cgen,checker: allow for pub type C.HINSTANCE = voidptr, being used in @[export: "wWinMain"] fn mymain(x C.HINSTANCE, xprev C.HINSTANCE, lpcmdline &C.WCHAR, cmdshow int) int { in module no_main programs (#23812)

Author: spytheman

vlib/v/checker/checker.v

@@ -550,8 +550,10 @@ fn (mut c Checker) alias_type_decl(mut node ast.AliasTypeDecl) {
 		}
 		.alias {
 			orig_sym := c.table.sym((parent_typ_sym.info as ast.Alias).parent_type)
-			c.error('type `${parent_typ_sym.str()}` is an alias, use the original alias type `${orig_sym.name}` instead',
-				node.type_pos)
+			if !node.name.starts_with('C.') {
+				c.error('type `${parent_typ_sym.str()}` is an alias, use the original alias type `${orig_sym.name}` instead',
+					node.type_pos)
+			}
 		}
 		.chan {
 			c.error('aliases of `chan` types are not allowed', node.type_pos)

vlib/v/gen/c/cgen.v

@@ -1815,6 +1815,12 @@ pub fn (mut g Gen) write_alias_typesymbol_declaration(sym ast.TypeSymbol) {
 		// TODO: remove this check; it is here just to fix V rebuilding in -cstrict mode with clang-12
 		return
 	}
+	if sym.name.starts_with('C.') {
+		// `pub type C.HINSTANCE = voidptr` means that `HINSTANCE` should be treated as a voidptr by V.
+		// The C type itself however already exists on the C side, so just treat C__HINSTANCE as a macro for it:
+		g.type_definitions.writeln('#define ${sym.cname} ${sym.cname#[3..]}')
+		return
+	}
 	if is_fixed_array_of_non_builtin && levels == 0 {
 		g.alias_definitions.writeln('typedef ${parent_styp} ${sym.cname};')
 	} else {

vlib/v/gen/c/testdata/multiple_c_cources/file3.c

@@ -0,0 +1 @@
+typedef struct { int i; float f; char c; } CStruct, *PCStruct;

vlib/v/tests/builtin_arrays/array_fixed_c_test.c.v

@@ -0,0 +1,39 @@
+#include "@VMODROOT/vlib/v/gen/c/testdata/multiple_c_cources/file3.c"
+
+@[typedef]
+struct C.CStruct {
+mut:
+	c char
+	i int
+	f f32
+}
+
+type C.PCStruct = &C.CStruct
+
+struct WrapperStruct {
+mut:
+	arr_fixed_c_type [2]C.PCStruct
+}
+
+fn test_main() {
+	s1 := &C.CStruct{
+		c: char(`A`)
+		f: 3.14
+		i: 42
+	}
+	s2 := &C.CStruct{
+		c: char(`B`)
+		f: 1.4142
+		i: 2
+	}
+	mut w := WrapperStruct{}
+	w.arr_fixed_c_type[0] = s1
+	w.arr_fixed_c_type[1] = s2
+	dump(w)
+	assert w.arr_fixed_c_type[0].c == char(`A`)
+	assert w.arr_fixed_c_type[1].c == char(`B`)
+	assert w.arr_fixed_c_type[0].f == 3.14
+	assert w.arr_fixed_c_type[1].f == 1.4142
+	assert w.arr_fixed_c_type[0].i == 42
+	assert w.arr_fixed_c_type[1].i == 2
+}