From 781111ef3591e4355c115593c4d75964b85555d6 Mon Sep 17 00:00:00 2001 From: Nicholas Nethercote Date: Thu, 4 May 2023 10:55:21 +1000 Subject: Use `Cow` in `{D,Subd}iagnosticMessage`. Each of `{D,Subd}iagnosticMessage::{Str,Eager}` has a comment: ``` // FIXME(davidtwco): can a `Cow<'static, str>` be used here? ``` This commit answers that question in the affirmative. It's not the most compelling change ever, but it might be worth merging. This requires changing the `impl<'a> From<&'a str>` impls to `impl From<&'static str>`, which involves a bunch of knock-on changes that require/result in call sites being a little more precise about exactly what kind of string they use to create errors, and not just `&str`. This will result in fewer unnecessary allocations, though this will not have any notable perf effects given that these are error paths. Note that I was lazy within Clippy, using `to_string` in a few places to preserve the existing string imprecision. I could have used `impl Into<{D,Subd}iagnosticMessage>` in various places as is done in the compiler, but that would have required changes to *many* call sites (mostly changing `&format("...")` to `format!("...")`) which didn't seem worthwhile. --- compiler/rustc_parse/src/parser/stmt.rs | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) (limited to 'compiler/rustc_parse/src/parser') diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs index 54f9fc5d2b9..9fcf51a04ec 100644 --- a/compiler/rustc_parse/src/parser/stmt.rs +++ b/compiler/rustc_parse/src/parser/stmt.rs @@ -23,6 +23,7 @@ use rustc_errors::{Applicability, DiagnosticBuilder, ErrorGuaranteed, PResult}; use rustc_span::source_map::{BytePos, Span}; use rustc_span::symbol::{kw, sym, Ident}; +use std::borrow::Cow; use std::mem; use thin_vec::{thin_vec, ThinVec}; @@ -364,7 +365,7 @@ impl<'a> Parser<'a> { // `let...else if`. Emit the same error that `parse_block()` would, // but explicitly point out that this pattern is not allowed. let msg = "conditional `else if` is not supported for `let...else`"; - return Err(self.error_block_no_opening_brace_msg(msg)); + return Err(self.error_block_no_opening_brace_msg(Cow::from(msg))); } let els = self.parse_block()?; self.check_let_else_init_bool_expr(&init); @@ -438,7 +439,7 @@ impl<'a> Parser<'a> { fn error_block_no_opening_brace_msg( &mut self, - msg: &str, + msg: Cow<'static, str>, ) -> DiagnosticBuilder<'a, ErrorGuaranteed> { let sp = self.token.span; let mut e = self.struct_span_err(sp, msg); @@ -502,7 +503,7 @@ impl<'a> Parser<'a> { fn error_block_no_opening_brace(&mut self) -> PResult<'a, T> { let tok = super::token_descr(&self.token); let msg = format!("expected `{{`, found {}", tok); - Err(self.error_block_no_opening_brace_msg(&msg)) + Err(self.error_block_no_opening_brace_msg(Cow::from(msg))) } /// Parses a block. Inner attributes are allowed. -- cgit 1.4.1-3-g733a5