[lldb] Implement a statusline in LLDB (#121860)

Add a statusline to command-line LLDB to display information about the
current state of the debugger. The statusline is a dedicated area
displayed at the bottom of the screen. The information displayed is
configurable through a setting consisting of LLDB’s format strings.

Enablement
----------

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

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

Configuration
-------------

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

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

The statusline supersedes the current progress reporting implementation.
Consequently, the following settings no longer have any effect (but
continue to exist to not break anyone's `.lldbinit`):

```
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.
```

Format Strings
--------------

LLDB's format strings are documented in the LLDB documentation and on
the website: https://lldb.llvm.org/use/formatting.html#format-strings.
The current implementation is relatively limited but various
improvements have been discussed in the RFC.

One such improvement is being to display a string when a format string
is empty. Right now, when launching LLDB without a target, the
statusline will be empty, which is expected, but looks rather odd.

RFC
---

The full RFC can be found on Discourse:
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;
@@ -412,6 +417,9 @@ class Debugger : public std::enable_shared_from_this<Debugger>,
   /// Decrement the "interrupt requested" counter.
   void CancelInterruptRequest();
 
+  /// Redraw the statusline if enabled.
+  void RedrawStatusline(bool update = true);
+
   /// This is the correct way to query the state of Interruption.
   /// If you are on the RunCommandInterpreter thread, it will check the
   /// command interpreter state, and if it is on another thread it will
@@ -599,11 +607,20 @@ 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 +673,8 @@ 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 +751,7 @@ 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 +768,12 @@ 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/IOHandler.h

@@ -406,6 +406,8 @@ class IOHandlerEditline : public IOHandler {
   std::optional<std::string> SuggestionCallback(llvm::StringRef line);
 
   void AutoCompleteCallback(CompletionRequest &request);
+
+  void RedrawCallback();
 #endif
 
 protected:

lldb/include/lldb/Core/Statusline.h

@@ -0,0 +1,67 @@
+//===-- 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 <cstdint>
+#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();
+
+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);
+
+  /// Update terminal dimensions.
+  void UpdateTerminalProperties();
+
+  enum ScrollWindowMode {
+    ScrollWindowExtend,
+    ScrollWindowShrink,
+  };
+
+  /// 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;
+};
+} // namespace lldb_private
+#endif // LLDB_CORE_STATUSLINE_H

lldb/include/lldb/Host/Editline.h

@@ -102,6 +102,8 @@ using SuggestionCallbackType =
 
 using CompleteCallbackType = llvm::unique_function<void(CompletionRequest &)>;
 
+using RedrawCallbackType = llvm::unique_function<void()>;
+
 /// Status used to decide when and how to start editing another line in
 /// multi-line sessions.
 enum class EditorStatus {
@@ -194,6 +196,11 @@ class Editline {
     m_suggestion_callback = std::move(callback);
   }
 
+  /// Register a callback for redrawing the statusline.
+  void SetRedrawCallback(RedrawCallbackType callback) {
+    m_redraw_callback = std::move(callback);
+  }
+
   /// Register a callback for the tab key
   void SetAutoCompleteCallback(CompleteCallbackType callback) {
     m_completion_callback = std::move(callback);
@@ -409,6 +416,7 @@ class Editline {
 
   CompleteCallbackType m_completion_callback;
   SuggestionCallbackType m_suggestion_callback;
+  RedrawCallbackType m_redraw_callback;
 
   bool m_color;
   std::string m_prompt_ansi_prefix;

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

@@ -772,7 +772,10 @@ def setUpCommands(cls):
             'settings set symbols.clang-modules-cache-path "{}"'.format(
                 configuration.lldb_module_cache_dir
             ),
+            # Disable colors by default.
             "settings set use-color false",
+            # Disable the statusline by default.
+            "settings set show-statusline false",
         ]
 
         # Set any user-overridden settings.

lldb/source/Core/CMakeLists.txt

@@ -46,6 +46,7 @@ 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<"The default statusline format string.">;
   def UseSourceCache: Property<"use-source-cache", "Boolean">,
     Global,
     DefaultTrue,