[BUG][RUST][CLIENT] Generated enum type used with `format!` but it doesn't impl `Display`

[eliaperantoni]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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Description

If an endpoint uses an enum as the path parameter, and the enum is defined in components rather than inline, then the generated default_api.rs creates the URL with the format! macro but the generated Rust enum doesn't implement Display (it does implement ToString instead).

error[E0277]: `Color` doesn't implement `std::fmt::Display`
  --> src/apis/default_api.rs:31:97
   |
31 |     let local_var_uri_str = format!("{}/demo/{color}", local_var_configuration.base_path, color=color);
   |                                                                                                 ^^^^^ `Color` cannot be formatted with the default formatter
   |
   = help: the trait `std::fmt::Display` is not implemented for `Color`
   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
   = note: this error originates in the macro `$crate::__export::format_args` which comes from the expansion of the macro `format` (in Nightly builds, run with -Z macro-backtrace for more info)

NOTE: You need to reference the enum like:

schema:
  allOf:
    - $ref: "#/components/schemas/Color"

otherwise you're going to run into issue #16974 first.

openapi-generator version

I'm using the Docker openapitools/openapi-generator-cli:latest image. openapi-generator-cli version prints 7.1.0-SNAPSHOT.

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  title: Demo
  version: 0.0.0
paths:
  /demo/{color}:
    get:
      parameters:
        - name: color
          required: true
          in: path
          schema:
            $ref: "#/components/schemas/Color"
      responses:
        200:
          description: OK
components:
  schemas:
    Color:
      type: string
      enum:
        - RED
        - GREEN
        - BLUE

Generation Details

$ openapi-generator generate -i openapi.yaml -g rust -o demo

[wing328]

NOTE: You need to reference the enum like:

I've filed #17694 to fix the issue