[Issue 24529] New: is expression ignores implicit conversion of enum when pattern matching

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24529

          Issue ID: 24529
           Summary: is expression ignores implicit conversion of enum when
                    pattern matching
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: major
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: snarwin+bugzilla at gmail.com

As of DMD 2.108.0, the following program fails to compile:

---
struct S(T) {}
enum E : S!int { a = S!int() }

static assert(is(E : S!int)); // ok
static assert(is(E : S!T, T)); // error
---

The error message is:

---
bug.d(5): Error: static assert:  `is(E : S!T, __isexp_id2, T)` is false
---

The expected behavior is for both static assert statements to pass.

See also issue 21975, in which the same error was caused by a struct with
`alias this`.

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