[Issue 23346] New: ImportC: pragma pack is not popped

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23346

          Issue ID: 23346
           Summary: ImportC: pragma pack is not popped
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Keywords: ImportC, wrong-code
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: dave287091 at gmail.com

It seems like #pragma pack(pop) in a C file does not undo a #pragma pack(push).

For example (on a target where sizeof(long) == 8):

#pragma pack(push, 4)
struct Packed {
    int x;
    long y;
};
#pragma pack(pop)

struct NotPacked {
    int x;
    // should have 4 bytes of padding
    long y;
};

_Static_assert(sizeof(long)==8, "long is not 8 bytes");
_Static_assert(sizeof(struct Packed)==12, "sizeof(Packed) != 12");
_Static_assert(sizeof(struct NotPacked)==16, "sizeof(NotPacked) != 16”); //
This static assertion fails.

Compiling with clang passes the static assertions.

I noticed this when compiling some code on macOS (which unfortunately uses
pragma pack in some system headers).

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