Bug 15094 – __traits(getMember) fails when the source is a struct/class field

Attempting to use `__traits(getMember)` with a sub-struct/field fails with a `need 'this'` error. Example code: import std.stdio; struct Foo { int i; } struct Bar { Foo foo; } void main() { Bar bar; writeln(__traits(getMember, bar.foo, "i")); } Output: $ rdmd ~/test.d /home/col/test.d(14): Error: need 'this' for 'i' of type 'int' Failed: ["dmd", "-v", "-o-", "/home/col/test.d", "-I/home/col"] It's possible, but annoying, to work around this by storing a local pointer to the field first. auto foo = &bar.foo; writeln(__traits(getMember, foo, "i"));

This appears to be a regression. Introduced in https://github.com/D-Programming-Language/dmd/pull/1687

(In reply to Vladimir Panteleev from comment #1) > This appears to be a regression. > > Introduced in https://github.com/D-Programming-Language/dmd/pull/1687 Not correct. With 2.062, compiling example code with `dmd -c` will make: test.d(16): Error: need 'this' to access member foo PR 1687 had moved many "need this" errors in glue layer to front-end, but such the field access is not yet supported. I think it's a reject-valid bug.

(In reply to Kenji Hara from comment #2) > PR 1687 had moved many "need this" errors in glue layer to front-end, but > such the field access is not yet supported. I think it's a reject-valid bug. Oh, OK.

Even after applying the PR (https://github.com/D-Programming-Language/dmd/pull/5215): ``` struct S { int i; } S s; unittest { import std.meta : Alias; alias GetMember1 = Alias!(__traits(getMember, mixin(__MODULE__), "s")); alias GetMember2 = Alias!(__traits(getMember, GetMember1, "i")); alias GetMember3 = Alias!(__traits(getMember, __traits(getMember, mixin(__MODULE__), "s"), "i")); // Works: auto a1 = &GetMember1; // Fails: auto a2 = &GetMember2; // Fails: auto a3 = &GetMember3; // Works: auto a4 = &__traits(getMember, __traits(getMember, mixin(__MODULE__), "s"), "i"); } ``` fails (in a2, a3).

Even after applying the PR (https://github.com/D-Programming-Language/dmd/pull/5215): ``` struct S { int i; } S s; unittest { import std.meta : Alias; alias GetMember1 = Alias!(__traits(getMember, mixin(__MODULE__), "s")); alias GetMember2 = Alias!(__traits(getMember, GetMember1, "i")); alias GetMember3 = Alias!(__traits(getMember, __traits(getMember, mixin(__MODULE__), "s"), "i")); // Works: auto a1 = &GetMember1; // Fails: auto a2 = &GetMember2; // Fails: auto a3 = &GetMember3; // Works: auto a4 = &__traits(getMember, __traits(getMember, mixin(__MODULE__), "s"), "i"); } ``` fails (in a2, a3).

This bit us in several places in the weka codebase.

Commits pushed to master at https://github.com/dlang/dmd https://github.com/dlang/dmd/commit/89c900316c02d7e845b151e02a460d89631a9d07 Fix Issue 15094 - __traits(getMember) fails when the source is a struct/class field https://github.com/dlang/dmd/commit/c9d988ebc0eca6137551eaacb961400acb2e7752 Merge pull request #7341 from JinShil/fix_15094 Fix Issue 15094 - __traits(getMember) fails when the source is a struct/class field

Commits pushed to stable at https://github.com/dlang/dmd https://github.com/dlang/dmd/commit/89c900316c02d7e845b151e02a460d89631a9d07 Fix Issue 15094 - __traits(getMember) fails when the source is a struct/class field https://github.com/dlang/dmd/commit/c9d988ebc0eca6137551eaacb961400acb2e7752 Merge pull request #7341 from JinShil/fix_15094

dlang/dmd pull request #12093 "[dmd-cxx] Backport more recent traits to the C++ port" was merged into dmd-cxx: - 542f9a47d165eb27b2d3b937cadd119c779b07fe by JinShil: [dmd-cxx] Fix Issue 15094 - __traits(getMember) fails when the source is a struct/class field https://github.com/dlang/dmd/pull/12093