlFile string, config *config.Config) error {
 			lookupKey := currentID + "|" + currentVal
 
 			if data, ok := lookup[lookupKey]; ok {
-				if strings.Contains(data.Match, "\n") {
+				// brittle: if replace has new lines, match has new line at start
+				if strings.Contains(data.Replace, "\n") {
 					newLines = append(newLines, fmt.Sprintf("%smatch: |", indent))
-					newLines = append(newLines, "") // Leading newline
 					newLines = append(newLines, indent+"  "+strings.TrimSpace(data.Match))
 				} else {
 					newLines = append(newLines, line) // Keep original if no newline

devtools/cmd/migrate-sidekick/main_test.go

@@ -789,15 +789,17 @@ func TestBuildConfig(t *testing.T) {
 
 func TestRunMigrateCommand(t *testing.T) {
 	for _, test := range []struct {
-		name                        string
-		path                        string
-		wantErr                     error
-		checkDocumentOverrideValues []string
+		name                         string
+		path                         string
+		wantErr                      error
+		checkDocumentOverrideReplace []string
+		checkDocumentOverrideMatch   []string
 	}{
 		{
-			name:                        "success",
-			path:                        "testdata/run/success",
-			checkDocumentOverrideValues: []string{"example replace", "\nAncestry subtrees must be in one of the following formats:\n"},
+			name:                         "success",
+			path:                         "testdata/run/success",
+			checkDocumentOverrideMatch:   []string{"example match", "Ancestry subtrees must be in one of the following formats:\n"},
+			checkDocumentOverrideReplace: []string{"example replace", "\nAncestry subtrees must be in one of the following formats:\n"},
 		},
 		{
 			name:    "tidy_command_fails",
@@ -840,12 +842,17 @@ func TestRunMigrateCommand(t *testing.T) {
 				if len(librarianConfig.Libraries) != 1 {
 					t.Fatalf("librarian yaml does not contain library")
 				}
-				if len(test.checkDocumentOverrideValues) > 0 {
-					for index, expected := range test.checkDocumentOverrideValues {
+				if len(test.checkDocumentOverrideReplace) > 0 {
+					for index, expected := range test.checkDocumentOverrideReplace {
 						got := librarianConfig.Libraries[0].Rust.DocumentationOverrides[index].Replace
 						if got != expected {
 							t.Fatalf("expected checkDocumentOverrideValue: %s got: %s", expected, got)
 						}
+						gotMatch := librarianConfig.Libraries[0].Rust.DocumentationOverrides[index].Match
+						if expected := test.checkDocumentOverrideMatch[index]; gotMatch != expected {
+							t.Fatalf("expected checkDocumentOverrideMatch: %s got: %s", expected, gotMatch)
+						}
+
 					}
 				}
 				if librarianConfig.Release == nil {