cgen: fix map comptime var type resolution on generic arg (fix #20037) (#20085)

Author: felipensp

vlib/v/gen/c/fn.v

@@ -1073,9 +1073,21 @@ fn (mut g Gen) change_comptime_args(func ast.Fn, mut node_ ast.CallExpr, concret
 						mut ctyp := g.get_comptime_var_type(call_arg.expr)
 						if ctyp != ast.void_type {
 							arg_sym := g.table.sym(ctyp)
-							if arg_sym.kind == .array && param_typ.has_flag(.generic)
-								&& g.table.final_sym(param_typ).kind == .array {
-								ctyp = (arg_sym.info as ast.Array).elem_type
+							param_sym := g.table.final_sym(param_typ)
+							if arg_sym.info is ast.Array && param_sym.kind == .array {
+								ctyp = arg_sym.info.elem_type
+							} else if arg_sym.info is ast.Map && param_sym.info is ast.Map {
+								if call_arg.expr.obj.ct_type_var == .value_var {
+									ctyp = arg_sym.info.value_type
+									if param_sym.info.value_type.nr_muls() > 0 && ctyp.nr_muls() > 0 {
+										ctyp = ctyp.set_nr_muls(0)
+									}
+								} else if call_arg.expr.obj.ct_type_var == .key_var {
+									ctyp = arg_sym.info.key_type
+									if param_sym.info.key_type.nr_muls() > 0 && ctyp.nr_muls() > 0 {
+										ctyp = ctyp.set_nr_muls(0)
+									}
+								}
 							}
 							comptime_args[i] = ctyp
 						}
@@ -1113,9 +1125,9 @@ fn (mut g Gen) change_comptime_args(func ast.Fn, mut node_ ast.CallExpr, concret
 									}
 								}
 							} else if arg_sym.kind == .any {
-								mut cparam_type_sym := g.table.sym(g.unwrap_generic(ctyp))
-								if param_typ_sym.kind == .array && cparam_type_sym.kind == .array {
-									ctyp = (cparam_type_sym.info as ast.Array).elem_type
+								cparam_type_sym := g.table.sym(g.unwrap_generic(ctyp))
+								if param_typ_sym.kind == .array && cparam_type_sym.info is ast.Array {
+									ctyp = cparam_type_sym.info.elem_type
 									comptime_args[i] = ctyp
 								} else {
 									if node_.args[i].expr.is_auto_deref_var() {

vlib/v/tests/comptime_for_map_arg_test.v

@@ -0,0 +1,33 @@
+fn merged[K, V](a map[K]V, b map[K]V) map[K]V {
+	mut o := a.clone()
+	for k, v in b {
+		$if V is $map {
+			o[k] = merged(o[k], v)
+		} $else {
+			o[k] = v
+		}
+	}
+	return o
+}
+
+fn test_main() {
+	a := {
+		'aa': {
+			'11': 1
+		}
+	}
+	b := {
+		'bb': {
+			'22': 2
+		}
+	}
+	c := merged(a, b)
+	assert c == {
+		'aa': {
+			'11': 1
+		}
+		'bb': {
+			'22': 2
+		}
+	}
+}