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 * @name Use of the return value of a procedure
 * @description The return value of a procedure (a function that does not return a value) is used. This is confusing to the reader as the value (None) has no meaning.
 * @kind problem
 * @tags quality
 *       maintainability
 *       readability
 * @problem.severity warning
 * @sub-severity low
 * @precision high
 * @id py/procedure-return-value-used
import python
private import LegacyPointsTo
import Testing.Mox
predicate is_used(Call c) {
  exists(Expr outer | outer != c and outer.containsInScope(c) |
    outer instanceof Call or outer instanceof Attribute or outer instanceof Subscript
  exists(Stmt s |
    c = s.getASubExpression() and
    not s instanceof ExprStmt and
    /* Ignore if a single return, as def f(): return g() is quite common. Covers implicit return in a lambda. */
    not (s instanceof Return and strictcount(Return r | r.getScope() = s.getScope()) = 1)
from Call c, FunctionValue func
  /* Call result is used, but callee is a procedure */
  is_used(c) and
  c.getFunc().(ExprWithPointsTo).pointsTo(func) and
  func.getScope().isProcedure() and
  /* All callees are procedures */
  forall(FunctionValue callee | c.getFunc().(ExprWithPointsTo).pointsTo(callee) |
    callee.getScope().isProcedure()
  /* Mox return objects have an `AndReturn` method */
  not useOfMoxInModule(c.getEnclosingModule())
select c, "The result of $@ is used even though it is always None.", func, func.getQualifiedName()

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UseImplicitNoneReturnValue.ql

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UseImplicitNoneReturnValue.ql

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