While trying out a patch for #33, TestLexers found this additional problem:

Lexing rust\Issue33.rs
C:\Users\Rob\source\git\scintilla-contib\lexilla\test\examples\rust\Issue33.rs:1: different styles between \r and \n at 21: 4, 0

C:\Users\Rob\source\git\scintilla-contib\lexilla\test\examples\rust\Issue33.rs:1: has different styles with \n versus \r\n line ends

SciTE (5.1.4) visually confirmed premature style switching after line comments in a file saved with Windows EOLs:

This patch attempts to correct the EOL splitting: LexRust-Fix-EOL-splitting-at-comment-ends.zip

It would be ideal to have an omnibus lexer test (e.g. "AllStyles.rs"), but I leave that for someone who knows the language better.