cgen: fix comptime if attributes for `test_` functions (#14756)

vlib/v/gen/c/cgen.v

@@ -210,6 +210,7 @@ mut:
 	generated_free_methods map[int]bool
 	autofree_scope_stmts   []string
 	use_segfault_handler   bool = true
+	test_function_names    []string
 }
 
 // global or const variable definition string
@@ -368,6 +369,7 @@ pub fn gen(files []&ast.File, table &ast.Table, pref &pref.Preferences) string {
 			global_g.pcs << g.pcs
 			global_g.json_types << g.json_types
 			global_g.hotcode_fn_names << g.hotcode_fn_names
+			global_g.test_function_names << g.test_function_names
 			unsafe { g.free_builders() }
 			for k, v in g.autofree_methods {
 				global_g.autofree_methods[k] = v
@@ -5538,24 +5540,21 @@ fn (mut g Gen) type_default(typ_ ast.Type) string {
 	}
 }
 
-fn (g &Gen) get_all_test_function_names() []string {
+fn (g Gen) get_all_test_function_names() []string {
 	mut tfuncs := []string{}
 	mut tsuite_begin := ''
 	mut tsuite_end := ''
-	for _, f in g.table.fns {
-		if !f.is_test {
+	for name in g.test_function_names {
+		if name.ends_with('.testsuite_begin') {
+			tsuite_begin = name
 			continue
 		}
-		if f.name.ends_with('.testsuite_begin') {
-			tsuite_begin = f.name
+		if name.contains('.test_') {
+			tfuncs << name
 			continue
 		}
-		if f.name.contains('.test_') {
-			tfuncs << f.name
-			continue
-		}
-		if f.name.ends_with('.testsuite_end') {
-			tsuite_end = f.name
+		if name.ends_with('.testsuite_end') {
+			tsuite_end = name
 			continue
 		}
 	}

vlib/v/gen/c/fn.v

@@ -32,6 +32,9 @@ fn (mut g Gen) fn_decl(node ast.FnDecl) {
 	if node.should_be_skipped {
 		return
 	}
+	if node.is_test {
+		g.test_function_names << node.name
+	}
 	if node.ninstances == 0 && node.generic_names.len > 0 {
 		$if trace_generics ? {
 			eprintln('skipping generic fn with no concrete instances: $node.mod $node.name')

vlib/v/gen/c/testdata/comptime_if_attribute_in_test.vv

@@ -0,0 +1,4 @@
+[if customflag ?]
+fn test_abcdef() {
+	println('this should not be in the c code')
+}

vlib/v/gen/c/testdata/comptime_if_attribute_in_test2.c.must_have

@@ -0,0 +1 @@
+println(_SLIT("this should be in the c code"));

vlib/v/gen/c/testdata/comptime_if_attribute_in_test2.vv

@@ -0,0 +1,5 @@
+// vtest vflags: -d customflag
+[if customflag ?]
+fn test_abcdef() {
+	println('this should be in the c code')
+}