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codeql/javascript/ql/src/RegExp/UnmatchableCaret.ql

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/**
* @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."