Constraints

Constraints are the part of a “full” rule that defines what condition the nodes found by a selector must satisfy. Each constraint takes a list of AST nodes and returns true if the condition is met, or false otherwise.

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Constraint Reference

is_required

Checks that the selector found at least one matching node. This is the most common constraint to enforce the presence of a required code element.

JSON `type`: "is_required"

Parameters:

Parameter	Type	Description
count	integer, optional	If provided, requires the number of found nodes to be exactly this value.

Example: Ensure that exactly one function named main was found. .. code-block:: json

“constraint”: {

“type”: “is_required”, “count”: 1

}

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is_forbidden

Checks that the selector found zero matching nodes. This is used to forbid certain language constructs or library uses.

JSON `type`: "is_forbidden" Parameters: None.

Example: Ensure that the eval function is never called. .. code-block:: json

“constraint”: { “type”: “is_forbidden” }

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must_inherit_from

Checks that a class (found by a class_def selector) inherits from a specific parent class. This works for both simple names and fully-qualified names.

JSON `type`: "must_inherit_from"

Parameters:

Parameter	Type	Description
parent_name	string, required	The expected name of the parent class (e.g., "Exception", "arcade.Window").

Example: Ensure the MyGame class inherits from arcade.Window. .. code-block:: json

“constraint”: {

“type”: “must_inherit_from”, “parent_name”: “arcade.Window”

}

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must_be_type

Checks the type of the value in an assignment statement. It works for simple literals (numbers, strings) and for calls to built-in type constructors (e.g., list(), dict()).

JSON `type`: "must_be_type"

Parameters:

Parameter	Type	Description
expected_type	string, required	The name of the required type. Supported: "str", "int", "float", "list", "dict", "bool", "set", "tuple".

Example: Ensure a global constant MAX_RETRIES is an integer. .. code-block:: json

“constraint”: {

“type”: “must_be_type”, “expected_type”: “int”

}

—

must_have_args

Checks that a function or method has a specific signature.

JSON `type`: "must_have_args"

Parameters:

Parameter	Type	Description
count	integer, optional	The exact number of required arguments (excluding self/cls).
names	list[str], optional	A list of exact argument names in the correct order.
exact_match	boolean, optional	Used with names. If false, only checks for presence, not order or exact count. Defaults to true.

Example: Ensure the __init__ method accepts width and height. .. code-block:: json

“constraint”: {

“type”: “must_have_args”, “names”: [“width”, “height”]

}

—

name_must_be_in

Checks if the name of each found node is present in an allowed list of names. Useful for restricting variable or function names.

JSON `type`: "name_must_be_in"

Parameters:

Parameter	Type	Description
allowed_names	list[str], required	A list of strings containing the allowed names.

Example: Ensure all global variables are from a pre-approved list of constants. .. code-block:: json

“constraint”: {

“type”: “name_must_be_in”, “allowed_names”: [“SCREEN_WIDTH”, “SCREEN_HEIGHT”, “TITLE”]

}

—

value_must_be_in

Checks if the value of each found literal node is in an allowed list. This is the primary tool for forbidding “magic numbers” or “magic strings”.

JSON `type`: "value_must_be_in"

Parameters:

Parameter	Type	Description
allowed_values	list, required	A list of allowed literal values (e.g., [0, 1], ["OK", "ERROR"]).

Example: Allow only specific status codes to be used as literals. .. code-block:: json

“constraint”: {

“type”: “value_must_be_in”, “allowed_values”: [200, 404, 500]

}