[[FIX]] Avoid crash when peeking past end of prog #2937
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The lexer returns `null` values when tokens are requested after all input has been consumed. Previously, the `peek` function would correctly produce the special "(end)" token in situations where the parser attempted to look beyond the end of the program. In such cases, however, it would also pollute the lookahead buffer with an invalid entry--the `null` value returned by the lexer. Future calls to `peek` could receive this buffered value. Because JSHint's internals are written with the assumption that `peek` always returns a token object, the `null` value would trigger a TypeError and subsequent program crash. Re-factor the `peek` function to only insert valid token objects into the lookahead buffer.
| t = lex.token(); | ||
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| // Peeking past the end of the program should produce the "(end)" token | ||
| // and should not extend the lookahead buffer. |
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Appreciate the explanation here
jugglinmike
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Sep 4, 2016
The lexer returns `null` values when tokens are requested after all input has been consumed. Previously, the `peek` function would correctly produce the special "(end)" token in situations where the parser attempted to look beyond the end of the program. In such cases, however, it would also pollute the lookahead buffer with an invalid entry--the `null` value returned by the lexer. Future calls to `peek` could receive this buffered value. Because JSHint's internals are written with the assumption that `peek` always returns a token object, the `null` value would trigger a TypeError and subsequent program crash. Re-factor the `peek` function to only insert valid token objects into the lookahead buffer.
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The lexer returns
nullvalues when tokens are requested after allinput has been consumed. Previously, the
peekfunction would correctlyproduce the special "(end)" token in situations where the parser
attempted to look beyond the end of the program. In such cases, however,
it would also pollute the lookahead buffer with an invalid entry--the
nullvalue returned by the lexer. Future calls topeekcould receivethis buffered value.
Because JSHint's internals are written with the assumption that
peekalways returns a token object, the
nullvalue would trigger aTypeError and subsequent program crash.
Re-factor the
peekfunction to only insert valid token objects intothe lookahead buffer.