Stop a backslash-newline in a string leaking to stdout - #4
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Flex's `.` never matches a newline, so `<STR>\\.` could not match a backslash escaping the end of a line. With no rule for it the backslash fell through to flex's DEFAULT ECHO rule and was printed straight to stdout -- a stray `\` on every parse of such a file, in the middle of whatever the program was writing. The newline was then picked up by the content-run rule and became part of the string. Both characters are now matched and kept verbatim in the literal. Kept rather than dropped on purpose. StringLiteral::toString() wraps the stored text in quotes to reproduce the source, so cooking escapes here would make the pretty-printer emit real newlines and quotes and corrupt the file it was formatting. Resolving escapes belongs where the literal is evaluated; this side's job is to describe the source faithfully.
This was referenced Aug 10, 2026
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Flex's
.never matches a newline, so<STR>\\.could not match a backslash escaping the end of a line. With no rule for it, the backslash fell through to flex's default ECHO rule and was printed straight to stdout — a stray\on every parse of such a file, in the middle of whatever the program was writing. The newline was then picked up by the content-run rule and became part of the string.Both characters are now matched and kept verbatim in the literal.
Why kept, not dropped
StringLiteral::toString()wraps the stored text in quotes to reproduce the source. Cooking escapes here would make the pretty-printer emit real newlines and quotes and corrupt the file it was formatting. Resolving escapes belongs where the literal is evaluated; this side's job is to describe the source faithfully.Testing
Two tests: the literal keeps
\+LF and\+CRLF verbatim, and the continued line still advances the line number (YY_USER_ACTIONcounts newlines per rule, so this comes for free — but it would be silent if it broke, and every position after a multi-line string would be one line short).632 tests pass. Negative-controlled: removing the rule fails the verbatim test, and the stray
\reappears in the test runner's own output.