UnreachableStatement.ql

/**
 * @name Unreachable statement
 * @description Unreachable statements are often indicative of missing code or latent bugs and should be avoided.
 * @kind problem
 * @problem.severity warning
 * @id js/unreachable-statement
 * @tags maintainability
 *       correctness
 *       external/cwe/cwe-561
 * @precision very-high
 */

import javascript
import semmle.javascript.RestrictedLocations

from Stmt s
where // `s` is unreachable in the CFG
      s.getFirstControlFlowNode().isUnreachable() and
      // the CFG does not model all possible exceptional control flow, so be conservative about catch clauses
      not s instanceof CatchClause and
      // function declarations are special and always reachable
      not s instanceof FunctionDeclStmt and
      // allow a spurious 'break' statement at the end of a switch-case
      not exists(Case c, int i | i = c.getNumBodyStmt() | (BreakStmt)s = c.getBodyStmt(i-1)) and
      // ignore ambient statements
      not s.isAmbient() and
      // ignore empty statements
      not s instanceof EmptyStmt
select (FirstLineOf)s, "This statement is unreachable."