fix: add import message via synth

Closes #227.
Closes #228.
Closes #229.

scripts/fixup_firestore_admin_v1_keywords.py

@@ -20,9 +20,10 @@
 
 try:
     import libcst as cst
-except ImportError as exception:
+except ImportError:
     raise ImportError('Run `python -m pip install "libcst >= 0.2.5"` to install libcst.')
 
+
 import pathlib
 import sys
 from typing import (Any, Callable, Dict, List, Sequence, Tuple)

scripts/fixup_firestore_v1_keywords.py

@@ -20,9 +20,10 @@
 
 try:
     import libcst as cst
-except ImportError as exception:
+except ImportError:
     raise ImportError('Run `python -m pip install "libcst >= 0.2.5"` to install libcst.')
 
+
 import pathlib
 import sys
 from typing import (Any, Callable, Dict, List, Sequence, Tuple)

synth.py

@@ -173,6 +173,24 @@ def lint_setup_py(session):
     """"mock", "pytest", "pytest-asyncio", "google-cloud-testutils",""",
 )
 
+
+# Add message for missing 'libcst' dependency
+s.replace(
+    "scripts/fixup*.py",
+    """\
+import libcst as cst
+""",
+    """\
+
+try:
+    import libcst as cst
+except ImportError:
+    raise ImportError('Run `python -m pip install "libcst >= 0.2.5"` to install libcst.')
+
+
+""",
+)
+
 s.shell.run(["nox", "-s", "blacken"], hide_output=False)
 
 s.replace(