gen: support returning large types from closures on amd64 (#12926)

vlib/v/gen/c/fn.v

@@ -457,6 +457,9 @@ fn (mut g Gen) gen_anon_fn(mut node ast.AnonFn) {
 	for param in node.decl.params {
 		size_sb.write_string('_REG_WIDTH(${g.typ(param.typ)}) + ')
 	}
+	if g.pref.arch == .amd64 && node.decl.return_type != ast.void_type {
+		size_sb.write_string('(_REG_WIDTH(${g.typ(node.decl.return_type)}) > 2) + ')
+	}
 	size_sb.write_string('1')
 	args_size := size_sb.str()
 	g.writeln('')

vlib/v/tests/closure_generator_test.v

@@ -7,6 +7,58 @@ const (
 	all_param_values = []string{len: max_params, init: '${it + 1}'}
 )
 
+struct ReturnType {
+	name         string
+	init         string
+	assertion    string
+	no_assert_kw bool
+}
+
+const return_types = [
+	ReturnType{
+		name: ''
+		init: ''
+		assertion: ''
+		no_assert_kw: true
+	},
+	ReturnType{
+		name: 'int'
+		init: '-123'
+		assertion: ' == -123'
+	},
+	ReturnType{
+		name: 'u64'
+		init: '123'
+		assertion: ' == 123'
+	},
+	ReturnType{
+		name: 'voidptr'
+		init: 'voidptr(123)'
+		assertion: ' == voidptr(123)'
+	},
+	ReturnType{
+		name: 'string'
+		init: "'hello'"
+		assertion: " == 'hello'"
+	},
+	ReturnType{
+		name: '?'
+		init: "error('an error')"
+		assertion: " or { assert err.msg == 'an error' return }\npanic('got no error')"
+		no_assert_kw: true
+	},
+	ReturnType{
+		name: '?string'
+		init: "'hello'"
+		assertion: "? == 'hello'"
+	},
+	ReturnType{
+		name: 'BigStruct'
+		init: 'BigStruct{ a3: 56, a27: 1234, a61: 5555 }'
+		assertion: ' == BigStruct{ a3: 56, a27: 1234, a61: 5555 }'
+	},
+]
+
 // test_closures_with_n_args generates a new V file containing closures of `i`
 // and parameters of type `typ`, to makes sure that all combinations work correctly
 fn test_closures_with_n_args() ? {
@@ -14,6 +66,12 @@ fn test_closures_with_n_args() ? {
 	// NB: the type or value of the captured arg doesn't matter for this test,
 	// as the entire closure context is always passed as one pointer anyways
 
+	v_code.write_string('struct BigStruct {')
+	for i in 0 .. 64 {
+		v_code.write_string('\ta$i int ')
+	}
+	v_code.writeln('}')
+
 	for typ in ['byte', 'u16', 'int', 'i64', 'voidptr', 'string'] {
 		for i in 0 .. max_params {
 			param_names := all_param_names[..i]
@@ -41,19 +99,59 @@ fn test_closures_with_n_args() ? {
 			// NB: the captured arg doesn't matter for this test, as closures always receive
 			// a pointer to the entire closure context as their last argument anyways
 			v_code.writeln("
-	fn test_big_closure_${typ}_${i}() {
-		println('test_big_closure_${typ}_$i')
-		mut z := $init_val
-		c := fn [z] (${params.join(', ')}) $return_type {
-			mut sum := z")
+fn test_big_closure_${typ}_${i}() {
+	println('test_big_closure_${typ}_$i')
+	mut local := 123
+	mut local_2 := 234
+	mut z := $init_val
+	c := fn [z] (${params.join(', ')}) $return_type {
+		mut sum := z")
 			for j in 0 .. i {
 				v_code.writeln('\t\tsum += ${return_type}(${param_names[j]})')
 			}
-			v_code.writeln('
-			return sum
+			v_code.writeln("
+		return sum
+	}
+	assert c(${values.join(', ')}) == $expected_val
+	// ensure stack wasn't overwritten:
+	assert local == 123
+	assert local_2 == 234
+}")
 		}
-		assert c(${values.join(', ')}) == $expected_val
-	}')
+	}
+
+	for return_type in return_types {
+		typ := return_type.name
+		styp := typ.replace('?', 'option_').to_lower()
+		init := return_type.init
+		assertion := return_type.assertion
+
+		for i in 0 .. 10 {
+			param_names := all_param_names[..i]
+			params := param_names.map('$it int')
+			values := all_param_values[..i]
+
+			assert_line := if !return_type.no_assert_kw {
+				'assert c(${values.join(', ')}) $assertion'
+			} else {
+				'c(${values.join(', ')}) $assertion'
+			}
+			// NB: the captured arg doesn't matter for this test, as closures always receive
+			// a pointer to the entire closure context as their last argument anyways
+			v_code.writeln("
+fn test_closure_return_${styp}_${i}() ? {
+	println('test_closure_return_${styp}_$i')
+	mut local := 123
+	mut local_2 := 234
+	mut z := 1234
+	c := fn [z] (${params.join(', ')}) $typ {
+		return $init
+	}
+	$assert_line
+	// ensure stack wasn't overwritten:
+	assert local == 123
+	assert local_2 == 234
+}")
 		}
 	}
 
@@ -62,9 +160,9 @@ fn test_closures_with_n_args() ? {
 	wrkdir := os.join_path(os.temp_dir(), 'vtests', 'closures')
 	os.mkdir_all(wrkdir) ?
 	os.chdir(wrkdir) ?
-	os.write_file('closure_args_test.v', code) ?
+	os.write_file('closure_return_test.v', code) ?
 	vexe := os.getenv('VEXE')
-	res := os.execute('"$vexe" closure_args_test.v')
+	res := os.execute('"$vexe" -keepc -cg -showcc closure_return_test.v')
 	if res.exit_code != 0 {
 		eprintln(res.output)
 		assert false