[Python] Add codegen (#2507)

## Changes
Add the code generator from the bundle schema to the Python code.
Currently, it's only enabled for the "jobs" package.

There is a new GitHub action to verify that codegen is always up-to-date
whenever we update bundle schema.

Depends on #2508

## Tests
- A few unit tests
- Primarily tested by diffing output

Author: kanterov

.github/workflows/push.yml

@@ -168,3 +168,28 @@ jobs:
           for file in ./bundle/internal/schema/testdata/fail/*.yml; do
             ajv test -s schema.json -d $file --invalid -c=./keywords.js
           done
+
+  validate-python-codegen:
+    needs: cleanups
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@0c5e2b8115b80b4c7c5ddf6ffdd634974642d182 # v5.4.1
+        with:
+          version: "0.6.5"
+
+      - name: Verify that python/codegen is up to date
+        working-directory: experimental/python
+        run: |
+          make codegen
+
+          if ! ( git diff --exit-code ); then
+            echo "Generated Python code is not up-to-date. Please run 'pushd experimental/python && make codegen' and commit the changes."
+
+            # TODO block PR if this fails once diffs are fixed
+            # exit 1
+          fi

experimental/python/Makefile

@@ -16,11 +16,20 @@ lint:
 	uv run pyright
 	uv run ruff format --diff
 
+codegen:
+	find databricks -name _models | xargs rm -rf
+
+	cd codegen; uv run -m pytest codegen_tests
+	cd codegen; uv run -m codegen.main --output ..
+
+	uv run ruff check --fix $(sources) || true
+	uv run ruff format
+
 test:
 	uv run python -m pytest databricks_tests --cov=databricks.bundles --cov-report html -vv
 
 build:
 	rm -rf build dist
 	uv build .
 
-.PHONY: fmt docs lint test build
+.PHONY: fmt docs lint codegen test build

experimental/python/codegen/codegen/code_builder.py

@@ -0,0 +1,36 @@
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from typing_extensions import Self
+
+
+class CodeBuilder:
+    def __init__(self):
+        self._code = ""
+
+    def append(self, *args: str) -> "Self":
+        for arg in args:
+            self._code += arg
+
+        return self
+
+    def indent(self):
+        return self.append("    ")
+
+    def newline(self) -> "Self":
+        return self.append("\n")
+
+    def append_list(self, args: list[str], sep: str = ",") -> "Self":
+        return self.append(sep.join(args))
+
+    def append_dict(self, args: dict[str, str], sep: str = ",") -> "Self":
+        return self.append_list([f"{k}={v}" for k, v in args.items()], sep)
+
+    def append_triple_quote(self) -> "Self":
+        return self.append('"""')
+
+    def append_repr(self, value) -> "Self":
+        return self.append(repr(value))
+
+    def build(self):
+        return self._code