Preserve packed attribute in C translated struct (#4085)

* Preserve packed attribute in C translated struct

* Add tests for packed C struct

src-self-hosted/clang.zig

@@ -768,6 +768,7 @@ pub extern fn ZigClangVarDecl_getCanonicalDecl(self: ?*const struct_ZigClangVarD
 pub extern fn ZigClangVarDecl_getSectionAttribute(self: *const ZigClangVarDecl, len: *usize) ?[*]const u8;
 pub extern fn ZigClangFunctionDecl_getAlignedAttribute(self: *const ZigClangFunctionDecl, *const ZigClangASTContext) c_uint;
 pub extern fn ZigClangVarDecl_getAlignedAttribute(self: *const ZigClangVarDecl, *const ZigClangASTContext) c_uint;
+pub extern fn ZigClangRecordDecl_getPackedAttribute(self: ?*const struct_ZigClangRecordDecl) bool;
 pub extern fn ZigClangRecordDecl_getDefinition(self: ?*const struct_ZigClangRecordDecl) ?*const struct_ZigClangRecordDecl;
 pub extern fn ZigClangEnumDecl_getDefinition(self: ?*const struct_ZigClangEnumDecl) ?*const struct_ZigClangEnumDecl;
 pub extern fn ZigClangRecordDecl_getLocation(self: ?*const struct_ZigClangRecordDecl) struct_ZigClangSourceLocation;

src-self-hosted/translate_c.zig

@@ -733,13 +733,16 @@ fn transRecordDecl(c: *Context, record_decl: *const ZigClangRecordDecl) Error!?*
             break :blk opaque;
         };
 
-        const extern_tok = try appendToken(c, .Keyword_extern, "extern");
+        const layout_tok = try if (ZigClangRecordDecl_getPackedAttribute(record_decl))
+            appendToken(c, .Keyword_packed, "packed")
+        else
+            appendToken(c, .Keyword_extern, "extern");
         const container_tok = try appendToken(c, container_kind, container_kind_name);
         const lbrace_token = try appendToken(c, .LBrace, "{");
 
         const container_node = try c.a().create(ast.Node.ContainerDecl);
         container_node.* = .{
-            .layout_token = extern_tok,
+            .layout_token = layout_tok,
             .kind_token = container_tok,
             .init_arg_expr = .None,
             .fields_and_decls = ast.Node.ContainerDecl.DeclList.init(c.a()),

src/zig_clang.cpp

@@ -1597,6 +1597,14 @@ const char* ZigClangVarDecl_getSectionAttribute(const struct ZigClangVarDecl *se
     return nullptr;
 }
 
+bool ZigClangRecordDecl_getPackedAttribute(const ZigClangRecordDecl *zig_record_decl) {
+    const clang::RecordDecl *record_decl = reinterpret_cast<const clang::RecordDecl *>(zig_record_decl);
+    if (record_decl->getAttr<clang::PackedAttr>()) {
+      return true;
+    }
+  return false;
+}
+
 unsigned ZigClangVarDecl_getAlignedAttribute(const struct ZigClangVarDecl *self, const ZigClangASTContext* ctx) {
     auto casted_self = reinterpret_cast<const clang::VarDecl *>(self);
     auto casted_ctx = const_cast<clang::ASTContext *>(reinterpret_cast<const clang::ASTContext *>(ctx));

src/zig_clang.h

@@ -863,6 +863,7 @@ ZIG_EXTERN_C const char* ZigClangVarDecl_getSectionAttribute(const struct ZigCla
 ZIG_EXTERN_C unsigned ZigClangVarDecl_getAlignedAttribute(const struct ZigClangVarDecl *self, const ZigClangASTContext* ctx);
 ZIG_EXTERN_C unsigned ZigClangFunctionDecl_getAlignedAttribute(const struct ZigClangFunctionDecl *self, const ZigClangASTContext* ctx);
 
+ZIG_EXTERN_C bool ZigClangRecordDecl_getPackedAttribute(const struct ZigClangRecordDecl *);
 ZIG_EXTERN_C const struct ZigClangRecordDecl *ZigClangRecordDecl_getDefinition(const struct ZigClangRecordDecl *);
 ZIG_EXTERN_C const struct ZigClangEnumDecl *ZigClangEnumDecl_getDefinition(const struct ZigClangEnumDecl *);
 

test/run_translated_c.zig

@@ -83,4 +83,17 @@ pub fn addCases(cases: *tests.RunTranslatedCContext) void {
         \\    return 0;
         \\}
     , "");
+
+    cases.add("struct initializer - packed",
+        \\#define _NO_CRT_STDIO_INLINE 1
+        \\#include <stdint.h>
+        \\#include <stdlib.h>
+        \\struct s {uint8_t x,y;
+        \\          uint32_t z;} __attribute__((packed)) s0 = {1, 2};
+        \\int main() {
+        \\  /* sizeof nor offsetof currently supported */
+        \\  if (((intptr_t)&s0.z - (intptr_t)&s0.x) != 2) abort();
+        \\  return 0;
+        \\}
+    , "");
 }

test/translate_c.zig

@@ -121,6 +121,21 @@ pub fn addCases(cases: *tests.TranslateCContext) void {
         \\}
     });
 
+    cases.add("struct initializer - packed",
+        \\struct {int x,y,z;} __attribute__((packed)) s0 = {1, 2};
+    , &[_][]const u8{
+        \\const struct_unnamed_1 = packed struct {
+        \\    x: c_int,
+        \\    y: c_int,
+        \\    z: c_int,
+        \\};
+        \\pub export var s0: struct_unnamed_1 = struct_unnamed_1{
+        \\    .x = @as(c_int, 1),
+        \\    .y = @as(c_int, 2),
+        \\    .z = 0,
+        \\};
+    });
+
     cases.add("align() attribute",
         \\__attribute__ ((aligned(128)))
         \\extern char my_array[16];