fix(schema): add basic support of Pattern type in schema generation

closes #1767

changes/1767-PrettyWood.md

@@ -0,0 +1 @@
+add basic support of Pattern type in schema generation

pydantic/schema.py

@@ -14,6 +14,7 @@
     Iterable,
     List,
     Optional,
+    Pattern,
     Sequence,
     Set,
     Tuple,
@@ -698,6 +699,12 @@ def field_singleton_schema(  # noqa: C901 (ignore complexity)
         field_type = literal_value.__class__
         f_schema['const'] = literal_value
 
+    # `typing.Pattern` is not a valid type and should be considered as a string.
+    # Note: We should probably add `pattern: <the regex>` in the schema
+    # but it requires `.schema()` to be an instance method instead of a class one.
+    if field_type is Pattern:
+        field_type = str
+
     if lenient_issubclass(field_type, Enum):
         enum_name = normalize_name(field_type.__name__)
         f_schema = {'$ref': ref_prefix + enum_name}

tests/test_types.py

@@ -2055,6 +2055,13 @@ class Foobar(BaseModel):
     f2 = Foobar(pattern=p)
     assert f2.pattern is p
 
+    assert Foobar.schema() == {
+        'type': 'object',
+        'title': 'Foobar',
+        'properties': {'pattern': {'type': 'string', 'title': 'Pattern'}},
+        'required': ['pattern'],
+    }
+
 
 def test_pattern_error():
     class Foobar(BaseModel):