• d-bugmail puremagic.com (28/46) Jan 06 2012 http://d.puremagic.com/issues/show_bug.cgi?id=7240

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=7240

           Summary: Possibilities of throwing Throwable should be
                    calculated
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: k.hara.pg gmail.com


--- Comment #0 from Kenji Hara <k.hara.pg gmail.com> 2012-01-06 09:20:03 PST ---
(This issue is derived from bug 7232)

In following code, statement #1 throws no exception, so #2 is never reachable.
But current dmd cannot detect it, 

bool addArticle()
{
    scope(failure) return false;  // #2
    return true;   // #1
}

My technical note from http://d.puremagic.com/issues/show_bug.cgi?id=7232#c2
 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.

I think dmd should also calculate the Throwable flow, not only the Exception
flow (it is related to 'nothrow' attribute).

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