[Issue 20388] New: Parse error when compiling lambdas in mixins as template parameters

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20388

          Issue ID: 20388
           Summary: Parse error when compiling lambdas in mixins as
                    template parameters
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: regression
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: johannes.riecken at gmail.com

Fails with dmd 2.088:

```
void main() {
    foo!(mixin("(int a) { return a; }"))();

}

void foo(alias t)() {
}
```

Error:
```
/tmp/foo.d-mixin-2(2): Error: basic type expected, not (
/tmp/foo.d-mixin-2(2): Error: function declaration without return type. (Note
that constructors are always named this)
```

This is expected to compile and did compile in previous dmd versions.

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