From: "nagachika (Tomoyuki Chikanaga) via ruby-core" <ruby-core@...>
Date: 2026-09-06T07:56:49+00:00
Subject: [ruby-core:126578] [Ruby Bug#22269] `Coverage.line_stub` clobbers already-collected coverage data

Issue #22269 has been updated by nagachika (Tomoyuki Chikanaga).

Backport changed from 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN to 3.3: UNKNOWN, 3.4: DONE, 4.0: DONE

merged backport PR: https://github.com/ruby/ruby/pull/18584

----------------------------------------
Bug #22269: `Coverage.line_stub` clobbers already-collected coverage data
https://bugs.ruby-lang.org/issues/22269#change-118788

* Author: mugikurash (Shuta Mugikura)
* Status: Closed
* ruby -v: ruby 4.1.0dev (2026-08-27T01:47:31Z master 5ee95de080) +PRISM [arm64-darwin25]
* Backport: 3.3: UNKNOWN, 3.4: DONE, 4.0: DONE
----------------------------------------
`Coverage.line_stub` compiles the file with `compile_file` only to read the ISeq's `trace_points`. Since https://bugs.ruby-lang.org/issues/22018 `compile_file` registers the file into the coverage table, so calling `line_stub` while `Coverage` is running resets the file's already-collected counters. 

This also reproduces on 3.4 and 4.0, so I would like it backported.

Reproduction:

```ruby
require "coverage"

f = File.expand_path("m.rb")
File.write(f, "def m\n  :ok\nend\n")

Coverage.start
require f
m
p Coverage.peek_result[f]

Coverage.line_stub(f)
p Coverage.peek_result[f]

m
p Coverage.result[f]
```

Expected:

```
[1, 1, nil]
[1, 1, nil]
[1, 2, nil]
```

Actual:

```
[1, 1, nil]
[0, 0, nil]
[0, 0, nil]
```




-- 
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