/**

* @name Unmatchable caret in regular expression

* @description If a caret assertion '^' appears in a regular expression after another term that

* cannot match the empty string, then this assertion can never match, so the entire

* regular expression cannot match any string.

* @kind problem

* @problem.severity error

* @id js/regex/unmatchable-caret

* @tags reliability

* correctness

* regular-expressions

* external/cwe/cwe-561

* @precision very-high

*/

import javascript

from RegExpCaret caret, RegExpTerm t

where

caret.isPartOfRegExpLiteral() and

t = caret.getPredecessor+() and

not t.isNullable() and

// conservative handling of multi-line regular expressions

not caret.getLiteral().isMultiline()

select caret, "This assertion can never match."