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Add AST_GREP_PATH environment variable for custom ast-grep command paths #27

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28 changes: 28 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,9 @@ This MCP server enables AI assistants (like Cursor, Claude Desktop, etc.) to sea
brew install ast-grep
nix-shell -p ast-grep
cargo install ast-grep --locked

# Or install via uv (Python package manager)
uv add ast-grep-cli
```

2. **Install uv**: Python package manager
Expand Down Expand Up @@ -100,6 +103,31 @@ You can provide the config file in two ways (in order of precedence):
1. **Command-line argument**: `--config /path/to/sgconfig.yaml`
2. **Environment variable**: `AST_GREP_CONFIG=/path/to/sgconfig.yaml`

### Custom ast-grep Command Path

If ast-grep is not in your PATH or you need to run it with a wrapper command (e.g., via `uv`), you can configure the command using the `AST_GREP_PATH` environment variable:

```json
{
"mcpServers": {
"ast-grep": {
"command": "uv",
"args": ["--directory", "/absolute/path/to/ast-grep-mcp", "run", "main.py"],
"env": {
"AST_GREP_PATH": "uv run ast-grep"
}
}
}
}
```

**Examples:**
- `AST_GREP_PATH="uv run ast-grep"` - Run ast-grep via uv
- `AST_GREP_PATH="/custom/path/to/ast-grep"` - Use ast-grep from a custom location
- `AST_GREP_PATH="npx ast-grep"` - Run ast-grep via npx

If not set, defaults to `ast-grep` (expects ast-grep to be in PATH).

## Usage

This repository includes comprehensive ast-grep rule documentation in [ast-grep.mdc](https://github.com/ast-grep/ast-grep-mcp/blob/main/ast-grep.mdc). The documentation covers all aspects of writing effective ast-grep rules, from simple patterns to complex multi-condition searches.
Expand Down
19 changes: 16 additions & 3 deletions main.py
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Expand Up @@ -39,11 +39,12 @@ def sigterm_handler(signum, frame):
CONFIG_PATH = None
TRANSPORT_TYPE = "stdio"
SERVER_PORT = 8000
AST_GREP_COMMAND = None


def parse_args_and_get_config():
"""Parse command-line arguments and determine config path and transport."""
global CONFIG_PATH, TRANSPORT_TYPE, SERVER_PORT
global CONFIG_PATH, TRANSPORT_TYPE, SERVER_PORT, AST_GREP_COMMAND

# Determine how the script was invoked
prog = None
Expand All @@ -58,6 +59,7 @@ def parse_args_and_get_config():
epilog="""
environment variables:
AST_GREP_CONFIG Path to sgconfig.yaml file (overridden by --config flag)
AST_GREP_PATH Custom command to run ast-grep (e.g., 'uv run ast-grep')

For more information, see: https://github.com/ast-grep/ast-grep-mcp
""",
Expand Down Expand Up @@ -92,6 +94,9 @@ def parse_args_and_get_config():
sys.exit(1)
CONFIG_PATH = env_config

# Determine ast-grep command from AST_GREP_PATH env variable
AST_GREP_COMMAND = os.environ.get("AST_GREP_PATH", "ast-grep")


# Initialize FastMCP server
mcp = FastMCP("ast-grep")
Expand Down Expand Up @@ -345,7 +350,14 @@ def run_command(args: List[str], input_text: Optional[str] = None) -> subprocess
try:
# On Windows, if ast-grep is installed via npm, it's a batch file
# that requires shell=True to execute properly
use_shell = sys.platform == "win32" and args[0] == "ast-grep"
# Also use shell if the command contains spaces (e.g., "uv run ast-grep")
use_shell = sys.platform == "win32" and args[0] in ("ast-grep", AST_GREP_COMMAND)
if not use_shell and len(args) > 0 and " " in args[0]:
# Command has spaces, need to split it into separate arguments
use_shell = False
split_cmd = args[0].split()
args = split_cmd + args[1:]

need_check = len(args) < 2 or args[1] != "run"

result = subprocess.run(
Expand Down Expand Up @@ -390,7 +402,8 @@ def run_command(args: List[str], input_text: Optional[str] = None) -> subprocess
def run_ast_grep(command: str, args: List[str], input_text: Optional[str] = None) -> subprocess.CompletedProcess:
if CONFIG_PATH:
args = ["--config", CONFIG_PATH] + args
return run_command(["ast-grep", command] + args, input_text)
ast_grep_cmd = AST_GREP_COMMAND or "ast-grep"
return run_command([ast_grep_cmd, command] + args, input_text)


def run_mcp_server() -> None:
Expand Down
38 changes: 38 additions & 0 deletions tests/test_unit.py
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Expand Up @@ -355,6 +355,7 @@ class TestRunAstGrep:

@patch("main.run_command")
@patch("main.CONFIG_PATH", None)
@patch("main.AST_GREP_COMMAND", None)
def test_without_config(self, mock_run):
"""Test running ast-grep without config"""
mock_result = Mock()
Expand All @@ -367,6 +368,7 @@ def test_without_config(self, mock_run):

@patch("main.run_command")
@patch("main.CONFIG_PATH", "/path/to/config.yaml")
@patch("main.AST_GREP_COMMAND", None)
def test_with_config(self, mock_run):
"""Test running ast-grep with config"""
mock_result = Mock()
Expand All @@ -387,6 +389,42 @@ def test_with_config(self, mock_run):
None,
)

@patch("main.run_command")
@patch("main.CONFIG_PATH", None)
@patch("main.AST_GREP_COMMAND", "uv run ast-grep")
def test_with_custom_command(self, mock_run):
"""Test running ast-grep with custom command path"""
mock_result = Mock()
mock_run.return_value = mock_result

result = run_ast_grep("run", ["--pattern", "test"])

assert result == mock_result
mock_run.assert_called_once_with(["uv run ast-grep", "run", "--pattern", "test"], None)

@patch("main.run_command")
@patch("main.CONFIG_PATH", "/path/to/config.yaml")
@patch("main.AST_GREP_COMMAND", "/custom/path/to/ast-grep")
def test_with_config_and_custom_command(self, mock_run):
"""Test running ast-grep with both config and custom command"""
mock_result = Mock()
mock_run.return_value = mock_result

result = run_ast_grep("scan", ["--inline-rules", "rule"])

assert result == mock_result
mock_run.assert_called_once_with(
[
"/custom/path/to/ast-grep",
"scan",
"--config",
"/path/to/config.yaml",
"--inline-rules",
"rule",
],
None,
)


if __name__ == "__main__":
pytest.main([__file__, "-v"])
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