fix(go): validate string enum exclusions

[AndreyVMarkelov]

Description

Fixes #25090

Fix Go client generation for string properties constrained by enum and not: { enum: [...] }.

Previously, generated models could accept values excluded by not: enum during JSON unmarshaling. This could make oneOf variants overlap when they were intended to be mutually exclusive.

This change adds validation during generated model unmarshaling so:

• allowed enum values are enforced;
• excluded enum values are rejected;
• nullable enums preserve null semantics;
• optional properties remain optional;
• untyped not: enum does not incorrectly force a string type;
• JSON property matching follows Go encoding/json case-insensitive field matching.

Existing UnmarshalJSON paths for required and additionalProperties models are preserved.

Related reports: #25065 (Java), #25069 (Python).

Tests

Added focused Go generator coverage for:

• allowed and excluded string enum values
• nullable allowed and excluded enums
• optional properties
• quoted string values
• typed and untyped not: enum
• case-insensitive JSON property names
• validating UnmarshalJSON generation

Generated Go code compiles and passes runtime validation with go test ./....

[cubic-dev-ai]

All reported issues were addressed across 4 files

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[cubic-dev-ai]

All reported issues were addressed across 17 files (changes from recent commits).

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[cubic-dev-ai]

All reported issues were addressed across 5 files (changes from recent commits).

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[cubic-dev-ai]

All reported issues were addressed across 3 files (changes from recent commits).

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[cubic-dev-ai]

All reported issues were addressed across 21 files

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[cubic-dev-ai]

3 issues found across 22 files (changes from recent commits).

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. When an issue isn't valid or won't be fixed in this PR, reply in its thread with the reason and then resolve the thread. If appropriate, use sub-agents to investigate and fix each issue separately.


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

<violation number="1" location="modules/openapi-generator/src/test/java/org/openapitools/codegen/go/GoClientCodegenTest.java:271">
P2: The guard treats any installed Go binary as suitable, but generated `go.mod` requires Go 1.23; an older local toolchain can fail this test instead of skipping. Check the reported version against the module directive before invoking `go test`.</violation>

<violation number="2" location="modules/openapi-generator/src/test/java/org/openapitools/codegen/go/GoClientCodegenTest.java:278">
P3: This copied test file is not registered for deletion, so it prevents the temporary output directory and generated files from being removed on JVM exit. Register the copied path with `deleteOnExit()`.</violation>
</file>

<file name="modules/openapi-generator/src/main/resources/go/model_simple.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/go/model_simple.mustache:510">
P2: For a required `Foo` with a default, `{"foo":""}` reaches this branch and leaves both `foo` and the defaulted `Foo` in `allProperties`; unmarshalling the marshaled map can let the alias overwrite the default. Remove or normalize the matched alias before adding the canonical default.</violation>
</file>

<sub>Tip: Review your code locally with the cubic CLI to iterate faster.

Re-trigger cubic</sub>

[cubic-dev-ai]

P2: The guard treats any installed Go binary as suitable, but generated go.mod requires Go 1.23; an older local toolchain can fail this test instead of skipping. Check the reported version against the module directive before invoking go test.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. When an issue isn't valid or won't be fixed in this PR, reply in its thread with the reason and then resolve the thread. At modules/openapi-generator/src/test/java/org/openapitools/codegen/go/GoClientCodegenTest.java, line 271:

<comment>The guard treats any installed Go binary as suitable, but generated `go.mod` requires Go 1.23; an older local toolchain can fail this test instead of skipping. Check the reported version against the module directive before invoking `go test`.</comment>

<file context>
@@ -256,13 +264,23 @@ public void testStringNotEnumValidation() throws IOException {
+                "validateStringEnumValues");
+
+        try {
+            Process goVersion = new ProcessBuilder("go", "version").start();
+            if (goVersion.waitFor() != 0) {
+                return;
</file context>

[cubic-dev-ai]

P2: For a required Foo with a default, {"foo":""} reaches this branch and leaves both foo and the defaulted Foo in allProperties; unmarshalling the marshaled map can let the alias overwrite the default. Remove or normalize the matched alias before adding the canonical default.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. When an issue isn't valid or won't be fixed in this PR, reply in its thread with the reason and then resolve the thread. At modules/openapi-generator/src/main/resources/go/model_simple.mustache, line 510:

<comment>For a required `Foo` with a default, `{"foo":""}` reaches this branch and leaves both `foo` and the defaulted `Foo` in `allProperties`; unmarshalling the marshaled map can let the alias overwrite the default. Remove or normalize the matched alias before adding the canonical default.</comment>

<file context>
@@ -491,18 +491,46 @@ func (o *{{{classname}}}) UnmarshalJSON(data []byte) (err error) {
 	for _, requiredProperty := range(requiredProperties) {
 		{{#useDefaultValuesForRequiredVars}}
+{{#vendorExtensions.x-go-enum-required-case-fold}}
+		if value, exists := lookupRequiredProperty(requiredProperty); !exists || value == "" {
+{{/vendorExtensions.x-go-enum-required-case-fold}}
+{{^vendorExtensions.x-go-enum-required-case-fold}}
</file context>

[cubic-dev-ai]

P3: This copied test file is not registered for deletion, so it prevents the temporary output directory and generated files from being removed on JVM exit. Register the copied path with deleteOnExit().

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. When an issue isn't valid or won't be fixed in this PR, reply in its thread with the reason and then resolve the thread. At modules/openapi-generator/src/test/java/org/openapitools/codegen/go/GoClientCodegenTest.java, line 278:

<comment>This copied test file is not registered for deletion, so it prevents the temporary output directory and generated files from being removed on JVM exit. Register the copied path with `deleteOnExit()`.</comment>

<file context>
@@ -256,13 +264,23 @@ public void testStringNotEnumValidation() throws IOException {
+        } catch (IOException ignored) {
+            return;
+        }
+        Files.copy(Paths.get("src/test/resources/3_1/go/oneof-not-enum_test.go"),
+                Paths.get(output.getAbsolutePath(), "oneof-not-enum_test.go"));
+        Process goTest = new ProcessBuilder("go", "test", "-mod=mod", "-run", "^TestStringEnumScope$", ".")
</file context>

Suggested change

	Files.copy(Paths.get("src/test/resources/3_1/go/oneof-not-enum_test.go"),
	Paths.get(output.getAbsolutePath(), "oneof-not-enum_test.go"));
	Files.copy(Paths.get("src/test/resources/3_1/go/oneof-not-enum_test.go"),
	Paths.get(output.getAbsolutePath(), "oneof-not-enum_test.go")).toFile().deleteOnExit();