feat(linter): add const_and_enum_conflict rule

[AcEKaycgR]

Summary

This PR introduces a new lint rule: const_and_enum_conflict.

The rule detects schemas that declare both const and enum keywords simultaneously.

{
  "const": 1,
  "enum": [1, 2, 3]
}

Using both const and enum together is redundant and contradictory. const is equivalent to a single-value enum, so having both is always an authoring mistake and should be reported to the user.

The rule emits a diagnostic when:

• const is defined
• enum is defined
• both exist on the same schema object

The diagnostic points to both the const and enum keyword locations.

This rule is non auto-fixable because the correct resolution depends on the schema author's intent (whether to keep const or enum).

Implementation

The rule follows the existing alterschema linter architecture:

• implemented as a header-only rule in src/extension/alterschema/linter/const_and_enum_conflict.h
• registered in alterschema.cc
• added to the SOURCES list in the alterschema CMake configuration

The rule checks:

• schema node is an object
• const keyword is defined
• enum keyword is defined

Note: The rule only applies from Draft 6 onward, as const was introduced in Draft 6.

If these conditions are met the rule returns:

APPLIES_TO_KEYWORDS("const", "enum")

Tests

Tests were added across supported dialects using the existing lint testing utilities.

The following scenarios are covered:

• Rule fires when both const and enum are present
• Rule does not fire when only const is present
• Rule does not fire when only enum is present
• Rule fires inside nested subschemas (e.g. inside properties)

All tests follow the patterns used by existing lint rule tests.

Related Work

This rule addresses one of the pending lint rules listed in:

Refs: #1975

---

@jviotti Could you please review this pull request when you have a moment?

If the approach looks good, I'd be happy to continue implementing additional linting rules listed in #1975.

cc @Karan-Palan

Note: PR description and test structure follow the same format as 2287 for consistency.

[cubic-dev-ai]

2 issues found across 7 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="test/alterschema/alterschema_lint_2019_09_test.cc">

<violation number="1" location="test/alterschema/alterschema_lint_2019_09_test.cc:4512">
P2: New const_and_enum_conflict tests do not assert both diagnostic keyword locations, so regressions in secondary-location reporting would go undetected.</violation>
</file>

<file name="test/alterschema/alterschema_lint_2020_12_test.cc">

<violation number="1" location="test/alterschema/alterschema_lint_2020_12_test.cc:9682">
P2: New `const_and_enum_conflict` tests do not assert the diagnostic’s dual keyword locations, so regressions in secondary-location reporting would go undetected.</violation>
</file>

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[cubic-dev-ai]

P2: New const_and_enum_conflict tests do not assert the diagnostic’s dual keyword locations, so regressions in secondary-location reporting would go undetected.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At test/alterschema/alterschema_lint_2020_12_test.cc, line 9682:

<comment>New `const_and_enum_conflict` tests do not assert the diagnostic’s dual keyword locations, so regressions in secondary-location reporting would go undetected.</comment>

<file context>
@@ -9664,3 +9664,77 @@ TEST(AlterSchema_lint_2020_12, object_oneof_required_not_required_6) {
+
+  EXPECT_FALSE(result.first);
+  EXPECT_EQ(traces.size(), 1);
+  EXPECT_LINT_TRACE(traces, 0, "", "const_and_enum_conflict",
+                    "The `const` and `enum` keywords are mutually exclusive; "
+                    "use one or the other, not both",
</file context>