From d03153c184f5ec5f2717cbe4d38e3a9ba27e0e31 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Tue, 21 Apr 2026 14:48:36 +0300
Subject: [PATCH] os: fix win_spawn_process with paths containing spaces (fixes
 #18812)

---
 vlib/os/process_test.v      | 41 +++++++++++++++++++++++++++++++++++++
 vlib/os/process_windows.c.v | 36 +++++++++++++++++++++++++++++---
 2 files changed, 74 insertions(+), 3 deletions(-)

diff --git a/vlib/os/process_test.v b/vlib/os/process_test.v
index 627be5531..3932c6789 100644
--- a/vlib/os/process_test.v
+++ b/vlib/os/process_test.v
@@ -14,6 +14,8 @@ const utf16le_output_exe_filename = os.join_path(tfolder, 'utf16le_output.exe')
 const utf16le_output_source_filename = os.join_path(tfolder, 'utf16le_output.v')
 const stdin_exit_exe_filename = os.join_path(tfolder, 'stdin_exit.exe')
 const stdin_exit_source_filename = os.join_path(tfolder, 'stdin_exit.v')
+const argv_echo_exe_filename = os.join_path(tfolder, 'argv_echo.exe')
+const argv_echo_source_filename = os.join_path(tfolder, 'argv_echo.v')
 const echo_process_source_code = '
 module main
 import io
@@ -63,6 +65,17 @@ fn main() {
 }
 '
 
+const argv_echo_source_code = '
+module main
+import os
+
+fn main() {
+	for arg in os.args[1..] {
+		println(arg)
+	}
+}
+'
+
 const echo_wait_timeout = 5 // seconds
 
 fn testsuite_begin() {
@@ -94,6 +107,10 @@ fn testsuite_begin() {
 	os.write_file(stdin_exit_source_filename, stdin_exit_source_code)!
 	os.system('${os.quoted_path(vexe)} -o ${os.quoted_path(stdin_exit_exe_filename)} ${os.quoted_path(stdin_exit_source_filename)}')
 	assert os.exists(stdin_exit_exe_filename)
+
+	os.write_file(argv_echo_source_filename, argv_echo_source_code)!
+	os.system('${os.quoted_path(vexe)} -o ${os.quoted_path(argv_echo_exe_filename)} ${os.quoted_path(argv_echo_source_filename)}')
+	assert os.exists(argv_echo_exe_filename)
 }
 
 fn testsuite_end() {
@@ -186,6 +203,30 @@ fn test_new_process_uses_exact_executable_path_when_folder_contains_spaces() {
 	assert !output.contains('stale-prefix-exe'), output
 }
 
+fn test_new_process_passes_spaced_path_args_on_windows() {
+	$if !windows {
+		return
+	}
+	eprintln(@FN)
+	file_arg := os.join_path(tfolder, 'path with spaces', 'child file.txt')
+	dir_arg := os.join_path(tfolder, 'path with spaces') + '\\'
+	quoted_arg := 'value with "quotes"'
+	mut p := os.new_process(argv_echo_exe_filename)
+	p.set_args([file_arg, dir_arg, quoted_arg, 'marker'])
+	p.set_redirect_stdio()
+	p.wait()
+	assert p.code == 0
+	output := p.stdout_slurp().trim_space()
+	errors := p.stderr_slurp().trim_space()
+	p.close()
+	lines := output.split_into_lines()
+	assert lines.len == 4, 'stdout:\n${output}\nstderr:\n${errors}'
+	assert lines[0] == file_arg
+	assert lines[1] == dir_arg
+	assert lines[2] == quoted_arg
+	assert lines[3] == 'marker'
+}
+
 fn test_new_process_uses_path_for_bare_command_names() {
 	$if windows {
 		return
diff --git a/vlib/os/process_windows.c.v b/vlib/os/process_windows.c.v
index 8f4375696..a0337c566 100644
--- a/vlib/os/process_windows.c.v
+++ b/vlib/os/process_windows.c.v
@@ -401,8 +401,38 @@ fn requote_args(cargs []string) string {
 }
 
 fn requote_arg(arg string) string {
-	if arg.starts_with('"') {
-		return arg
+	if arg.len == 0 {
+		return '""'
 	}
-	return '"${arg}"'
+	// Escape a literal argv entry using the same backslash+quote rules that
+	// Windows uses when reconstructing argc/argv from CreateProcessW.
+	mut sb := strings.new_builder(arg.len + 8)
+	defer { unsafe { sb.free() } }
+	sb.write_u8(`"`)
+	mut pending_backslashes := 0
+	for i := 0; i < arg.len; i++ {
+		ch := arg[i]
+		if ch == `\\` {
+			pending_backslashes++
+			continue
+		}
+		if ch == `"` {
+			for _ in 0 .. pending_backslashes * 2 + 1 {
+				sb.write_u8(`\\`)
+			}
+			sb.write_u8(`"`)
+			pending_backslashes = 0
+			continue
+		}
+		for _ in 0 .. pending_backslashes {
+			sb.write_u8(`\\`)
+		}
+		pending_backslashes = 0
+		sb.write_u8(ch)
+	}
+	for _ in 0 .. pending_backslashes * 2 {
+		sb.write_u8(`\\`)
+	}
+	sb.write_u8(`"`)
+	return sb.str()
 }
-- 
2.39.5