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/**

* @name Unused global variable

* @description Global variable is defined but not used

* @kind problem

* @tags quality

* maintainability

* useless-code

* external/cwe/cwe-563

* @problem.severity recommendation

* @sub-severity low

* @precision high

* @id py/unused-global-variable

*/

import python

private import LegacyPointsTo

import Definition

/**

* Whether the module contains an __all__ definition,

* but it is more complex than a simple list of strings

*/

predicate complex_all(Module m) {

exists(Assign a, GlobalVariable all |

a.defines(all) and a.getScope() = m and all.getId() = "__all__"

|

not a.getValue() instanceof List

or

exists(Expr e | e = a.getValue().(List).getAnElt() | not e instanceof StringLiteral)

)

or

exists(Call c, GlobalVariable all |

c.getFunc().(Attribute).getObject() = all.getALoad() and

c.getScope() = m and

all.getId() = "__all__"

)

}

predicate used_in_forward_declaration(Name used, Module mod) {

exists(StringLiteral s, Annotation annotation |

s.getS() = used.getId() and

s.getEnclosingModule() = mod and

annotation.getASubExpression*() = s

)

}

predicate unused_global(Name unused, GlobalVariable v) {

not exists(ImportingStmt is | is.contains(unused)) and

forex(DefinitionNode defn | defn.getNode() = unused |

not defn.getValue().getNode() instanceof FunctionExpr and

not defn.getValue().getNode() instanceof ClassExpr and

not exists(Name u |

// A use of the variable

u.uses(v)

|

// That is reachable from this definition, directly

defn.strictlyReaches(u.getAFlowNode())

or

// indirectly

defn.getBasicBlock().reachesExit() and u.getScope() != unused.getScope()

) and

not unused.getEnclosingModule().(ModuleWithPointsTo).getAnExport() = v.getId() and

not exists(unused.getParentNode().(ClassDef).getDefinedClass().getADecorator()) and

not exists(unused.getParentNode().(FunctionDef).getDefinedFunction().getADecorator()) and

unused.defines(v) and

not name_acceptable_for_unused_variable(v) and

not complex_all(unused.getEnclosingModule())

) and

not used_in_forward_declaration(unused, unused.getEnclosingModule())

}

from Name unused, GlobalVariable v

where

unused_global(unused, v) and

// If unused is part of a tuple, count it as unused if all elements of that tuple are unused.

forall(Name el | el = unused.getParentNode().(Tuple).getAnElt() | unused_global(el, _))

select unused, "The global variable '" + v.getId() + "' is not used."