Add support for @extend rules

pkg/sass-parser/lib/src/interpolation.ts

@@ -112,9 +112,8 @@ export class Interpolation extends Node {
    */
   get asPlain(): string | null {
     if (this.nodes.length === 0) return '';
-    if (this.nodes.length !== 1) return null;
-    if (typeof this.nodes[0] !== 'string') return null;
-    return this.nodes[0] as string;
+    if (this.nodes.some(node => typeof node !== 'string')) return null;
+    return this.nodes.join('');
   }
 
   /**

pkg/sass-parser/lib/src/sass-internal.ts

@@ -89,6 +89,11 @@ declare namespace SassInternal {
     readonly expression: Expression;
   }
 
+  class ExtendRule extends Statement {
+    readonly selector: Interpolation;
+    readonly isOptional: boolean;
+  }
+
   class Stylesheet extends ParentStatement<Statement[]> {}
 
   class StyleRule extends ParentStatement<Statement[]> {
@@ -129,6 +134,7 @@ export type AtRule = SassInternal.AtRule;
 export type DebugRule = SassInternal.DebugRule;
 export type EachRule = SassInternal.EachRule;
 export type ErrorRule = SassInternal.ErrorRule;
+export type ExtendRule = SassInternal.ExtendRule;
 export type Stylesheet = SassInternal.Stylesheet;
 export type StyleRule = SassInternal.StyleRule;
 export type Interpolation = SassInternal.Interpolation;
@@ -142,6 +148,7 @@ export interface StatementVisitorObject<T> {
   visitDebugRule(node: DebugRule): T;
   visitEachRule(node: EachRule): T;
   visitErrorRule(node: ErrorRule): T;
+  visitExtendRule(node: ExtendRule): T;
   visitStyleRule(node: StyleRule): T;
 }
 

pkg/sass-parser/lib/src/statement/at-root-rule.test.ts

@@ -12,7 +12,7 @@ describe('an @at-root rule', () => {
       () => void (node = scss.parse('@at-root {}').nodes[0] as GenericAtRule)
     );
 
-    it('has a name', () => expect(node.name.toString()).toBe('at-root'));
+    it('has a name', () => expect(node.name).toBe('at-root'));
 
     it('has no paramsInterpolation', () =>
       expect(node.paramsInterpolation).toBeUndefined());
@@ -27,7 +27,7 @@ describe('an @at-root rule', () => {
           .nodes[0] as GenericAtRule)
     );
 
-    it('has a name', () => expect(node.name.toString()).toBe('at-root'));
+    it('has a name', () => expect(node.name).toBe('at-root'));
 
     it('has a paramsInterpolation', () =>
       expect(node).toHaveInterpolation('paramsInterpolation', '(with: rule)'));
@@ -44,7 +44,7 @@ describe('an @at-root rule', () => {
           .nodes[0] as GenericAtRule)
     );
 
-    it('has a name', () => expect(node.name.toString()).toBe('at-root'));
+    it('has a name', () => expect(node.name).toBe('at-root'));
 
     it('has a paramsInterpolation', () => {
       const params = node.paramsInterpolation!;
@@ -63,7 +63,7 @@ describe('an @at-root rule', () => {
         void (node = scss.parse('@at-root .foo {}').nodes[0] as GenericAtRule)
     );
 
-    it('has a name', () => expect(node.name.toString()).toBe('at-root'));
+    it('has a name', () => expect(node.name).toBe('at-root'));
 
     it('has no paramsInterpolation', () =>
       expect(node.paramsInterpolation).toBeUndefined());

pkg/sass-parser/lib/src/statement/extend-rule.test.ts

@@ -0,0 +1,61 @@
+// Copyright 2024 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import {GenericAtRule, Rule, scss} from '../..';
+
+describe('an @extend rule', () => {
+  let node: GenericAtRule;
+
+  describe('with no interpolation', () => {
+    beforeEach(
+      () =>
+        void (node = (scss.parse('.foo {@extend .bar}').nodes[0] as Rule)
+          .nodes[0] as GenericAtRule)
+    );
+
+    it('has a name', () => expect(node.name).toBe('extend'));
+
+    it('has a paramsInterpolation', () =>
+      expect(node).toHaveInterpolation('paramsInterpolation', '.bar'));
+
+    it('has matching params', () => expect(node.params).toBe('.bar'));
+  });
+
+  describe('with interpolation', () => {
+    beforeEach(
+      () =>
+        void (node = (scss.parse('.foo {@extend .#{bar}}').nodes[0] as Rule)
+          .nodes[0] as GenericAtRule)
+    );
+
+    it('has a name', () => expect(node.name).toBe('extend'));
+
+    it('has a paramsInterpolation', () => {
+      const params = node.paramsInterpolation!;
+      expect(params.nodes[0]).toBe('.');
+      expect(params).toHaveStringExpression(1, 'bar');
+    });
+
+    it('has matching params', () => expect(node.params).toBe('.#{bar}'));
+  });
+
+  describe('with !optional', () => {
+    beforeEach(
+      () =>
+        void (node = (
+          scss.parse('.foo {@extend .bar !optional}').nodes[0] as Rule
+        ).nodes[0] as GenericAtRule)
+    );
+
+    it('has a name', () => expect(node.name).toBe('extend'));
+
+    it('has a paramsInterpolation', () =>
+      expect(node).toHaveInterpolation(
+        'paramsInterpolation',
+        '.bar !optional'
+      ));
+
+    it('has matching params', () => expect(node.params).toBe('.bar !optional'));
+  });
+});

pkg/sass-parser/lib/src/statement/index.ts

@@ -125,6 +125,15 @@ const visitor = sassInternal.createStatementVisitor<Statement>({
   visitDebugRule: inner => new DebugRule(undefined, inner),
   visitErrorRule: inner => new ErrorRule(undefined, inner),
   visitEachRule: inner => new EachRule(undefined, inner),
+  visitExtendRule: inner => {
+    const paramsInterpolation = new Interpolation(undefined, inner.selector);
+    if (inner.isOptional) paramsInterpolation.append('!optional');
+    return new GenericAtRule({
+      name: 'extend',
+      paramsInterpolation,
+      source: new LazySource(inner),
+    });
+  },
   visitStyleRule: inner => new Rule(undefined, inner),
 });