fix(migrations): preserve comments when removing unused imports (angular#61674)

Updates the unused imports schematic to preserve comments inside the array. THis is necessary for some internal use cases.

PR Close angular#61674

Author: crisbeto

packages/core/schematics/ng-generate/cleanup-unused-imports/BUILD.bazel

@@ -21,6 +21,7 @@ ts_project(
         "//packages/compiler-cli/src/ngtsc/core:api",
         "//packages/core/schematics/utils",
         "//packages/core/schematics/utils/tsurge",
+        "//packages/core/schematics/utils/tsurge/helpers/ast",
         "//packages/core/schematics/utils/tsurge/helpers/angular_devkit",
     ],
     deps = [

packages/core/schematics/ng-generate/cleanup-unused-imports/unused_imports_migration.ts

@@ -17,9 +17,10 @@ import {
   TsurgeFunnelMigration,
 } from '../../utils/tsurge';
 import {ErrorCode, FileSystem, ngErrorCode} from '@angular/compiler-cli';
-import {DiagnosticCategoryLabel, NgCompilerOptions} from '@angular/compiler-cli/src/ngtsc/core/api';
+import {DiagnosticCategoryLabel} from '@angular/compiler-cli/src/ngtsc/core/api';
 import {ImportManager} from '@angular/compiler-cli/private/migrations';
 import {applyImportManagerChanges} from '../../utils/tsurge/helpers/apply_import_manager';
+import {getLeadingLineWhitespaceOfNode} from '../../utils/tsurge/helpers/ast/leading_space';
 
 /** Data produced by the migration for each compilation unit. */
 export interface CompilationUnitData {
@@ -283,6 +284,7 @@ export class UnusedImportsMigration extends TsurgeFunnelMigration<
     const {fullRemovals, partialRemovals, allRemovedIdentifiers} = removalLocations;
     const {importedSymbols, identifierCounts} = usages;
     const importManager = new ImportManager();
+    const sourceText = sourceFile.getFullText();
 
     // Replace full arrays with empty ones. This allows preserves more of the user's formatting.
     fullRemovals.forEach((node) => {
@@ -299,22 +301,15 @@ export class UnusedImportsMigration extends TsurgeFunnelMigration<
     });
 
     // Filter out the unused identifiers from an array.
-    partialRemovals.forEach((toRemove, node) => {
-      const newNode = ts.factory.updateArrayLiteralExpression(
-        node,
-        node.elements.filter((el) => !toRemove.has(el)),
-      );
-
-      replacements.push(
-        new Replacement(
-          projectFile(sourceFile, info),
-          new TextUpdate({
-            position: node.getStart(),
-            end: node.getEnd(),
-            toInsert: this.printer.printNode(ts.EmitHint.Unspecified, newNode, sourceFile),
-          }),
-        ),
-      );
+    partialRemovals.forEach((toRemove, parent) => {
+      toRemove.forEach((node) => {
+        replacements.push(
+          new Replacement(
+            projectFile(sourceFile, info),
+            getArrayElementRemovalUpdate(node, parent, sourceText),
+          ),
+        );
+      });
     });
 
     // Attempt to clean up unused import declarations. Note that this isn't foolproof, because we
@@ -336,3 +331,49 @@ export class UnusedImportsMigration extends TsurgeFunnelMigration<
     applyImportManagerChanges(importManager, replacements, [sourceFile], info);
   }
 }
+
+/** Generates a `TextUpdate` for the removal of an array element. */
+function getArrayElementRemovalUpdate(
+  node: ts.Expression,
+  parent: ts.ArrayLiteralExpression,
+  sourceText: string,
+): TextUpdate {
+  let position = node.getStart();
+  let end = node.getEnd();
+  let toInsert = '';
+  const whitespaceOrLineFeed = /\s/;
+
+  // Usually the way we'd remove the nodes would be to recreate the `parent` while excluding
+  // the nodes that should be removed. The problem with this is that it'll strip out comments
+  // inside the array which can have special meaning internally. We work around it by removing
+  // only the node's own offsets. This comes with another problem in that it won't remove the commas
+  // that separate array elements which in turn can look weird if left in place (e.g.
+  // `[One, Two, Three, Four]` can turn into `[One,,Four]`). To account for them, we start with the
+  // node's end offset and then expand it to include trailing commas, whitespace and line breaks.
+  for (let i = end; i < sourceText.length; i++) {
+    if (sourceText[i] === ',' || whitespaceOrLineFeed.test(sourceText[i])) {
+      end++;
+    } else {
+      break;
+    }
+  }
+
+  // If we're removing the last element in the array, adjust the starting offset so that
+  // it includes the previous comma on the same line. This avoids turning something like
+  // `[One, Two, Three]` into `[One,]`. We only do this within the same like, because
+  // trailing comma at the end of the line is fine.
+  if (parent.elements[parent.elements.length - 1] === node) {
+    for (let i = position - 1; i >= 0; i--) {
+      if (sourceText[i] === ',' || sourceText[i] === ' ') {
+        position--;
+      } else {
+        break;
+      }
+    }
+
+    // Replace the node with its leading whitespace to preserve the formatting.
+    toInsert = getLeadingLineWhitespaceOfNode(node);
+  }
+
+  return new TextUpdate({position, end, toInsert});
+}

packages/core/schematics/test/cleanup_unused_imports_migration_spec.ts

@@ -297,4 +297,78 @@ describe('cleanup unused imports schematic', () => {
     `),
     );
   });
+
+  it('should preserve comments when removing unused imports', async () => {
+    writeFile(
+      'comp.ts',
+      `
+        import {Component} from '@angular/core';
+        import {One, Two, Three} from './directives';
+
+        @Component({
+          imports: [
+            // Start
+            Three,
+            One,
+            Two,
+            // End
+          ],
+          template: '<div one></div>',
+        })
+        export class Comp {}
+      `,
+    );
+
+    await runMigration();
+
+    expect(logs.pop()).toBe('Removed 2 imports in 1 file');
+    expect(stripWhitespace(tree.readContent('comp.ts'))).toBe(
+      stripWhitespace(`
+        import {Component} from '@angular/core';
+        import {One} from './directives';
+
+        @Component({
+          imports: [
+            // Start
+            One,
+            // End
+          ],
+          template: '<div one></div>',
+        })
+        export class Comp {}
+    `),
+    );
+  });
+
+  it('should preserve inline comments and strip trailing comma when removing imports from same line', async () => {
+    writeFile(
+      'comp.ts',
+      `
+        import {Component} from '@angular/core';
+        import {One, Two, Three} from './directives';
+
+        @Component({
+          imports: [/* Start */ Three, One, Two /* End */],
+          template: '<div one></div>',
+        })
+        export class Comp {}
+      `,
+    );
+
+    await runMigration();
+
+    expect(logs.pop()).toBe('Removed 2 imports in 1 file');
+    expect(stripWhitespace(tree.readContent('comp.ts'))).toBe(
+      stripWhitespace(`
+        import {Component} from '@angular/core';
+        import {One} from './directives';
+
+        @Component({
+          imports: [/* Start */ One /* End */],
+          template: '<div one></div>',
+        })
+        export class Comp {}
+    `),
+    );
+  });
 });