Fix regex_engine config not applied to RootModel generic

pyproject.toml

@@ -186,10 +186,12 @@ lint.per-file-ignores."tests/**/*.py" = [
   "INP001",  # no implicit namespace
   "PLC0415", # local imports in tests are fine
   "PLC2701", # private import is fine
+  "PLR0904", # too many public methods in test classes is fine
   "PLR0913", # as many arguments as want
   "PLR0915", # can have longer test methods
   "PLR0917", # as many arguments as want
   "PLR2004", # Magic value used in comparison, consider replacing with a constant variable
+  "PLR6301", # test methods don't need to use self
   "S",       # no safety concerns
   "SLF001",  # can test private methods
 ]

src/datamodel_code_generator/model/base.py

@@ -220,6 +220,15 @@ def _build_union_type_hint(self) -> str | None:
             return f"Union[{', '.join(parts)}]"
         return None  # pragma: no cover
 
+    def _build_base_union_type_hint(self) -> str | None:  # pragma: no cover
+        """Build Union[] base type hint from data_type.data_types if forward reference requires it."""
+        if not (self._use_union_operator != self.data_type.use_union_operator and self.data_type.is_union):
+            return None
+        parts = [dt.base_type_hint for dt in self.data_type.data_types if dt.base_type_hint]
+        if len(parts) > 1:
+            return f"Union[{', '.join(parts)}]"
+        return None
+
     @property
     def type_hint(self) -> str:  # noqa: PLR0911
         """Get the type hint string for this field, including nullability."""
@@ -241,6 +250,33 @@ def type_hint(self) -> str:  # noqa: PLR0911
             return get_optional_type(type_hint, self._use_union_operator)
         return type_hint
 
+    @property
+    def base_type_hint(self) -> str:
+        """Get the base type hint without constrained type kwargs.
+
+        This returns the type without kwargs (e.g., 'str' instead of 'constr(pattern=...)').
+        Used in RootModel generics when regex_engine config is needed for lookaround patterns.
+        """
+        base_hint = self._build_base_union_type_hint() or self.data_type.base_type_hint
+
+        if not base_hint:  # pragma: no cover
+            return NONE
+
+        needs_optional = (
+            (self.nullable is True)
+            or (self.required and self.type_has_null)
+            or (self.nullable is None and not self.required and self.fall_back_to_nullable)
+        )
+        skip_optional = (
+            self.has_default_factory
+            or (self.data_type.is_optional and self.data_type.type != ANY)
+            or (self.nullable is False)
+        )
+
+        if needs_optional and not skip_optional:  # pragma: no cover
+            return get_optional_type(base_hint, self._use_union_operator)
+        return base_hint
+
     @property
     def imports(self) -> tuple[Import, ...]:
         """Get all imports required for this field's type hint."""

src/datamodel_code_generator/model/pydantic_v2/base_model.py

@@ -228,15 +228,8 @@ def __init__(  # noqa: PLR0913
                 config_parameters["arbitrary_types_allowed"] = True
                 break
 
-        for field in self.fields:
-            # Check if a regex pattern uses lookarounds.
-            # Depending on the generation configuration, the pattern may end up in two different places.
-            pattern = (isinstance(field.constraints, Constraints) and field.constraints.pattern) or (
-                field.data_type.kwargs or {}
-            ).get("pattern")
-            if pattern and re.search(r"\(\?<?[=!]", pattern):
-                config_parameters["regex_engine"] = '"python-re"'
-                break
+        if self._has_lookaround_pattern():
+            config_parameters["regex_engine"] = '"python-re"'
 
         if isinstance(self.extra_template_data.get("config"), dict):
             for key, value in self.extra_template_data["config"].items():
@@ -265,3 +258,16 @@ def _get_config_extra(self) -> Literal["'allow'", "'forbid'", "'ignore'"] | None
         elif additional_properties is False:
             config_extra = "'forbid'"
         return config_extra
+
+    def _has_lookaround_pattern(self) -> bool:
+        """Check if any field has a regex pattern with lookaround assertions."""
+        lookaround_regex = re.compile(r"\(\?<?[=!]")
+        for field in self.fields:
+            pattern = isinstance(field.constraints, Constraints) and field.constraints.pattern
+            if pattern and lookaround_regex.search(pattern):
+                return True
+            for data_type in field.data_type.all_data_types:
+                pattern = (data_type.kwargs or {}).get("pattern")
+                if pattern and lookaround_regex.search(pattern):
+                    return True
+        return False

src/datamodel_code_generator/model/template/pydantic_v2/RootModel.jinja2

@@ -1,16 +1,22 @@
-{%- macro get_type_hint(_fields) -%}
+{%- macro get_type_hint(_fields, use_base_type) -%}
 {%- if _fields -%}
 {#There will only ever be a single field for RootModel#}
+{%- if use_base_type -%}
+{{- _fields[0].base_type_hint}}
+{%- else -%}
 {{- _fields[0].type_hint}}
 {%- endif -%}
+{%- endif -%}
 {%- endmacro -%}
 
 
 {% for decorator in decorators -%}
 {{ decorator }}
 {% endfor -%}
 
-class {{ class_name }}({{ base_class }}{%- if fields -%}[{{get_type_hint(fields)}}]{%- endif -%}):{% if comment is defined %}  # {{ comment }}{% endif %}
+{#- Use base_type_hint in generic when regex_engine is set to avoid evaluating pattern before config is processed -#}
+{%- set use_base_type = config and config.regex_engine -%}
+class {{ class_name }}({{ base_class }}{%- if fields -%}[{{get_type_hint(fields, use_base_type)}}]{%- endif -%}):{% if comment is defined %}  # {{ comment }}{% endif %}
 {%- if description %}
     """
     {{ description | indent(4) }}

src/datamodel_code_generator/types.py

@@ -422,9 +422,11 @@ def full_name(self) -> str:
 
     @property
     def all_data_types(self) -> Iterator[DataType]:
-        """Recursively yield all nested DataTypes including self."""
+        """Recursively yield all nested DataTypes including self and dict_key."""
         for data_type in self.data_types:
             yield from data_type.all_data_types
+        if self.dict_key:
+            yield from self.dict_key.all_data_types
         yield self
 
     def find_source(self, source_type: type[SourceT]) -> SourceT | None:
@@ -618,6 +620,124 @@ def is_union(self) -> bool:
         """Return whether this DataType represents a union of multiple types."""
         return len(self.data_types) > 1
 
+    # Mapping from constrained type functions to their base Python types.
+    # Only constr is included because it's the only type with a 'pattern' parameter
+    # that can trigger lookaround regex detection. Other constrained types (conint,
+    # confloat, condecimal, conbytes) don't have pattern constraints, so they will
+    # never need base_type_hint conversion in the regex_engine context.
+    _CONSTRAINED_TYPE_TO_BASE: ClassVar[dict[str, str]] = {
+        "constr": "str",
+    }
+
+    @property
+    def base_type_hint(self) -> str:  # noqa: PLR0912, PLR0915
+        """Return the base type hint without constrained type kwargs.
+
+        For types like constr(pattern=..., min_length=...), this returns just 'str'.
+        This works recursively for nested types like list[constr(pattern=...)] -> list[str].
+
+        This is useful when the pattern contains lookaround assertions that require
+        regex_engine="python-re", which must be set in model_config. In such cases,
+        the RootModel generic cannot use the constrained type because it would be
+        evaluated at class definition time before model_config is processed.
+        """
+        if self.is_func and self.kwargs:
+            type_: str | None = self.alias or self.type
+            if type_:  # pragma: no branch
+                base_type = self._CONSTRAINED_TYPE_TO_BASE.get(type_)
+                if base_type is None:
+                    # Not a constrained type we convert (e.g., conint, confloat)
+                    # Return the full type_hint with kwargs to avoid returning bare function name
+                    return self.type_hint
+                if self.is_optional and base_type != ANY:  # pragma: no cover
+                    return get_optional_type(base_type, self.use_union_operator)
+                return base_type
+
+        type_: str | None = self.alias or self.type
+        if not type_:
+            if self.is_tuple:  # pragma: no cover
+                tuple_type = STANDARD_TUPLE if self.use_standard_collections else TUPLE
+                inner_types = [item.base_type_hint or ANY for item in self.data_types]
+                type_ = f"{tuple_type}[{', '.join(inner_types)}]" if inner_types else f"{tuple_type}[()]"
+            elif self.is_union:
+                data_types: list[str] = []
+                for data_type in self.data_types:
+                    data_type_type = data_type.base_type_hint
+                    if not data_type_type or data_type_type in data_types:  # pragma: no cover
+                        continue
+
+                    if data_type_type == NONE:
+                        self.is_optional = True
+                        continue
+
+                    non_optional_data_type_type = _remove_none_from_union(
+                        data_type_type, use_union_operator=self.use_union_operator
+                    )
+
+                    if non_optional_data_type_type != data_type_type:  # pragma: no cover
+                        self.is_optional = True
+
+                    data_types.append(non_optional_data_type_type)
+                if not data_types:  # pragma: no cover
+                    type_ = ANY
+                    self.import_ = self.import_ or IMPORT_ANY
+                elif len(data_types) == 1:
+                    type_ = data_types[0]
+                elif self.use_union_operator:
+                    type_ = UNION_OPERATOR_DELIMITER.join(data_types)
+                else:  # pragma: no cover
+                    type_ = f"{UNION_PREFIX}{UNION_DELIMITER.join(data_types)}]"
+            elif len(self.data_types) == 1:
+                type_ = self.data_types[0].base_type_hint
+            elif self.enum_member_literals:  # pragma: no cover
+                parts = [f"{enum_class}.{member}" for enum_class, member in self.enum_member_literals]
+                type_ = f"{LITERAL}[{', '.join(parts)}]"
+            elif self.literals:  # pragma: no cover
+                type_ = f"{LITERAL}[{', '.join(repr(literal) for literal in self.literals)}]"
+            elif self.reference:  # pragma: no cover
+                type_ = self.reference.short_name
+                type_ = self._get_wrapped_reference_type_hint(type_)
+            else:  # pragma: no cover
+                type_ = ""
+        if self.reference:  # pragma: no cover
+            source = self.reference.source
+            if isinstance(source, Nullable) and source.nullable:
+                self.is_optional = True
+        if self.is_list:
+            if self.use_generic_container:
+                list_ = SEQUENCE
+            elif self.use_standard_collections:
+                list_ = STANDARD_LIST
+            else:  # pragma: no cover
+                list_ = LIST
+            type_ = f"{list_}[{type_}]" if type_ else list_
+        elif self.is_set:  # pragma: no cover
+            if self.use_generic_container:
+                set_ = STANDARD_FROZEN_SET if self.use_standard_collections else FROZEN_SET
+            elif self.use_standard_collections:
+                set_ = STANDARD_SET
+            else:
+                set_ = SET
+            type_ = f"{set_}[{type_}]" if type_ else set_
+        elif self.is_dict:
+            if self.use_generic_container:
+                dict_ = MAPPING
+            elif self.use_standard_collections:
+                dict_ = STANDARD_DICT
+            else:  # pragma: no cover
+                dict_ = DICT
+            if self.dict_key or type_:
+                key = self.dict_key.base_type_hint if self.dict_key else STR
+                type_ = f"{dict_}[{key}, {type_ or ANY}]"
+            else:  # pragma: no cover
+                type_ = dict_
+
+        if self.is_optional and type_ != ANY:
+            return get_optional_type(type_, self.use_union_operator)
+        if self.is_func:  # pragma: no cover
+            return f"{type_}()"
+        return type_
+
 
 DataTypeT = TypeVar("DataTypeT", bound=DataType)
 

tests/cli_doc/test_cli_doc_coverage.py

@@ -46,9 +46,7 @@ def collected_options(collection_data: dict[str, Any]) -> set[str]:  # pragma: n
 class TestCLIDocCoverage:  # pragma: no cover
     """Documentation coverage tests."""
 
-    def test_all_options_have_cli_doc_markers(  # noqa: PLR6301
-        self, collected_options: set[str]
-    ) -> None:
+    def test_all_options_have_cli_doc_markers(self, collected_options: set[str]) -> None:
         """Verify that all CLI options (except MANUAL_DOCS) have cli_doc markers."""
         all_options = get_all_canonical_options()
         documentable_options = all_options - MANUAL_DOCS
@@ -60,7 +58,7 @@ def test_all_options_have_cli_doc_markers(  # noqa: PLR6301
                 + "\n\nAdd @pytest.mark.cli_doc(...) to tests for these options."
             )
 
-    def test_meta_options_not_manual(self) -> None:  # noqa: PLR6301
+    def test_meta_options_not_manual(self) -> None:
         """Verify that CLI_OPTION_META options are not in MANUAL_DOCS."""
         meta_options = set(CLI_OPTION_META.keys())
         overlap = meta_options & MANUAL_DOCS
@@ -70,9 +68,7 @@ def test_meta_options_not_manual(self) -> None:  # noqa: PLR6301
                 + "\n".join(f"  - {opt}" for opt in sorted(overlap))
             )
 
-    def test_collection_schema_version(  # noqa: PLR6301
-        self, collection_data: dict[str, Any]
-    ) -> None:
+    def test_collection_schema_version(self, collection_data: dict[str, Any]) -> None:
         """Verify that collection data has expected schema version."""
         version = collection_data.get("schema_version")
         assert version is not None, "Collection data missing 'schema_version'"
@@ -83,7 +79,7 @@ class TestCoverageStats:  # pragma: no cover
     """Informational tests for coverage statistics."""
 
     @pytest.mark.skip(reason="Informational: run with -v --no-skip to see stats")
-    def test_show_coverage_stats(self, collected_options: set[str]) -> None:  # noqa: PLR6301
+    def test_show_coverage_stats(self, collected_options: set[str]) -> None:
         """Display documentation coverage statistics."""
         all_options = get_all_canonical_options()
         documentable = all_options - MANUAL_DOCS
@@ -94,9 +90,7 @@ def test_show_coverage_stats(self, collected_options: set[str]) -> None:  # noqa
             print(f"  {opt}")  # noqa: T201
 
     @pytest.mark.skip(reason="Informational: run with -v --no-skip to see stats")
-    def test_show_documented_options(  # noqa: PLR6301
-        self, collected_options: set[str]
-    ) -> None:
+    def test_show_documented_options(self, collected_options: set[str]) -> None:
         """Display currently documented options."""
         print(f"\nDocumented options ({len(collected_options)}):")  # noqa: T201
         for opt in sorted(collected_options):

tests/cli_doc/test_cli_options_sync.py

@@ -31,7 +31,7 @@ def test_get_canonical_option() -> None:
 class TestCLIOptionMetaSync:  # pragma: no cover
     """Synchronization tests for CLI_OPTION_META."""
 
-    def test_all_registered_options_exist_in_argparse(self) -> None:  # noqa: PLR6301
+    def test_all_registered_options_exist_in_argparse(self) -> None:
         """Verify that all options in CLI_OPTION_META exist in argparse."""
         argparse_options = get_all_canonical_options()
         registered = set(CLI_OPTION_META.keys())
@@ -44,7 +44,7 @@ def test_all_registered_options_exist_in_argparse(self) -> None:  # noqa: PLR630
                 + "\n\nRemove them from CLI_OPTION_META or add them to arguments.py."
             )
 
-    def test_manual_doc_options_exist_in_argparse(self) -> None:  # noqa: PLR6301
+    def test_manual_doc_options_exist_in_argparse(self) -> None:
         """Verify that all options in MANUAL_DOCS exist in argparse."""
         argparse_options = get_all_canonical_options()
 
@@ -56,7 +56,7 @@ def test_manual_doc_options_exist_in_argparse(self) -> None:  # noqa: PLR6301
                 + "\n\nRemove them from MANUAL_DOCS or add them to arguments.py."
             )
 
-    def test_no_overlap_between_meta_and_manual(self) -> None:  # noqa: PLR6301
+    def test_no_overlap_between_meta_and_manual(self) -> None:
         """Verify that CLI_OPTION_META and MANUAL_DOCS don't overlap."""
         overlap = set(CLI_OPTION_META.keys()) & MANUAL_DOCS
         if overlap:
@@ -66,7 +66,7 @@ def test_no_overlap_between_meta_and_manual(self) -> None:  # noqa: PLR6301
                 + "\n\nAn option should be in one or the other, not both."
             )
 
-    def test_meta_names_match_keys(self) -> None:  # noqa: PLR6301
+    def test_meta_names_match_keys(self) -> None:
         """Verify that CLIOptionMeta.name matches the dict key."""
         mismatches = []
         for key, meta in CLI_OPTION_META.items():
@@ -76,7 +76,7 @@ def test_meta_names_match_keys(self) -> None:  # noqa: PLR6301
         if mismatches:
             pytest.fail("CLIOptionMeta.name mismatches:\n" + "\n".join(mismatches))
 
-    def test_all_argparse_options_are_documented_or_excluded(self) -> None:  # noqa: PLR6301
+    def test_all_argparse_options_are_documented_or_excluded(self) -> None:
         """Verify that all argparse options are either documented or explicitly excluded.
 
         This test fails when a new CLI option is added to arguments.py
@@ -96,7 +96,7 @@ def test_all_argparse_options_are_documented_or_excluded(self) -> None:  # noqa:
                 "or add to MANUAL_DOCS if they should have manual documentation."
             )
 
-    def test_canonical_option_determination_is_stable(self) -> None:  # noqa: PLR6301
+    def test_canonical_option_determination_is_stable(self) -> None:
         """Verify that canonical option determination is deterministic.
 
         The canonical option should be the longest option string for each action.