__traits(isDeprecated) returns false on deprecated aliases

[dlangBugzillaToGithub]

JR reported this on 2019-09-17T18:21:35Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=20221

Description

Manjaro/Arch x86_64, dmd v2.087.1, ldc v1.16.0.

__traits(isDeprecated, deprecatedAlias) evaluates whether the aliased symbol is deprecated, not whether the alias is.

struct Foo
{
    string good;
    deprecated alias bad = good;
}

void main()
{
    Foo f;
    string good = f.bad;
    static assert(__traits(isDeprecated, f.bad));
}

onlineapp.d(10): Deprecation: alias `onlineapp.Foo.bad` is deprecated
onlineapp.d(11): Error: static assert:  __traits(isDeprecated, good) is false

https://run.dlang.io/is/tLS1o2