TypeError: cannot use 'list' as a set element when rendering OpenAPI 3.1 schemas with array-valued type

[dcode]

Description

Rendering any OpenAPI 3.1 schema that uses an array-valued type field (the 3.1-native way to express nullable fields) crashes with:

TypeError: cannot use 'list' as a set element (unhashable type: 'list')

Root cause

OpenAPI 3.1 replaced the nullable: true extension with multi-type arrays:

  { "type": ["string", "null"] }   // 3.1 — nullable string
  { "type": "string", "nullable": true }  // 3.0 equivalent

The Jinja2 template partial/schema-repr.html (line 17) does:

  {%- with type_name = schema["type"] -%}
  ...
  {%- if type_name in scalar_types -%}

scalar_types is a Python set({"string", "integer", "boolean", "number"}). When type_name is a list, Python's in operator attempts to hash it for set membership, raising TypeError. The same pattern exists in all four view variants (views_mkdocs, views_markdown,
views_plantuml_api, views_plantuml_schemas).

Minimal reproducer

  import json, tempfile
  from pathlib import Path
  from openapidocs.mk.v3 import OpenAPIV3DocumentationHandler
  from openapidocs.utils.source import read_from_source

  schema = {
      "openapi": "3.1.0",
      "info": {"title": "Repro", "version": "0.0.1"},
      "paths": {
          "/example": {
              "get": {
                  "summary": "Get example",
                  "responses": {
                      "200": {
                          "description": "OK",
                          "content": {
                              "application/json": {
                                  "schema": {"$ref": "#/components/schemas/Example"}
                              }
                          },
                      }
                  },
              }
          }
      },
      "components": {
          "schemas": {
              "Example": {
                  "type": "object",
                  "properties": {
                      "name": {"type": ["string", "null"]}  # OpenAPI 3.1 nullable
                  },
              }
          }
      },
  }

  with tempfile.NamedTemporaryFile(suffix=".json", mode="w", delete=False) as f:
      json.dump(schema, f)
      path = f.name

  data = read_from_source(path, Path(path).parent)
  handler = OpenAPIV3DocumentationHandler(data, source=path)
  handler.write()  # TypeError: cannot use 'list' as a set element (unhashable type: 'list')

Environment

• essentials-openapi 1.3.0
• Python 3.14

Suggested fix

In each schema-repr.html template, guard type_name before the set membership check, e.g.:

  {%- if type_name is string and type_name in scalar_types -%}

Or normalise type_name to a list first and iterate — which would also enable proper rendering of multi-type unions rather than silently skipping them.