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/**

* @name Global shadowed by local variable

* @description Defining a local variable with the same name as a global variable

* makes the global variable unusable within the current scope and makes the code

* more difficult to read.

* @kind problem

* @tags quality

* maintainability

* readability

* correctness

* @problem.severity recommendation

* @sub-severity low

* @precision medium

* @id py/local-shadows-global

*/

import python

private import LegacyPointsTo

import Shadowing

import semmle.python.types.Builtins

predicate shadows(Name d, GlobalVariable g, Function scope, int line) {

g.getScope() = scope.getScope() and

d.getScope() = scope and

exists(LocalVariable l |

d.defines(l) and

l.getId() = g.getId()

) and

not exists(Import il, Import ig, Name gd | il.contains(d) and gd.defines(g) and ig.contains(gd)) and

not exists(Assign a | a.getATarget() = d and a.getValue() = g.getAnAccess()) and

not exists(Builtin::builtin(g.getId())) and

d.getLocation().getStartLine() = line and

exists(Name defn | defn.defines(g) | not exists(If i | i.isNameEqMain() | i.contains(defn))) and

not optimizing_parameter(d)

}

/* pytest dynamically populates its namespace so, we cannot look directly for the pytest.fixture function */

AttrNode pytest_fixture_attr() {

exists(ModuleValue pytest |

result.getObject("fixture").(ControlFlowNodeWithPointsTo).pointsTo(pytest)

)

}

Value pytest_fixture() {

exists(CallNode call |

call.getFunction() = pytest_fixture_attr()

or

call.getFunction().(CallNode).getFunction() = pytest_fixture_attr()

|

call.(ControlFlowNodeWithPointsTo).pointsTo(result)

)

}

/* pytest fixtures require that the parameter name is also a global */

predicate assigned_pytest_fixture(GlobalVariable v) {

exists(NameNode def |

def.defines(v) and

def.(DefinitionNode).getValue().(ControlFlowNodeWithPointsTo).pointsTo(pytest_fixture())

)

}

predicate first_shadowing_definition(Name d, GlobalVariable g) {

exists(int first, Scope scope |

shadows(d, g, scope, first) and

first = min(int line | shadows(_, g, scope, line))

)

}

from Name d, GlobalVariable g, Name def

where

first_shadowing_definition(d, g) and

not exists(Name n | n.deletes(g)) and

def.defines(g) and

not assigned_pytest_fixture(g) and

not g.getId() = "_"

select d, "Local variable '" + g.getId() + "' shadows a $@.", def, "global variable"