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.

Author: CountBleck

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(
@@ -607,18 +609,20 @@ 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(
@@ -753,9 +757,10 @@ 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 +1793,8 @@ export class BlockStatement extends Statement {
   constructor(
     /** Contained statements. */
     public statements: Statement[],
+    /** Label, if any. */
+    public label: IdentifierExpression | null,
     /** Source range. */
     range: Range
   ) {
@@ -1858,6 +1865,8 @@ 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 +2031,8 @@ 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 +2049,8 @@ 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
   ) {
@@ -2382,6 +2395,8 @@ 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/parser.ts

@@ -2899,7 +2899,34 @@ export class Parser extends DiagnosticEmitter {
 
     let state = tn.mark();
     let token = tn.next();
+    let label: IdentifierExpression | null = null;
     let statement: Statement | null = null;
+
+    // Detect labeled statements
+    if (token == Token.Identifier) {
+      const preIdentifierState = tn.mark();
+      const identifier = tn.readIdentifier();
+      const range = tn.range();
+
+      if (tn.skip(Token.Colon)) {
+        label = Node.createIdentifierExpression(identifier, range);
+        token = tn.next();
+
+        switch (token) {
+          case Token.For:
+          case Token.While:
+          case Token.Do:
+          case Token.OpenBrace:
+            // Do nothing
+            break;
+          default:
+            this.error(DiagnosticCode.A_label_is_not_allowed_here, range);
+        }
+      } else {
+        tn.reset(preIdentifierState);
+      }
+    }
+
     switch (token) {
       case Token.Break: {
         statement = this.parseBreak(tn);
@@ -2914,11 +2941,11 @@ export class Parser extends DiagnosticEmitter {
         break;
       }
       case Token.Do: {
-        statement = this.parseDoStatement(tn);
+        statement = this.parseDoStatement(tn, label);
         break;
       }
       case Token.For: {
-        statement = this.parseForStatement(tn);
+        statement = this.parseForStatement(tn, label);
         break;
       }
       case Token.If: {
@@ -2934,7 +2961,7 @@ export class Parser extends DiagnosticEmitter {
         break;
       }
       case Token.OpenBrace: {
-        statement = this.parseBlockStatement(tn, topLevel);
+        statement = this.parseBlockStatement(tn, topLevel, label);
         break;
       }
       case Token.Return: {
@@ -2967,7 +2994,7 @@ export class Parser extends DiagnosticEmitter {
         break;
       }
       case Token.While: {
-        statement = this.parseWhileStatement(tn);
+        statement = this.parseWhileStatement(tn, label);
         break;
       }
       case Token.Type: { // also identifier
@@ -2994,7 +3021,8 @@ export class Parser extends DiagnosticEmitter {
 
   parseBlockStatement(
     tn: Tokenizer,
-    topLevel: bool
+    topLevel: bool,
+    label: IdentifierExpression | null = null
   ): BlockStatement | null {
 
     // at '{': Statement* '}' ';'?
@@ -3013,7 +3041,7 @@ export class Parser extends DiagnosticEmitter {
         statements.push(statement);
       }
     }
-    let ret = Node.createBlockStatement(statements, tn.range(startPos, tn.pos));
+    let ret = Node.createBlockStatement(statements, label, tn.range(startPos, tn.pos));
     if (topLevel) tn.skip(Token.Semicolon);
     return ret;
   }
@@ -3051,7 +3079,8 @@ export class Parser extends DiagnosticEmitter {
   }
 
   parseDoStatement(
-    tn: Tokenizer
+    tn: Tokenizer,
+    label: IdentifierExpression | null
   ): DoStatement | null {
 
     // at 'do': Statement 'while' '(' Expression ')' ';'?
@@ -3067,7 +3096,7 @@ export class Parser extends DiagnosticEmitter {
         if (!condition) return null;
 
         if (tn.skip(Token.CloseParen)) {
-          let ret = Node.createDoStatement(statement, condition, tn.range(startPos, tn.pos));
+          let ret = Node.createDoStatement(statement, condition, label, tn.range(startPos, tn.pos));
           tn.skip(Token.Semicolon);
           return ret;
         } else {
@@ -3106,7 +3135,8 @@ export class Parser extends DiagnosticEmitter {
   }
 
   parseForStatement(
-    tn: Tokenizer
+    tn: Tokenizer,
+    label: IdentifierExpression | null
   ): Statement | null {
 
     // at 'for': '(' Statement? Expression? ';' Expression? ')' Statement
@@ -3139,7 +3169,7 @@ export class Parser extends DiagnosticEmitter {
               );
               return null;
             }
-            return this.parseForOfStatement(tn, startPos, initializer);
+            return this.parseForOfStatement(tn, startPos, initializer, label);
           }
           if (initializer.kind == NodeKind.Variable) {
             let declarations = (<VariableStatement>initializer).declarations;
@@ -3153,7 +3183,7 @@ export class Parser extends DiagnosticEmitter {
                 ); // recoverable
               }
             }
-            return this.parseForOfStatement(tn, startPos, initializer);
+            return this.parseForOfStatement(tn, startPos, initializer, label);
           }
           this.error(
             DiagnosticCode.Identifier_expected,
@@ -3215,6 +3245,7 @@ export class Parser extends DiagnosticEmitter {
               : null,
             incrementor,
             statement,
+            label,
             tn.range(startPos, tn.pos)
           );
 
@@ -3243,6 +3274,7 @@ export class Parser extends DiagnosticEmitter {
     tn: Tokenizer,
     startPos: i32,
     variable: Statement,
+    label: IdentifierExpression | null
   ): ForOfStatement | null {
 
     // at 'of': Expression ')' Statement
@@ -3265,6 +3297,7 @@ export class Parser extends DiagnosticEmitter {
       variable,
       iterable,
       statement,
+      label,
       tn.range(startPos, tn.pos)
     );
   }
@@ -3609,7 +3642,8 @@ export class Parser extends DiagnosticEmitter {
   }
 
   parseWhileStatement(
-    tn: Tokenizer
+    tn: Tokenizer,
+    label: IdentifierExpression | null
   ): WhileStatement | null {
 
     // at 'while': '(' Expression ')' Statement ';'?
@@ -3621,7 +3655,7 @@ export class Parser extends DiagnosticEmitter {
       if (tn.skip(Token.CloseParen)) {
         let statement = this.parseStatement(tn);
         if (!statement) return null;
-        let ret = Node.createWhileStatement(expression, statement, tn.range(startPos, tn.pos));
+        let ret = Node.createWhileStatement(expression, statement, label, tn.range(startPos, tn.pos));
         tn.skip(Token.Semicolon);
         return ret;
       } else {