Windows: Tesseract and the --control tools start without a console window (#6735)

crates/ocr/src/tesseract.rs

@@ -343,8 +343,17 @@ impl TesseractCli {
         // Known limit: only the direct child is killed at the timeout or on an early cap. A
         // wrapper script's children (grandchildren of this process) may survive the kill; the
         // cap and the timeout still bound what this run reads and how long it waits.
+        let mut command = std::process::Command::new(&self.program);
+        #[cfg(windows)]
+        {
+            use std::os::windows::process::CommandExt as _;
+            // `CREATE_NO_WINDOW`: tesseract is a console program and the app is not, so without
+            // it Windows opens a console window for every run, which flashes up during OCR. The
+            // output files above are unaffected.
+            command.creation_flags(0x0800_0000);
+        }
         let mut child =
-            std::process::Command::new(&self.program)
+            command
                 .args(args)
                 .stdin(std::process::Stdio::null())
                 .stdout(out_file)
@@ -894,6 +903,28 @@ mod tests {
         let _ = std::fs::remove_dir_all(&dir);
     }
 
+    /// The program starts without a console window (Windows): the app has no console, so a
+    /// console program that isn't told otherwise gets a window of its own, which flashes up on
+    /// every OCR run. PowerShell stands in for tesseract and reports, through the same output file
+    /// a reading comes back in, its console's window and the processes attached to that console.
+    /// Both are checked, because a program started without the flag by a process that has a
+    /// console shares it instead, and that console may itself have no window.
+    #[cfg(windows)]
+    #[test]
+    fn the_program_starts_without_a_console_window() {
+        const PROBE: &str = r#"Add-Type -Namespace PdfCraftOcrProbe -Name Console -MemberDefinition '[DllImport("kernel32.dll")] public static extern System.IntPtr GetConsoleWindow(); [DllImport("kernel32.dll")] public static extern uint GetConsoleProcessList(uint[] ids, uint count);'
+$ids = New-Object uint32[] 256
+$n = [PdfCraftOcrProbe.Console]::GetConsoleProcessList($ids, 256)
+"$([PdfCraftOcrProbe.Console]::GetConsoleWindow()) $($ids[0..($n-1)] -join ',')""#;
+        let root = std::env::var_os("SystemRoot").map_or_else(|| PathBuf::from(r"C:\Windows"), PathBuf::from);
+        let t = TesseractCli::new(root.join(r"System32\WindowsPowerShell\v1.0\powershell.exe"));
+        let text = t.run(&["-NoProfile", "-NonInteractive", "-Command", PROBE], t.timeout, t.max_output).unwrap();
+        let (window, attached) = text.trim().split_once(' ').unwrap();
+        assert_eq!(window, "0", "the program has a console window: {text}");
+        let attached: Vec<u32> = attached.split(',').map(|id| id.parse().unwrap()).collect();
+        assert!(!attached.is_empty() && !attached.contains(&std::process::id()), "the program shares this process's console: {text}");
+    }
+
     #[cfg(unix)]
     fn make_executable(p: &Path) {
         use std::os::unix::fs::PermissionsExt;

crates/platform/src/owner_only.rs

@@ -132,10 +132,19 @@ const ICACLS: &str = "icacls.exe";
 /// A tool Windows ships, started by its full path (review on #3956). Started by bare name, a
 /// `whoami.exe`, `powershell.exe` or `icacls.exe` found first (next to the app, or earlier on the
 /// search path) would answer instead, and `whoami`'s answer is what every check here trusts.
+///
+/// Each tool is a console program and the app is not, so without `CREATE_NO_WINDOW` Windows gives
+/// every one of them a console window of its own, which flashes up while the app writes its
+/// `--control` file. The flag doesn't touch the pipes `output()` reads the answer through.
 #[cfg(windows)]
 fn system_tool(relative: &str) -> std::process::Command {
+    use std::os::windows::process::CommandExt as _;
+    /// `CREATE_NO_WINDOW`, from the Windows process creation flags.
+    const CREATE_NO_WINDOW: u32 = 0x0800_0000;
     let root = std::env::var_os("SystemRoot").map_or_else(|| std::path::PathBuf::from(r"C:\Windows"), std::path::PathBuf::from);
-    std::process::Command::new(root.join("System32").join(relative))
+    let mut command = std::process::Command::new(root.join("System32").join(relative));
+    command.creation_flags(CREATE_NO_WINDOW);
+    command
 }
 
 #[cfg(windows)]
@@ -384,6 +393,28 @@ mod tests {
         }
     }
 
+    /// The tools start without a console window: the app has no console, so a tool that isn't
+    /// told otherwise gets a window of its own, which flashes up. The started PowerShell reports
+    /// its console's window and the processes attached to that console. Both are checked, because
+    /// a tool started without the flag by a process that has a console shares it instead, and that
+    /// console may itself have no window (a test run started by a service or an IDE).
+    #[cfg(windows)]
+    #[test]
+    fn the_tools_start_without_a_console_window() {
+        const PROBE: &str = r#"Add-Type -Namespace PdfCraftProbe -Name Console -MemberDefinition '[DllImport("kernel32.dll")] public static extern System.IntPtr GetConsoleWindow(); [DllImport("kernel32.dll")] public static extern uint GetConsoleProcessList(uint[] ids, uint count);'
+$ids = New-Object uint32[] 256
+$n = [PdfCraftProbe.Console]::GetConsoleProcessList($ids, 256)
+"$([PdfCraftProbe.Console]::GetConsoleWindow()) $($ids[0..($n-1)] -join ',')""#;
+        let out = system_tool(POWERSHELL).args(["-NoProfile", "-NonInteractive", "-Command", PROBE]).output().unwrap();
+        // The answer still comes back through the pipe.
+        let text = String::from_utf8_lossy(&out.stdout);
+        assert!(out.status.success(), "{text} {}", String::from_utf8_lossy(&out.stderr));
+        let (window, attached) = text.trim().split_once(' ').unwrap();
+        assert_eq!(window, "0", "the tool has a console window: {text}");
+        let attached: Vec<u32> = attached.split(',').map(|id| id.parse().unwrap()).collect();
+        assert!(!attached.is_empty() && !attached.contains(&std::process::id()), "the tool shares this process's console: {text}");
+    }
+
     #[test]
     fn other_owners_readers_and_missing_lists_are_refused() {
         let other = "S-1-5-21-1-2-3-1002";