From 010a591de352890a21d3fd212883ad1c6b7124e7 Mon Sep 17 00:00:00 2001
From: Felipe Pena <felipensp@gmail.com>
Date: Thu, 16 Oct 2025 09:19:36 -0300
Subject: [PATCH] cgen, type_resolver: Fix resolution type Map[string]T  when T
 is AliasToMap (fix #25494) (#25510)

---
 vlib/v/ast/table.v                            |  5 +++++
 vlib/v/gen/c/for.v                            | 15 ++++++++++++++
 .../v/tests/generics/generic_map_alias_test.v | 20 +++++++++++++++++++
 vlib/v/type_resolver/generic_resolver.v       |  2 +-
 4 files changed, 41 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/tests/generics/generic_map_alias_test.v

diff --git a/vlib/v/ast/table.v b/vlib/v/ast/table.v
index f72868bab..9c4b05cb9 100644
--- a/vlib/v/ast/table.v
+++ b/vlib/v/ast/table.v
@@ -1876,6 +1876,11 @@ pub fn (mut t Table) convert_generic_type(generic_type Type, generic_names []str
 				type_changed = true
 			}
 			if type_changed {
+				// map[Type]T where T is an alias to map type
+				if to_types.len == 1 && sym.info.value_type.has_flag(.generic)
+					&& t.type_kind(to_types[0]) == .alias && t.final_sym(to_types[0]).kind == .map {
+					return unwrapped_value_type
+				}
 				idx := t.find_or_register_map(unwrapped_key_type, unwrapped_value_type)
 				if unwrapped_key_type.has_flag(.generic) || unwrapped_value_type.has_flag(.generic) {
 					return new_type(idx).derive_add_muls(generic_type).set_flag(.generic)
diff --git a/vlib/v/gen/c/for.v b/vlib/v/gen/c/for.v
index a98690ffe..02d550927 100644
--- a/vlib/v/gen/c/for.v
+++ b/vlib/v/gen/c/for.v
@@ -201,6 +201,21 @@ fn (mut g Gen) for_in_stmt(node_ ast.ForInStmt) {
 		}
 		node.val_type = g.table.value_type(unwrapped_typ)
 		node.scope.update_var_type(node.val_var, node.val_type)
+	} else if node.kind == .alias {
+		mut unwrapped_typ := g.unwrap_generic(node.cond_type)
+		mut unwrapped_sym := g.table.final_sym(unwrapped_typ)
+		node.kind = unwrapped_sym.kind
+		node.cond_type = unwrapped_typ
+		if node.key_var.len > 0 {
+			key_type := match unwrapped_sym.kind {
+				.map { unwrapped_sym.map_info().key_type }
+				else { ast.int_type }
+			}
+			node.key_type = key_type
+			node.scope.update_var_type(node.key_var, key_type)
+		}
+		node.val_type = g.table.value_type(g.table.unaliased_type(unwrapped_typ))
+		node.scope.update_var_type(node.val_var, node.val_type)
 	}
 	g.loop_depth++
 	if node.label.len > 0 {
diff --git a/vlib/v/tests/generics/generic_map_alias_test.v b/vlib/v/tests/generics/generic_map_alias_test.v
new file mode 100644
index 000000000..43698c241
--- /dev/null
+++ b/vlib/v/tests/generics/generic_map_alias_test.v
@@ -0,0 +1,20 @@
+import x.json2
+
+pub struct AppJsonValue {
+pub:
+	file  string
+	md5   string
+	creat i64
+}
+
+pub type AppJson = map[string]AppJsonValue
+
+fn test_main() {
+	app_json1 := map[string]AppJsonValue{}
+	res1 := json2.encode(app_json1)
+	assert '${res1}' == '{}'
+
+	app_json2 := AppJson{}
+	res2 := json2.encode(app_json2)
+	assert '${res2}' == '{}'
+}
diff --git a/vlib/v/type_resolver/generic_resolver.v b/vlib/v/type_resolver/generic_resolver.v
index b6f5b3987..a032824f6 100644
--- a/vlib/v/type_resolver/generic_resolver.v
+++ b/vlib/v/type_resolver/generic_resolver.v
@@ -222,7 +222,7 @@ pub fn (mut t TypeResolver) resolve_args(cur_fn &ast.FnDecl, func &ast.Fn, mut n
 								}
 							}
 						} else if arg_sym.kind == .any {
-							cparam_type_sym := t.table.sym(t.resolver.unwrap_generic(ctyp))
+							cparam_type_sym := t.table.final_sym(t.resolver.unwrap_generic(ctyp))
 							if param_typ_sym.kind == .array && cparam_type_sym.info is ast.Array {
 								comptime_args[k] = cparam_type_sym.info.elem_type
 							} else if param_typ_sym.info is ast.Map
-- 
2.39.5