fix(rust): use serde_repr for integer property enums (#23580)

Author: ericbsantana

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractRustCodegen.java

@@ -391,8 +391,14 @@ public String toEnumName(CodegenProperty property) {
 
     @Override
     public String toEnumValue(String value, String datatype) {
-        // This is the representation of the enum that will be serialized / deserialized
-        // Note: generators currently only support string enums, so checking the type here is pointless
+        if ("integer".equals(datatype) || "number".equals(datatype)
+                || "i8".equals(datatype) || "i16".equals(datatype)
+                || "i32".equals(datatype) || "i64".equals(datatype)
+                || "u8".equals(datatype) || "u16".equals(datatype)
+                || "u32".equals(datatype) || "u64".equals(datatype)
+                || "f32".equals(datatype) || "f64".equals(datatype)) {
+            return value;
+        }
         return escapeText(value);
     }
 

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/RustClientCodegen.java

@@ -379,6 +379,16 @@ public ModelsMap postProcessModels(ModelsMap objs) {
                 }
             }
 
+            // Flag structs with integer-enum properties so the template can emit serde_repr import once
+            if (!cm.isEnum) {
+                for (CodegenProperty cp : cm.vars) {
+                    if (cp.isEnum && cp.isInteger) {
+                        cm.vendorExtensions.put("x-rust-has-integer-property-enum", true);
+                        break;
+                    }
+                }
+            }
+
             // Compute documentation type for each property
             // This matches the actual generated code type, including HashSet for uniqueItems
             for (CodegenProperty cp : cm.vars) {

modules/openapi-generator/src/main/resources/rust/model.mustache

@@ -5,7 +5,9 @@ use serde::{Deserialize, Serialize};
 {{#model}}
 {{^isEnum}}{{#vendorExtensions.x-rust-has-byte-array}}
 use serde_with::serde_as;
-{{/vendorExtensions.x-rust-has-byte-array}}{{/isEnum}}
+{{/vendorExtensions.x-rust-has-byte-array}}{{#vendorExtensions.x-rust-has-integer-property-enum}}
+use serde_repr::{Serialize_repr,Deserialize_repr};
+{{/vendorExtensions.x-rust-has-integer-property-enum}}{{/isEnum}}
 {{#isEnum}}
 {{#isInteger}}
 use serde_repr::{Serialize_repr,Deserialize_repr};
@@ -200,6 +202,31 @@ impl Default for {{classname}} {
 {{!-- for properties that are of enum type --}}
 {{#vars}}
 {{#isEnum}}
+{{#isInteger}}
+/// {{{description}}}
+#[repr(i64)]
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd, Hash, Serialize_repr, Deserialize_repr)]
+pub enum {{{enumName}}} {
+{{#allowableValues}}
+{{#enumVars}}
+    {{{name}}} = {{{value}}},
+{{/enumVars}}
+{{/allowableValues}}
+}
+
+impl std::fmt::Display for {{{enumName}}} {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", match self {
+            {{#allowableValues}}
+            {{#enumVars}}
+            Self::{{{name}}} => "{{{value}}}",
+            {{/enumVars}}
+            {{/allowableValues}}
+        })
+    }
+}
+{{/isInteger}}
+{{^isInteger}}
 /// {{{description}}}
 #[derive(Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd, Hash, Serialize, Deserialize)]
 pub enum {{{enumName}}} {
@@ -210,6 +237,7 @@ pub enum {{{enumName}}} {
 {{/enumVars}}
 {{/allowableValues}}
 }
+{{/isInteger}}
 
 impl Default for {{{enumName}}} {
     fn default() -> {{{enumName}}} {

modules/openapi-generator/src/test/java/org/openapitools/codegen/rust/RustClientCodegenTest.java

@@ -272,6 +272,27 @@ public void testMultipleArrayTypesEnum() throws IOException {
         TestUtils.assertFileContains(outputPath, enumSpec);
     }
 
+    @Test
+    public void testIntegerPropertyEnum() throws IOException {
+        Path target = Files.createTempDirectory("test");
+        target.toFile().deleteOnExit();
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName("rust")
+                .setInputSpec("src/test/resources/3_1/rust_integer_property_enum.yaml")
+                .setSkipOverwrite(false)
+                .setOutputDir(target.toAbsolutePath().toString().replace("\\", "/"));
+        new DefaultGenerator().opts(configurator.toClientOptInput()).generate();
+        Path outputPath = Path.of(target.toString(), "/src/models/signed_message_signature.rs");
+        TestUtils.assertFileExists(outputPath);
+        // The integer-enum property must use serde_repr (not string rename)
+        TestUtils.assertFileContains(outputPath, "use serde_repr::{Serialize_repr,Deserialize_repr}");
+        TestUtils.assertFileContains(outputPath, "Serialize_repr, Deserialize_repr");
+        TestUtils.assertFileContains(outputPath, "= 0");
+        TestUtils.assertFileContains(outputPath, "= 1");
+        // Must NOT contain a string rename for an integer variant
+        TestUtils.assertFileNotContains(outputPath, linearize("#[serde(rename = \"0\")]"));
+    }
+
     @Test
     public void testArrayWithObjectEnumValues() throws IOException {
         Path target = Files.createTempDirectory("test");

modules/openapi-generator/src/test/resources/3_1/rust_integer_property_enum.yaml

@@ -0,0 +1,18 @@
+openapi: 3.1.0
+info:
+  title: Integer property enum
+  description: Struct with a type:integer property constrained to an enum should use serde_repr, not string rename.
+  version: 1.0.0
+paths: {}
+components:
+  schemas:
+    SignedMessageSignature:
+      type: object
+      properties:
+        v:
+          type: integer
+          enum: [0, 1]
+        r:
+          type: string
+        s:
+          type: string