Fix stack overflow in Deferred parsers with infinite recursion

[Copilot]

Deferred and Recursive parsers crash with stack overflow when configured with infinite recursion (e.g., loop.Parser = loop or Recursive(c => c)).

var loop = Deferred<string>();
loop.Parser = loop;  // Direct self-reference
var result = loop.Parse("test");  // Stack overflow

var recursive = Recursive<string>(c => c);  // Self-reference via constructor
var result2 = recursive.Parse("test");  // Stack overflow

Changes

• ParseContext: Added position-aware cycle detection via _activeParserPositions HashSet tracking parser-position pairs using an optimized private ParserPosition record struct

  • IsParserActiveAtPosition(): Check if parser already active at current input offset
  • PushParserAtPosition() / PopParserAtPosition(): Manage active parser stack
  • DisableLoopDetection: New property to disable loop detection when needed (e.g., when ParseContext is mutated during loops)

• Deferred.Parse(): Check for cycles before recursing; return false (parse failure) when same parser invoked at same position. Respects the DisableLoopDetection flag.

• Tests: Added coverage for direct self-reference, recursive constructor, valid recursion scenarios, and DisableLoopDetection flag

Valid recursive parsers that consume input between invocations remain unaffected. Loop detection can be disabled by setting ParseContext.DisableLoopDetection = true when needed.

• Fixes Access Violation exception #77

Original prompt

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This section details on the original issue you should resolve

<issue_title>Access Violation exception</issue_title>
<issue_description>@sebastienros is there any cycle detection mechanism in parlot?

example code which will break your app:

var loop = Deferred<string>();

loop.Parser = loop;

var test = loop.Parse("hello parlot");

or

var loop = Recursive<string>(c => c);

var test = loop.Parse("hello parlot");

I would expect this will detect infinite loop and return null instead of crashing.

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Access Violation exception #77

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[sebastienros]

@copilot add an option in ParseContext to disable this feature. For instance bool DisableLoopDetection { get; set; } = false; since the ParseContext itself could be mutated during loops and change the end result of parsing at the same location.

[Copilot]

@copilot add an option in ParseContext to disable this feature. For instance bool DisableLoopDetection { get; set; } = false; since the ParseContext itself could be mutated during loops and chan...

Added the DisableLoopDetection property to ParseContext in commit 8069841.

The property defaults to false (loop detection enabled), and when set to true, the cycle detection is bypassed. The implementation checks the flag in Deferred.Parse() before performing position tracking and cycle detection.