Resolve edge case with error recovery and repetitions

Which may cause a stack overflow when the repetition is entered but never consumed anything.
Chevrotain · Jun 21, 2019 · 211d410 · 211d410
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diff --git a/packages/chevrotain/docs/changes/CHANGELOG.md b/packages/chevrotain/docs/changes/CHANGELOG.md
@@ -1,32 +1,38 @@
+## X.Y.Z (INSERT_DATE_HERE)
+
+#### Bug Fixes
+
+-   [Resolved edge case in repetition error recovery which may cause "Maximum call stack size exceeded".]()
+
 ## 4.8.0 (6-14-2019)
 
 #### Minor Changes
 
--   [Custom Token Patterns and "Custom Payloads".](https://github.com/SAP/chevrotain/issues/888).
+-   [Custom Token Patterns and "Custom Payloads".](https://github.com/SAP/chevrotain/issues/888)
 
 ## 4.7.0 (6-8-2019)
 
 #### Minor Changes
 
--   [CST location information.](https://github.com/SAP/chevrotain/issues/932).
+-   [CST location information.](https://github.com/SAP/chevrotain/issues/932)
 
 ## 4.6.0 (6-1-2019)
 
 #### Minor Changes
 
--   [Expose two base Parser classes: CstParser and EmbeddedActionsParser.](https://github.com/SAP/chevrotain/issues/967).
+-   [Expose two base Parser classes: CstParser and EmbeddedActionsParser.](https://github.com/SAP/chevrotain/issues/967)
 
 ## 4.5.0 (5-25-2019)
 
 #### Minor Changes
 
--   [Consider Token Categories in Lookahead Functions Calculation.](https://github.com/SAP/chevrotain/issues/962).
+-   [Consider Token Categories in Lookahead Functions Calculation.](https://github.com/SAP/chevrotain/issues/962)
 
 ## 4.4.0 (5-24-2019)
 
 #### Minor Changes
 
--   [Better handling of infinite loops in repetitions.](https://github.com/SAP/chevrotain/issues/958).
+-   [Better handling of infinite loops in repetitions.](https://github.com/SAP/chevrotain/issues/958)
 
 ## 4.3.3 (4-12-2019)
 

diff --git a/packages/chevrotain/src/parse/parser/traits/recognizer_engine.ts b/packages/chevrotain/src/parse/parser/traits/recognizer_engine.ts
@@ -620,7 +620,13 @@ export class RecognizerEngine {
             <any>lookaheadFunction,
             MANY_IDX,
             prodOccurrence,
-            NextTerminalAfterManyWalker
+            NextTerminalAfterManyWalker,
+            // The notStuck parameter is only relevant when "attemptInRepetitionRecovery"
+            // is invoked from manyInternal, in the MANY_SEP case and AT_LEAST_ONE[_SEP]
+            // An infinite loop cannot occur as:
+            // - Either the lookahead is guaranteed to consume something (Single Token Separator)
+            // - AT_LEAST_ONE by definition is guaranteed to consume something (or error out).
+            notStuck
         )
     }
 

diff --git a/packages/chevrotain/src/parse/parser/traits/recoverable.ts b/packages/chevrotain/src/parse/parser/traits/recoverable.ts
@@ -148,9 +148,16 @@ export class Recoverable {
 
     shouldInRepetitionRecoveryBeTried(
         this: MixedInParser,
-        expectTokAfterLastMatch?: TokenType,
-        nextTokIdx?: number
+        expectTokAfterLastMatch: TokenType,
+        nextTokIdx: number,
+        notStuck: boolean | undefined
     ): boolean {
+        // Edge case of arriving from a MANY repetition which is stuck
+        // Attempting recovery in this case could cause an infinite loop
+        if (notStuck === false) {
+            return false
+        }
+
         // arguments to try and perform resync into the next iteration of the many are missing
         if (expectTokAfterLastMatch === undefined || nextTokIdx === undefined) {
             return false
@@ -383,7 +390,8 @@ export class Recoverable {
         lookaheadFunc: () => boolean,
         dslMethodIdx: number,
         prodOccurrence: number,
-        nextToksWalker: typeof AbstractNextTerminalAfterProductionWalker
+        nextToksWalker: typeof AbstractNextTerminalAfterProductionWalker,
+        notStuck?: boolean
     ): void {
         // by default this is a NO-OP
         // The actual implementation is with the function(not method) below
@@ -425,7 +433,8 @@ export function attemptInRepetitionRecovery(
     lookaheadFunc: () => boolean,
     dslMethodIdx: number,
     prodOccurrence: number,
-    nextToksWalker: typeof AbstractNextTerminalAfterProductionWalker
+    nextToksWalker: typeof AbstractNextTerminalAfterProductionWalker,
+    notStuck?: boolean
 ) {
     let key = this.getKeyForAutomaticLookahead(dslMethodIdx, prodOccurrence)
     let firstAfterRepInfo = this.firstAfterRepMap.get(<any>key)
@@ -458,7 +467,8 @@ export function attemptInRepetitionRecovery(
     if (
         this.shouldInRepetitionRecoveryBeTried(
             expectTokAfterLastMatch,
-            nextTokIdx
+            nextTokIdx,
+            notStuck
         )
     ) {
         // TODO: performance optimization: instead of passing the original args here, we modify