aro_translate_c: handle opaque struct defs in prototypes

lib/compiler/aro_translate_c.zig

@@ -398,6 +398,11 @@ fn transRecordDecl(c: *Context, scope: *Scope, record_ty: Type) Error!void {
 
     const is_pub = toplevel and !is_unnamed;
     const init_node = blk: {
+        if (record_decl.isIncomplete()) {
+            try c.opaque_demotes.put(c.gpa, @intFromPtr(record_decl), {});
+            break :blk ZigTag.opaque_literal.init();
+        }
+
         var fields = try std.ArrayList(ast.Payload.Record.Field).initCapacity(c.gpa, record_decl.fields.len);
         defer fields.deinit();
 

test/cases/translate_c/struct prototype used in func.c

@@ -0,0 +1,10 @@
+struct Foo;
+struct Foo *some_func(struct Foo *foo, int x);
+
+// translate-c
+// c_frontend=clang,aro
+//
+// pub const struct_Foo = opaque {};
+// pub extern fn some_func(foo: ?*struct_Foo, x: c_int) ?*struct_Foo;
+//
+// pub const Foo = struct_Foo;

test/translate_c.zig

@@ -879,17 +879,6 @@ pub fn addCases(cases: *tests.TranslateCContext) void {
         \\pub const Foo = struct_Foo;
     });
 
-    cases.add("struct prototype used in func",
-        \\struct Foo;
-        \\struct Foo *some_func(struct Foo *foo, int x);
-    , &[_][]const u8{
-        \\pub const struct_Foo = opaque {};
-        ,
-        \\pub extern fn some_func(foo: ?*struct_Foo, x: c_int) ?*struct_Foo;
-        ,
-        \\pub const Foo = struct_Foo;
-    });
-
     cases.add("#define an unsigned integer literal",
         \\#define CHANNEL_COUNT 24
     , &[_][]const u8{