http://d.puremagic.com/issues/show_bug.cgi?id=5069

           Summary: No missing extern(C) error
           Product: D
           Version: D2
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Keywords: accepts-invalid, diagnostic
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nob...@puremagic.com
        ReportedBy: bearophile_h...@eml.cc


--- Comment #0 from bearophile_h...@eml.cc 2010-10-17 05:21:22 PDT ---
This is a wrong D2 program:


import std.c.stdlib: qsort;
import std.c.stdio: printf;

int compare(const void *a, const void *b) {
    return *cast(int*)a - *cast(int*)b;
}

void main () {
    int[] values = [40, 10, 100, 90, 20, 25];

    for (int n = 0; n < 6; n++)
        printf ("%d ", values[n]);
    printf("\n");

    qsort(values.ptr, 6, int.sizeof, &compare);

    for (int n = 0; n < 6; n++)
        printf ("%d ", values[n]);
    printf("\n");
}


With DMD 2.049 it compiles with no errors, and then sefaults at runtime.

To fix it the compare() must have a C calling convention:

extern(C) int compare(const void *a, const void *b) {


DMD 1.026 avoids that runtime error with a useful compile-time error message
that I'd like in DMD2 too:

Line 15: function std.c.stdlib.qsort (void*,uint,uint,int(C *)(void*, void*))
does not match parameter types (int*,int,uint,int(*)(void*, void*))
Line 15: Error: cannot implicitly convert expression (& compare) of type
int(*)(void*, void*) to int(C *)(void*, void*)


A better single error message for D2 may say "extern(C)" too somewhere in the
error message, instead of just saying a less clear "expression (& compare) of
type int(*)(void*, void*) to int(C *)(void*, void*)". Something like:

Line 15: Error: cannot implicitly convert expression (& compare) of type int
function(const void*, const void*) to extern(C) int function(const void*, const
void*)

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