[BUG] [rust-axum] In PUT requests with arrays, a body type string fails to fulfil Validate trait in generated server code

[Chrystalkey]

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?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

With this spec
The generation of the client with openapi-generator-cli (OPENAPI_GENERATOR_VERSION=7.12.0) succeeds, but compilation with cargo build (rustc 1.85, 2024 edition) fails due to:

error[E0599]: the method `validate` exists for reference `&&Vec<String>`, but its trait bounds were not satisfied
    --> oapicode\src\server\mod.rs:1508:14
     |
1508 |     #[derive(validator::Validate)]
     |              ^^^^^^^^^^^^^^^^^^^
     |
    ::: C:\Users\Benedikt\.rustup\toolchains\stable-x86_64-pc-windows-gnu\lib/rustlib/src/rust\library\alloc\src\vec\mod.rs:397:1
     |
397  | pub struct Vec<T, #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global> {
     | ------------------------------------------------------------------------------------------------ doesn't satisfy `Vec<std::string::String>: Validate`
     |
    ::: C:\Users\Benedikt\.rustup\toolchains\stable-x86_64-pc-windows-gnu\lib/rustlib/src/rust\library\alloc\src\string.rs:362:1
     |
362  | pub struct String {
     | ----------------- doesn't satisfy `std::string::String: Validate`
     |
     = note: the following trait bounds were not satisfied:
             `Vec<std::string::String>: Validate`
             which is required by `&Vec<std::string::String>: Validate`
             `&Vec<std::string::String>: Validate`
             which is required by `&&Vec<std::string::String>: Validate`
             `std::string::String: Validate`
             which is required by `Vec<std::string::String>: Validate`
             `std::string::String: Validate`
             which is required by `[std::string::String]: Validate`
     = note: this error originates in the derive macro `validator::Validate` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0599`.
error: could not compile `openapi` (lib) due to 1 previous error

openapi-generator version

7.12.0

OpenAPI declaration file content or url

With Error
https://raw.githubusercontent.com/Chrystalkey/landtagszusammenfasser/refs/tags/rust-axum-plain-string/docs/specs/openapi.yml
Without Error
https://github.com/Chrystalkey/landtagszusammenfasser/blob/rust-axum-body-wrapped/docs/specs/openapi.yml

Generation Details

with OPENAPI_GENERATOR_VERSION=7.12.0 set:

java -jar "./oapi-generator/openapi-generator-cli.jar" generate -g rust-axum -i "$(Get-Location)/openapi.yml" -o "$(Get-Location)/oapicode"
(on linux replace $(Get-Location) by $(pwd))

Steps to reproduce

with OPENAPI_GENERATOR_VERSION=7.12.0 set:

& Invoke-WebRequest -OutFile openapi-generator-cli.jar https://repo1.maven.org/maven2/org/openapitools/openapi-generator-cli/7.12.0/openapi-generator-cli-7.12.0.jar
& Invoke-WebRequest -OutFile openapi.yml https://raw.githubusercontent.com/Chrystalkey/landtagszusammenfasser/refs/tags/rust-axum-plain-string/docs/specs/openapi.yml
java -jar "./oapi-generator/openapi-generator-cli.jar" generate -g rust-axum -i "$(Get-Location)/openapi.yml" -o "$(Get-Location)/oapicode"
cd oapicode
& cargo build

(on linux replace $(Get-Location) by $(pwd))

Related issues/PRs

This is a bug that happens after the generic arguments in oapicode/src/server/mod are grep-replaced:
"<I, A, E>" -> "<I, A, E, C>"
There is a seperate issue for that, #21144

Suggest a fix

This is worked around (not fixed!) when wrapping the body of operationId: enum_put into an object:

type: object
properties:
  entry:
    type: string

as was done in this version

However I still think this is an issue and should be possible just using plain strings.