textChanges: Simplify getChanges (#21971)

* textChanges: Simplify getChanges

* Return ReadonlyArray

Author: Andy

src/compiler/core.ts

@@ -1438,6 +1438,14 @@ namespace ts {
         }
     }
 
+    export function group<T>(values: ReadonlyArray<T>, getGroupId: (value: T) => string): ReadonlyArray<ReadonlyArray<T>> {
+        const groupIdToGroup = createMultiMap<T>();
+        for (const value of values) {
+            groupIdToGroup.add(getGroupId(value), value);
+        }
+        return arrayFrom(groupIdToGroup.values());
+    }
+
     /**
      * Tests whether a value is an array.
      */

src/services/textChanges.ts

@@ -593,32 +593,12 @@ namespace ts.textChanges {
 
         public getChanges(): FileTextChanges[] {
             this.finishInsertNodeAtClassStart();
-
-            const changesPerFile = createMap<Change[]>();
-            // group changes per file
-            for (const c of this.changes) {
-                let changesInFile = changesPerFile.get(c.sourceFile.path);
-                if (!changesInFile) {
-                    changesPerFile.set(c.sourceFile.path, changesInFile = []);
-                }
-                changesInFile.push(c);
-            }
-            // convert changes
-            const fileChangesList: FileTextChanges[] = [];
-            changesPerFile.forEach(changesInFile => {
+            return group(this.changes, c => c.sourceFile.path).map(changesInFile => {
                 const sourceFile = changesInFile[0].sourceFile;
-                const fileTextChanges: FileTextChanges = { fileName: sourceFile.fileName, textChanges: [] };
-                for (const c of ChangeTracker.normalize(changesInFile)) {
-                    fileTextChanges.textChanges.push(createTextChange(this.computeSpan(c, sourceFile), this.computeNewText(c, sourceFile)));
-                }
-                fileChangesList.push(fileTextChanges);
+                const textChanges = ChangeTracker.normalize(changesInFile).map(c =>
+                    createTextChange(createTextSpanFromRange(c.range), this.computeNewText(c, sourceFile)));
+                return { fileName: sourceFile.fileName, textChanges };
             });
-
-            return fileChangesList;
-        }
-
-        private computeSpan(change: Change, _sourceFile: SourceFile): TextSpan {
-            return createTextSpanFromRange(change.range);
         }
 
         private computeNewText(change: Change, sourceFile: SourceFile): string {
@@ -675,7 +655,7 @@ namespace ts.textChanges {
             return applyFormatting(nonformattedText, sourceFile, initialIndentation, delta, this.formatContext);
         }
 
-        private static normalize(changes: Change[]): Change[] {
+        private static normalize(changes: ReadonlyArray<Change>): ReadonlyArray<Change> {
             // order changes by start position
             const normalized = stableSort(changes, (a, b) => a.range.pos - b.range.pos);
             // verify that change intervals do not overlap, except possibly at end points.