[Issue 10455] New: Print range computed by expression range analysis in error messages

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=10455

           Summary: Print range computed by expression range analysis in
                    error messages
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: diagnostic
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: bearophile_hugs at eml.cc


--- Comment #0 from bearophile_hugs at eml.cc 2013-06-23 13:11:24 PDT ---
A low-priority enhancement request.


For this code:

void main() {
    ubyte x;
    ubyte y = x << 1;
}


The range analysis determines that it's conceivable to the result of that
expression to not fit in y, so the D compiler 2.064alpha gives:


temp.d(3): Error: cannot implicitly convert expression (cast(int)x << 1) of
type int to ubyte


To help the programmer understand faster the mistake in his/her code when
expressions become more complex I think it's also useful to print the range
resulting from the analysis, like:


temp.d(3): Error: cannot implicitly convert expression (cast(int)x << 1) in
interval [0 ... 510] of type int to ubyte


It uses 3 dots because it's an interval that includes the right end. Otherwise
if you print an interval open on the right in a case like this you have to
print a ulong.max+1 value:


void main() {
    ulong x;
    int y = x;
}


One downside: those error messages become a little longer (and a bit more
noisy).

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