Fix reuse discriminator literals

Author: koxudaxi

src/datamodel_code_generator/parser/base.py

@@ -1618,6 +1618,16 @@ def get_discriminator_field_value(
                         if discriminator_value is not None:
                             discriminator_values = [discriminator_value]
                             break
+                    # Reuse models are created as empty subclasses with a "/reuse" path suffix.
+                    # Scan inherited fields to recover the discriminator literal from the base.
+                    if not discriminator_values and discriminator_model.path.endswith("/reuse"):
+                        for discriminator_field in discriminator_model.iter_all_fields():  # pragma: no branch
+                            if field_name not in {discriminator_field.original_name, discriminator_field.name}:
+                                continue
+                            discriminator_value = get_discriminator_field_value(discriminator_field)
+                            if discriminator_value is not None:  # pragma: no branch
+                                discriminator_values = [discriminator_value]
+                                break
 
                     if not discriminator_values and mapping:
                         check_paths(discriminator_model, mapping)  # ty: ignore

tests/data/expected/main/jsonschema/reuse_model_discriminator_literal.py

@@ -0,0 +1,44 @@
+# generated by datamodel-codegen:
+#   filename:  reuse_model_discriminator_literal.json
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from typing import Literal
+
+from pydantic import BaseModel, Field
+
+
+class SignalId(BaseModel):
+    domain: str
+    source: Literal['catalog']
+
+
+class SignalId1(BaseModel):
+    url: str
+    source: Literal['agent']
+
+
+class FirstThing(BaseModel):
+    signal_id: SignalId | SignalId1 | None = Field(
+        None, discriminator='source', title='Signal ID'
+    )
+
+
+class SignalId2(SignalId):
+    source: Literal['catalog']
+
+
+class SignalId3(SignalId1):
+    source: Literal['agent']
+
+
+class SecondThing(BaseModel):
+    signal_id: SignalId2 | SignalId3 | None = Field(
+        None, discriminator='source', title='Signal ID'
+    )
+
+
+class Root(BaseModel):
+    first_thing: FirstThing | None = None
+    second_thing: SecondThing | None = None

tests/data/jsonschema/reuse_model_discriminator_literal.json

@@ -0,0 +1,93 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "title": "Root",
+  "type": "object",
+  "properties": {
+    "first_thing": {
+      "type": "object",
+      "properties": {
+        "signal_id": {
+          "title": "Signal ID",
+          "discriminator": {
+            "propertyName": "source"
+          },
+          "oneOf": [
+            {
+              "type": "object",
+              "properties": {
+                "domain": {
+                  "type": "string"
+                },
+                "source": {
+                  "const": "catalog"
+                }
+              },
+              "required": [
+                "source",
+                "domain"
+              ]
+            },
+            {
+              "type": "object",
+              "properties": {
+                "url": {
+                  "type": "string"
+                },
+                "source": {
+                  "const": "agent"
+                }
+              },
+              "required": [
+                "source",
+                "url"
+              ]
+            }
+          ]
+        }
+      }
+    },
+    "second_thing": {
+      "type": "object",
+      "properties": {
+        "signal_id": {
+          "title": "Signal ID",
+          "discriminator": {
+            "propertyName": "source"
+          },
+          "oneOf": [
+            {
+              "type": "object",
+              "properties": {
+                "domain": {
+                  "type": "string"
+                },
+                "source": {
+                  "const": "catalog"
+                }
+              },
+              "required": [
+                "source",
+                "domain"
+              ]
+            },
+            {
+              "type": "object",
+              "properties": {
+                "url": {
+                  "type": "string"
+                },
+                "source": {
+                  "const": "agent"
+                }
+              },
+              "required": [
+                "source",
+                "url"
+              ]
+            }
+          ]
+        }
+      }
+    }
+  }
+}

tests/main/jsonschema/test_main_jsonschema.py

@@ -1214,6 +1214,26 @@ def test_main_reuse_model_collapse_inline_definitions(output_file: Path) -> None
     )
 
 
+def test_main_reuse_model_discriminator_literal(output_file: Path) -> None:
+    """Reuse inherited discriminator literals instead of injecting the reuse path segment."""
+    run_main_and_assert(
+        input_path=JSON_SCHEMA_DATA_PATH / "reuse_model_discriminator_literal.json",
+        output_path=output_file,
+        input_file_type="jsonschema",
+        assert_func=assert_file_content,
+        extra_args=[
+            "--reuse-model",
+            "--use-union-operator",
+            "--use-standard-collections",
+            "--output-model-type",
+            "pydantic_v2.BaseModel",
+            "--target-python-version",
+            "3.10",
+        ],
+        force_exec_validation=True,
+    )
+
+
 def test_main_reuse_model_collapse_with_root(output_file: Path) -> None:
     """Test --reuse-model --collapse-reuse-models skips RootModel deduplication."""
     run_main_and_assert(