On 31.08.2019 19:45, Markus Elfring wrote:

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+# nested likely/unlikely calls
+        if ($line =~ /\b(?:(?:un)?likely)\s*\(\s*!?\s*(IS_ERR(?:_OR_NULL|_VALUE)?|WARN)/) {
+            WARN("LIKELY_MISUSE",

How do you think about to use the specification “(?:IS_ERR(?:_(?:OR_NULL|VALUE))?|WARN)”
in this regular expression?

…

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   IS_ERR
   (?:_ <- Another atomic group just to show that '_' is a common prefix?

Yes. - I hope that this specification detail can help a bit.

I'm not sure that another pair of brackets for a single char worth it.

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           Usually, Perl interpreter is very good at optimizing such things.

The interpreter optimizes it internally:
echo 'IS_ERR_OR_NULL' | perl -Mre=debug -ne '/IS_ERR(?:_OR_NULL|_VALUE)?/ && print'
Compiling REx "IS_ERR(?:_OR_NULL|_VALUE)?"
Final program:
   1: EXACT <IS_ERR> (4)
   4: CURLYX[0]{0,1} (16)
   6:   EXACT <_> (8)      <-- common prefix
   8:   TRIE-EXACT[OV] (15)
        <OR_NULL> 
        <VALUE>
...

Would you like to help this software component by omitting a pair of
non-capturing parentheses at the beginning?

\b(?:un)?likely\s*

This pair of brackets is required to match "unlikely" and it's
optional in order to match "likely".

Regards,
Denis