[Issue 17939] New: extern(C) function support with non-C attributes/types should be documented

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=17939

          Issue ID: 17939
           Summary: extern(C) function support with non-C attributes/types
                    should be documented
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Keywords: spec
          Severity: enhancement
          Priority: P1
         Component: dlang.org
          Assignee: nobody at puremagic.com
          Reporter: schveiguy at yahoo.com

In issue 7854, Walter says that allowing non-C attributes in extern(C) function
parameters is a "feature":

https://issues.dlang.org/show_bug.cgi?id=7854#c15

Therefore, I'm opening this enhancement request for making the spec reflect
definitively how this feature works. I think a clear explanation will help
compiler developers, and will help users understand what actually happens.

See also Walter's PR that uses this feature:
https://github.com/dlang/druntime/pull/1917

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