Adding release notes for September release (core) (#2407)

docs/release-notes/release-2023-09-12.md

@@ -0,0 +1,87 @@
+---
+title: September 2023
+---
+
+# Release Notes September 2023 (2023-09-12)
+
+:::danger
+This release contains **breaking changes**
+:::
+
+## New Features
+
+### `@typespec/compiler` New Features
+
+- Allow library authors to precisely define the visibility of operation templates with new decorators `@parameterVisibility` and `@returnTypeVisibility`, paired with corresponding accessor methods `getParameterVisibility` and `getReturnTypeVisibility`.
+- Add coloring for documentation comments in Visual Studio and Visual Studio Code language extensions.
+- Change yaml parser from `js-yaml` to `yaml`, enabling more precise validation and error reporting in `tspconfig.yaml`
+- Added validation to ensure that properties of a derived model (using `extends`) are compatible with the base model indexer.
+- Export `CompilerOptions` TypeScript type.
+- Report library information when library code crashes during `$onValidate` execution.
+- Diagnostics reported on a node with an `id` property will highlight the id instead of the entire node. For example, if a diagnostic is reported on a `model` type, the model name will be highlighted, instead of the entire model definition.
+
+### `@typespec/http` New Features
+
+- Add new helper method `resolveRequestVisibility` which incorporates settings from new core decorators `@parameterVisibility` and `@returnTypeVisibility`. This replaces the deprecated `getRequestVisibility` helper.
+- Add new helper method `getDefaultVisibilityForVerb` which returns the default visibility for Http verbs.
+- Add validation step to issue a warning when an `operation is` statement does not include route information from the original operation container (`interface` or `namespace`). This helps to prevent unexpected route changes when using operation references.
+- Add validation to prevent runtime errors when `OAuth2Auth` is given invalid `OAuth2Flow` arguments.
+
+### `@typespec/json-schema` New Features
+
+- Support decimal scalar types.
+
+### `@typespec/openapi3` New Features
+
+- Allow library authors to override default Http verb visibility in operation declarations.
+
+### `@typespec/protobuf` New features
+
+- Support `omit-unreachable-types` option.
+- Automatically convert empty operation parameters into a reference to `google.protobuf.Empty` instead of synthesizing an empty model.
+
+### `typespec-vscode` New features
+
+- Add color definition for `@param` tag in documentation comments
+
+## Bug Fixes
+
+### `@typespec/compiler` Bug Fixes
+
+- Fix issue where specifying a directory using the `--config` command line option would search the parent folder hierarchy looking for `tspconfig.yaml`.
+- Fix Stack overflow when a model property references itself.
+- Fix compiler crash when using the alias of a namespace that has decorators.
+- Fix compiler freeze when an invalid token appears between doc comment and type.
+- Fix compiler crash when relating recursive types.
+- Fix typo in format error diagnostic.
+
+### `@typespec/openapi3` Bug Fixes
+
+- Fixed issue where parameters marked with visibility \"create\" did not appear in a `PATCH` request body.
+- Fixed incorrect usage of `exclusiveMinimum` and `exclusiveMaximum` boolean properties.
+- Use `anyOf` instead of `oneOf` for operations with shared routes and different request or response bodies.
+- Fix handling of `Record<T>` in `model is` and `model extends` statements.
+
+### `@typespec/versioning` Bug Fixes
+
+- Fixed validation in `@typeChangedFrom` for incorrect versioned references.
+
+## Deprecations
+
+### `@typespec/compiler` Deprecations
+
+- The `@deprecated` decorator has been marked as deprecated. Use `#deprecated` directive instead.
+
+### `@typespec/http` Deprecations
+
+- The `getRequestVisibility` helper function is now deprecated. Use `resolveRequestVisibility` or `getDefaultVisibilityForVerb` instead.
+
+## Breaking Changes
+
+### `@typespec/compiler` Breaking Changes
+
+- A semicolon is now required at the end of augment decorator statements. The formatter was already inserting the semicolon, if omitted. For example:
+
+  ```tsp
+  @@doc(MyType.myProperty, "Documentation for myProperty");
+  ```