48 lines
1.9 KiB
Python
48 lines
1.9 KiB
Python
"""Custom rule demonstrating pluggable extensibility (A1b)."""
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import ast
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from typing import Optional
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from app.dataset.rules.base import Mutation, MutationRule
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class UnusedVariableRule(MutationRule):
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"""A custom rule: replace a variable read with an undefined name.
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This is intentionally simple and demonstrates that adding a new file under
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app/dataset/rules/<language>/ is enough to register a rule.
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"""
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name = "unused_variable_demo"
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language = "python"
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defect_type = "custom_demo"
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def detect_and_mutate(self, source: str, filename: str = "") -> Optional[Mutation]:
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try:
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tree = ast.parse(source)
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except SyntaxError:
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return None
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for node in ast.walk(tree):
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if isinstance(node, ast.FunctionDef) and node.body:
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first = node.body[0]
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if isinstance(first, ast.Assign) and isinstance(first.targets[0], ast.Name):
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var_name = first.targets[0].id
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line_no = first.lineno
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lines = source.splitlines(keepends=True)
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line = lines[line_no - 1]
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mutated_line = line.replace(var_name, "__undefined_" + var_name, 1)
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if mutated_line == line:
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continue
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mutated = "".join(lines[:line_no - 1] + [mutated_line] + lines[line_no:])
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return Mutation(
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defect_type=self.defect_type,
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language=self.language,
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line_start=line_no,
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line_end=line_no,
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mutated_source=mutated,
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reference_fix=f"Use the original variable name '{var_name}'.",
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description=f"Custom rule: replaced '{var_name}' with an undefined placeholder.",
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)
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return None
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