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Avoid copying input for identifier lookahead - #834
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identifier_colon?copied the remaining input for every identifier, causing quadratic cumulative copying. Duplicate the scanner instead, sharing its input while keeping the lookahead cursor independent.Parser#parse benchmarks, median of five runs on Ruby 4.0.6 (arm64 macOS):
Synthetic inputs use short r
NNNNN: TOKEN TOKEN;rules. Ruby's parse.y uses its standard id2token.rb preprocessing. For 16,000 rules, cumulative suffix copying drops from 8.06 GB to zero.