feat: added new duplicate tag names rule

.changeset/orange-ghosts-hug.md

@@ -0,0 +1,6 @@
+---
+"@redocly/openapi-core": minor
+"@redocly/cli": minor
+---
+
+Added the `no-duplicated-tag-names` rule to check for duplications in the `tags` field in API descriptions.

__tests__/lint/no-duplicated-tag-names/openapi.yaml

@@ -0,0 +1,33 @@
+openapi: 3.0.2
+info:
+  title: No Duplicated Tag Names Test
+  version: '1.0.0'
+tags:
+  - name: pet
+    description: Everything about your Pets
+  - name: store
+    description: Access to Petstore orders
+  - name: store
+    description: YOU DO NOT SEE THIS
+paths:
+  /pet:
+    get:
+      summary: Get a pet
+      operationId: getPet
+      responses:
+        '200':
+          description: OK
+  /store:
+    get:
+      summary: Get store info
+      operationId: getStore
+      responses:
+        '200':
+          description: OK
+  /store2:
+    get:
+      summary: Get store info 2
+      operationId: getStore2
+      responses:
+        '200':
+          description: OK

__tests__/lint/no-duplicated-tag-names/redocly.yaml

@@ -0,0 +1,6 @@
+apis:
+  main:
+    root: ./openapi.yaml
+
+rules:
+  no-duplicated-tag-names: warn

__tests__/lint/no-duplicated-tag-names/snapshot.txt

@@ -0,0 +1,23 @@
+[1] openapi.yaml:10:5 at #/tags/2
+
+Duplicate tag name found: 'store'.
+
+ 8 |   - name: store
+ 9 |     description: Access to Petstore orders
+10 |   - name: store
+   |     ^^^^^^^^^^^
+11 |     description: YOU DO NOT SEE THIS
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+12 | paths:
+13 |   /pet:
+
+Warning was generated by the no-duplicated-tag-names rule.
+
+
+
+validating openapi.yaml...
+openapi.yaml: validated in <test>ms
+
+Woohoo! Your API description is valid. 🎉
+You have 1 warning.
+

docs/@v2/rules/async/no-duplicated-tag-names.md

@@ -0,0 +1,89 @@
+# no-duplicated-tag-names
+
+Ensures that tag names in the `tags` array are unique.
+This rule prevents duplication of tag names which could lead to inconsistent API documentation.
+
+| AsyncAPI | Compatibility |
+| -------- | ------------- |
+| 2.6      | ✅            |
+| 3.0      | ✅            |
+
+## API design principles
+
+Tags are used to group operations in AsyncAPI specifications.
+Create unique tags to clearly categorize operations.
+Having duplicate tags can cause confusion in documentation rendering tools, makes the specification harder to maintain,
+and may lead to operations being grouped incorrectly.
+
+## Configuration
+
+| Option     | Type    | Description                                                                         |
+| ---------- | ------- | ----------------------------------------------------------------------------------- |
+| severity   | string  | Possible values: `off`, `warn`, `error`. Default `warn`.                            |
+| ignoreCase | boolean | Possible values: `true`, `false`. Default `false` (in `recommended` configuration). |
+
+An example configuration:
+
+```yaml
+rules:
+  no-duplicated-tag-names: error
+```
+
+Configuration that ignores case:
+
+```yaml
+rules:
+  no-duplicated-tag-names:
+    severity: error
+    ignoreCase: true
+```
+
+## Examples
+
+Given this configuration:
+
+```yaml
+rules:
+  no-duplicated-tag-names: error
+```
+
+Example of **incorrect** tags:
+
+```yaml Bad example
+tags:
+  - name: pet
+    description: Everything about your Pets
+  - name: store
+    description: Access to Petstore orders
+  - name: store
+    description: Duplicated store tag
+```
+
+Example of **correct** tags:
+
+```yaml Good example
+tags:
+  - name: pet
+    description: Everything about your Pets
+  - name: store
+    description: Access to Petstore orders
+  - name: user
+    description: Operations about user
+```
+
+With `ignoreCase: true`, this would also be incorrect:
+
+```yaml
+tags:
+  - name: pet
+    description: Everything about your Pets
+  - name: store
+    description: Access to Petstore orders
+  - name: Store
+    description: Case-sensitive duplicate
+```
+
+## Resources
+
+- [Rule source](https://github.com/Redocly/redocly-cli/blob/main/packages/core/src/rules/common/no-duplicated-tag-names.ts)
+- [Tags docs](https://redocly.com/docs/openapi-visual-reference/tags/)

docs/@v2/rules/oas/no-duplicated-tag-names.md

@@ -0,0 +1,98 @@
+---
+slug: /docs/cli/v2/rules/oas/no-duplicated-tag-names
+---
+
+# no-duplicated-tag-names
+
+Ensures that tag names in the `tags` array are unique.
+This rule prevents duplication of tag names which could lead to inconsistent API documentation.
+
+| OAS | Compatibility |
+| --- | ------------- |
+| 2.0 | ✅            |
+| 3.0 | ✅            |
+| 3.1 | ✅            |
+
+## API design principles
+
+Tags are used to group operations in OpenAPI specifications.
+Create unique tags to clearly categorize operations.
+Having duplicate tags can cause confusion in documentation rendering tools, makes the specification harder to maintain,
+and may lead to operations being grouped incorrectly.
+
+## Configuration
+
+| Option     | Type    | Description                                                                                                                                                                  |
+| ---------- | ------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| severity   | string  | Possible values: `off`, `warn`, `error`. Default `warn` (in `recommended` configuration).                                                                                    |
+| ignoreCase | boolean | Possible values: `true`, `false`. Default `false` (in `recommended` configuration). Set to `true` to treat tags with different casing as duplicates (e.g., "Pet" and "pet"). |
+
+An example configuration:
+
+```yaml
+rules:
+  no-duplicated-tag-names: error
+```
+
+Configuration that ignores case:
+
+```yaml
+rules:
+  no-duplicated-tag-names:
+    severity: error
+    ignoreCase: true
+```
+
+## Examples
+
+Given this configuration:
+
+```yaml
+rules:
+  no-duplicated-tag-names: error
+```
+
+Example of **incorrect** tags:
+
+```yaml Bad example
+tags:
+  - name: pet
+    description: Everything about your Pets
+  - name: store
+    description: Access to Petstore orders
+  - name: store
+    description: Duplicated store tag
+```
+
+Example of **correct** tags:
+
+```yaml Good example
+tags:
+  - name: pet
+    description: Everything about your Pets
+  - name: store
+    description: Access to Petstore orders
+  - name: user
+    description: Operations about user
+```
+
+With `ignoreCase: true`, this would also be incorrect:
+
+```yaml
+tags:
+  - name: pet
+    description: Everything about your Pets
+  - name: store
+    description: Access to Petstore orders
+  - name: Store
+    description: Case-sensitive duplicate
+```
+
+## Related rules
+
+- [tag-description](./tag-description.md)
+
+## Resources
+
+- [Rule source](https://github.com/Redocly/redocly-cli/blob/main/packages/core/src/rules/common/no-duplicated-tag-names.ts)
+- [Tags docs](https://redocly.com/docs/openapi-visual-reference/tags/)

docs/@v2/rules/ruleset-templates.md

@@ -74,6 +74,7 @@ rules:
   response-contains-property: off
   response-mime-type: off
   array-parameter-serialization: off
+  no-duplicated-tag-names: off
 ```
 
 ### Minimal ruleset: OpenAPI 3.0
@@ -136,6 +137,7 @@ rules:
   response-contains-property: off
   response-mime-type: off
   array-parameter-serialization: off
+  no-duplicated-tag-names: off
 ```
 
 ### Minimal ruleset: OpenAPI 2.0
@@ -186,6 +188,7 @@ rules:
   request-mime-type: off
   response-contains-property: off
   response-mime-type: off
+  no-duplicated-tag-names: off
 ```
 
 ### Minimal ruleset: AsyncAPI 3.0
@@ -200,6 +203,7 @@ rules:
   tags-alphabetical: off
   channels-kebab-case: off
   no-channel-trailing-slash: off
+  no-duplicated-tag-names: off
 ```
 
 ### Minimal ruleset: AsyncAPI 2.6
@@ -214,6 +218,7 @@ rules:
   tags-alphabetical: off
   channels-kebab-case: off
   no-channel-trailing-slash: off
+  no-duplicated-tag-names: off
 ```
 
 ### Minimal ruleset: Arazzo 1.0
@@ -346,6 +351,7 @@ oas3_1Rules:
   response-contains-property: off
   response-mime-type: off
   array-parameter-serialization: off
+  no-duplicated-tag-names: warn
 ```
 
 ### Recommended ruleset: OpenAPI 3.0
@@ -408,6 +414,7 @@ rules:
   response-contains-property: off
   response-mime-type: off
   array-parameter-serialization: off
+  no-duplicated-tag-names: warn
 ```
 
 ### Recommended ruleset: OpenAPI 2.0
@@ -458,6 +465,7 @@ rules:
   request-mime-type: off
   response-contains-property: off
   response-mime-type: off
+  no-duplicated-tag-names: warn
 ```
 
 ### Recommended ruleset: AsyncAPI 3.0
@@ -472,6 +480,7 @@ rules:
   tags-alphabetical: off
   channels-kebab-case: off
   no-channel-trailing-slash: off
+  no-duplicated-tag-names: warn
 ```
 
 ### Recommended ruleset: AsyncAPI 2.6
@@ -486,6 +495,7 @@ rules:
   tags-alphabetical: off
   channels-kebab-case: off
   no-channel-trailing-slash: off
+  no-duplicated-tag-names: warn
 ```
 
 ### Recommended ruleset: Arazzo 1.0