[lldb] Add fzf_history command to examples (#128571)

Adds a `fzf_history` to the examples directory.

This python command invokes [fzf](https://github.com/junegunn/fzf) to
select from lldb's command history.

Tighter integration is available on macOS, via commands for copy and
paste. The user's chosen history entry back is pasted into the lldb
console (via AppleScript). By pasting it, users have the opportunity to
edit it before running it. This matches how fzf's history search works.

Without copy and paste, the user's chosen history entry is printed to
screen and then run automatically.

Author: kastiglione

lldb/examples/python/fzf_history.py

@@ -0,0 +1,110 @@
+import os
+import re
+import sys
+import subprocess
+import tempfile
+
+import lldb
+
+
+@lldb.command()
+def fzf_history(debugger, cmdstr, ctx, result, _):
+    """Use fzf to search and select from lldb command history."""
+    history_file = os.path.expanduser("~/.lldb/lldb-widehistory")
+    if not os.path.exists(history_file):
+        result.SetError("history file does not exist")
+        return
+    history = _load_history(history_file)
+
+    if sys.platform != "darwin":
+        # The ability to integrate fzf's result into lldb uses copy and paste.
+        # In absense of copy and paste, run the selected command directly.
+        temp_file = tempfile.NamedTemporaryFile("r")
+        fzf_command = (
+            "fzf",
+            "--no-sort",
+            f"--query={cmdstr}",
+            f"--bind=enter:execute-silent(echo -n {{}} > {temp_file.name})+accept",
+        )
+        subprocess.run(fzf_command, input=history, text=True)
+        command = temp_file.read()
+        debugger.HandleCommand(command)
+        return
+
+    # Capture the current pasteboard contents to restore after overwriting.
+    paste_snapshot = subprocess.run("pbpaste", text=True, capture_output=True).stdout
+
+    # On enter, copy the selected history entry into the pasteboard.
+    fzf_command = (
+        "fzf",
+        "--no-sort",
+        f"--query={cmdstr}",
+        "--bind=enter:execute-silent(echo -n {} | pbcopy)+close",
+    )
+    completed = subprocess.run(fzf_command, input=history, text=True)
+    # 130 is used for CTRL-C or ESC.
+    if completed.returncode not in (0, 130):
+        result.SetError("fzf failed")
+        return
+
+    # Get the user's selected history entry.
+    selected_command = subprocess.run("pbpaste", text=True, capture_output=True).stdout
+    if selected_command == paste_snapshot:
+        # Nothing was selected, no cleanup needed.
+        return
+
+    _handle_command(debugger, selected_command)
+
+    # Restore the pasteboard's contents.
+    subprocess.run("pbcopy", input=paste_snapshot, text=True)
+
+
+def _handle_command(debugger, command):
+    """Try pasting the command, and failing that, run it directly."""
+    if not command:
+        return
+
+    # Use applescript to paste the selected result into lldb's console.
+    paste_command = (
+        "osascript",
+        "-e",
+        'tell application "System Events" to keystroke "v" using command down',
+    )
+    completed = subprocess.run(paste_command, capture_output=True)
+
+    if completed.returncode != 0:
+        # The above applescript requires the "control your computer" permission.
+        #     Settings > Private & Security > Accessibility
+        # If not enabled, fallback to running the command.
+        debugger.HandleCommand(command)
+
+
+def _load_history(history_file):
+    """Load, decode, parse, and prepare an lldb history file for fzf."""
+    with open(history_file) as f:
+        history_contents = f.read()
+
+    history_decoded = re.sub(r"\\0([0-7][0-7])", _decode_char, history_contents)
+    history_lines = history_decoded.splitlines()
+
+    # Skip the header line (_HiStOrY_V2_)
+    del history_lines[0]
+    # Reverse to show latest first.
+    history_lines.reverse()
+
+    history_commands = []
+    history_seen = set()
+    for line in history_lines:
+        line = line.strip()
+        # Skip empty lines, single character commands, and duplicates.
+        if line and len(line) > 1 and line not in history_seen:
+            history_commands.append(line)
+            history_seen.add(line)
+
+    return "\n".join(history_commands)
+
+
+def _decode_char(match):
+    """Decode octal strings ('\0NN') into a single character string."""
+    code = int(match.group(1), base=8)
+    return chr(code)