Bug 11132 – Odd diagnostic with C-style struct initializer when union field is present

----- struct S { int x; union { int a; int b; } int z; } void main() { S s = { 1, 2, 3 }; } ----- $ dmd test.d test.d(15): Error: variable test.main.s is not a static and cannot have static initializer A more appropriate diagnostic is emitted when using the regular D-style syntax: S s = S(1, 2, 3); test.d(17): Error: overlapping initialization for b *However*, C (or is it just C++?) supports a special syntax for initializing union fields: S s = { 1, { 2 }, 3 }; But the above is an error in D: test.d(17): Error: a struct is not a valid initializer for a int I don't know if we want to support this. But we at least have to fix the diagnostic in the first example.

In case you're wondering, I've ran into it while porting this code: ----- struct STGMEDIUM { DWORD tymed; union { HBITMAP hBitmap; PVOID hMetaFilePict; HENHMETAFILE hEnhMetaFile; HGLOBAL hGlobal; LPWSTR lpszFileName; LPSTREAM pstm; LPSTORAGE pstg; } LPUNKNOWN pUnkForRelease; } STGMEDIUM stgmed = { TYMED.TYMED_HGLOBAL, { 0 }, 0 }; ----- Speaking of which, what is a union field initialized to in D? I mean, what does .init equal to for multiple types? Is it just the bit-pattern zero?

https://github.com/D-Programming-Language/dmd/pull/2605 After merging the PR, compier will report more better message for the OP code: test.d(22): Error: overlapping initialization for field a and b

Commit pushed to master at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/3f671f1bee0e769efc45c7684b891210707806cb fix Issue 11132 - Odd diagnostic with C-style struct initializer when union field is present

(In reply to comment #1) > Speaking of which, what is a union field initialized to in D? It's supposed to be set to the .init of its first field, and any remaining bytes set to 0.