[Issue 23651] New: Order dependency in semantic analysis of template members

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23651

          Issue ID: 23651
           Summary: Order dependency in semantic analysis of template
                    members
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: bugzilla at digitalmars.com

Consider, reduced from 
https://github.com/jmdavis/dxml/blob/d8eb8cff883d78a6258fc1e829484262c6f009fb/source/dxml/parser.d#L3628
:

---
template isCallable(alias callable)
{
    static if (is(typeof(&callable!())))
        enum bool isCallable = isCallable!(typeof(&callable!()));
    else
        enum bool isCallable = true;
}

string foo();

template FunctionTypeOf(alias func)
if (isCallable!func)
{
    alias FunctionTypeOf = typeof(foo);
}

template ReturnType(alias func)
{
    static if (is(FunctionTypeOf!func R == return))
        alias ReturnType = R;
}

template isAttrRange(R)
{
    alias NameType  = ReturnType!((R r) => r);
    pragma(msg, is(NameType == string));  // prints true

    enum isAttrRange = is(NameType == string);
}

static assert(isAttrRange!string); // fails
---

The trouble boils down to `enum isAttrRange` being evaluated before `NameType`
is, so the `is(NameType == string)` fails.

This is a blocker for https://github.com/dlang/dmd/pull/14838

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