Add no-replace-inherited-props linting rule for ARM

[Copilot]

New ARM linter rule that flags redefining a property already declared on a base model — an Azure API anti-pattern that currently crashes the breaking-change tool (azure-rest-api-specs#42903).

Rule

arm-no-replace-inherited-props walks baseModel ancestry. A redefinition is permitted when either:

• Identical type — property.type === inherited.type. Because aliases share identity and template instantiations are cached, this covers systemData: SystemData (alias) over Foundations.SystemData, the implicit tags: Record<string> cloned by model X is TrackedResource<...>, etc.
• Same scalar family — both sides reduce to string, numeric, or boolean. Walks baseScalar chains, classifies enum members by value type, reduces unions via getUnionAsEnum from @azure-tools/typespec-azure-core, and unwraps UnionVariants and literals. No special-case needed for ARM name or @discriminator overrides.

Changes

• packages/typespec-azure-resource-manager/src/rules/arm-no-replace-inherited-props.ts — rule implementation.
• Registered in src/linter.ts (all ruleset) and enabled in packages/typespec-azure-rulesets/src/rulesets/resource-manager.ts.
• 18 tests covering: derived-model overrides (warn), and allowed cases for identical type, alias, is TrackedResource tags clone (implicit and explicit), and the full scalar-family matrix (scalar, derived scalar, literal value, closed/open union, named union variant, ARM name, @discriminator literal).
• Docs: new rule page, regenerated linter.md reference and package README.md.
• Changeset under .chronus/changes/ for @azure-tools/typespec-azure-resource-manager and @azure-tools/typespec-azure-rulesets.

Example

@armProviderNamespace
namespace MyService;

@discriminator("kind")
model Pet {
  kind: string;
  weight: int32;
}

model Cat extends Pet {
  kind: "cat";    // OK — same scalar family (string)
  weight: int32;  // OK — same scalar family (numeric)
}

model FooProperties { p: string; }
model FooResource is TrackedResource<FooProperties> {
  ...ResourceNameParameter<FooResource>;
  tags?: Record<string>;  // OK — identical type to inherited tags
}

model InnerBase { a: string; }
model InnerDerived extends InnerBase { b: string; }
model Base { nested: InnerBase; }
model Child extends Base {
  nested: InnerDerived;  // ⚠ arm-no-replace-inherited-props
}

[markcowl]

There is a merge conflict. Pull the latest from main, resolve the conflict, ensure all properties are correctly formatted and all tests pass and that only the chnages associated with this PR are in the PR diff

[Copilot]

There is a merge conflict. Pull the latest from main, resolve the conflict, ensure all properties are correctly formatted and all tests pass and that only the chnages associated with this PR are in ...

Merged latest main and resolved the conflict in the auto-generated website/.../reference/linter.md (took main's link-format change and re-ran regen-docs to add the new rule entry). Also enabled the new rule in packages/typespec-azure-rulesets/src/rulesets/resource-manager.ts. Verified git diff origin/main shows only the 8 files associated with this PR. Targeted tests pass (147 ARM rule tests + 3 rulesets tests) and pnpm format is clean. Done in 49acb48.

[github-actions]

⚡ Benchmark Results

⚠️ 1 metric(s) regressed above the +5% threshold:

Metric	Baseline	Current	Change
↳ emit/@azure-tools/typespec-autorest	🟢 166.1ms	🟢 193.6ms	+16.5% 🔴

Full details – comparing 792e97a vs baseline 8cd8304

Metric	Baseline	Current	Change
total	🔴 6.59s	🔴 6.51s	-1.3%
loader	🟡 212.7ms	🟢 177.6ms	-16.5% 🟢
resolver	🟢 20.3ms	🟢 16.4ms	-18.8% 🟢
checker	🟢 187.3ms	🟢 183.5ms	-2.0%
validation	🟢 43.4ms	🟢 43.3ms	-0.1%
↳ validation/@azure-tools/typespec-azure-core	🟢 6.2ms	🟢 6.5ms	+4.7%
↳ validation/@typespec/http	🟢 5.4ms	🟢 5.6ms	+4.1%
↳ validation/@typespec/rest	🟢 0.6ms	🟢 0.6ms	-8.0%
↳ validation/@typespec/versioning	🔴 28.4ms	🔴 29.3ms	+3.1%
↳ validation/compiler	🟢 1.8ms	🟢 1.4ms	-23.8%
linter	🟡 212.3ms	🟢 130.8ms	-38.4% 🟢
↳ linter/@azure-tools/typespec-azure-core/auth-required	🟢 0.0ms	🟢 0.0ms	+4.1%
↳ linter/@azure-tools/typespec-azure-core/bad-record-type	🟢 0.4ms	🟢 0.3ms	-40.5%
↳ linter/@azure-tools/typespec-azure-core/byos	🟢 9.0ms	🟢 5.5ms	-38.4% 🟢
↳ linter/@azure-tools/typespec-azure-core/casing-style	🟢 0.8ms	🟢 0.6ms	-23.7%
↳ linter/@azure-tools/typespec-azure-core/composition-over-inheritance	🟢 0.1ms	🟢 0.1ms	-1.5%
↳ linter/@azure-tools/typespec-azure-core/documentation-required	🟢 0.9ms	🟢 0.8ms	-11.3%
↳ linter/@azure-tools/typespec-azure-core/friendly-name	🟢 0.8ms	🟢 0.6ms	-13.7%
↳ linter/@azure-tools/typespec-azure-core/key-visibility-required	🟢 0.2ms	🟢 0.2ms	+0.9%
↳ linter/@azure-tools/typespec-azure-core/known-encoding	🟢 0.3ms	🟢 0.3ms	+0.0%
↳ linter/@azure-tools/typespec-azure-core/long-running-polling-operation-required	🟢 0.3ms	🟢 0.3ms	-10.6%
↳ linter/@azure-tools/typespec-azure-core/no-case-mismatch	🟢 0.2ms	🟢 0.2ms	-4.6%
↳ linter/@azure-tools/typespec-azure-core/no-closed-literal-union	🟢 0.3ms	🟢 0.2ms	-7.5%
↳ linter/@azure-tools/typespec-azure-core/no-enum	🟢 0.0ms	🟢 0.0ms	+3.3%
↳ linter/@azure-tools/typespec-azure-core/no-error-status-codes	🟢 0.1ms	🟢 0.1ms	-8.4%
↳ linter/@azure-tools/typespec-azure-core/no-explicit-routes-resource-ops	🟢 0.1ms	🟢 0.1ms	-6.0%
↳ linter/@azure-tools/typespec-azure-core/no-format	🟢 0.9ms	🟢 0.6ms	-25.8%
↳ linter/@azure-tools/typespec-azure-core/no-generic-numeric	🟢 0.4ms	🟢 0.4ms	-13.9%
↳ linter/@azure-tools/typespec-azure-core/no-header-explode	🔴 31.4ms	🟡 18.6ms	-40.8% 🟢
↳ linter/@azure-tools/typespec-azure-core/no-legacy-usage	🟢 1.1ms	🟢 1.1ms	-4.7%
↳ linter/@azure-tools/typespec-azure-core/no-multiple-discriminator	🟢 0.1ms	🟢 0.1ms	-0.6%
↳ linter/@azure-tools/typespec-azure-core/no-nullable	🟢 0.3ms	🟢 0.3ms	-1.0%
↳ linter/@azure-tools/typespec-azure-core/no-offsetdatetime	🟢 1.2ms	🟢 1.1ms	-5.1%
↳ linter/@azure-tools/typespec-azure-core/no-openapi	🟢 3.0ms	🟢 2.1ms	-31.9%
↳ linter/@azure-tools/typespec-azure-core/no-private-usage	🟢 2.1ms	🟢 1.9ms	-10.6%
↳ linter/@azure-tools/typespec-azure-core/no-query-explode	🔴 31.3ms	🟡 19.6ms	-37.6% 🟢
↳ linter/@azure-tools/typespec-azure-core/no-response-body	🔴 43.5ms	🔴 24.4ms	-44.0% 🟢
↳ linter/@azure-tools/typespec-azure-core/no-rest-library-interfaces	🟢 0.0ms	🟢 0.0ms	-11.9%
↳ linter/@azure-tools/typespec-azure-core/no-route-parameter-name-mismatch	🟢 7.8ms	🟢 4.7ms	-39.7% 🟢
↳ linter/@azure-tools/typespec-azure-core/no-rpc-path-params	🟢 0.3ms	🟢 0.2ms	-35.0%
↳ linter/@azure-tools/typespec-azure-core/no-string-discriminator	🟢 0.0ms	🟢 0.0ms	-8.0%
↳ linter/@azure-tools/typespec-azure-core/no-unknown	🟢 0.3ms	🟢 0.2ms	-35.8%
↳ linter/@azure-tools/typespec-azure-core/no-unnamed-union	🟢 0.4ms	🟢 0.4ms	+5.2%
↳ linter/@azure-tools/typespec-azure-core/operation-missing-api-version	🟢 0.2ms	🟢 0.2ms	+1.3%
↳ linter/@azure-tools/typespec-azure-core/request-body-problem	🟢 0.3ms	🟢 0.3ms	-18.7%
↳ linter/@azure-tools/typespec-azure-core/require-versioned	🟢 0.0ms	🟢 0.0ms	-13.7%
↳ linter/@azure-tools/typespec-azure-core/response-schema-problem	🔴 38.2ms	🔴 22.0ms	-42.5% 🟢
↳ linter/@azure-tools/typespec-azure-core/rpc-operation-request-body	🟢 0.4ms	🟢 0.3ms	-28.8%
↳ linter/@azure-tools/typespec-azure-core/spread-discriminated-model	🟢 0.3ms	🟢 0.3ms	-1.1%
↳ linter/@azure-tools/typespec-azure-core/use-standard-names	🟡 10.2ms	🟢 4.9ms	-52.2% 🟢
↳ linter/@azure-tools/typespec-azure-core/use-standard-operations	🟢 0.1ms	🟢 0.1ms	-9.1%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-common-types-version	🟢 3.7ms	🟢 3.8ms	+1.1%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-custom-resource-no-key	🟢 0.1ms	🟢 0.1ms	+2.4%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-custom-resource-usage-discourage	🟢 0.1ms	🟢 0.1ms	-7.8%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-delete-operation-response-codes	🟢 4.6ms	🟢 4.8ms	+5.3%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-no-path-casing-conflicts	🟢 4.0ms	🟢 4.4ms	+9.1%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-no-record	🟢 0.4ms	🟢 0.4ms	+3.5%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-post-operation-response-codes	🟢 0.4ms	🟢 0.5ms	+14.7%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-put-operation-response-codes	🟢 0.0ms	🟢 0.0ms	+23.7%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-resource-action-no-segment	🟢 0.2ms	🟢 0.3ms	+15.8%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-resource-duplicate-property	🟢 0.1ms	🟢 0.1ms	+2.5%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-resource-interface-requires-decorator	🟢 0.0ms	🟢 0.0ms	-12.3%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-resource-invalid-action-verb	🟢 0.1ms	🟢 0.1ms	+6.2%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-resource-invalid-envelope-property	🟢 0.1ms	🟢 0.1ms	+5.8%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-resource-invalid-version-format	🟢 0.0ms	🟢 0.0ms	-0.5%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-resource-key-invalid-chars	🟢 0.2ms	🟢 0.2ms	-2.5%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-resource-name-pattern	🟢 0.0ms	🟢 0.0ms	+4.8%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-resource-operation	🟢 0.2ms	🟢 0.2ms	-1.2%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-resource-operation-response	🟢 4.4ms	🟢 4.3ms	-1.4%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-resource-patch	🟢 0.3ms	🟢 0.3ms	+22.1%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-resource-path-segment-invalid-chars	🟢 0.2ms	🟢 0.2ms	+4.0%
↳ linter/@azure-tools/typespec-azure-resource-manager/arm-resource-provisioning-state	🟢 0.1ms	🟢 0.1ms	+6.8%
↳ linter/@azure-tools/typespec-azure-resource-manager/beyond-nesting-levels	🟢 0.1ms	🟢 0.1ms	-3.5%
↳ linter/@azure-tools/typespec-azure-resource-manager/empty-updateable-properties	🟢 0.1ms	🟢 0.1ms	+6.1%
↳ linter/@azure-tools/typespec-azure-resource-manager/improper-subscription-list-operation	🟢 0.0ms	🟢 0.0ms	+12.6%
↳ linter/@azure-tools/typespec-azure-resource-manager/lro-location-header	🟡 12.3ms	🟡 12.9ms	+5.3%
↳ linter/@azure-tools/typespec-azure-resource-manager/missing-operations-endpoint	🟢 0.0ms	🟢 0.0ms	+8.2%
↳ linter/@azure-tools/typespec-azure-resource-manager/missing-x-ms-identifiers	🟢 0.3ms	🟢 0.3ms	-0.4%
↳ linter/@azure-tools/typespec-azure-resource-manager/no-empty-model	🟢 0.1ms	🟢 0.1ms	+0.2%
↳ linter/@azure-tools/typespec-azure-resource-manager/no-replace-inherited-props	🟢 0.0ms	🟢 0.1ms	+100.0%
↳ linter/@azure-tools/typespec-azure-resource-manager/no-resource-delete-operation	🟢 0.2ms	🟢 0.2ms	-3.6%
↳ linter/@azure-tools/typespec-azure-resource-manager/no-response-body	🟡 19.7ms	🟡 19.7ms	-0.1%
↳ linter/@azure-tools/typespec-azure-resource-manager/patch-envelope	🟢 0.1ms	🟢 0.1ms	-9.4%
↳ linter/@azure-tools/typespec-azure-resource-manager/resource-name	🟢 0.1ms	🟢 0.1ms	+1.7%
↳ linter/@azure-tools/typespec-azure-resource-manager/secret-prop	🟢 2.4ms	🟢 2.2ms	-10.7%
↳ linter/@azure-tools/typespec-azure-resource-manager/unsupported-type	🟢 0.4ms	🟢 0.3ms	-5.0%
↳ linter/@azure-tools/typespec-azure-resource-manager/version-progression	🟢 0.0ms	🟢 0.0ms	+3.6%
↳ linter/@azure-tools/typespec-client-generator-core/property-name-conflict	🟢 1.2ms	🟢 1.0ms	-12.9%
↳ linter/@azure-tools/typespec-client-generator-core/require-client-suffix	🟢 0.2ms	🟢 0.2ms	-8.6%
emit	🔴 5.83s	🔴 5.87s	+0.6%
↳ emit/@azure-tools/typespec-autorest	🟢 166.1ms	🟢 193.6ms	+16.5% 🔴
↳ emit/@azure-tools/typespec-python	🔴 4.33s	🔴 4.29s	-0.8%
↳ emit/@typespec/http-client-js	🔴 1.14s	🔴 1.16s	+1.9%
↳ emit/@typespec/openapi3	🟢 147.1ms	🟢 146.9ms	-0.2%
↳ emit/@typespec/openapi3/compute	🟢 130.7ms	🟢 129.5ms	-0.9%
↳ emit/@typespec/openapi3/write	🟢 16.9ms	🟢 17.5ms	+3.7%

Averaged across 3 specs (azure-arm-resource-manager, azure-core-dataplane, azure-full).
Threshold: changes > ±5% are highlighted.
🟢 Fast · 🟡 Moderate (stages >200ms, rules >10ms) · 🔴 Slow (stages >400ms, rules >20ms)

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@azure-tools/typespec-azure-resource-manager@4384

npm i https://pkg.pr.new/@azure-tools/typespec-azure-rulesets@4384

commit: ffad4ac

[markcowl]

Update the changeset to include your change to the rulesets.

Pull the latest from main, ensure all files are well formatted and only the changes associated with this PR are in the PR diff.

[Copilot]

Update the changeset to include your change to the rulesets.

Pull the latest from main, ensure all files are well formatted and only the changes associated with this PR are in the PR diff.

Updated the changeset to include @azure-tools/typespec-azure-rulesets (6d60f84). Also pulled latest from main (clean merge, no conflicts) and verified pnpm format is clean. git diff origin/main --stat shows only the 8 files associated with this PR.

[markcowl]

@copilot Please follow the instuctio0ns in the comment

[Copilot]

@copilot Please follow the instuctio0ns in the comment

Done — addressed the review feedback in 5180f69. Details in the inline reply.

[markcowl]

Suppression PR for the Microsoft.Security/SecuritySolutionsAPI violations: Azure/azure-rest-api-specs#43657

[markcowl]

Please pull the latest from main, make the rename suggested in the review comments, validate correct build and rebuild documents, validate that all files are correctly formatted and only changes associated with thsi pr are in the pr diff.