Bug 18617 – need __traits(deprecated, expr) to check whether an expression would trigger deprecation

we need __traits(deprecated, expr) to check whether an expression would trigger deprecation this is analog to __traits(compiles, expr) but checks for deprecation instead of whether something compiles. eg use case (from https://github.com/dlang/phobos/pull/6178#pullrequestreview-104095990) ``` static assert(__traits(deprecated, {int[] a2 = [1, 2].asStatic;})); instead of simply having a comment: // NOTE: correctly issues a deprecation // int[] a2 = [1, 2].asStatic; ```

NOTE: IMO std.traits.isDeprecated is not applicable for this use case

@Geod24 created dlang/dmd pull request #10398 "Issue 18617 - Need ability to check if a symbol would trigger a deprecation" mentioning this issue: - Issue 18617 - Need ability to check if a symbol would trigger a deprecation ... without triggering it ! __traits(isDeprecated, Symbol) currently triggers a deprecation message, which makes it pretty useless for library writers. Note that a pitfall is that a library would fail to get a deprecation message, leading to a failure to remove the access to a symbol if the symbol is hard-coded. However, the prime usage of __traits(isDeprecated) is for meta-programming, hence it shouldn't be a problem in practice. https://github.com/dlang/dmd/pull/10398

dlang/dmd pull request #10398 "Fix Issue 18617 - Need ability to check if a symbol would trigger a deprecation" was merged into master: - 54574166b70cb0fd03cf5305833c4088923b7976 by Geod24: Fix Issue 18617 - Need ability to check if a symbol would trigger a deprecation ... without triggering it ! __traits(isDeprecated, Symbol) currently triggers a deprecation message, which makes it pretty useless for library writers. Note that a pitfall is that a library would fail to get a deprecation message, leading to a failure to remove the access to a symbol if the symbol is hard-coded. However, the prime usage of __traits(isDeprecated) is for meta-programming, hence it shouldn't be a problem in practice. https://github.com/dlang/dmd/pull/10398

dlang/dmd pull request #12093 "[dmd-cxx] Backport more recent traits to the C++ port" was merged into dmd-cxx: - 596401fa8d815314f1d34540c52075df4de7a713 by Geod24: [dmd-cxx] Fix Issue 18617 - Need ability to check if a symbol would trigger a deprecation without triggering it https://github.com/dlang/dmd/pull/12093