Use an enum for keywords and intern them to improve parser performance#6737

dotdash · 2013-05-25T15:59:47Z

Currently, keywords are stored in hashsets that are recreated for every
Parser instance, which is quite expensive since macro expansion creates
lots of them. Additionally, the parser functions that look for a keyword
currently accept a string and have a runtime check to validate that they
actually received a keyword.

By creating an enum for the keywords and inserting them into the
ident interner, we can avoid the creation of the hashsets and get static
checks for the keywords.

For libstd, this cuts the parse+expansion part from ~2.6s to ~1.6s.

Currently, keywords are stored in hashsets that are recreated for every Parser instance, which is quite expensive since macro expansion creates lots of them. Additionally, the parser functions that look for a keyword currently accept a string and have a runtime check to validate that they actually received a keyword. By creating an enum for the keywords and inserting them into the ident interner, we can avoid the creation of the hashsets and get static checks for the keywords. For libstd, this cuts the parse+expansion part from ~2.6s to ~1.6s.

Downgrade option_if_let_else to nursery I believe that this lint's loose understanding of ownership (rust-lang#5822, rust-lang#6737) makes it unsuitable to be enabled by default in its current state, even as a pedantic lint. Additionally the lint has known problems with type inference (rust-lang#6137), though I may be willing to consider this a non-blocker in isolation if it weren't for the ownership false positives. A fourth false positive involving const fn: rust-lang#7567. But on top of these, for me the biggest issue is I basically fully agree with rust-lang/rust-clippy#6137 (comment). In my experience this lint universally makes code worse even when the resulting code does compile. --- changelog: remove [`option_if_let_else`] from default set of enabled lints

Fix `option_if_let_else` fixes: rust-lang#5822 fixes: rust-lang#6737 fixes: rust-lang#7567 The inference from rust-lang#6137 still exists so I'm not sure if this should be moved from the nursery. Before doing that though I'd almost want to see this split into two lints. One suggesting `map_or` and the other suggesting `map_or_else`. `map_or_else` tends to have longer expressions for both branches so it doesn't end up much shorter than a match expression in practice. It also seems most people find it harder to read. `map_or` at least has the terseness benefit of being on one line most of the time, especially when the `None` branch is just a literal or path expression. changelog: `break` and `continue` statments local to the would-be closure are allowed in `option_if_let_else` changelog: don't lint in const contexts in `option_if_let_else` changelog: don't lint when yield expressions are used in `option_if_let_else` changelog: don't lint when the captures made by the would-be closure conflict with the other branch in `option_if_let_else` changelog: don't lint when a field of a local is used when the type could be pontentially moved from in `option_if_let_else` changelog: in some cases, don't lint when scrutinee expression conflicts with the captures of the would-be closure in `option_if_let_else`

bors closed this May 25, 2013

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Use an enum for keywords and intern them to improve parser performance#6737