Issue #15980 has been updated by mame (Yusuke Endoh).


I talked with @ko1, and decide to introduce a stopgap measurement: stop the optimization in question only when coverage measurement is enabled.  This is because this issue is critical in coverage measurement, but minor in TracePoint.

The current compiler has many minor flaws, so we need to revamp it anyway in near future.

I will commit a patch soon.

----------------------------------------
Bug #15980: Coverage shows while/until after raise if/unless as uncovered line
https://bugs.ruby-lang.org/issues/15980#change-82956

* Author: jeremyevans0 (Jeremy Evans)
* Status: Assigned
* Priority: Normal
* Assignee: mame (Yusuke Endoh)
* Target version: 
* ruby -v: ruby 2.7.0dev (2019-07-03) [x86_64-openbsd6.5]
* Backport: 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: REQUIRED
----------------------------------------
The following code shows line 2 (`while true`) as uncovered:

```ruby
raise if 1 == 2
while true
  break
end
```

Coverage reports the following for this file: `[1, 0, 1, nil]`.  Note that `true` isn't important, any `while` condition will work.  However, if you change line 1 to `raise if false`, line 1 shows `nil` coverage, and line 2 shows as covered (`[nil, 1, 1, nil]`).  That leads me to believe this issue is related to the optimizer.

I bisected this to commit:100bf2757468439106775a7d95a791a8c10b874a, which certainly appears related.

This is not a theoretical case, it affected three lines in Sequel.  While not a major problem, I do think a fix should be backported to 2.6.

Note that this only affects line coverage.  Branch coverage shows:

```ruby
{"file.rb"=>
  {:branches=>
    {[:if, 0, 1, 0, 1, 15]=>
      {[:then, 1, 1, 0, 1, 5]=>0, [:else, 2, 1, 0, 1, 15]=>1},
     [:while, 3, 2, 0, 4, 3]=>{[:body, 4, 3, 2, 3, 7]=>1}}}}
```

If you run with both branch and line coverage, line coverage shows correctly.

This affects `while`/`until` after a line with `raise ... if ...` or `raise ... unless ...`.  If you switch to `if ...; raise ...; end`, then line coverage shows correctly.



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