[Issue 12555] New: Incorrect error ungagging for speculatively instantiated class

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=12555

          Issue ID: 12555
           Summary: Incorrect error ungagging for speculatively
                    instantiated class
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Keywords: rejects-valid
          Severity: normal
          Priority: P1
         Component: DMD
          Assignee: nobody at puremagic.com
          Reporter: k.hara.pg at gmail.com
            Blocks: 11622

This test case should not produce any errors, but doesn't.

class A(T)
{
    Undef error;
}

static assert(!__traits(compiles, {
    class C : A!C  { }
}));

----
test.d(3): Error: undefined identifier Undef
test.d(8): Error: template instance test.A!(C) error instantiating

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