builtin: fix lf automatically converted to crlf on windows (fixes #25640)

(cherry picked from commit 21cb51dd27f08c405bc3c450ac48f5b5695fcd32)

Author: medvednikov

vlib/builtin/builtin_stdout_flushed_by_default_test.v

@@ -22,3 +22,28 @@ fn test_stdout_is_flushed_by_default() {
 	assert stdout == ready_marker, stdout
 	assert stderr == ''
 }
+
+fn redirected_stdout_bytes(snippet string) ![]u8 {
+	stamp := time.now().unix_milli()
+	source_path := os.join_path(os.vtmp_dir(), 'redirected_stdout_${stamp}.v')
+	output_path := os.join_path(os.vtmp_dir(), 'redirected_stdout_${stamp}.bin')
+	os.write_file(source_path, 'fn main() {\n\t${snippet}\n}\n')!
+	defer {
+		os.rm(source_path) or {}
+		os.rm(output_path) or {}
+	}
+	cmd := '${os.quoted_path(@VEXE)} run ${os.quoted_path(source_path)} > ${os.quoted_path(output_path)}'
+	res := os.execute(cmd)
+	assert res.exit_code == 0, 'command failed: ${cmd}\noutput:\n${res.output}'
+	return os.read_bytes(output_path)!
+}
+
+fn assert_redirected_stdout_bytes(snippet string, expected []u8) ! {
+	bytes := redirected_stdout_bytes(snippet)!
+	assert bytes == expected, 'expected ${expected}, got ${bytes}'
+}
+
+fn test_redirected_stdout_preserves_newline_bytes() ! {
+	assert_redirected_stdout_bytes(r"print('\n')", [u8(`\n`)])!
+	assert_redirected_stdout_bytes(r"print('\r\n')", [u8(`\r`), `\n`])!
+}

vlib/builtin/builtin_windows.c.v

@@ -4,6 +4,9 @@
 @[has_globals]
 module builtin
 
+#include <io.h>
+#include <fcntl.h>
+
 // See https://learn.microsoft.com/en-us/windows/win32/winprog/windows-data-types
 // See https://www.codeproject.com/KB/string/cppstringguide1.aspx
 pub type C.BOOL = int
@@ -40,6 +43,18 @@ pub type C.LPCTSTR = &C.TCHAR
 
 fn C.WriteConsoleW(voidptr, &u16, u32, &u32, voidptr) bool
 
+fn C._fileno(&C.FILE) int
+
+fn C._setmode(int, int) int
+
+// set_stream_binary_mode disables CRT newline translation for redirected stdio streams.
+fn set_stream_binary_mode(stream &C.FILE) {
+	fd := C._fileno(stream)
+	if fd >= 0 {
+		C._setmode(fd, C._O_BINARY)
+	}
+}
+
 fn is_terminal(fd int) int {
 	mut mode := u32(0)
 	osfh := voidptr(C._get_osfhandle(fd))
@@ -106,6 +121,8 @@ fn builtin_init() {
 			gc_set_warn_proc(internal_gc_warn_proc_none)
 		}
 	}
+	set_stream_binary_mode(C.stdout)
+	set_stream_binary_mode(C.stderr)
 	if is_terminal(1) > 0 {
 		C.SetConsoleMode(C.GetStdHandle(std_output_handle),
 			enable_processed_output | enable_wrap_at_eol_output | evable_virtual_terminal_processing)