Bug #20464: Redundant returns are unreachable in coverage

• Status: Open
• Assignee: -
• Target version: -
• Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN

[kddnewton (Kevin Newton)]

With the following code:

def meth_return(a)
  return if a
  return
end

If you run coverage on it, it's not possible for it to hit line 3, because there isn't a line event, because the return node was eliminated from the AST before it was compiled. There is a putnil instruction, so it's possible for us to attach a line event for it, but the compiler doesn't today.

[kddnewton (Kevin Newton)]

Just for the record in case this gets updated, this PR for the prism compiler (https://github.com/ruby/ruby/pull/10713) is what we have to do to make it work the same way. (It effectively checks if the return is redundant and if it is, disallows it from emitting a line event.)

[mame (Yusuke Endoh)]

Is this the same issue as #20457?

[kddnewton (Kevin Newton)]

It's a little different. In that one the issue is the parser, in this one the issue is the compiler. Even if the node isn't eliminated from the AST, there will still likely need to be a fix in the compiler.

[mame (Yusuke Endoh)]

If the parser does not remove the NODE_RETURN, the compiler can detect the line event, so I think it will be automatically fixed. In fact, I tried nobu's patch and it fixed this problem on my machine.

[mame (Yusuke Endoh)]

• Related to Bug #20457: Final `return` is eliminated from the AST added

[kddnewton (Kevin Newton)]

In that case this can probably be closed.