https://issues.dlang.org/show_bug.cgi?id=24688

          Issue ID: 24688
           Summary: Parameter by-value keeps const (only in templates)
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: dominikus@scherkl.de

```d
int fun(int x) { return ++x; }
T tpl(T)(T x) { return ++x; }

main
{
   const int i = 1;
   const range r; // some type that cannot create mutable copies
   int z = i;  // works, the compiler makes a mutable copy
   range s = r; // error **
   z = fun(i); // works, the compiler makes a mutable copy
   z = tpl(i); // error
}
```
The compiler should at least try to make a mutable copy also for templates.
If that is not possible, it should give the same error as in the line with **.
I'm ok if it instead tries a constant copy, but that should not be the default.

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