cgen: add @[reused] attribute to mark methods, reusing the receiver memory on return (needed for autofree) (fix #25221) (#25235)

vlib/builtin/string_charptr_byteptr_helpers.v

@@ -3,7 +3,7 @@ module builtin
 // Note: this file will be removed soon
 
 // byteptr.vbytes() - makes a V []u8 structure from a C style memory buffer. Note: the data is reused, NOT copied!
-@[unsafe]
+@[reused; unsafe]
 pub fn (data byteptr) vbytes(len int) []u8 {
 	return unsafe { voidptr(data).vbytes(len) }
 }
@@ -11,7 +11,7 @@ pub fn (data byteptr) vbytes(len int) []u8 {
 // vstring converts a C style string to a V string. Note: the string data is reused, NOT copied.
 // strings returned from this function will be normal V strings beside that (i.e. they would be
 // freed by V's -autofree mechanism, when they are no longer used).
-@[unsafe]
+@[reused; unsafe]
 pub fn (bp byteptr) vstring() string {
 	return string{
 		str: bp
@@ -21,7 +21,7 @@ pub fn (bp byteptr) vstring() string {
 
 // vstring_with_len converts a C style string to a V string.
 // Note: the string data is reused, NOT copied.
-@[unsafe]
+@[reused; unsafe]
 pub fn (bp byteptr) vstring_with_len(len int) string {
 	return string{
 		str:    bp
@@ -32,7 +32,7 @@ pub fn (bp byteptr) vstring_with_len(len int) string {
 
 // vstring converts C char* to V string.
 // Note: the string data is reused, NOT copied.
-@[unsafe]
+@[reused; unsafe]
 pub fn (cp charptr) vstring() string {
 	return string{
 		str:    byteptr(cp)
@@ -43,7 +43,7 @@ pub fn (cp charptr) vstring() string {
 
 // vstring_with_len converts C char* to V string.
 // Note: the string data is reused, NOT copied.
-@[unsafe]
+@[reused; unsafe]
 pub fn (cp charptr) vstring_with_len(len int) string {
 	return string{
 		str:    byteptr(cp)
@@ -59,7 +59,7 @@ pub fn (cp charptr) vstring_with_len(len int) string {
 // This is suitable for readonly strings, C string literals etc,
 // that can be read by the V program, but that should not be
 // managed by it, for example `os.args` is implemented using it.
-@[unsafe]
+@[reused; unsafe]
 pub fn (bp byteptr) vstring_literal() string {
 	return string{
 		str:    bp
@@ -70,7 +70,7 @@ pub fn (bp byteptr) vstring_literal() string {
 
 // vstring_with_len converts a C style string to a V string.
 // Note: the string data is reused, NOT copied.
-@[unsafe]
+@[reused; unsafe]
 pub fn (bp byteptr) vstring_literal_with_len(len int) string {
 	return string{
 		str:    bp
@@ -82,7 +82,7 @@ pub fn (bp byteptr) vstring_literal_with_len(len int) string {
 // vstring_literal converts C char* to V string.
 // See also vstring_literal defined on byteptr for more details.
 // Note: the string data is reused, NOT copied.
-@[unsafe]
+@[reused; unsafe]
 pub fn (cp charptr) vstring_literal() string {
 	return string{
 		str:    byteptr(cp)
@@ -94,7 +94,7 @@ pub fn (cp charptr) vstring_literal() string {
 // vstring_literal_with_len converts C char* to V string.
 // See also vstring_literal_with_len defined on byteptr.
 // Note: the string data is reused, NOT copied.
-@[unsafe]
+@[reused; unsafe]
 pub fn (cp charptr) vstring_literal_with_len(len int) string {
 	return string{
 		str:    byteptr(cp)

vlib/v/gen/c/autofree.v

@@ -98,6 +98,21 @@ fn (mut g Gen) autofree_scope_vars2(scope &ast.Scope, start_pos int, end_pos int
 				if obj.expr is ast.IfGuardExpr {
 					continue
 				}
+				if obj.expr is ast.UnsafeExpr && obj.expr.expr is ast.CallExpr
+					&& (obj.expr.expr as ast.CallExpr).is_method {
+					if left_var := scope.objects[obj.expr.expr.left.str()] {
+						if func := g.table.find_method(g.table.final_sym(left_var.typ),
+							obj.expr.expr.name)
+						{
+							if func.attrs.contains('reused') && left_var is ast.Var
+								&& left_var.expr is ast.CastExpr {
+								if left_var.expr.expr.is_literal() {
+									continue
+								}
+							}
+						}
+					}
+				}
 				g.autofree_variable(obj)
 			}
 			else {}

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

@@ -0,0 +1,10 @@
+VV_LOC void main__main(void) {
+	byteptr b = ((byteptr)("a"));
+	Array_u8 s = byteptr_vbytes(b, 1);
+	string _t1 = Array_u8_str(s); println(_t1); string_free(&_t1);
+	;
+	byteptr bb = ((byteptr)("a"));
+	string ss = byteptr_vstring(bb);
+	println(ss);
+}
+

vlib/v/gen/c/testdata/autofree_reused.out

@@ -0,0 +1,2 @@
+[97]
+a

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

@@ -0,0 +1,10 @@
+// vtest vflags: -autofree
+fn main() {
+	b := byteptr(c'a')
+	s := unsafe { b.vbytes(1) }
+	println(s)
+
+	bb := byteptr(c'a')
+	ss := unsafe { bb.vstring() }
+	println(ss)
+}