Swift: cleanup and some docstrings for codegen

Also added code generation and clang formatting to the pre-commit
configuration.

.pre-commit-config.yaml

@@ -2,28 +2,41 @@
 # See https://pre-commit.com/hooks.html for more hooks
 exclude: /test/.*$(?<!\.ql)(?<!\.qll)(?<!\.qlref)
 repos:
--   repo: https://github.com/pre-commit/pre-commit-hooks
+  - repo: https://github.com/pre-commit/pre-commit-hooks
     rev: v3.2.0
     hooks:
-    -   id: trailing-whitespace
-    -   id: end-of-file-fixer
+      - id: trailing-whitespace
+      - id: end-of-file-fixer
 
--   repo: local
+  - repo: https://github.com/pre-commit/mirrors-clang-format
+    rev: v13.0.1
     hooks:
-    -   id: codeql-format
+      - id: clang-format
+        files: ^swift/.*\.(h|c|cpp)$
+
+  - repo: local
+    hooks:
+      - id: codeql-format
         name: Fix QL file formatting
         files: \.qll?$
         language: system
         entry: codeql query format --in-place
 
-    -   id: sync-files
+      - id: sync-files
         name: Fix files required to be identical
         language: system
         entry: python3 config/sync-files.py --latest
         pass_filenames: false
 
-    -   id: qhelp
+      - id: qhelp
         name: Check query help generation
         files: \.qhelp$
         language: system
         entry: python3 misc/scripts/check-qhelp.py
+
+      - id: swift-codegen
+        name: Run Swift checked in code generation
+        files: ^swift/(codegen/|.*/generated/|ql/lib/swift\.dbscheme$)
+        language: system
+        entry: bazel run //swift/codegen
+        pass_filenames: false