6bed56fba9
* Modify rule S5857: Add Python as covered language * Remove unsupported possessive quantifier from rule description and compliant solutions
31 lines
1.1 KiB
Plaintext
31 lines
1.1 KiB
Plaintext
Using reluctant quantifiers (also known as lazy or non-greedy quantifiers) in patterns can often lead to needless backtracking, making the regex needlessly inefficient and potentially vulnerable to https://www.regular-expressions.info/catastrophic.html[catastrophic backtracking]. Particularly when using ``++.*?++`` or ``++.+?++`` to match anything up to some terminating character, it is usually a better idea to instead use a greedily or quantified negated character class containing the terminating character. For example ``++<.+?>++`` should be replaced with ``<[^>]*>`` or ``<[^>]+>``.
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== Noncompliant Code Example
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----
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r'<.+?>'
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r'".*?"'
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----
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== Compliant Solution
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----
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r'<[^>]+>'
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r'"[^"]*"'
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----
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== Exceptions
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This rule only applies in cases where the reluctant quantifier can easily be replaced with a negated character class. That means the repetition has to be terminated by a single character or character class. Patterns such as the following, where the alternatives without reluctant quantifiers are more complicated, are therefore not subject to this rule:
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----
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/<!--.*?-->/
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-/\*.*?\*/-
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----
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