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Performance: make readDollarExpr fail early if no $

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Vidar Holen
2016-06-30 10:01:03 -07:00
parent 43c26061b9
commit 6c1abb2dee
1 changed files with 6 additions and 1 deletions
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7
ShellCheck/Parser.hs
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@@ -1328,7 +1328,12 @@ prop_readDollarExpression1 = isOk readDollarExpression "$(((1) && 3))"
prop_readDollarExpression2 = isWarning readDollarExpression "$(((1)) && 3)"
prop_readDollarExpression3 = isWarning readDollarExpression "$((\"$@\" &); foo;)"
readDollarExpression :: Monad m => SCParser m Token
readDollarExpression = arithmetic <|> readDollarExpansion <|> readDollarBracket <|> readDollarBraceCommandExpansion <|> readDollarBraced <|> readDollarVariable
readDollarExpression = do
-- The grammar should have been designed along the lines of readDollarExpr = char '$' >> stuff, but
-- instead, each subunit parses its own $. This results in ~7 1-3 char lookaheads instead of one 1-char.
-- Instead of optimizing the grammar, here's a green cut that decreases shellcheck runtime by 10%:
lookAhead $ char '$'
arithmetic <|> readDollarExpansion <|> readDollarBracket <|> readDollarBraceCommandExpansion <|> readDollarBraced <|> readDollarVariable
where
arithmetic = readAmbiguous "$((" readDollarArithmetic readDollarExpansion (\pos ->
parseNoteAt pos WarningC 1102 "Shells disambiguate $(( differently or not at all. If the first $( should start command substitution, add a space after it.")