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
Download patch file Download diff file Expand all files Collapse all files

8
compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs
View file

@ -272,7 +272,7 @@ fn check_duplicate_params<'tcx>(
if let (_, [duplicate, ..]) = base_params.partition_dedup() {
let param = impl1_substs[duplicate.0 as usize];
tcx.sess
.struct_span_err(span, &format!("specializing impl repeats parameter `{}`", param))
.struct_span_err(span, format!("specializing impl repeats parameter `{}`", param))
.emit();
}
}
@ -464,7 +464,7 @@ fn check_specialization_on<'tcx>(tcx: TyCtxt<'tcx>, predicate: ty::Predicate<'tc
tcx.sess
.struct_span_err(
span,
&format!(
format!(
"cannot specialize on trait `{}`",
tcx.def_path_str(trait_ref.def_id),
),
@ -479,7 +479,7 @@ fn check_specialization_on<'tcx>(tcx: TyCtxt<'tcx>, predicate: ty::Predicate<'tc
tcx.sess
.struct_span_err(
span,
&format!("cannot specialize on associated type `{projection_ty} == {term}`",),
format!("cannot specialize on associated type `{projection_ty} == {term}`",),
)
.emit();
}
@ -495,7 +495,7 @@ fn check_specialization_on<'tcx>(tcx: TyCtxt<'tcx>, predicate: ty::Predicate<'tc
}
_ => {
tcx.sess
.struct_span_err(span, &format!("cannot specialize on predicate `{}`", predicate))
.struct_span_err(span, format!("cannot specialize on predicate `{}`", predicate))
.emit();
}
}