fix Issue 22674 - ImportC: compatible types declared in different tra…

…nslation units are not treated equivalent in D

compiler/src/dmd/dmangle.d

@@ -833,6 +833,22 @@ public:
                 printf("  parent = %s %s", s.parent.kind(), s.parent.toChars());
             printf("\n");
         }
+        if (s.parent)
+        {
+            if (auto m = s.parent.isModule())
+            {
+                if (m.filetype == FileType.c)
+                {
+                    /* C types at global level get mangled into the __C global namespace
+                     * to get the same mangling regardless of which module it
+                     * is declared in. This works because types are the same if the mangling
+                     * is the same.
+                     */
+                    mangleIdentifier(Id.ImportC, s);
+                    return;
+                }
+            }
+        }
         mangleParent(s);
         if (s.ident)
             mangleIdentifier(s.ident, s);

compiler/src/dmd/frontend.h

@@ -8522,6 +8522,7 @@ struct Id final
     static Identifier* udaMustUse;
     static Identifier* TRUE;
     static Identifier* FALSE;
+    static Identifier* ImportC;
     static Identifier* dllimport;
     static Identifier* dllexport;
     static Identifier* vector_size;

compiler/src/dmd/id.d

@@ -512,6 +512,7 @@ immutable Msgtable[] msgtable =
     { "wchar_t" },
 
     // for C compiler
+    { "ImportC", "__C" },
     { "__tag" },
     { "dllimport" },
     { "dllexport" },

compiler/test/compilable/imports/cimports2a.i

@@ -1 +1,4 @@
 extern int xx;
+
+typedef struct Foo *FooRef;
+FooRef make_foo(void);

compiler/test/compilable/imports/cimports2b.i

@@ -1 +1,4 @@
 extern int xx;
+
+typedef struct Foo *FooRef;
+void free_foo(FooRef foo);

compiler/test/compilable/test22674.d

@@ -0,0 +1,9 @@
+// https://issues.dlang.org/show_bug.cgi?id=22674
+
+import imports.cimports2a;
+import imports.cimports2b;
+
+void do_foo(){
+    FooRef f = make_foo(); // use_foo.d(5)
+    free_foo(f);           // use_foo.d(6)
+}