1 files changed, 59 insertions, 0 deletions
diff --git a/src/prompt_toolkit/contrib/regular_languages/validation.py b/src/prompt_toolkit/contrib/regular_languages/validation.py
new file mode 100644
index 0000000..8e56e05
--- /dev/null
+++ b/src/prompt_toolkit/contrib/regular_languages/validation.py
@@ -0,0 +1,59 @@
+"""
+Validator for a regular language.
+"""
+from __future__ import annotations
+
+from prompt_toolkit.document import Document
+from prompt_toolkit.validation import ValidationError, Validator
+
+from .compiler import _CompiledGrammar
+
+__all__ = [
+    "GrammarValidator",
+]
+
+
+class GrammarValidator(Validator):
+    """
+    Validator which can be used for validation according to variables in
+    the grammar. Each variable can have its own validator.
+
+    :param compiled_grammar: `GrammarCompleter` instance.
+    :param validators: `dict` mapping variable names of the grammar to the
+                       `Validator` instances to be used for each variable.
+    """
+
+    def __init__(
+        self, compiled_grammar: _CompiledGrammar, validators: dict[str, Validator]
+    ) -> None:
+        self.compiled_grammar = compiled_grammar
+        self.validators = validators
+
+    def validate(self, document: Document) -> None:
+        # Parse input document.
+        # We use `match`, not `match_prefix`, because for validation, we want
+        # the actual, unambiguous interpretation of the input.
+        m = self.compiled_grammar.match(document.text)
+
+        if m:
+            for v in m.variables():
+                validator = self.validators.get(v.varname)
+
+                if validator:
+                    # Unescape text.
+                    unwrapped_text = self.compiled_grammar.unescape(v.varname, v.value)
+
+                    # Create a document, for the completions API (text/cursor_position)
+                    inner_document = Document(unwrapped_text, len(unwrapped_text))
+
+                    try:
+                        validator.validate(inner_document)
+                    except ValidationError as e:
+                        raise ValidationError(
+                            cursor_position=v.start + e.cursor_position,
+                            message=e.message,
+                        ) from e
+        else:
+            raise ValidationError(
+                cursor_position=len(document.text), message="Invalid command"
+            )