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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8
compiler/rustc_builtin_macros/src/asm.rs
View file

@ -553,7 +553,7 @@ fn expand_preparsed_asm(ecx: &mut ExtCtxt<'_>, args: AsmArgs) -> Option<ast::Inl
let mut e = ecx.struct_span_err(err_sp, msg);
e.span_label(err_sp, err.label + " in asm template string");
if let Some(note) = err.note {
e.note(&note);
e.note(note);
}
if let Some((label, span)) = err.secondary_label {
let err_sp = template_span.from_inner(InnerSpan::new(span.start, span.end));
@ -600,7 +600,7 @@ fn expand_preparsed_asm(ecx: &mut ExtCtxt<'_>, args: AsmArgs) -> Option<ast::Inl
1 => format!("there is 1 {}argument", positional),
x => format!("there are {} {}arguments", x, positional),
};
err.note(&msg);
err.note(msg);
if named_pos.contains_key(&idx) {
err.span_label(args.operands[idx].1, "named argument");
@ -703,7 +703,7 @@ fn expand_preparsed_asm(ecx: &mut ExtCtxt<'_>, args: AsmArgs) -> Option<ast::Inl
let (sp, msg) = unused_operands.into_iter().next().unwrap();
let mut err = ecx.struct_span_err(sp, msg);
err.span_label(sp, msg);
err.help(&format!(
err.help(format!(
"if this argument is intentionally unused, \
consider using it in an asm comment: `\"/*{} */\"`",
help_str
@ -718,7 +718,7 @@ fn expand_preparsed_asm(ecx: &mut ExtCtxt<'_>, args: AsmArgs) -> Option<ast::Inl
for (sp, msg) in unused_operands {
err.span_label(sp, msg);
}
err.help(&format!(
err.help(format!(
"if these arguments are intentionally unused, \
consider using them in an asm comment: `\"/*{} */\"`",
help_str