https://issues.dlang.org/show_bug.cgi?id=13053

          Issue ID: 13053
           Summary: Wrong warning on implicitly generated __xtoHash
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Keywords: diagnostic
          Severity: regression
          Priority: P1
         Component: DMD
          Assignee: nobody@puremagic.com
          Reporter: k.hara.pg@gmail.com

Test case:

@system:
struct S
{
    int[] a;
}

Output:
Warning: toHash() must be declared as extern (D) size_t toHash() const nothrow
@safe, not nothrow @system uint(ref const(S) p)

The error message is pointless and has no line number.

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