[a119] #Warn Unreachable detection failure Topic is solved

[swagfag]

minimal example

Code: Select all

#Requires AutoHotkey v2.0-a119-179d27fd
#Warn Unreachable

{
	return
}

MsgBox ; unreachable

real-world example: see https://www.autohotkey.com/boards/viewtopic.php?f=82&t=79521&p=346012#warn_fail

Before the script starts to run, show a warning for each line that immediately follows a Return, Break, Continue, Throw or Goto at the same nesting level, unless that line is the target of a label.

despite the braces, its at the same nesting level

[Helgef]

I didn't see this before I posted in the other thread. It's not a bug. But I wouldn't use blocks like this to circumvent the warning.

[lexikos]

return is nested inside the block. It is not at the same nesting level as MsgBox.

For one, if it was at the same nesting level, you could do this:

Code: Select all

goto lbl
{
lbl:
MsgBox
}

A control flow statement such as If or Loop takes a single statement as its body. You can use an entire block because the content of the block (and its block-end) is nested under the block-begin, allowing the overall block to act as a compound statement. Lines are grouped within blocks this way regardless of what happens to be above the block.

Also, the warning is shown "for each line that immediately follows a Return [etc.]". In your example, the line immediately following return is }, but common sense says it must be permitted. (In this case common sense might say to not use a block at all, but if there's a warning, it should be about that and not } being unreachable.) The exception is that function definitions are skipped; otherwise, only the line immediately after the return is considered.

Also, "this does not detect all unreachable code".

The detection is intentionally simplistic, to minimize code size and complexity and the risk of showing warnings for legitimate code. All block-ends are treated the same, without regard to where the corresponding block-begin is or what is above it.

Compilers of other languages would tend to eliminate the braces during compilation, but that doesn't happen here, as you can see by checking ListLines. Those compilers do a lot more work (for other reasons than detecting unreachable code), breaking the code into smaller units and analyzing each code path.