[lldb] Implement a statusline in LLDB

Add a statusline to command-line LLDB to display progress events and
other information related to the current state of the debugger. The
statusline is a dedicated area displayed the bottom of the screen. The
contents of the status line are configurable through a setting
consisting of LLDB’s format strings.

The statusline is configurable through the `statusline-format` setting.
The default configuration shows the target name, the current file, the
stop reason and the current progress event.

```
(lldb) settings show statusline-format
statusline-format (format-string) = "${ansi.bg.cyan}${ansi.fg.black}{${target.file.basename}}{ | ${line.file.basename}:${line.number}:${line.column}}{ | ${thread.stop-reason}}{ | {${progress.count} }${progress.message}}"
```

The statusline is enabled by default, but can be disabled with the
following setting:

```
(lldb) settings set show-statusline false
```

The statusline supersedes the current progress reporting implementation.
Consequently, the following settings no longer have any effect (but
continue to exist):

```
show-progress             -- Whether to show progress or not if the debugger's output is an interactive color-enabled terminal.
show-progress-ansi-prefix -- When displaying progress in a color-enabled terminal, use the ANSI terminal code specified in this format immediately before the progress message.
show-progress-ansi-suffix -- When displaying progress in a color-enabled terminal, use the ANSI terminal code specified in this format immediately after the progress message.
```

RFC: https://discourse.llvm.org/t/rfc-lldb-statusline/83948

Author: JDevlieghere

lldb/include/lldb/Core/Debugger.h

@@ -19,6 +19,7 @@
 #include "lldb/Core/FormatEntity.h"
 #include "lldb/Core/IOHandler.h"
 #include "lldb/Core/SourceManager.h"
+#include "lldb/Core/Statusline.h"
 #include "lldb/Core/UserSettingsController.h"
 #include "lldb/Host/HostThread.h"
 #include "lldb/Host/StreamFile.h"
@@ -303,6 +304,10 @@ class Debugger : public std::enable_shared_from_this<Debugger>,
 
   bool SetShowProgress(bool show_progress);
 
+  bool GetShowStatusline() const;
+
+  const FormatEntity::Entry *GetStatuslineFormat() const;
+
   llvm::StringRef GetShowProgressAnsiPrefix() const;
 
   llvm::StringRef GetShowProgressAnsiSuffix() const;
@@ -599,11 +604,20 @@ class Debugger : public std::enable_shared_from_this<Debugger>,
     return m_source_file_cache;
   }
 
+  struct ProgressReport {
+    uint64_t id;
+    uint64_t completed;
+    uint64_t total;
+    std::string message;
+  };
+  std::optional<ProgressReport> GetCurrentProgressReport() const;
+
 protected:
   friend class CommandInterpreter;
   friend class REPL;
   friend class Progress;
   friend class ProgressManager;
+  friend class Statusline;
 
   /// Report progress events.
   ///
@@ -656,6 +670,8 @@ class Debugger : public std::enable_shared_from_this<Debugger>,
   lldb::LockableStreamFileSP GetErrorStreamSP() { return m_error_stream_sp; }
   /// @}
 
+  bool StatuslineSupported();
+
   void PushIOHandler(const lldb::IOHandlerSP &reader_sp,
                      bool cancel_top_handler = true);
 
@@ -732,7 +748,7 @@ class Debugger : public std::enable_shared_from_this<Debugger>,
   IOHandlerStack m_io_handler_stack;
   std::recursive_mutex m_io_handler_synchronous_mutex;
 
-  std::optional<uint64_t> m_current_event_id;
+  std::optional<Statusline> m_statusline;
 
   llvm::StringMap<std::weak_ptr<LogHandler>> m_stream_handlers;
   std::shared_ptr<CallbackLogHandler> m_callback_handler_sp;
@@ -749,6 +765,12 @@ class Debugger : public std::enable_shared_from_this<Debugger>,
   lldb::TargetSP m_dummy_target_sp;
   Diagnostics::CallbackID m_diagnostics_callback_id;
 
+  /// Bookkeeping for command line progress events.
+  /// @{
+  llvm::SmallVector<ProgressReport, 4> m_progress_reports;
+  mutable std::mutex m_progress_reports_mutex;
+  /// @}
+
   std::mutex m_destroy_callback_mutex;
   lldb::callback_token_t m_destroy_callback_next_token = 0;
   struct DestroyCallbackInfo {

lldb/include/lldb/Core/FormatEntity.h

@@ -100,7 +100,9 @@ struct Entry {
     LineEntryColumn,
     LineEntryStartAddress,
     LineEntryEndAddress,
-    CurrentPCArrow
+    CurrentPCArrow,
+    ProgressCount,
+    ProgressMessage,
   };
 
   struct Definition {

lldb/include/lldb/Core/Statusline.h

@@ -0,0 +1,58 @@
+//===-- Statusline.h -----------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLDB_CORE_STATUSLINE_H
+#define LLDB_CORE_STATUSLINE_H
+
+#include "lldb/lldb-forward.h"
+#include "llvm/ADT/StringRef.h"
+#include <csignal>
+#include <string>
+
+namespace lldb_private {
+class Statusline {
+public:
+  Statusline(Debugger &debugger);
+  ~Statusline();
+
+  /// Reduce the scroll window and draw the statusline.
+  void Enable();
+
+  /// Hide the statusline and extend the scroll window.
+  void Disable();
+
+  /// Redraw the statusline. If update is false, this will redraw the last
+  /// string.
+  void Redraw(bool update = true);
+
+  /// Inform the statusline that the terminal dimensions have changed.
+  void TerminalSizeChanged();
+
+private:
+  /// Draw the statusline with the given text.
+  void Draw(std::string msg);
+
+  /// Update terminal dimensions.
+  void UpdateTerminalProperties();
+
+  /// Set the scroll window to the given height.
+  void SetScrollWindow(uint64_t height);
+
+  /// 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;
+  uint64_t m_scroll_height = 0;
+};
+} // namespace lldb_private
+#endif // LLDB_CORE_STATUSLINE_H

lldb/packages/Python/lldbsuite/test/lldbtest.py

@@ -765,6 +765,8 @@ def setUpCommands(cls):
             # Disable fix-its by default so that incorrect expressions in tests don't
             # pass just because Clang thinks it has a fix-it.
             "settings set target.auto-apply-fixits false",
+            # Disable the statusline in PExpect tests.
+            "settings set show-statusline false",
             # Testsuite runs in parallel and the host can have also other load.
             "settings set plugin.process.gdb-remote.packet-timeout 60",
             'settings set symbols.clang-modules-cache-path "{}"'.format(

lldb/source/Core/CMakeLists.txt

@@ -50,6 +50,7 @@ add_lldb_library(lldbCore
   Opcode.cpp
   PluginManager.cpp
   Progress.cpp
+  Statusline.cpp
   RichManglingContext.cpp
   SearchFilter.cpp
   Section.cpp

lldb/source/Core/CoreProperties.td

@@ -172,6 +172,14 @@ let Definition = "debugger" in {
     Global,
     DefaultStringValue<"${ansi.normal}">,
     Desc<"When displaying progress in a color-enabled terminal, use the ANSI terminal code specified in this format immediately after the progress message.">;
+  def ShowStatusline: Property<"show-statusline", "Boolean">,
+    Global,
+    DefaultTrue,
+    Desc<"Whether to show a statusline at the bottom of the terminal.">;
+  def StatuslineFormat: Property<"statusline-format", "FormatEntity">,
+    Global,
+    DefaultStringValue<"${ansi.bg.blue}${ansi.fg.black}{${target.file.basename}}{ | ${line.file.basename}:${line.number}:${line.column}}{ | ${thread.stop-reason}}{ | {${progress.count} }${progress.message}}">,
+    Desc<"List of statusline format entities.">;
   def UseSourceCache: Property<"use-source-cache", "Boolean">,
     Global,
     DefaultTrue,