112 lines
3.7 KiB
Python
112 lines
3.7 KiB
Python
import subprocess
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from typing import Callable, Dict, List, NamedTuple, Optional, Sequence
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import bashlex
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# a function that takes a command and the environment, and returns the result
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EnvironmentExecutor = Callable[[List[str], Dict[str, str]], str]
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def local_environment_executor(command: List[str], env: Dict[str, str]) -> str:
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return subprocess.run(
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command, env=env, universal_newlines=True, stdout=subprocess.PIPE, check=True
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).stdout
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class NodeExecutionContext(NamedTuple):
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environment: Dict[str, str]
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input: str
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executor: EnvironmentExecutor
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def evaluate(
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value: str, environment: Dict[str, str], executor: Optional[EnvironmentExecutor] = None
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) -> str:
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if not value:
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# empty string evaluates to empty string
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# (but trips up bashlex)
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return ""
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command_node = bashlex.parsesingle(value)
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if len(command_node.parts) != 1:
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raise ValueError(f'"{value}" has too many parts')
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value_word_node = command_node.parts[0]
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return evaluate_node(
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value_word_node,
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context=NodeExecutionContext(
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environment=environment, input=value, executor=executor or local_environment_executor
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),
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)
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def evaluate_node(node: bashlex.ast.node, context: NodeExecutionContext) -> str:
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if node.kind == "word":
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return evaluate_word_node(node, context=context)
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elif node.kind == "commandsubstitution":
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node_result = evaluate_command_node(node.command, context=context)
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# bash removes training newlines in command substitution
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return node_result.rstrip()
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elif node.kind == "parameter":
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return evaluate_parameter_node(node, context=context)
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else:
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raise ValueError(f'Unsupported bash construct: "{node.kind}"')
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def evaluate_word_node(node: bashlex.ast.node, context: NodeExecutionContext) -> str:
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value: str = node.word
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for part in node.parts:
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part_string = context.input[part.pos[0] : part.pos[1]]
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part_value = evaluate_node(part, context=context)
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if part_string not in value:
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raise RuntimeError(
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f'bash parse failed. part "{part_string}" not found in "{value}". '
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f'Word was "{node.word}". Full input was "{context.input}"'
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)
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value = value.replace(part_string, part_value, 1)
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return value
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def evaluate_command_node(node: bashlex.ast.node, context: NodeExecutionContext) -> str:
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if any(n.kind == "operator" for n in node.parts):
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return evaluate_nodes_as_compound_command(node.parts, context=context)
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else:
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return evaluate_nodes_as_simple_command(node.parts, context=context)
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def evaluate_nodes_as_compound_command(
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nodes: Sequence[bashlex.ast.node], context: NodeExecutionContext
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) -> str:
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# bashlex doesn't support any operators besides ';' inside command
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# substitutions, so we only need to handle that case. We do so assuming
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# that `set -o errexit` is on, because it's easier to code!
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result = ""
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for node in nodes:
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if node.kind == "command":
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result += evaluate_command_node(node, context=context)
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elif node.kind == "operator":
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if node.op != ";":
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raise ValueError(f'Unsupported bash operator: "{node.op}"')
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else:
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raise ValueError(f'Unsupported bash node in compound command: "{node.kind}"')
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return result
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def evaluate_nodes_as_simple_command(
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nodes: List[bashlex.ast.node], context: NodeExecutionContext
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) -> str:
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command = [evaluate_node(part, context=context) for part in nodes]
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return context.executor(command, context.environment)
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def evaluate_parameter_node(node: bashlex.ast.node, context: NodeExecutionContext) -> str:
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return context.environment.get(node.value, "")
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