Add an error about unused path parameter definitions in paths

[hkosova]

As an editor, I want to know when path parameters are not properly defined.

Swagger Editor currently has a validation for path templates that are missing path parameter definitions (e.g. /foo/{bar} without the bar parameter defined). It would be great to also check for the opposite situation - when a path parameter is defined but not included in the actual path string.

Definitions containing path parameters that are not included in the path string are invalid according to the OpenAPI Specification:

If in is "path", the name field MUST correspond to the associated path segment from the path field in the Paths Object.

Swagger/OpenAPI definition

In the examples below, the /foo path contains 4 path parameter definitions none of which are actually used by the /foo path.

OAS2:

swagger: '2.0'
info:
  title: Unused path parameters
  version: 1.0.0
paths:
  /foo:
    parameters:
      - name: param1
        in: path
        required: true
        type: string
      - $ref: '#/parameters/param2'
    get:
      parameters:
        - name: param3
          in: path
          required: true
          type: string
        - $ref: '#/parameters/param4'
      responses:
        '200':
          description: OK

parameters:
  param2:
    name: param2
    in: path
    required: true
    type: string
  param4:
    name: param4
    in: path
    required: true
    type: string

OAS3:

openapi: 3.0.2
info:
 title: Unused path parameters
 version: 1.0.0
paths:
 /foo:
   parameters:
     - name: param1
       in: path
       required: true
       schema:
         type: string
     - $ref: '#/components/parameters/param2'
   get:
     parameters:
       - name: param3
         in: path
         required: true
         schema:
           type: string
       - $ref: '#/components/parameters/param4'
     responses:
       '200':
         description: OK

components:
 parameters:
   param2:
     name: param2
     in: path
     required: true
     schema:
       type: string
   param4:
     name: param4
     in: path
     required: true
     schema:
       type: string

Is your feature request related to a problem?

Swagger Editor should ideally report as many syntax issues as possible to help the users write valid OpenAPI definitions. This particular validation would help avoid swagger-api/swagger-ui/issues/5447.

Describe the solution you'd like

Each path parameter in the examples above should trigger an error that says this parameter is unused.

Possible wording:

Path parameter "param1" must have the corresponding {param1} segment in the "/foo" path

Path parameter "param1" is defined but there is no {param1} segment in the "/foo" path

or similar. Suggestions are welcome!