[Issue 21255] New: "overload alias ... forward declaration" when overload set of imported template functions is passed to alias template parameter

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21255

          Issue ID: 21255
           Summary: "overload alias ... forward declaration" when overload
                    set of imported template functions is passed to alias
                    template parameter
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: default_357-line at yahoo.de

Consider the following code:

```
--- a.d
void decode()() { }
--- b.d
void decode()() { }
--- test.d
import a : decode;
import b : decode;

void foo(alias A)() { }

void main() { foo!decode; }
```

https://run.dlang.io/is/P00CPB

This results in "Error: overload alias test.decode forward declaration".

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