checker: fix generics with nested generic fn call (#15361)

vlib/v/checker/check_types.v

@@ -667,10 +667,6 @@ pub fn (mut c Checker) infer_fn_generic_types(func ast.Fn, mut node ast.CallExpr
 				if param.typ.nr_muls() > 0 && to_set.nr_muls() > 0 {
 					to_set = to_set.set_nr_muls(0)
 				}
-				// If the parent fn param is a generic too
-				if to_set.has_flag(.generic) {
-					to_set = c.unwrap_generic(to_set)
-				}
 			} else if param.typ.has_flag(.generic) {
 				arg_sym := c.table.sym(arg.typ)
 				if param.typ.has_flag(.variadic) {
@@ -759,21 +755,7 @@ pub fn (mut c Checker) infer_fn_generic_types(func ast.Fn, mut node ast.CallExpr
 				}
 			}
 
-			if to_set != ast.void_type {
-				if typ != ast.void_type {
-					// try to promote
-					// only numbers so we don't promote pointers
-					if typ.is_number() && to_set.is_number() {
-						promoted := c.promote_num(typ, to_set)
-						if promoted != ast.void_type {
-							to_set = promoted
-						}
-					}
-					if !c.check_types(typ, to_set) {
-						c.error('inferred generic type `$gt_name` is ambiguous: got `${c.table.sym(to_set).name}`, expected `${c.table.sym(typ).name}`',
-							arg.pos)
-					}
-				}
+			if to_set != ast.void_type && typ == ast.void_type {
 				typ = to_set
 			}
 		}

vlib/v/checker/tests/generics_type_ambiguous.out

@@ -1,5 +1,5 @@
-vlib/v/checker/tests/generics_type_ambiguous.vv:7:19: error: inferred generic type `B` is ambiguous: got `int`, expected `string`
-    5 | 
+vlib/v/checker/tests/generics_type_ambiguous.vv:7:19: error: cannot use `int literal` as `string` in argument 4 to `test`
+    5 |
     6 | fn main() {
     7 |   test(2, 2, "2", 2)
       |                   ^

vlib/v/tests/generics_with_nested_generics_fn_infer_call_test.v

@@ -0,0 +1,26 @@
+module main
+
+pub struct Reptile {}
+
+pub struct Insect {}
+
+fn test_generics_with_nested_generic_fn_infer_call() {
+	mut r := Reptile{}
+	mut i := Insect{}
+
+	ret1 := node_search(mut r)
+	println(ret1)
+	assert ret1 == Reptile{}
+
+	ret2 := node_search(mut i)
+	println(ret2)
+	assert ret2 == Insect{}
+}
+
+pub fn node_search<T>(mut t T) T {
+	return hydrate(mut t)
+}
+
+fn hydrate<T>(mut t T) T {
+	return t
+}