Add vendor extension docs

docs/generator-vendor-extensions.md

@@ -0,0 +1,106 @@
+---
+id: generator-vendor-extensions
+title: Vendor Extensions
+---
+
+This is a list of [vendor extensions](https://github.com/OAI/OpenAPI-Specification/blob/master/versions/2.0.md#specification-extensions) used by different generators.
+
+<!-- TODO: Auto-generate this list using generator metadata -->
+
+The list may not be up-to-date, the best way is to look for "x-" in the mustache templates.
+
+(All examples are in YAML format)
+
+## ObjC
+### x-objc-operationId
+
+To customize the method name, you can provide a different name in x-objc-operationId, e.g.
+```yaml
+summary: Add a new pet to the store
+description: ''
+operationId: addPet
+x-objc-operationId: CreateNewPet
+```  
+
+## Java (Feign)
+### x-accepts
+
+A single `Accepts` value as the Feign API client needs a single value for `Accepts` header, e.g.
+```yaml
+consumes:
+  - application/json
+  - application/xml
+x-accepts: application/json
+```
+
+### x-content-type
+
+A single "Content-Type" value as the Feign API client needs a single value for `Content-Type` header, e.g.
+```yaml
+produces:
+  - application/xml
+  - application/json
+x-content-type: application/json
+```
+
+## Rust-server
+
+### x-responseId
+
+Each response may specify a unique `x-responseId`. `rust-server` will use this to name the corresponding enum variant in the code. e.g.
+
+```yaml
+paths:
+  /ping:
+    get:
+      responses:
+        200:
+          description: OK
+          x-responseId: Pong
+```
+
+## MySQL Schema
+
+### x-mysqlSchema
+
+MySQL schema generator creates vendor extensions based on openapi `dataType` and `dataFormat`. When user defined extensions with same key already exists codegen accepts those as is. It means it won't validate properties or correct it for you. Every model in `definitions` can contain table related and column related extensions like in example below: 
+
+```yaml
+definitions:
+  Order:
+    description: This should be most common InnoDB table
+    type: object
+    properties:
+      id:
+        description: >-
+          This column should be unsigned BIGINT with AUTO_INCREMENT
+        type: integer
+        format: int64
+        x-mysqlSchema:
+          columnDefinition:
+            colName: id
+            colDataType: DECIMAL
+            colDataTypeArguments:
+              - argumentValue: 16
+                isString: false
+                hasMore: true
+              - argumentValue: 4
+                isString: false
+                hasMore: false
+            colUnsigned: true
+            colNotNull: true
+            colDefault:
+              defaultValue: AUTO_INCREMENT
+              isString: false
+              isNumeric: false
+              isKeyword: true
+            colComment: >-
+              Column comment. This column should be unsigned BIGINT with AUTO_INCREMENT
+    x-mysqlSchema:
+      tableDefinition:
+        tblName: orders
+        tblStorageEngine: InnoDB
+        tblComment: >-
+          Table comment. This should be most common InnoDB table
+```
+> :exclamation: There are properties that are not implemented by now(`tblStorageEngine`), but you can see how generator can be enhanced in future.

website/sidebars.json

@@ -8,6 +8,7 @@
     ],
     "Extending": [
       "templating",
+      "generator-vendor-extensions",
       "customization",
       "integrations"
     ],