fix(cpp-httplib-server): generate top-level enum models

[stefanwitkowskiwmb]

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---

Fix for #23902

@ravinikam @stkrwork @etherealjoy @MartinDelille @muttleyxd @aminya

---

Summary by cubic

Fixes the cpp-httplib-server generator so top-level enum schemas are emitted as enum class types with JSON serialization helpers. Previously, standalone enum models were not produced.

• Adds to_json/from_json implementations in the model header template.
• Includes the enum header in the model source template.
• Expands the feature-test schema and samples with a TopLevelStatus enum.
• Updates the model test to assert top-level enums are preserved and processed.

^{Written for commit f186960. Summary will update on new commits.}

[cubic-dev-ai]

3 issues found across 6 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="modules/openapi-generator/src/main/resources/cpp-httplib-server/model-header.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/cpp-httplib-server/model-header.mustache:32">
P1: For string enum values containing `&`, `<`, or quotes, Mustache HTML-escapes `{{value}}` after the C++ escaping step. The generated `to_json` sends entities such as `&amp;`, and `from_json` then rejects the correct wire value; use triple-mustache `{{{value}}}` for the string value in both enum helpers.</violation>

<violation number="2" location="modules/openapi-generator/src/main/resources/cpp-httplib-server/model-header.mustache:40">
P2: The generated from_json in model-header.mustache compares `j == "active"`, but the committed sample TopLevelStatus.h (the expected generator output) uses `const std::string serializedValue = j.get<std::string>(); if (serializedValue == "active")`. The two implementations behave differently for non-string JSON and the sample will not match what the generator emits, so samples and generated code are out of sync. Align the template's from_json with the sample (or regenerate the sample to match the template).</violation>
</file>

<file name="modules/openapi-generator/src/test/java/org/openapitools/codegen/cpphttplibserver/CppHttplibServerCodegenModelTest.java">

<violation number="1" location="modules/openapi-generator/src/test/java/org/openapitools/codegen/cpphttplibserver/CppHttplibServerCodegenModelTest.java:288">
P2: The test asserts enumVars after calling only postProcessAllModels, but enumVars is only populated by postProcessModelsEnum. DefaultCodegen.postProcessAllModels (lines 515-654) never invokes postProcessModelsEnum, and neither AbstractCppCodegen.postProcessAllModels (405-413) nor CppHttplibServerCodegen.postProcessAllModels adds it. The CppHttplibServerCodegen path that computes enumVars (DefaultCodegen.postProcessModelsEnum at 899-910, reached via AbstractCppCodegen.postProcessModels at line 401) is not triggered here, so `processedModel.allowableValues.get("enumVars")` returns null and `.size()` throws a NullPointerException, failing the test that this PR relies on to validate top-level enum handling. Run the model through the enum post-processing step before asserting, mirroring the DefaultGenerator pipeline.</violation>
</file>

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

P1: For string enum values containing &, <, or quotes, Mustache HTML-escapes {{value}} after the C++ escaping step. The generated to_json sends entities such as &, and from_json then rejects the correct wire value; use triple-mustache {{{value}}} for the string value in both enum helpers.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At modules/openapi-generator/src/main/resources/cpp-httplib-server/model-header.mustache, line 32:

<comment>For string enum values containing `&`, `<`, or quotes, Mustache HTML-escapes `{{value}}` after the C++ escaping step. The generated `to_json` sends entities such as `&amp;`, and `from_json` then rejects the correct wire value; use triple-mustache `{{{value}}}` for the string value in both enum helpers.</comment>

<file context>
@@ -16,6 +17,37 @@
+    switch (value)
+    {
+        {{#allowableValues}}{{#enumVars}}
+        case {{vendorExtensions.modelClassName}}::{{name}}: j = {{#isString}}"{{value}}"{{/isString}}{{^isString}}{{value}}{{/isString}}; break;
+        {{/enumVars}}{{/allowableValues}}
+    }
</file context>

[cubic-dev-ai]

P2: The test asserts enumVars after calling only postProcessAllModels, but enumVars is only populated by postProcessModelsEnum. DefaultCodegen.postProcessAllModels (lines 515-654) never invokes postProcessModelsEnum, and neither AbstractCppCodegen.postProcessAllModels (405-413) nor CppHttplibServerCodegen.postProcessAllModels adds it. The CppHttplibServerCodegen path that computes enumVars (DefaultCodegen.postProcessModelsEnum at 899-910, reached via AbstractCppCodegen.postProcessModels at line 401) is not triggered here, so processedModel.allowableValues.get("enumVars") returns null and .size() throws a NullPointerException, failing the test that this PR relies on to validate top-level enum handling. Run the model through the enum post-processing step before asserting, mirroring the DefaultGenerator pipeline.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At modules/openapi-generator/src/test/java/org/openapitools/codegen/cpphttplibserver/CppHttplibServerCodegenModelTest.java, line 288:

<comment>The test asserts enumVars after calling only postProcessAllModels, but enumVars is only populated by postProcessModelsEnum. DefaultCodegen.postProcessAllModels (lines 515-654) never invokes postProcessModelsEnum, and neither AbstractCppCodegen.postProcessAllModels (405-413) nor CppHttplibServerCodegen.postProcessAllModels adds it. The CppHttplibServerCodegen path that computes enumVars (DefaultCodegen.postProcessModelsEnum at 899-910, reached via AbstractCppCodegen.postProcessModels at line 401) is not triggered here, so `processedModel.allowableValues.get("enumVars")` returns null and `.size()` throws a NullPointerException, failing the test that this PR relies on to validate top-level enum handling. Run the model through the enum post-processing step before asserting, mirroring the DefaultGenerator pipeline.</comment>

<file context>
@@ -274,15 +274,18 @@ public void enumModelTest() {
+                wrapForPostProcessAllModels("Status", model))
+                .get("Status").getModels().get(0).getModel();
+        Assert.assertNotNull(processedModel.vendorExtensions.get("modelClassName"));
+        Assert.assertEquals(((List<?>) processedModel.allowableValues.get("enumVars")).size(), 3);
     }
 
</file context>

[cubic-dev-ai]

P2: The generated from_json in model-header.mustache compares j == "active", but the committed sample TopLevelStatus.h (the expected generator output) uses const std::string serializedValue = j.get<std::string>(); if (serializedValue == "active"). The two implementations behave differently for non-string JSON and the sample will not match what the generator emits, so samples and generated code are out of sync. Align the template's from_json with the sample (or regenerate the sample to match the template).

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At modules/openapi-generator/src/main/resources/cpp-httplib-server/model-header.mustache, line 40:

<comment>The generated from_json in model-header.mustache compares `j == "active"`, but the committed sample TopLevelStatus.h (the expected generator output) uses `const std::string serializedValue = j.get<std::string>(); if (serializedValue == "active")`. The two implementations behave differently for non-string JSON and the sample will not match what the generator emits, so samples and generated code are out of sync. Align the template's from_json with the sample (or regenerate the sample to match the template).</comment>

<file context>
@@ -16,6 +17,37 @@
+inline void from_json(const nlohmann::json& j, {{vendorExtensions.modelClassName}}& value)
+{
+    {{#allowableValues}}{{#enumVars}}
+    if (j == {{#isString}}"{{value}}"{{/isString}}{{^isString}}{{value}}{{/isString}})
+    {
+        value = {{vendorExtensions.modelClassName}}::{{name}};
</file context>