fix(rust): use serde_repr for integer property enums

[ericbsantana]

Problem

When an OpenAPI schema defines a struct property with type: integer and an enum constraint, Rust generator was producing a string-renamed enum:

// Generated (wrong)
#[derive(... Serialize, Deserialize)]
pub enum V {
    #[serde(rename = "0")]
    Variant0,
    #[serde(rename = "1")]
    Variant1,
}

#[serde(rename = "0")] expects the JSON string "0", but the API returns the integer 0. Thus serialization fails.

Issue related: #23450

Root cause

The {{#vars}}{{#isEnum}} section in model.mustache had only a string-rename path. The isInteger flag was already set correctly on CodegenProperty but was never checked. Additionally, AbstractRustCodegen.toEnumValue() always escaped values as strings regardless of the property datatype.

In order to fix this, we configured a similar approach as other strictly typed languages generators by returning the raw integer datatypes instead of escaping as a string (as it was being done). It also sets x-rust-has-integer-property-enum vendor extension on any struct model that contains at least one integer-enum property. model.mustache was changed too adding {{#isInteger}} / {{^isInteger}} branching inside the enum section.

Generated output after fix

use serde_repr::{Serialize_repr,Deserialize_repr};

pub struct SignedMessageSignature {
    pub v: Option<V>,
    // ...
}

#[repr(i64)]
#[derive(Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd, Hash, Serialize_repr, Deserialize_repr)]
pub enum V {
    Variant0 = 0,
    Variant1 = 1,
}

Schema that triggers the bug

SignedMessageSignature:
  type: object
  properties:
    v:
      type: integer
      enum: [0, 1]

Source: Fireblocks OpenAPI spec.

---

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  Commit all changed files.
• File the PR against the master
• @mention the Rust technical committee members for review: @frol @farcaller @richardwhiuk @paladinzh @jacob-pro @dsteeley

---

Summary by cubic

Fix Rust generator to serialize integer-backed property enums as numbers using serde_repr, preventing JSON string/number mismatches. Models with such properties now emit numeric #[repr(i64)] enums.

• Bug Fixes
  • Generate #[repr(i64)] enums with Serialize_repr/Deserialize_repr for integer property enums; variants use numeric discriminants.
  • Return raw numbers from toEnumValue for numeric datatypes.
  • Add x-rust-has-integer-property-enum to import serde_repr once per model and branch enum rendering on isInteger; string enums unchanged.
  • Add test and sample spec to verify serde_repr usage and absence of string renames.

^{Written for commit 1ccaaff. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 5 files