[Lldb-commits] [lldb] [lldb][Windows] Check for EOF before the ctrl-c retry in GetLine (PR #212745)

[Charles Zablit via lldb-commits]

https://github.com/charles-zablit created https://github.com/llvm/llvm-project/pull/212745

On Windows `lldb --repl` can hang forever instead of exiting at EOF.

`IOHandlerEditline::GetLine` checks `GetLastError() == ERROR_OPERATION_ABORTED` and does a `continue` before checking `feof`.
However `fgets` is a CRT function and does not set the Win32 last error value, so the `GetLastError` read is not the expected error. When it happens to be `ERROR_OPERATION_ABORTED` (995) the loop never reaches the EOF check.

This reorders the checks so EOF wins unconditionally, and adds `clearerr` before the ctrl-c retry (a real interrupt leaves the error flag set, which would fail the next `fgets`). ctrl-c handling is otherwise unchanged.

rdar://183335061

>From 773ecbd8b0822c8a5a7246dfa4555b6df0d6f56e Mon Sep 17 00:00:00 2001
From: Charles Zablit <c_zablit at apple.com>
Date: Wed, 29 Jul 2026 12:35:23 +0100
Subject: [PATCH] [lldb][Windows] Check for EOF before the ctrl-c retry in
 GetLine

---
 lldb/source/Core/IOHandler.cpp | 29 +++++++++++++++--------------
 1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/lldb/source/Core/IOHandler.cpp b/lldb/source/Core/IOHandler.cpp
index 0bb8b58f24bff..a4477e4931b15 100644
--- a/lldb/source/Core/IOHandler.cpp
+++ b/lldb/source/Core/IOHandler.cpp
@@ -395,23 +395,24 @@ bool IOHandlerEditline::GetLine(std::string &line, bool &interrupted) {
     while (!got_line) {
       char *r = fgets(buffer, sizeof(buffer), in);
 #ifdef _WIN32
-      // ReadFile on Windows is supposed to set ERROR_OPERATION_ABORTED
-      // according to the docs on MSDN. However, this has evidently been a
-      // known bug since Windows 8. Therefore, we can't detect if a signal
-      // interrupted in the fgets. So pressing ctrl-c causes the repl to end
-      // and the process to exit. A temporary workaround is just to attempt to
-      // fgets twice until this bug is fixed.
-      if (r == nullptr)
-        r = fgets(buffer, sizeof(buffer), in);
-      // this is the equivalent of EINTR for Windows
-      if (r == nullptr && GetLastError() == ERROR_OPERATION_ABORTED)
-        continue;
-#endif
       if (r == nullptr) {
+        if (feof(in)) {
+          got_line = SplitLineEOF(m_line_buffer);
+          break;
+        }
         if (ferror(in) && errno == EINTR)
           continue;
-        if (feof(in))
-          got_line = SplitLineEOF(m_line_buffer);
+        // ReadFile on Windows is supposed to set ERROR_OPERATION_ABORTED
+        // according to the docs on MSDN. However, this has evidently been a
+        // known bug since Windows 8. Therefore, we can't detect if a signal
+        // interrupted in the fgets. So pressing ctrl-c causes the repl to end
+        // and the process to exit. A temporary workaround is just to attempt
+        // to fgets twice until this bug is fixed.
+        if (GetLastError() == ERROR_OPERATION_ABORTED) {
+          clearerr(in);
+          continue;
+        }
+#endif
         break;
       }
       m_line_buffer += buffer;