From 551cd53a826782e35174f1cb61cf1708482944fb Mon Sep 17 00:00:00 2001
From: fan wu <336798967+FanWu-ai@users.noreply.github.com>
Date: Sun, 11 Oct 2026 10:19:28 -0700
Subject: [PATCH] Unescape regular-language matches only once

AI assistance: OpenAI Codex was used for investigation, implementation, regression tests, and automated validation.
---
 .../contrib/regular_languages/completion.py   |  9 +--
 .../contrib/regular_languages/validation.py   |  6 +-
 tests/test_regular_languages.py               | 62 ++++++++++++++++++-
 3 files changed, 66 insertions(+), 11 deletions(-)

diff --git a/src/prompt_toolkit/contrib/regular_languages/completion.py b/src/prompt_toolkit/contrib/regular_languages/completion.py
index 2181a42cc..bccaba67c 100644
--- a/src/prompt_toolkit/contrib/regular_languages/completion.py
+++ b/src/prompt_toolkit/contrib/regular_languages/completion.py
@@ -57,19 +57,16 @@ def _get_completions_for_match(
             completer = self.completers.get(varname)
 
             if completer:
+                # Match.end_nodes() has already unescaped this value.
                 text = match_variable.value
 
-                # Unwrap text.
-                unwrapped_text = self.compiled_grammar.unescape(varname, text)
-
                 # Create a document, for the completions API (text/cursor_position)
-                document = Document(unwrapped_text, len(unwrapped_text))
+                document = Document(text, len(text))
 
                 # Call completer
                 for completion in completer.get_completions(document, complete_event):
                     new_text = (
-                        unwrapped_text[: len(text) + completion.start_position]
-                        + completion.text
+                        text[: len(text) + completion.start_position] + completion.text
                     )
 
                     # Wrap again.
diff --git a/src/prompt_toolkit/contrib/regular_languages/validation.py b/src/prompt_toolkit/contrib/regular_languages/validation.py
index e6cfd7413..7a895a689 100644
--- a/src/prompt_toolkit/contrib/regular_languages/validation.py
+++ b/src/prompt_toolkit/contrib/regular_languages/validation.py
@@ -41,11 +41,9 @@ def validate(self, document: Document) -> None:
                 validator = self.validators.get(v.varname)
 
                 if validator:
-                    # Unescape text.
-                    unwrapped_text = self.compiled_grammar.unescape(v.varname, v.value)
-
+                    # Match.variables() has already unescaped this value.
                     # Create a document, for the completions API (text/cursor_position)
-                    inner_document = Document(unwrapped_text, len(unwrapped_text))
+                    inner_document = Document(v.value, len(v.value))
 
                     try:
                         validator.validate(inner_document)
diff --git a/tests/test_regular_languages.py b/tests/test_regular_languages.py
index 3d55dbc51..50ad89e47 100644
--- a/tests/test_regular_languages.py
+++ b/tests/test_regular_languages.py
@@ -1,10 +1,21 @@
 from __future__ import annotations
 
-from prompt_toolkit.completion import CompleteEvent, Completer, Completion
+import re
+
+import pytest
+
+from prompt_toolkit.completion import (
+    CompleteEvent,
+    Completer,
+    Completion,
+    WordCompleter,
+)
 from prompt_toolkit.contrib.regular_languages import compile
 from prompt_toolkit.contrib.regular_languages.compiler import Match, Variables
 from prompt_toolkit.contrib.regular_languages.completion import GrammarCompleter
+from prompt_toolkit.contrib.regular_languages.validation import GrammarValidator
 from prompt_toolkit.document import Document
+from prompt_toolkit.validation import Validator
 
 
 def test_simple_match():
@@ -100,3 +111,52 @@ def get_completions(self, document, complete_event):
     assert completions[0].start_position == -3
     assert completions[1].text == "before2-def-after2-B"
     assert completions[1].start_position == -3
+
+
+def _escape_argument(text):
+    return re.sub(r"([\\ ])", r"\\\1", text)
+
+
+def _unescape_argument(text):
+    return re.sub(r"\\(.)", r"\1", text)
+
+
+@pytest.mark.parametrize("text", [r"foo\b", r"foo\ b", r"foo\\b", "foo b", "foo"])
+@pytest.mark.parametrize("suffix", ["", " trailing"])
+def test_completer_unescapes_once(text, suffix):
+    grammar = compile(
+        r"cmd\s+(?P<arg>.*)",
+        escape_funcs={"arg": _escape_argument},
+        unescape_funcs={"arg": _unescape_argument},
+    )
+    target = text + "ar"
+    completer = GrammarCompleter(
+        grammar, {"arg": WordCompleter([target], sentence=True)}
+    )
+    escaped = _escape_argument(text)
+    before_cursor = "cmd " + escaped
+    document = Document(before_cursor + suffix, len(before_cursor))
+
+    completions = list(completer.get_completions(document, CompleteEvent()))
+
+    assert len(completions) == 1
+    assert completions[0].text == _escape_argument(target)
+    assert completions[0].start_position == -len(escaped)
+
+
+@pytest.mark.parametrize("text", [r"foo\b", r"foo\ b", r"foo\\b", "foo b", "foo"])
+def test_validator_unescapes_once(text):
+    received = []
+
+    class RecordingValidator(Validator):
+        def validate(self, document):
+            received.append((document.text, document.cursor_position))
+
+    grammar = compile(
+        r"cmd\s+(?P<arg>.*)",
+        unescape_funcs={"arg": _unescape_argument},
+    )
+    validator = GrammarValidator(grammar, {"arg": RecordingValidator()})
+    validator.validate(Document("cmd " + _escape_argument(text)))
+
+    assert received == [(text, len(text))]