[Issue 21453] New: Struct opCmp selection does not try rewrites

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21453

          Issue ID: 21453
           Summary: Struct opCmp selection does not try rewrites
           Product: D
           Version: D2
          Hardware: x86
                OS: Windows
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: qs.il.paperinik at gmail.com

https://dlang.org/spec/operatoroverloading.html#compare says:

> Both rewrites are tried. If only one compiles,
> that one is taken. If they both resolve to the
> same function, the first rewrite is done. If
> they resolve to different functions, the best
> matching one is used. If they both match the
> same, but are different functions, an
> ambiguity error results.

This is not true. Comparison should *never ever* depend on the order of
arguments, i.e. x < y should in all cases be equivalent to y > x. Programmers
largely expect those to be equivalent in action the only difference being style
or readability.

All compilers since 2.060 accept this basic code [1] while clearly the spec
says the compiler must issue an ambiguity error (and the spec is right about
that).

[1] https://run.dlang.io/is/V3LrEU

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