Close Bug #71 ParseRuleContext in empty input has undefined stop token

Signed-off-by: Mike Lischke <[email protected]>

src/BufferedTokenStream.ts

@@ -303,13 +303,27 @@ export class BufferedTokenStream implements TokenStream {
     }
 
     /**
-     * Given a starting index, return the index of the previous token on channel.
-     * Return i if tokens[i] is on channel. Return -1 if there are no tokens
-     * on channel between i and 0.
+     * Given a starting index, return the index of the previous token on
+     * channel. Return `i` if `tokens[i]` is on channel. Return -1
+     * if there are no tokens on channel between `i` and 0.
+     *
+     * If `i` specifies an index at or after the EOF token, the EOF token
+     * index is returned. This is due to the fact that the EOF token is treated
+     * as though it were on every channel.
      */
     public previousTokenOnChannel(i: number, channel: number): number {
-        while (i >= 0 && this.tokens[i].channel !== channel) {
-            i -= 1;
+        if (i >= this.tokens.length) {
+            // The EOF token is on every channel.
+            return this.tokens.length - 1;
+        }
+
+        while (i >= 0) {
+            const token = this.tokens[i];
+            if (token.type === Token.EOF || token.channel === channel) {
+                return i;
+            }
+
+            --i;
         }
 
         return i;

src/Parser.ts

@@ -121,6 +121,7 @@ export abstract class Parser extends Recognizer<ParserATNSimulator> {
         this.errorHandler.reset(this);
         this.context = null;
         this.syntaxErrors = 0;
+        this.matchedEOF = false;
         this.setTrace(false);
         this.precedenceStack = [];
         this.precedenceStack.push(0);
@@ -150,6 +151,10 @@ export abstract class Parser extends Recognizer<ParserATNSimulator> {
     public match(ttype: number): Token {
         let t = this.getCurrentToken();
         if (t.type === ttype) {
+            if (ttype === Token.EOF) {
+                this.matchedEOF = true;
+            }
+
             this.errorHandler.reportMatch(this);
             this.consume();
         } else {
@@ -473,8 +478,14 @@ export abstract class Parser extends Recognizer<ParserATNSimulator> {
     }
 
     public exitRule(): void {
-        this.context!.stop = this.inputStream.LT(-1);
-        // trigger event on _ctx, before it reverts to parent
+        if (this.matchedEOF) {
+            // If we have matched EOF, it cannot consume past EOF so we use LT(1) here.
+            this.context!.stop = this.inputStream.LT(1); // LT(1) will be end of file
+        } else {
+            this.context!.stop = this.inputStream.LT(-1); // stop node is what we just matched
+        }
+
+        // Trigger event on context, before it reverts to parent.
         this.triggerExitRuleEvent();
         this.state = this.context!.invokingState;
         this.context = this.context!.parent;