fix: permission prompt stuffing on Windows (#11969)

runtime/permissions.rs

@@ -16,8 +16,6 @@ use log::debug;
 use std::collections::HashSet;
 use std::fmt;
 use std::hash::Hash;
-#[cfg(not(test))]
-use std::io;
 use std::path::{Path, PathBuf};
 #[cfg(test)]
 use std::sync::atomic::AtomicBool;
@@ -1203,13 +1201,95 @@ fn permission_prompt(message: &str) -> bool {
 
   #[cfg(not(unix))]
   fn clear_stdin() {
+    use winapi::shared::minwindef::TRUE;
+    use winapi::shared::minwindef::UINT;
+    use winapi::shared::minwindef::WORD;
+    use winapi::shared::ntdef::WCHAR;
+    use winapi::um::processenv::GetStdHandle;
+    use winapi::um::winbase::STD_INPUT_HANDLE;
+    use winapi::um::wincon::FlushConsoleInputBuffer;
+    use winapi::um::wincon::PeekConsoleInputW;
+    use winapi::um::wincon::WriteConsoleInputW;
+    use winapi::um::wincontypes::INPUT_RECORD;
+    use winapi::um::wincontypes::KEY_EVENT;
+    use winapi::um::winnt::HANDLE;
+    use winapi::um::winuser::MapVirtualKeyW;
+    use winapi::um::winuser::MAPVK_VK_TO_VSC;
+    use winapi::um::winuser::VK_RETURN;
+
     unsafe {
-      let stdin = winapi::um::processenv::GetStdHandle(
-        winapi::um::winbase::STD_INPUT_HANDLE,
-      );
-      let flags =
-        winapi::um::winbase::PURGE_TXCLEAR | winapi::um::winbase::PURGE_RXCLEAR;
-      winapi::um::commapi::PurgeComm(stdin, flags);
+      let stdin = GetStdHandle(STD_INPUT_HANDLE);
+      // emulate an enter key press to clear any line buffered console characters
+      emulate_enter_key_press(stdin);
+      // read the buffered line or enter key press
+      read_stdin_line();
+      // check if our emulated key press was executed
+      if is_input_buffer_empty(stdin) {
+        // if so, move the cursor up to prevent a blank line
+        move_cursor_up();
+      } else {
+        // the emulated key press is still pending, so a buffered line was read
+        // and we can flush the emulated key press
+        flush_input_buffer(stdin);
+      }
+    }
+
+    unsafe fn flush_input_buffer(stdin: HANDLE) {
+      let success = FlushConsoleInputBuffer(stdin);
+      if success != TRUE {
+        panic!(
+          "Error flushing console input buffer: {}",
+          std::io::Error::last_os_error().to_string()
+        )
+      }
+    }
+
+    unsafe fn emulate_enter_key_press(stdin: HANDLE) {
+      // https://github.com/libuv/libuv/blob/a39009a5a9252a566ca0704d02df8dabc4ce328f/src/win/tty.c#L1121-L1131
+      let mut input_record: INPUT_RECORD = std::mem::zeroed();
+      input_record.EventType = KEY_EVENT;
+      input_record.Event.KeyEvent_mut().bKeyDown = TRUE;
+      input_record.Event.KeyEvent_mut().wRepeatCount = 1;
+      input_record.Event.KeyEvent_mut().wVirtualKeyCode = VK_RETURN as WORD;
+      input_record.Event.KeyEvent_mut().wVirtualScanCode =
+        MapVirtualKeyW(VK_RETURN as UINT, MAPVK_VK_TO_VSC) as WORD;
+      *input_record.Event.KeyEvent_mut().uChar.UnicodeChar_mut() =
+        '\r' as WCHAR;
+
+      let mut record_written = 0;
+      let success =
+        WriteConsoleInputW(stdin, &input_record, 1, &mut record_written);
+      if success != TRUE {
+        panic!(
+          "Error emulating enter key press: {}",
+          std::io::Error::last_os_error().to_string()
+        )
+      }
+    }
+
+    unsafe fn is_input_buffer_empty(stdin: HANDLE) -> bool {
+      let mut buffer = Vec::with_capacity(1);
+      let mut events_read = 0;
+      let success =
+        PeekConsoleInputW(stdin, buffer.as_mut_ptr(), 1, &mut events_read);
+      if success != TRUE {
+        panic!(
+          "Error peeking console input buffer: {}",
+          std::io::Error::last_os_error().to_string()
+        )
+      }
+      events_read == 0
+    }
+
+    fn move_cursor_up() {
+      use std::io::Write;
+      write!(std::io::stderr(), "\x1B[1A").expect("expected to move cursor up");
+    }
+
+    fn read_stdin_line() {
+      let mut input = String::new();
+      let stdin = std::io::stdin();
+      stdin.read_line(&mut input).expect("expected to read line");
     }
   }
 
@@ -1226,7 +1306,7 @@ fn permission_prompt(message: &str) -> bool {
   eprint!("{}", colors::bold(&msg));
   loop {
     let mut input = String::new();
-    let stdin = io::stdin();
+    let stdin = std::io::stdin();
     let result = stdin.read_line(&mut input);
     if result.is_err() {
       return false;