Prevent ICE when formatting an empty-ish macro arm #5833
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Fixes 5730
Previously rustfmt was attempting to slice a string with an invalid
range (`start > end`), leading to the ICE.
When formatting a macro transcriber snippet consisting of a lone
semicolon, the snippet was being formatted into the empty string,
leading the enclosing `fn main() {\n}` added by `format_code_block` to
be formatted into `fn main() {}`. However, rustfmt was assuming that the
enclosing function string's length had been left unchanged. This was
leading to an invalid range being constructed when attempting to trim
off the enclosing function.
The fix is to just clamp the range's start to be less than or equal
to the range's end, since if `end < start` there's nothing to iterate
over anyway.
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Fixes #5730
Previously rustfmt was attempting to slice a string with an invalid range (
start > end), leading to the ICE.When formatting a macro transcriber snippet consisting of a lone semicolon, the snippet was being formatted into the empty string, leading the enclosing
fn main() {\n}added byformat_code_blockto be formatted intofn main() {}. However, rustfmt was assuming that the enclosing function string's length had been left unchanged. This was leading to an invalid range being constructed when attempting to trim off the enclosing function.The fix is to just clamp the range's start to be less than or equal to the range's end, since if
end < startthere's nothing to iterate over anyway.Hi rustfmt'ers! This is my first PR to the project. I'm still not too familiar with the codebase, so hopefully I'm doing this right. Any feedback is welcome.