feat(Python)!: Python codegen raises error if formatters aren't insta…

…lled (#709)

**BREAKING CHANGE:** You must install `docformatter` and `black` to run Python codegen. Smithy-Dafny Python codegen will now raise an error when these formatters are not found. This was previously treated as a warning. This change may disrupt existing workflows that generated Python code without these formatters installed.

.github/workflows/test_models_python_tests.yml

@@ -88,6 +88,9 @@ jobs:
           arguments: :smithy-dafny-codegen:pTML
           build-root-directory: codegen
 
+      - name: Install formatters
+        run: make setup_smithy_dafny_python
+
       - name: Execute smithy-dafny-codegen-test tests
         uses: gradle/gradle-build-action@v2
         env:

README.md

@@ -71,6 +71,14 @@ See the [`codegen/smithy-dafny-codegen-cli`](codegen/smithy-dafny-codegen-cli) d
    make mvn_local_deploy_polymorph
    ```
 
+### Python
+
+1. To generate Python code with Smithy-Dafny, you must install Python libraries that format the code. Run:
+   ```
+   make setup_smithy_dafny_python
+   ```
+   The packages installed by this step must be accessible via a `bash` invocation of `python3`.
+
 ## Limitations
 
 ### Completeness

codegen/smithy-dafny-codegen-modules/smithy-python/codegen/smithy-python-codegen/src/main/java/software/amazon/smithy/python/codegen/DirectedPythonCodegen.java

@@ -346,8 +346,7 @@ private void formatCode(FileManifest fileManifest) {
         try {
             CodegenUtils.runCommand("python3 -m black -h", fileManifest.getBaseDir());
         } catch (CodegenException e) {
-            LOGGER.warning("Unable to find the python package black. Skipping formatting.");
-            return;
+            throw new CodegenException("Unable to find the python package black. Run `make setup_smithy_dafny_python` and ensure `python3 -m black` indicates the package is installed.", e);
         }
         LOGGER.info("Running code formatter on generated code");
         CodegenUtils.runCommand("python3 -m black . --exclude \"\"", fileManifest.getBaseDir());
@@ -357,8 +356,7 @@ private void formatDocstrings(FileManifest fileManifest) {
         try {
             CodegenUtils.runCommand("python3 -m docformatter -h", fileManifest.getBaseDir());
         } catch (CodegenException e) {
-            LOGGER.warning("Unable to find the python package docformatter. Skipping formatting.");
-            return;
+            throw new CodegenException("Unable to find the python package docformatter. Run `make setup_smithy_dafny_python` and ensure `python3 -m docformatter` indicates the package is installed.", e);
         }
         LOGGER.info("Running docformatter on generated code");
         // docformatter exit codes: