cgen: fix multi generics fn name (fix #23886) (#25673)

Author: kbkpbot

vlib/v/gen/c/fn.v

@@ -7,7 +7,9 @@ import strings
 import v.ast
 import v.util
 
-const c_fn_name_escape_seq = ['[', '_T_', ']', '']
+// has[int]() => has_T_int()
+// has[int, string]() => has_T_int_string()
+const c_fn_name_escape_seq = ['[', '_T_', ', ', '_', ']', '']
 
 fn (mut g Gen) is_used_by_main(node ast.FnDecl) bool {
 	$if trace_unused_by_main ? {

vlib/v/tests/generics/generics_with_multi_generics_fn_name_test.v

@@ -0,0 +1,35 @@
+pub struct ValueWithErrors[T, E] {
+pub:
+	value  T
+	errors E
+}
+
+@[inline]
+pub fn (self ValueWithErrors[T, E]) has_errors() bool {
+	return self.errors.len > 0
+}
+
+pub fn transform_and_validate[T](data map[string]string) ValueWithErrors[T, map[string][]IError] {
+	mut new_object := T{}
+	mut errors := map[string][]IError{}
+	return ValueWithErrors[T, map[string][]IError]{
+		errors: errors
+		value:  new_object
+	}
+}
+
+struct BasicStruct {
+	str    string @[max_length: 15; min_length: 3; req]
+	number int    @[max: 100; min: 3; req]
+	b      bool   @[req]
+}
+
+fn test_generics_with_multi_generics_fn_name() {
+	data_with_errors := transform_and_validate[BasicStruct]({
+		'str':    '1234567890123456'
+		'number': '11'
+	})
+
+	dump(data_with_errors)
+	assert data_with_errors.errors.len == 0
+}