boostorg/spirit_x4

The domain of integral bounds given to `repeat_directive` is underspecified

Open

#62 opened on Oct 5, 2025

View on GitHub
 (0 comments) (0 reactions) (0 assignees)C++ (3 forks)auto 404
documentationenhancementgood first issuehelp wanted

Repository metrics

Stars
 (37 stars)
PR merge metrics
 (No merged PRs in 30d)

Description

Perhaps this should be both rejected in the code and described in the new documentation.

  • The documentation should note that repeat operates on closed bounds.
  • x4::repeat(negative) should be rejected
  • x4::repat(negative, ...) and x4::repat(..., negative) should be rejected
  • x4::repeat(max, min) should be rejected
  • x4::repeat(0) should be rejected
    • This is semantically very vague.
    • As of now, I confirmed that it actually results in always succeeding parser (regardless of the underlying parser p given to repeat(0)[p]), similar to eps

Proposed solution:

  • The basic concept should be changed from std::integral to std::unsigned_integral
  • x4::repeat(max, min) should throw std::domain_error
  • x4::repeat(0) should throw std::domain_error

Contributor guide

Research direction
Examine the repeat directive implementation in spirit x4 to understand how bounds are currently handled, then enforce that bounds must be unsigned integers and throw std::domain error for invalid combinations like negative, zero, or reversed bounds (max < min).
Tech stack
cpp
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
C++
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30