Modify `AttributeTemplate` to support list of alternatives for list and name value attribute styles.
Suggestions now provide more correct suggested code:
```
error[E0805]: malformed `used` attribute input
--> $DIR/used_with_multi_args.rs:3:1
|
LL | #[used(compiler, linker)]
| ^^^^^^------------------^
| |
| expected a single argument here
|
help: try changing it to one of the following valid forms of the attribute
|
LL - #[used(compiler, linker)]
LL + #[used(compiler)]
|
LL - #[used(compiler, linker)]
LL + #[used(linker)]
|
LL - #[used(compiler, linker)]
LL + #[used]
|
```
instead of the prior "masking" of the lack of this feature by suggesting pipe-separated lists:
```
error[E0805]: malformed `used` attribute input
--> $DIR/used_with_multi_args.rs:3:1
|
LL | #[used(compiler, linker)]
| ^^^^^^------------------^
| |
| expected a single argument here
|
help: try changing it to one of the following valid forms of the attribute
|
LL - #[used(compiler, linker)]
LL + #[used(compiler|linker)]
|
LL - #[used(compiler, linker)]
LL + #[used]
|
```
I'm removing empty identifiers everywhere, because in practice they
always mean "no identifier" rather than "empty identifier". (An empty
identifier is impossible.) It's better to use `Option` to mean "no
identifier" because you then can't forget about the "no identifier"
possibility.
Some specifics:
- When testing an attribute for a single name, the commit uses the
`has_name` method.
- When testing an attribute for multiple names, the commit uses the new
`has_any_name` method.
- When using `match` on an attribute, the match arms now have `Some` on
them.
In the tests, we now avoid printing empty identifiers by not printing
the identifier in the `error:` line at all, instead letting the carets
point out the problem.
`rustc_span::symbol` defines some things that are re-exported from
`rustc_span`, such as `Symbol` and `sym`. But it doesn't re-export some
closely related things such as `Ident` and `kw`. So you can do `use
rustc_span::{Symbol, sym}` but you have to do `use
rustc_span::symbol::{Ident, kw}`, which is inconsistent for no good
reason.
This commit re-exports `Ident`, `kw`, and `MacroRulesNormalizedIdent`,
and changes many `rustc_span::symbol::` qualifiers in `compiler/` to
`rustc_span::`. This is a 200+ net line of code reduction, mostly
because many files with two `use rustc_span` items can be reduced to
one.
