fix compilation error in rust when using enums as part of the path

[ctron]

When an enum is used as part of the path, the compilation will fail as the enum implements ToString but not Display.

However, implementing Display automatically implements ToString. So this PR implements Display in favor of ToString.

Also see: https://doc.rust-lang.org/std/string/trait.ToString.html

This trait is automatically implemented for any type which implements the Display trait. As such, ToString shouldn’t be implemented directly: Display should be implemented instead, and you get the ToString implementation for free.

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@frol @farcaller @richardwhiuk @paladinzh

[wing328]

@ctron thanks for the PR. May I know if you can provide a spec to reproduce the issue?

I tried to repeat the issue locally but couldn't.

[ctron]

Sure, like this:

info:
  title: Sample Pet Store App
  version: 1.0.1
openapi: 3.0.3
paths:
  /pets/{type}:
    get:
      responses:
        '200':
          description: Some value
    parameters:
      - name: type
        in: path
        schema:
          $ref: '#/components/schemas/test'
components:
  schemas:
    test:
      type: string
      enum:
        - foo
        - bar
        - baz

[wing328]

@ctron I tested your PR with the spec you provided but got errors when running cargo check:

    Checking reqwest v0.11.11
    Checking openapi v1.0.1 (/private/tmp/rust2)
error[E0412]: cannot find type `Test` in this scope
  --> src/apis/default_api.rs:26:88
   |
26 | pub async fn pets_type_get(configuration: &configuration::Configuration, _type: Option<Test>) -> Result<(), Error<PetsTypeGetError>> {
   |                                                                                        ^^^^ not found in this scope
   |
help: consider importing this enum
   |
12 | use crate::models::Test;
   |

For more information about this error, try `rustc --explain E0412`.
error: could not compile `openapi` due to previous error

Does cargo check work fine for you in your machine?

[ctron]

Yea, that seems to be another issue. You can import that manually though.