Add support for labeled statements to the parser/AST

This is a prerequisite for supporting labeled breaks/continues. Clearly
unusable labels, such as `x: let foo = 1;` report an error by default,
similar to TS's behavior.

src/ast.ts

@@ -440,9 +440,10 @@ export abstract class Node {
 
   static createBlockStatement(
     statements: Statement[],
+    label: IdentifierExpression | null,
     range: Range
   ): BlockStatement {
-    return new BlockStatement(statements, range);
+    return new BlockStatement(statements, label, range);
   }
 
   static createBreakStatement(
@@ -475,9 +476,10 @@ export abstract class Node {
   static createDoStatement(
     body: Statement,
     condition: Expression,
+    label: IdentifierExpression | null,
     range: Range
   ): DoStatement {
-    return new DoStatement(body, condition, range);
+    return new DoStatement(body, condition, label, range);
   }
 
   static createEmptyStatement(
@@ -548,9 +550,10 @@ export abstract class Node {
     condition: Expression,
     ifTrue: Statement,
     ifFalse: Statement | null,
+    label: IdentifierExpression | null,
     range: Range
   ): IfStatement {
-    return new IfStatement(condition, ifTrue, ifFalse, range);
+    return new IfStatement(condition, ifTrue, ifFalse, label, range);
   }
 
   static createImportStatement(
@@ -607,18 +610,20 @@ export abstract class Node {
     condition: Expression | null,
     incrementor: Expression | null,
     body: Statement,
+    label: IdentifierExpression | null,
     range: Range
   ): ForStatement {
-    return new ForStatement(initializer, condition, incrementor, body, range);
+    return new ForStatement(initializer, condition, incrementor, body, label, range);
   }
 
   static createForOfStatement(
     variable: Statement,
     iterable: Expression,
     body: Statement,
+    label: IdentifierExpression | null,
     range: Range
   ): ForOfStatement {
-    return new ForOfStatement(variable, iterable, body, range);
+    return new ForOfStatement(variable, iterable, body, label, range);
   }
 
   static createFunctionDeclaration(
@@ -675,9 +680,10 @@ export abstract class Node {
   static createSwitchStatement(
     condition: Expression,
     cases: SwitchCase[],
+    label: IdentifierExpression | null,
     range: Range
   ): SwitchStatement {
-    return new SwitchStatement(condition, cases, range);
+    return new SwitchStatement(condition, cases, label, range);
   }
 
   static createSwitchCase(
@@ -700,9 +706,10 @@ export abstract class Node {
     catchVariable: IdentifierExpression | null,
     catchStatements: Statement[] | null,
     finallyStatements: Statement[] | null,
+    label: IdentifierExpression | null,
     range: Range
   ): TryStatement {
-    return new TryStatement(bodyStatements, catchVariable, catchStatements, finallyStatements, range);
+    return new TryStatement(bodyStatements, catchVariable, catchStatements, finallyStatements, label, range);
   }
 
   static createTypeDeclaration(
@@ -753,9 +760,10 @@ export abstract class Node {
   static createWhileStatement(
     condition: Expression,
     statement: Statement,
+    label: IdentifierExpression | null,
     range: Range
   ): WhileStatement {
-    return new WhileStatement(condition, statement, range);
+    return new WhileStatement(condition, statement, label, range);
   }
 
   /** Tests if this node is a literal of the specified kind. */
@@ -1788,6 +1796,8 @@ export class BlockStatement extends Statement {
   constructor(
     /** Contained statements. */
     public statements: Statement[],
+    /** Label, if any. */
+    public label: IdentifierExpression | null,
     /** Source range. */
     range: Range
   ) {
@@ -1858,6 +1868,8 @@ export class DoStatement extends Statement {
     public body: Statement,
     /** Condition when to repeat. */
     public condition: Expression,
+    /** Label, if any. */
+    public label: IdentifierExpression | null,
     /** Source range. */
     range: Range
   ) {
@@ -2022,6 +2034,8 @@ export class ForStatement extends Statement {
     public incrementor: Expression | null,
     /** Body statement being looped over. */
     public body: Statement,
+    /** Label, if any. */
+    public label: IdentifierExpression | null,
     /** Source range. */
     range: Range
   ) {
@@ -2038,6 +2052,8 @@ export class ForOfStatement extends Statement {
     public iterable: Expression,
     /** Body statement being looped over. */
     public body: Statement,
+    /** Label, if any. */
+    public label: IdentifierExpression | null,
     /** Source range. */
     range: Range
   ) {
@@ -2108,6 +2124,8 @@ export class IfStatement extends Statement {
     public ifTrue: Statement,
     /** Statement executed when condition is `false`. */
     public ifFalse: Statement | null,
+    /** Label, if any. */
+    public label: IdentifierExpression | null,
     /** Source range. */
     range: Range
   ) {
@@ -2258,6 +2276,8 @@ export class SwitchStatement extends Statement {
     public condition: Expression,
     /** Contained cases. */
     public cases: SwitchCase[],
+    /** Label, if any. */
+    public label: IdentifierExpression | null,
     /** Source range. */
     range: Range
   ) {
@@ -2288,6 +2308,8 @@ export class TryStatement extends Statement {
     public catchStatements: Statement[] | null,
     /** Statements being executed afterwards, if a `finally` clause is present. */
     public finallyStatements: Statement[] | null,
+    /** Label, if any. */
+    public label: IdentifierExpression | null,
     /** Source range. */
     range: Range
   ) {
@@ -2382,6 +2404,8 @@ export class WhileStatement extends Statement {
     public condition: Expression,
     /** Body statement being looped over. */
     public body: Statement,
+    /** Label, if any. */
+    public label: IdentifierExpression | null,
     /** Source range. */
     range: Range
   ) {

src/diagnosticMessages.json

@@ -125,6 +125,7 @@
   "A class may only extend another class.": 1311,
   "A parameter property cannot be declared using a rest parameter.": 1317,
   "A default export can only be used in a module.": 1319,
+  "A label is not allowed here.": 1344,
   "An expression of type '{0}' cannot be tested for truthiness.": 1345,
   "An identifier or keyword cannot immediately follow a numeric literal.": 1351,
 

src/extra/ast.ts

@@ -801,6 +801,7 @@ export class ASTBuilder {
     let sb = this.sb;
     let statements = node.statements;
     let numStatements = statements.length;
+    this.visitLabel(node.label);
     if (numStatements) {
       sb.push("{\n");
       let indentLevel = ++this.indentLevel;
@@ -815,6 +816,15 @@ export class ASTBuilder {
     }
   }
 
+  private visitLabel(label: IdentifierExpression | null) {
+    if (!label) return;
+
+    let sb = this.sb;
+    this.visitIdentifierExpression(label);
+    sb.push(":\n");
+    indent(sb, this.indentLevel);
+  }
+
   visitBreakStatement(node: BreakStatement): void {
     let label = node.label;
     if (label) {
@@ -908,6 +918,7 @@ export class ASTBuilder {
 
   visitDoStatement(node: DoStatement): void {
     let sb = this.sb;
+    this.visitLabel(node.label);
     sb.push("do ");
     this.visitNode(node.body);
     if (node.body.kind == NodeKind.Block) {
@@ -1070,6 +1081,7 @@ export class ASTBuilder {
 
   visitForStatement(node: ForStatement): void {
     let sb = this.sb;
+    this.visitLabel(node.label);
     sb.push("for (");
     let initializer = node.initializer;
     if (initializer) {
@@ -1095,6 +1107,7 @@ export class ASTBuilder {
 
   visitForOfStatement(node: ForOfStatement): void {
     let sb = this.sb;
+    this.visitLabel(node.label);
     sb.push("for (");
     this.visitNode(node.variable);
     sb.push(" of ");
@@ -1205,6 +1218,7 @@ export class ASTBuilder {
 
   visitIfStatement(node: IfStatement): void {
     let sb = this.sb;
+    this.visitLabel(node.label);
     sb.push("if (");
     this.visitNode(node.condition);
     sb.push(") ");
@@ -1397,6 +1411,7 @@ export class ASTBuilder {
 
   visitSwitchStatement(node: SwitchStatement): void {
     let sb = this.sb;
+    this.visitLabel(node.label);
     sb.push("switch (");
     this.visitNode(node.condition);
     sb.push(") {\n");
@@ -1418,6 +1433,7 @@ export class ASTBuilder {
 
   visitTryStatement(node: TryStatement): void {
     let sb = this.sb;
+    this.visitLabel(node.label);
     sb.push("try {\n");
     let indentLevel = ++this.indentLevel;
     let bodyStatements = node.bodyStatements;
@@ -1528,6 +1544,7 @@ export class ASTBuilder {
 
   visitWhileStatement(node: WhileStatement): void {
     let sb = this.sb;
+    this.visitLabel(node.label);
     sb.push("while (");
     this.visitNode(node.condition);
     let body = node.body;