[lldb] Fix statusline terminal resizing

Simplify and fix the logic to clear the old statusline when the terminal
window dimensions have changed. I accidentally broke the terminal
resizing behavior when addressing code review feedback.

I'd really like to figure out a way to test this. PExpect isn't a good
fit for this, because I really need to check the result, rather than the
control characters, as the latter doesn't tell me whether any part of
the old statusline is still visible.

(cherry picked from commit aa889ed)

Author: JDevlieghere

lldb/include/lldb/Core/Statusline.h

@@ -10,8 +10,6 @@
 #define LLDB_CORE_STATUSLINE_H
 
 #include "lldb/lldb-forward.h"
-#include "llvm/ADT/StringRef.h"
-#include <csignal>
 #include <cstdint>
 #include <string>
 
@@ -34,10 +32,6 @@ class Statusline {
   /// Inform the statusline that the terminal dimensions have changed.
   void TerminalSizeChanged();
 
-protected:
-  /// Pad and trim the given string to fit to the given width.
-  static std::string TrimAndPad(std::string str, size_t width);
-
 private:
   /// Draw the statusline with the given text.
   void Draw(std::string msg);
@@ -46,20 +40,15 @@ class Statusline {
   void UpdateTerminalProperties();
 
   enum ScrollWindowMode {
-    ScrollWindowExtend,
-    ScrollWindowShrink,
+    EnableStatusline,
+    DisableStatusline,
   };
 
   /// Set the scroll window for the given mode.
   void UpdateScrollWindow(ScrollWindowMode mode);
 
-  /// Clear the statusline (without redrawing the background).
-  void Reset();
-
   Debugger &m_debugger;
   std::string m_last_str;
-
-  volatile std::sig_atomic_t m_terminal_size_has_changed = 1;
   uint64_t m_terminal_width = 0;
   uint64_t m_terminal_height = 0;
 };

lldb/source/Core/Statusline.cpp

@@ -23,50 +23,49 @@
 #define ANSI_SAVE_CURSOR ESCAPE "7"
 #define ANSI_RESTORE_CURSOR ESCAPE "8"
 #define ANSI_CLEAR_BELOW ESCAPE "[J"
-#define ANSI_CLEAR_LINE "\r\x1B[2K"
+#define ANSI_CURSOR_DOWN ESCAPE "[B"
+#define ANSI_CLEAR_LINE ESCAPE "[2K"
 #define ANSI_SET_SCROLL_ROWS ESCAPE "[0;%ur"
 #define ANSI_TO_START_OF_ROW ESCAPE "[%u;0f"
 #define ANSI_UP_ROWS ESCAPE "[%dA"
 
 using namespace lldb;
 using namespace lldb_private;
 
-Statusline::Statusline(Debugger &debugger) : m_debugger(debugger) { Enable(); }
+Statusline::Statusline(Debugger &debugger)
+    : m_debugger(debugger), m_terminal_width(m_debugger.GetTerminalWidth()),
+      m_terminal_height(m_debugger.GetTerminalHeight()) {
+  Enable();
+}
 
 Statusline::~Statusline() { Disable(); }
 
 void Statusline::TerminalSizeChanged() {
-  m_terminal_size_has_changed = 1;
+  UpdateTerminalProperties();
 
   // This definitely isn't signal safe, but the best we can do, until we
   // have proper signal-catching thread.
   Redraw(/*update=*/false);
 }
 
 void Statusline::Enable() {
-  UpdateTerminalProperties();
-
   // Reduce the scroll window to make space for the status bar below.
-  UpdateScrollWindow(ScrollWindowShrink);
+  UpdateScrollWindow(EnableStatusline);
 
   // Draw the statusline.
-  Redraw();
+  Redraw(/*update=*/true);
 }
 
 void Statusline::Disable() {
-  UpdateTerminalProperties();
-
   // Extend the scroll window to cover the status bar.
-  UpdateScrollWindow(ScrollWindowExtend);
+  UpdateScrollWindow(DisableStatusline);
 }
 
 void Statusline::Draw(std::string str) {
   lldb::LockableStreamFileSP stream_sp = m_debugger.GetOutputStreamSP();
   if (!stream_sp)
     return;
 
-  UpdateTerminalProperties();
-
   m_last_str = str;
 
   str = ansi::TrimAndPad(str, m_terminal_width);
@@ -80,58 +79,37 @@ void Statusline::Draw(std::string str) {
   locked_stream << ANSI_RESTORE_CURSOR;
 }
 
-void Statusline::Reset() {
-  lldb::LockableStreamFileSP stream_sp = m_debugger.GetOutputStreamSP();
-  if (!stream_sp)
-    return;
-
-  LockedStreamFile locked_stream = stream_sp->Lock();
-  locked_stream << ANSI_SAVE_CURSOR;
-  locked_stream.Printf(ANSI_TO_START_OF_ROW,
-                       static_cast<unsigned>(m_terminal_height));
-  locked_stream << ANSI_CLEAR_LINE;
-  locked_stream << ANSI_RESTORE_CURSOR;
-}
-
 void Statusline::UpdateTerminalProperties() {
-  if (m_terminal_size_has_changed == 0)
-    return;
-
-  // Clear the previous statusline using the previous dimensions.
-  Reset();
-
+  UpdateScrollWindow(DisableStatusline);
   m_terminal_width = m_debugger.GetTerminalWidth();
   m_terminal_height = m_debugger.GetTerminalHeight();
-
-  // Set the scroll window based on the new terminal height.
-  UpdateScrollWindow(ScrollWindowShrink);
-
-  // Clear the flag.
-  m_terminal_size_has_changed = 0;
+  UpdateScrollWindow(EnableStatusline);
 }
 
 void Statusline::UpdateScrollWindow(ScrollWindowMode mode) {
+  assert(m_terminal_width != 0 && m_terminal_height != 0);
+
   lldb::LockableStreamFileSP stream_sp = m_debugger.GetOutputStreamSP();
   if (!stream_sp)
     return;
 
   const unsigned scroll_height =
-      (mode == ScrollWindowExtend) ? m_terminal_height : m_terminal_height - 1;
+      (mode == DisableStatusline) ? m_terminal_height : m_terminal_height - 1;
 
   LockedStreamFile locked_stream = stream_sp->Lock();
   locked_stream << ANSI_SAVE_CURSOR;
   locked_stream.Printf(ANSI_SET_SCROLL_ROWS, scroll_height);
   locked_stream << ANSI_RESTORE_CURSOR;
   switch (mode) {
-  case ScrollWindowExtend:
-    // Clear the screen below to hide the old statusline.
-    locked_stream << ANSI_CLEAR_BELOW;
-    break;
-  case ScrollWindowShrink:
+  case EnableStatusline:
     // Move everything on the screen up.
     locked_stream.Printf(ANSI_UP_ROWS, 1);
     locked_stream << '\n';
     break;
+  case DisableStatusline:
+    // Clear the screen below to hide the old statusline.
+    locked_stream << ANSI_CLEAR_BELOW;
+    break;
   }
 }