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digitalmars.D.bugs - [Issue 7232] New: Warning: statement is not reachable has no line number

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7232

           Summary: Warning: statement is not reachable has no line number
           Product: D
           Version: D2
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: robert octarineparrot.com


--- Comment #0 from Robert Clipsham <robert octarineparrot.com> 2012-01-05
15:52:33 GMT ---
When the following is compiled with -w or -wi, it will give a warning without a
line number
----
bool addArticle()
{
    scope(failure) return false;
    return true;
}
----
Tested on dmd 2.057 on OS X 64 and Ubuntu 32.

$ dmd -w test.d
Warning: statement is not reachable

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7232


Kenji Hara <k.hara.pg gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch


--- Comment #1 from Kenji Hara <k.hara.pg gmail.com> 2012-01-06 08:51:01 PST ---
https://github.com/D-Programming-Language/dmd/pull/610

In addArticle function, dmd translates the body code like follows:

try {
  return true;
}
catch (Throwable __o) {
  return false;
  throw __o;  // #1 rethrow catched exception object
}

The "statement is not reachable" warning is caused by line #1.

After my patch, the translation result would change like follows:

try {
  return true;
}
catch (Throwable __o) {
  return false;   // this statement never fall through next.
                  // so next unreachable rethrowing is implicitly removed.
}

Finally, original warning would never be generated.

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--- Comment #2 from Kenji Hara <k.hara.pg gmail.com> 2012-01-06 09:03:30 PST ---
Technical note:

Maybe, the original issue by Robert Clipsham is "unreachable scope(failure)
should warn "statement is not reachable" _with line number_.
But today it is technically enhancement. Because:

1. Current D2 dmd does only check Exception throwing possibilities in flow
analysis.
That means Throwable is not the target of the analysis. In above code,

    scope(failure) return false;
    return true;    // (a)

dmd does not consider the statement (a) throws Throwable or not.

2. scope(failure) catches Throwable object and rethrow it. Therefore the
scope(failure) statement is always analysed as *may be reachable*.

From the two reasons, current dmd cannot detect that the `scope(failure) return
false;` is not reachable.

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--- Comment #3 from Kenji Hara <k.hara.pg gmail.com> 2012-01-06 09:21:19 PST ---
Posted bug 7240 as an enhancement.

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prev sibling parent d-bugmail puremagic.com writes:
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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bugzilla digitalmars.com
         Resolution|                            |FIXED


--- Comment #4 from Walter Bright <bugzilla digitalmars.com> 2012-01-06
13:30:16 PST ---
https://github.com/D-Programming-Language/dmd/commit/458065293bd4cf990fb99bcd01fc294e7df21c17

https://github.com/D-Programming-Language/dmd/commit/986404479ea9eac7a9caa32be1f92c22a8aee38a

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