[Issue 21205] New: Struct comparison does not follow spec

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21205

          Issue ID: 21205
           Summary: Struct comparison does not follow spec
           Product: D
           Version: D2
          Hardware: All
                OS: Windows
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: simen.kjaras at gmail.com

>From https://dlang.org/spec/operatoroverloading.html#equals:

2. [T]he expressions a.opEquals(b) and b.opEquals(a) are tried. If both resolve
to the same opEquals function, then the expression is rewritten to be
a.opEquals(b).
3. If one is a better match than the other, or one compiles and the other does
not, the first is selected.
4. Otherwise, an error results.

Clearly, this is not the case:

struct S1 {
    bool opEquals(S2 a) {
        return true;
    }
}
struct S2 {
    bool opEquals(S1 a) {
        return false;
    }
}
static assert((S1.init == S2.init) == (S2.init == S1.init)); // Fails

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