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/**

* @name Unreachable code

* @description Code is unreachable

* @kind problem

* @tags quality

* maintainability

* useless-code

* external/cwe/cwe-561

* @problem.severity warning

* @sub-severity low

* @precision very-high

* @id py/unreachable-statement

*/

import python

private import semmle.python.ApiGraphs

predicate typing_import(ImportingStmt is) {

exists(Module m |

is.getScope() = m and

exists(TypeHintComment tc | tc.getLocation().getFile() = m.getFile())

)

}

/** Holds if `s` contains the only `yield` in scope */

predicate unique_yield(Stmt s) {

exists(Yield y | s.contains(y)) and

exists(Function f |

f = s.getScope() and

strictcount(Yield y | f.containsInScope(y)) = 1

)

}

/** Holds if `contextlib.suppress` may be used in the same scope as `s` */

predicate suppression_in_scope(Stmt s) {

exists(With w |

w.getContextExpr() = API::moduleImport("contextlib").getMember("suppress").getACall().asExpr() and

w.getScope() = s.getScope()

)

}

/** Holds if `s` is a statement that raises an exception at the end of an if-elif-else chain. */

predicate marks_an_impossible_else_branch(Stmt s) {

exists(If i | i.getOrelse().getItem(0) = s |

s.(Assert).getTest() instanceof False

or

s instanceof Raise

)

}

predicate reportable_unreachable(Stmt s) {

s.isUnreachable() and

not typing_import(s) and

not suppression_in_scope(s) and

not exists(Stmt other | other.isUnreachable() |

other.contains(s)

or

exists(StmtList l, int i, int j | l.getItem(i) = other and l.getItem(j) = s and i < j)

) and

not unique_yield(s) and

not marks_an_impossible_else_branch(s)

}

from Stmt s

where reportable_unreachable(s)

select s, "This statement is unreachable."