/**
 * @name Non-linear pattern
 * @description If the same pattern variable appears twice in an array or object pattern,
 * the second binding will silently overwrite the first binding, which is probably
 * unintentional.
 * @kind problem
 * @problem.severity error
 * @id js/non-linear-pattern
 * @tags reliability
 * correctness
 * language-features
 * @precision very-high
 */

import javascript

class RootDestructuringPattern extends DestructuringPattern {
 RootDestructuringPattern() {
 not this = any(PropertyPattern p).getValuePattern() and
 not this = any(ArrayPattern p).getAnElement()
 }

 /** Holds if this pattern has multiple bindings for `name`. */
 predicate hasConflictingBindings(string name) {
 exists(VarRef v, VarRef w |
 v = this.getABindingVarRef() and
 w = this.getABindingVarRef() and
 name = v.getName() and
 name = w.getName() and
 v != w
 )
 }

 /** Gets the first occurrence of the conflicting binding `name`. */
 VarDecl getFirstClobberedVarDecl(string name) {
 this.hasConflictingBindings(name) and
 result =
 min(VarDecl decl |
 decl = this.getABindingVarRef() and decl.getName() = name
 |
 decl order by decl.getLocation().getStartLine(), decl.getLocation().getStartColumn()
 )
 }

 /** Holds if variables in this pattern may resemble type annotations. */
 predicate resemblesTypeAnnotation() {
 this.hasConflictingBindings(_) and // Restrict size of predicate.
 this instanceof Parameter and
 this instanceof ObjectPattern and
 not exists(this.getTypeAnnotation()) and
 this.getFile().getFileType().isTypeScript()
 }
}

from RootDestructuringPattern p, string n, VarDecl v, VarDecl w, string message
where
 v = p.getFirstClobberedVarDecl(n) and
 w = p.getABindingVarRef() and
 w.getName() = n and
 v != w and
 if p.resemblesTypeAnnotation()
 then message = "The pattern variable '" + n + "' appears to be a type, but is a variable $@."
 else message = "Repeated binding of pattern variable '" + n + "' $@."
select w, message, v, "previously bound"