bjoernager/rust
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Restrict From<S> for {D,Subd}iagnosticMessage.

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Currently a `{D,Subd}iagnosticMessage` can be created from any type that
impls `Into<String>`. That includes `&str`, `String`, and `Cow<'static,
str>`, which are reasonable. It also includes `&String`, which is pretty
weird, and results in many places making unnecessary allocations for
patterns like this:
```
self.fatal(&format!(...))
```
This creates a string with `format!`, takes a reference, passes the
reference to `fatal`, which does an `into()`, which clones the
reference, doing a second allocation. Two allocations for a single
string, bleh.

This commit changes the `From` impls so that you can only create a
`{D,Subd}iagnosticMessage` from `&str`, `String`, or `Cow<'static,
str>`. This requires changing all the places that currently create one
from a `&String`. Most of these are of the `&format!(...)` form
described above; each one removes an unnecessary static `&`, plus an
allocation when executed. There are also a few places where the existing
use of `&String` was more reasonable; these now just use `clone()` at
the call site.

As well as making the code nicer and more efficient, this is a step
towards possibly using `Cow<'static, str>` in
`{D,Subd}iagnosticMessage::{Str,Eager}`. That would require changing
the `From<&'a str>` impls to `From<&'static str>`, which is doable, but
I'm not yet sure if it's worthwhile.
This commit is contained in:
Nicholas Nethercote 2023-04-20 13:26:58 +10:00
parent a368898de7
commit 6b62f37402
177 changed files with 791 additions and 787 deletions
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4
compiler/rustc_passes/src/check_const.rs
View file

@ -148,7 +148,7 @@ impl<'tcx> CheckConstVisitor<'tcx> {
[missing_primary, ref missing_secondary @ ..] => {
let msg =
format!("{} is not allowed in a `{}`", expr.name(), const_kind.keyword_name());
let mut err = feature_err(&tcx.sess.parse_sess, *missing_primary, span, &msg);
let mut err = feature_err(&tcx.sess.parse_sess, *missing_primary, span, msg);
// If multiple feature gates would be required to enable this expression, include
// them as help messages. Don't emit a separate error for each missing feature gate.
@ -161,7 +161,7 @@ impl<'tcx> CheckConstVisitor<'tcx> {
"add `#![feature({})]` to the crate attributes to enable",
gate,
);
err.help(&note);
err.help(note);
}
}