os: fix args quoting in win_spawn_process (fix #26261) (#26339)

Author: spytheman

cmd/tools/test_os_args.v

@@ -0,0 +1 @@
+println(arguments()#[1..])

vlib/os/process_args_test.v

@@ -0,0 +1,20 @@
+import os
+
+const vexe = os.getenv('VEXE')
+const vroot = os.dir(vexe)
+
+fn test_v_run_simple() {
+	echo_os_args := os.join_path(vroot, 'cmd/tools/test_os_args.v')
+	res123 := os.execute('${os.quoted_path(vexe)} run ${os.quoted_path(echo_os_args)} 1 2 3')
+	println(res123)
+	assert res123.exit_code == 0
+	assert res123.output.starts_with("['1', '2', '3']")
+}
+
+fn test_v_run_quoted_args_with_spaces() {
+	echo_os_args := os.join_path(vroot, 'cmd/tools/test_os_args.v')
+	res := os.execute('${os.quoted_path(vexe)} run ${os.quoted_path(echo_os_args)} 1 "Learn V" 3')
+	println(res)
+	assert res.exit_code == 0
+	assert res.output.starts_with("['1', 'Learn V', '3']")
+}

vlib/os/process_windows.c.v

@@ -108,7 +108,7 @@ fn (mut p Process) win_spawn_process() int {
 		start_info.h_std_error = wdata.child_stderr_write
 		start_info.dw_flags = u32(C.STARTF_USESTDHANDLES)
 	}
-	cmd := '${p.filename} ' + p.args.join(' ')
+	cmd := '${p.filename} ' + requote_args(p.args)
 	cmd_wide_ptr := cmd.to_wide()
 	to_be_freed << cmd_wide_ptr
 	C.ExpandEnvironmentStringsW(cmd_wide_ptr, voidptr(&wdata.command_line[0]), 32768)
@@ -367,3 +367,23 @@ fn (mut p Process) unix_wait() {
 fn (mut p Process) unix_is_alive() bool {
 	return false
 }
+
+@[manualfree]
+fn requote_args(cargs []string) string {
+	mut sb := strings.new_builder(128)
+	defer { unsafe { sb.free() } }
+	for idx, a in cargs {
+		if idx > 0 {
+			sb.write_rune(` `)
+		}
+		if !a.starts_with('"') {
+			sb.write_string('"')
+			sb.write_string(a)
+			sb.write_string('"')
+		} else {
+			sb.write_string(a)
+		}
+	}
+	res := sb.str()
+	return res
+}