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55b6f649024b372af901b3412a6d36c4284ccf3d
rust/tests/ui/proc-macro/auxiliary/issue-79242.rs

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Cache pretty-print/retokenize result to avoid compile time blowup Fixes #79242 If a `macro_rules!` recursively builds up a nested nonterminal (passing it to a proc-macro at each step), we will end up repeatedly pretty-printing/retokenizing the same nonterminals. Unfortunately, the 'probable equality' check we do has a non-trivial cost, which leads to a blowup in compilation time. As a workaround, we cache the result of the 'probable equality' check, which eliminates the compilation time blowup for the linked issue. This commit only touches a single file (other than adding tests), so it should be easy to backport. The proper solution is to remove the pretty-print/retokenize hack entirely. However, this will almost certainly break a large number of crates that were relying on hygiene bugs created by using the reparsed `TokenStream`. As a result, we will definitely not want to backport such a change.
2020-11-23 00:32:51 -05:00
// force-host
// no-prefer-dynamic
#![crate_type = "proc-macro"]
extern crate proc_macro;
use proc_macro::TokenStream;
#[proc_macro]
pub fn dummy(input: TokenStream) -> TokenStream {
// Iterate to force internal conversion of nonterminals
// to `proc_macro` structs
for _ in input {}
TokenStream::new()
}
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