Overhaul char_lit() #36485
Overhaul char_lit() #36485
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| } | ||
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| let unicode_escape = || -> Option<(char, isize)> { | ||
| if lit.as_bytes()[2] == b'{' { | ||
| match lit.as_bytes()[1] as char { |
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In general I find this code a bit harder to follow than the original one, because handling of of non-escapes and escapes have been split up. Previously it was pretty obvious from (Some('\\'), Some(c)) that something of the \_ form is being handled in that branch.
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That's interesting. The old code had two matches, a local function, and a local closure, with the handling of the non-escaped case combined with the handling of some (but not all) of the escaped cases in one of the matches. I found it very messy and I had to come back to it multiple times to understand it fully. (Indeed, I had a first go at improving this function in #36414.)
In contrast, the new code handles the common non-escaped case first, and then handles all the escaped cases in a single match, with no need for local functions or closures.
BTW, do these comments constitute a proper review, or are they just "drive-by" comments? Will the commit receive attention from anybody else? It's not clear to me what I need to do now for this PR to receive r+.
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BTW, do these comments constitute a proper review, or are they just "drive-by" comments? Will the commit receive attention from anybody else?
They do constitute a proper review. Usually a bot would have commented and assigned a reviewer for you, but seems like it has bugged out for some reason.
It's not clear to me what I need to do now for this PR to receive r+.
Now that I read it again, it sort of makes sense to handle no-escape case outside of escape case.
Perhaps something like following could be better:
if first_byte == b'\\' {
/* handle escape */
} else {
/* handle non-escape case */
}so the escape handling is still tied to the \\ that is supposed to go before the escape sequence, rather than to the no-escape case like it is now.
Once you adjust the PR for error handling and making \\ thing more tied to parsing of escape sequences (in any way), I feel this PR would be in a great shape to r+.
| u32::from_str_radix(&lit[2..len], 16).ok() | ||
| .and_then(char::from_u32) | ||
| .map(|x| (x, len as isize)) | ||
| let err = |i| format!("lexer accepted invalid char literal {} step {}", lit, i); |
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I see no reason to do this as opposed to plain unwrap/expect where necessary, its just noise.
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I did it this more verbose way to match existing functions like byte_lit. I agree that it's unnecessary and I'd be happy to change it to use vanilla assert! and unwrap.
This commit does the following. - Removes parsing support for '\X12', '\u123456' and '\U12345678' char literals. These are no longer valid Rust and rejected by the lexer. (This strange-sounding situation occurs because the parser rescans char literals to compute their value.) - Rearranges the function so that all the escaped values are handled in a single `match`, and changes the error-handling to use vanilla assert!() and unwrap().
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@nagisa: I changed the error-handling to use vanilla I didn't change the structure w.r.t. the '' handling, though I did add a couple of brief comments. I left it alone because I think dealing with the common and simple case (i.e. an unescaped char) first is good, and I didn't want to introduce unnecessary rightward drift for the escaped case. If you still think this form is bad, I will change it again. |
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@bors r=nagisa |
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📌 Commit 63ded05 has been approved by |
Overhaul char_lit() This commit does the following. - Removes parsing support for '\X12', '\u123456' and '\U12345678' char literals. These are no longer valid Rust and rejected by the lexer. (This strange-sounding situation occurs because the parser rescans char literals to compute their value.) - Rearranges the function so that all the escaped values are handled in a single `match`. The error-handling strategy is based on the one used by byte_lit().
This commit does the following.
literals. These are no longer valid Rust and rejected by the lexer.
(This strange-sounding situation occurs because the parser rescans
char literals to compute their value.)
a single
match. The error-handling strategy is based on the one usedby byte_lit().