Fix segfault when Ruby coverage is enabled with Rails 8.1 ERB templates#2541
Fix segfault when Ruby coverage is enabled with Rails 8.1 ERB templates#2541george-bit wants to merge 1 commit intoViewComponent:mainfrom
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v4.2.0 introduced a fix for incorrect line numbers in stack traces on Rails 8.1 by using negative lineno values (-1) in class_eval. However, negative line numbers cause segmentation faults when Ruby's Coverage module is enabled (e.g., when using SimpleCov in CI). This is a known Ruby bug: https://bugs.ruby-lang.org/issues/19363 The fix detects whether coverage is running via Coverage.running? and adapts the lineno value accordingly: - Coverage OFF: Use -1 (correct line numbers in stack traces) - Coverage ON: Use 1 (avoids segfault, line numbers off by ~2) Note: lineno=0 was also tested but causes the same segfault, so 1 is the minimum safe value when coverage is enabled. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Question: Is there a cleaner solution?While this fix works, I wanted to raise a question about the underlying approach. The
Alternative approaches worth considering:
I'm not deeply familiar with the history here, so I wanted to ask: is the current approach (adjusting lineno) the right long-term solution, or is there a cleaner way to handle Rails 8.1 compatibility that doesn't require these workarounds? |
joelhawksley
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Thanks for taking a crack at fixing this issue! I added a couple of comments, but one key thing is missing: a test to reproduce the issue to prevent regression in the future. Please add a failing test that this PR fixes ❤️
| lineno = | ||
| if Rails::VERSION::MAJOR >= 8 && Rails::VERSION::MINOR > 0 && details.handler == :erb | ||
| inline_template.lineno - 1 | ||
| coverage_running? ? inline_template.lineno : inline_template.lineno - 1 |
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Inline templates are defined inside a class, so they will almost always start on line 2 or later, making this change unnecessary.
| lineno = | ||
| if Rails::VERSION::MAJOR >= 8 && Rails::VERSION::MINOR > 0 && details.handler == :erb | ||
| - 1 | ||
| coverage_running? ? 1 : -1 |
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If coverage is running, let's strip the first line of the compiled template in this case and only if template annotations are enabled.
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Summary
Fixes segmentation fault when running tests with code coverage enabled (e.g., SimpleCov) on Rails 8.1+ with Ruby 3.4+.
Problem
v4.2.0 introduced negative
linenovalues (-1) inclass_evalto fix incorrect line numbers in stack traces for Rails 8.1 ERB templates. However, this causes a segmentation fault when Ruby'sCoveragemodule is enabled.Root Cause
Rails 8.1 change: Rails added annotation comments to compiled ERB output (rails/rails#53731), which added an extra line and caused stack trace line numbers to be off by 1.
v4.2.0 fix: Used
lineno = -1inclass_evalto compensate for the extra line.Ruby bug: Negative line numbers in
eval/class_evalcause segmentation faults when Ruby's Coverage module is running (bugs.ruby-lang.org/issues/19363). This bug exists in Ruby 3.4 and has been known since 2022.Result: Rails 8.1 + Ruby 3.4 + view_component 4.2.0 + SimpleCov = crash.
Solution
Detect whether coverage is running via
Coverage.running?and adapt:Why not 0? Testing showed
lineno=0also causes the segfault.1is the minimum safe value.Trade-off
This is the best possible fix given the Ruby bug. Most users (development, production) get correct line numbers. Only CI/coverage users see slightly off line numbers—but their tests actually run instead of crashing.
Fixes #2540