checker: add an interface check for mutability, fixes #1081, fixes #7038 (#11963)

vlib/io/io.v

@@ -4,7 +4,7 @@ const (
 	buf_max_len = 1024
 )
 
-pub fn cp(src Reader, mut dst Writer) ? {
+pub fn cp(mut src Reader, mut dst Writer) ? {
 	mut buf := []byte{len: io.buf_max_len}
 	for {
 		len := src.read(mut buf) or { break }

vlib/io/io_cp_test.v

@@ -8,6 +8,6 @@ fn test_cp() ? {
 	}
 	mut r := io.new_buffered_reader(reader: f)
 	mut stdout := os.stdout()
-	io.cp(r, mut stdout) ?
+	io.cp(mut r, mut stdout) ?
 	assert true
 }

vlib/io/io_test.v

@@ -30,12 +30,12 @@ fn (mut w Writ) write(buf []byte) ?int {
 }
 
 fn test_copy() {
-	src := Buf{
+	mut src := Buf{
 		bytes: 'abcdefghij'.repeat(10).bytes()
 	}
 	mut dst := Writ{
 		bytes: []byte{}
 	}
-	io.cp(src, mut dst) or { assert false }
+	io.cp(mut src, mut dst) or { assert false }
 	assert dst.bytes == src.bytes
 }

vlib/io/reader.v

@@ -6,6 +6,7 @@ pub interface Reader {
 	// them into buf.
 	// A type that implements this should return
 	// `none` on end of stream (EOF) instead of just returning 0
+mut:
 	read(mut buf []byte) ?int
 }
 
@@ -17,14 +18,15 @@ const (
 // ReadAllConfig allows options to be passed for the behaviour
 // of read_all
 pub struct ReadAllConfig {
-	reader                Reader
 	read_to_end_of_stream bool
+mut:
+	reader Reader
 }
 
 // read_all reads all bytes from a reader until either a 0 length read
 // or if read_to_end_of_stream is true then the end of the stream (`none`)
 pub fn read_all(config ReadAllConfig) ?[]byte {
-	r := config.reader
+	mut r := config.reader
 	read_till_eof := config.read_to_end_of_stream
 
 	mut b := []byte{len: io.read_all_len}
@@ -44,7 +46,7 @@ pub fn read_all(config ReadAllConfig) ?[]byte {
 
 // read_any reads any available bytes from a reader
 // (until the reader returns a read of 0 length)
-pub fn read_any(r Reader) ?[]byte {
+pub fn read_any(mut r Reader) ?[]byte {
 	mut b := []byte{len: io.read_all_len}
 	mut read := 0
 	for {

vlib/io/readerwriter.v

@@ -3,6 +3,7 @@ module io
 // ReaderWriter represents a stream that can be read from and wrote to
 pub interface ReaderWriter {
 	// from Reader
+mut:
 	read(mut buf []byte) ?int
 	// from Writer
 	write(buf []byte) ?int
@@ -11,8 +12,8 @@ pub interface ReaderWriter {
 // ReaderWriterImpl is a ReaderWriter that can be made from
 // a seperate reader and writer (see fn make_readerwriter)
 struct ReaderWriterImpl {
-	r Reader
 mut:
+	r Reader
 	w Writer
 }
 

vlib/io/writer.v

@@ -2,6 +2,7 @@ module io
 
 // Writer represents a stream of data that can be wrote to
 pub interface Writer {
+mut:
 	write(buf []byte) ?int
 }