Use union types rather than base classes for Sass nodes (#2537)

Author: nex3

pkg/sass-parser/CHANGELOG.md

@@ -1,5 +1,9 @@
 ## 0.4.16-dev
 
+* Use union types rather than base classes for Sass nodes wherever possible.
+  This makes it possible for TypeScript to automatically narrow node types based
+  on `sassType` checks.
+
 * Add support for parsing null literals.
 
 * Add support for parsing parenthesized expressions.

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

@@ -4,7 +4,7 @@
 
 import * as postcss from 'postcss';
 
-import {Expression, ExpressionProps} from './expression';
+import {AnyExpression, ExpressionProps} from './expression';
 import {fromProps} from './expression/from-props';
 import {Node, NodeProps} from './node';
 import {ArgumentList} from './argument-list';
@@ -60,7 +60,7 @@ export interface ArgumentRaws {
  */
 export type ArgumentObjectProps = NodeProps & {
   raws?: ArgumentRaws;
-  value: Expression | ExpressionProps;
+  value: AnyExpression | ExpressionProps;
 } & ({name?: string; rest?: never} | {name?: never; rest?: boolean});
 
 /**
@@ -70,7 +70,7 @@ export type ArgumentObjectProps = NodeProps & {
  * ArgumentDeclarationProps}.
  */
 export type ArgumentExpressionProps =
-  | Expression
+  | AnyExpression
   | ExpressionProps
   | Omit<ArgumentObjectProps, 'name'>;
 
@@ -81,7 +81,7 @@ export type ArgumentExpressionProps =
  */
 export type ArgumentProps =
   | ArgumentObjectProps
-  | Expression
+  | AnyExpression
   | ExpressionProps
   | [string, ArgumentExpressionProps];
 
@@ -115,16 +115,16 @@ export class Argument extends Node {
   private declare _name?: string;
 
   /** The argument's value. */
-  get value(): Expression {
+  get value(): AnyExpression {
     return this._value!;
   }
-  set value(value: Expression | ExpressionProps) {
+  set value(value: AnyExpression | ExpressionProps) {
     if (this._value) this._value.parent = undefined;
-    if (!('sassType' in value)) value = fromProps(value);
-    if (value) value.parent = this;
-    this._value = value;
+    const built = 'sassType' in value ? value : fromProps(value);
+    built.parent = this;
+    this._value = built;
   }
-  private declare _value?: Expression;
+  private declare _value?: AnyExpression;
 
   /**
    * Whether this is a rest argument (indicated by `...` in Sass).
@@ -147,14 +147,14 @@ export class Argument extends Node {
       if ('sassType' in props || !('value' in props)) {
         defaults = {
           name,
-          value: props as Expression | ExpressionProps,
+          value: props as AnyExpression | ExpressionProps,
         };
       } else {
         defaults = {name, ...props} as ArgumentObjectProps;
       }
     } else if ('sassType' in defaults || !('value' in defaults)) {
       defaults = {
-        value: defaults as Expression | ExpressionProps,
+        value: defaults as AnyExpression | ExpressionProps,
       };
     }
     super(defaults);
@@ -193,7 +193,7 @@ export class Argument extends Node {
   }
 
   /** @hidden */
-  get nonStatementChildren(): ReadonlyArray<Expression> {
+  get nonStatementChildren(): ReadonlyArray<AnyExpression> {
     return [this.value];
   }
 }

pkg/sass-parser/lib/src/configured-variable.ts

@@ -6,7 +6,7 @@ import * as postcss from 'postcss';
 
 import {Configuration} from './configuration';
 import {convertExpression} from './expression/convert';
-import {Expression, ExpressionProps} from './expression';
+import {AnyExpression, ExpressionProps} from './expression';
 import {fromProps} from './expression/from-props';
 import {LazySource} from './lazy-source';
 import {Node, NodeProps} from './node';
@@ -56,7 +56,7 @@ export interface ConfiguredVariableRaws {
 export interface ConfiguredVariableObjectProps extends NodeProps {
   raws?: ConfiguredVariableRaws;
   name: string;
-  expression: Expression | ExpressionProps;
+  expression: AnyExpression | ExpressionProps;
   guarded?: boolean;
 }
 
@@ -70,7 +70,7 @@ export interface ConfiguredVariableObjectProps extends NodeProps {
  * creates an unguarded {@link ConfiguredVariable}.
  */
 export type ConfiguredVariableExpressionProps =
-  | Expression
+  | AnyExpression
   | ExpressionProps
   | Omit<ConfiguredVariableObjectProps, 'name'>;
 
@@ -103,16 +103,16 @@ export class ConfiguredVariable extends Node {
   declare name: string;
 
   /** The expression whose value the variable is assigned. */
-  get expression(): Expression {
+  get expression(): AnyExpression {
     return this._expression!;
   }
-  set expression(value: Expression | ExpressionProps) {
+  set expression(value: AnyExpression | ExpressionProps) {
     if (this._expression) this._expression.parent = undefined;
-    if (!('sassType' in value)) value = fromProps(value);
-    if (value) value.parent = this;
-    this._expression = value;
+    const built = 'sassType' in value ? value : fromProps(value);
+    built.parent = this;
+    this._expression = built;
   }
-  private declare _expression: Expression;
+  private declare _expression: AnyExpression;
 
   /** Whether this has a `!default` guard. */
   declare guarded: boolean;
@@ -129,7 +129,7 @@ export class ConfiguredVariable extends Node {
       if ('sassType' in rest || !('expression' in rest)) {
         defaults = {
           name,
-          expression: rest as Expression | ExpressionProps,
+          expression: rest as AnyExpression | ExpressionProps,
         };
       } else {
         defaults = {name, ...rest};
@@ -178,7 +178,7 @@ export class ConfiguredVariable extends Node {
   }
 
   /** @hidden */
-  get nonStatementChildren(): ReadonlyArray<Expression> {
+  get nonStatementChildren(): ReadonlyArray<AnyExpression> {
     return [this.expression];
   }
 }

pkg/sass-parser/lib/src/dynamic-import.ts

@@ -7,10 +7,10 @@ import * as postcss from 'postcss';
 import {StringExpression} from './expression/string';
 import {ImportList} from './import-list';
 import {LazySource} from './lazy-source';
-import {Node, NodeProps} from './node';
+import {AnyNode, Node, NodeProps} from './node';
 import * as sassInternal from './sass-internal';
 import {RawWithValue} from './raw-with-value';
-import {Statement} from './statement';
+import {AnyStatement} from './statement';
 import * as utils from './utils';
 
 /**
@@ -103,7 +103,7 @@ export class DynamicImport extends Node {
   }
 
   /** @hidden */
-  get nonStatementChildren(): ReadonlyArray<Exclude<Node, Statement>> {
+  get nonStatementChildren(): ReadonlyArray<Exclude<AnyNode, AnyStatement>> {
     return [];
   }
 }

pkg/sass-parser/lib/src/expression/binary-operation.ts

@@ -8,7 +8,7 @@ import {LazySource} from '../lazy-source';
 import {NodeProps} from '../node';
 import type * as sassInternal from '../sass-internal';
 import * as utils from '../utils';
-import {Expression, ExpressionProps} from '.';
+import {AnyExpression, Expression, ExpressionProps} from '.';
 import {convertExpression} from './convert';
 import {fromProps} from './from-props';
 
@@ -36,8 +36,8 @@ export type BinaryOperator =
  */
 export interface BinaryOperationExpressionProps extends NodeProps {
   operator: BinaryOperator;
-  left: Expression | ExpressionProps;
-  right: Expression | ExpressionProps;
+  left: AnyExpression | ExpressionProps;
+  right: AnyExpression | ExpressionProps;
   raws?: BinaryOperationExpressionRaws;
 }
 
@@ -80,30 +80,30 @@ export class BinaryOperationExpression extends Expression {
   private declare _operator: BinaryOperator;
 
   /** The expression on the left-hand side of this operation. */
-  get left(): Expression {
+  get left(): AnyExpression {
     return this._left;
   }
-  set left(left: Expression | ExpressionProps) {
+  set left(left: AnyExpression | ExpressionProps) {
     // TODO - postcss/postcss#1957: Mark this as dirty
     if (this._left) this._left.parent = undefined;
-    if (!('sassType' in left)) left = fromProps(left);
-    left.parent = this;
-    this._left = left;
+    const built = 'sassType' in left ? left : fromProps(left);
+    built.parent = this;
+    this._left = built;
   }
-  private declare _left: Expression;
+  private declare _left: AnyExpression;
 
   /** The expression on the right-hand side of this operation. */
-  get right(): Expression {
+  get right(): AnyExpression {
     return this._right;
   }
-  set right(right: Expression | ExpressionProps) {
+  set right(right: AnyExpression | ExpressionProps) {
     // TODO - postcss/postcss#1957: Mark this as dirty
     if (this._right) this._right.parent = undefined;
-    if (!('sassType' in right)) right = fromProps(right);
-    right.parent = this;
-    this._right = right;
+    const built = 'sassType' in right ? right : fromProps(right);
+    built.parent = this;
+    this._right = built;
   }
-  private declare _right: Expression;
+  private declare _right: AnyExpression;
 
   constructor(defaults: BinaryOperationExpressionProps);
   /** @hidden */
@@ -146,7 +146,7 @@ export class BinaryOperationExpression extends Expression {
   }
 
   /** @hidden */
-  get nonStatementChildren(): ReadonlyArray<Expression> {
+  get nonStatementChildren(): ReadonlyArray<AnyExpression> {
     return [this.left, this.right];
   }
 }

pkg/sass-parser/lib/src/expression/boolean.ts

@@ -77,7 +77,7 @@ export class BooleanExpression extends Expression {
   }
 
   /** @hidden */
-  get nonStatementChildren(): ReadonlyArray<Expression> {
+  get nonStatementChildren(): ReadonlyArray<never> {
     return [];
   }
 }

pkg/sass-parser/lib/src/expression/color.ts

@@ -115,7 +115,7 @@ export class ColorExpression extends Expression {
   }
 
   /** @hidden */
-  get nonStatementChildren(): ReadonlyArray<Expression> {
+  get nonStatementChildren(): ReadonlyArray<never> {
     return [];
   }
 }

pkg/sass-parser/lib/src/expression/convert.ts

@@ -7,7 +7,7 @@ import * as sassInternal from '../sass-internal';
 import {ArgumentList} from '../argument-list';
 import {Interpolation} from '../interpolation';
 import {LazySource} from '../lazy-source';
-import {Expression} from '.';
+import {AnyExpression} from '.';
 import {BinaryOperationExpression} from './binary-operation';
 import {BooleanExpression} from './boolean';
 import {ColorExpression} from './color';
@@ -22,7 +22,7 @@ import {SelectorExpression} from './selector';
 import {StringExpression} from './string';
 
 /** The visitor to use to convert internal Sass nodes to JS. */
-const visitor = sassInternal.createExpressionVisitor<Expression>({
+const visitor = sassInternal.createExpressionVisitor<AnyExpression>({
   visitBinaryOperationExpression: inner =>
     new BinaryOperationExpression(undefined, inner),
   visitBooleanExpression: inner => new BooleanExpression(undefined, inner),
@@ -57,6 +57,6 @@ const visitor = sassInternal.createExpressionVisitor<Expression>({
 /** Converts an internal expression AST node into an external one. */
 export function convertExpression(
   expression: sassInternal.Expression,
-): Expression {
+): AnyExpression {
   return expression.accept(visitor);
 }

pkg/sass-parser/lib/src/expression/from-props.ts

@@ -3,7 +3,7 @@
 // https://opensource.org/licenses/MIT.
 
 import * as sass from 'sass';
-import {Expression, ExpressionProps} from '.';
+import {AnyExpression, ExpressionProps} from '.';
 import {BinaryOperationExpression} from './binary-operation';
 import {BooleanExpression} from './boolean';
 import {ColorExpression} from './color';
@@ -17,7 +17,7 @@ import {ParenthesizedExpression} from './parenthesized';
 import {StringExpression} from './string';
 
 /** Constructs an expression from {@link ExpressionProps}. */
-export function fromProps(props: ExpressionProps): Expression {
+export function fromProps(props: ExpressionProps): AnyExpression {
   if ('text' in props) return new StringExpression(props);
   if ('left' in props) return new BinaryOperationExpression(props);
   if ('separator' in props) return new ListExpression(props);

pkg/sass-parser/lib/src/expression/interpolated-function.ts

@@ -7,7 +7,8 @@ import * as postcss from 'postcss';
 import {ArgumentList, ArgumentListProps} from '../argument-list';
 import {Interpolation, InterpolationProps} from '../interpolation';
 import {LazySource} from '../lazy-source';
-import {Node, NodeProps} from '../node';
+import {AnyNode, NodeProps} from '../node';
+import {AnyStatement} from '../statement';
 import type * as sassInternal from '../sass-internal';
 import * as utils from '../utils';
 import {Expression} from '.';
@@ -102,7 +103,7 @@ export class InterpolatedFunctionExpression extends Expression {
   }
 
   /** @hidden */
-  get nonStatementChildren(): ReadonlyArray<Node> {
+  get nonStatementChildren(): ReadonlyArray<Exclude<AnyNode, AnyStatement>> {
     return [this.name, this.arguments];
   }
 }