NonLinearPattern.ql

/**
 * @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

classRootDestructuringPatternextendsDestructuringPattern{
RootDestructuringPattern(){
notthis=any(PropertyPatternp).getValuePattern()and
notthis=any(ArrayPatternp).getAnElement()
}

/** Holds if this pattern has multiple bindings for `name`. */
predicatehasConflictingBindings(stringname){
exists(VarRefv,VarRefw|
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`. */
VarDeclgetFirstClobberedVarDecl(stringname){
this.hasConflictingBindings(name)and
result=
min(VarDecldecl|
decl=this.getABindingVarRef()anddecl.getName()=name
|
declorderbydecl.getLocation().getStartLine(),decl.getLocation().getStartColumn()
)
}

/** Holds if variables in this pattern may resemble type annotations. */
predicateresemblesTypeAnnotation(){
this.hasConflictingBindings(_)and// Restrict size of predicate.
thisinstanceofParameterand
thisinstanceofObjectPatternand
notexists(this.getTypeAnnotation())and
this.getFile().getFileType().isTypeScript()
}
}

fromRootDestructuringPatternp,stringn,VarDeclv,VarDeclw,stringmessage
where
v=p.getFirstClobberedVarDecl(n)and
w=p.getABindingVarRef()and
w.getName()=nand
v!=wand
ifp.resemblesTypeAnnotation()
thenmessage="The pattern variable '"+n+"' appears to be a type, but is a variable $@."
elsemessage="Repeated binding of pattern variable '"+n+"' $@."
selectw,message,v,"previously bound"