do

.pre-commit-config.yaml

@@ -28,3 +28,10 @@ repos:
             "--ignore=E203,W503,E501,E704",
             "--per-file-ignores=__init__.py:F401",
           ]
+  - repo: local
+    hooks:
+      - id: cyan
+        name: cyan
+        entry: poetry run cyan
+        language: python
+        files: \.(py)$

README.md

@@ -0,0 +1 @@
+# Cyan

cyan/errors.py

@@ -1,7 +1,7 @@
-import sys
+import ast
 
 
 class CyanError(Exception):
-    def __init__(self, message):
-        print(f"CyanError: {message}", file=sys.stderr)
-        super().__init__(message)
+    def __init__(self, node: ast.AST, message: str):
+        self.node = node
+        self.message = message

cyan/main.py

@@ -10,19 +10,25 @@ class AssertVisitor(ast.NodeVisitor):
     def visit_Assert(self, node: ast.Assert):
         if isinstance(node.test, ast.BoolOp) and isinstance(node.test.op, ast.And):
             raise CyanError(
-                f"Assert with 'and' found at line {node.lineno}: Use multiple asserts instead."
+                node=node,
+                message="Assert with 'and' found. Use multiple asserts instead.",
             )
         if node.msg is None:
             raise CyanError(
-                f"Assert without a message found at line {node.lineno}: Always include a message."
+                node=node,
+                message="Assert without message found.",
             )
 
 
 def check_file(filename: str):
     with open(filename, "r") as file:
         tree = ast.parse(file.read(), filename=filename)
     visitor = AssertVisitor()
-    visitor.visit(tree)
+    try:
+        visitor.visit(tree)
+    except CyanError as e:
+        print(f"{filename}:{e.node.lineno}:{e.node.col_offset}: {e.message}")
+        sys.exit(1)
 
 
 def main(argv: Optional[Sequence[str]] = None, stdin: Optional[TextIOWrapper] = None):