- Rename `ast::Lit::token` as `ast::Lit::token_lit`, because its type is
`token::Lit`, which is not a token. (This has been confusing me for a
long time.)
reasonable because we have an `ast::token::Lit` inside an `ast::Lit`.
- Rename `LitKind::{from,to}_lit_token` as
`LitKind::{from,to}_token_lit`, to match the above change and
`token::Lit`.
Adjust span of fn argument declaration
Span of a fn argument declaration goes from:
```
fn foo(i : i32 , ...)
^^^^^^^^
```
to:
```
fn foo(i : i32 , ...)
^^^^^^^
```
That is, we don't include the extra spacing up to the trailing comma, which I think is more correct.
cc https://github.com/rust-lang/rust/pull/99646#discussion_r944568074
r? ``@estebank``
---
The two tests that had dramatic changes in their rendering I think actually are improved, though they are kinda poor spans both before and after the changes. 🤷 Thoughts?
`Parser::parse_bottom_expr` currently constructs an empty `attrs` and
then passes it to a large number of other functions. This makes the code
harder to read than it should be, because it's not clear that many
`attrs` arguments are always empty.
This commit removes `attrs` and the passing, simplifying a lot of
functions. The commit also renames `Parser::mk_expr` (which takes an
`attrs` argument) as `mk_expr_with_attrs`, and introduces a new
`mk_expr` which creates an expression with no attributes, which is the
more common case.
Stringify non-shorthand visibility correctly
This makes `stringify!(pub(in crate))` evaluate to `pub(in crate)` rather than `pub(crate)`, matching the behavior before the `crate` shorthand was removed. Further, this changes `stringify!(pub(in super))` to evaluate to `pub(in super)` rather than the current `pub(super)`. If the latter is not desired (it is _technically_ breaking), it can be undone.
Fixes#99981
`@rustbot` label +C-bug +regression-from-stable-to-beta +T-compiler
Use `&mut Diagnostic` instead of `&mut DiagnosticBuilder` unless needed
This seems to be the established convention (02ff9e0) when `DiagnosticBuilder` was first added. I am guilty of introducing some of these.
Improve diagnostics for `const a: = expr;`
Adds a suggestion to write a type when there is a colon, but the type is not present.
I've also shrunk spans a little, so the suggestions are a little nicer.
Resolves#100146
r? `@compiler-errors`
Use Parser's `restrictions` instead of `let_expr_allowed`
This also means that the `ALLOW_LET` flag is reset properly for subexpressions, so we can properly deny things like `a && (b && let c = d)`. Also the parser is a tiny bit smaller now.
It doesn't reject _all_ bad `let` expr usages, just a bit more.
cc `@c410-f3r`
Rollup of 5 pull requests
Successful merges:
- #99311 (change maybe_body_owned_by to take local def id)
- #99862 (Improve type mismatch w/ function signatures)
- #99895 (don't call type ascription "cast")
- #99900 (remove some manual hash stable impls)
- #99903 (Add diagnostic when using public instead of pub)
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
Add diagnostic when using public instead of pub
Forwarding from https://github.com/rust-lang/rust/pull/99706
I accidentally broke something(??) in git and the commits in that PR are absolutely not what I did in that branch
Anyways, this is the PR for this now. Adding tests again in a minute.
cc `@davidtwco`
Remove `TreeAndSpacing`.
A `TokenStream` contains a `Lrc<Vec<(TokenTree, Spacing)>>`. But this is
not quite right. `Spacing` makes sense for `TokenTree::Token`, but does
not make sense for `TokenTree::Delimited`, because a
`TokenTree::Delimited` cannot be joined with another `TokenTree`.
This commit fixes this problem, by adding `Spacing` to `TokenTree::Token`,
changing `TokenStream` to contain a `Lrc<Vec<TokenTree>>`, and removing the
`TreeAndSpacing` typedef.
The commit removes these two impls:
- `impl From<TokenTree> for TokenStream`
- `impl From<TokenTree> for TreeAndSpacing`
These were useful, but also resulted in code with many `.into()` calls
that was hard to read, particularly for anyone not highly familiar with
the relevant types. This commit makes some other changes to compensate:
- `TokenTree::token()` becomes `TokenTree::token_{alone,joint}()`.
- `TokenStream::token_{alone,joint}()` are added.
- `TokenStream::delimited` is added.
This results in things like this:
```rust
TokenTree::token(token::Semi, stmt.span).into()
```
changing to this:
```rust
TokenStream::token_alone(token::Semi, stmt.span)
```
This makes the type of the result, and its spacing, clearer.
These changes also simplifies `Cursor` and `CursorRef`, because they no longer
need to distinguish between `next` and `next_with_spacing`.
r? `@petrochenkov`
A `TokenStream` contains a `Lrc<Vec<(TokenTree, Spacing)>>`. But this is
not quite right. `Spacing` makes sense for `TokenTree::Token`, but does
not make sense for `TokenTree::Delimited`, because a
`TokenTree::Delimited` cannot be joined with another `TokenTree`.
This commit fixes this problem, by adding `Spacing` to `TokenTree::Token`,
changing `TokenStream` to contain a `Lrc<Vec<TokenTree>>`, and removing the
`TreeAndSpacing` typedef.
The commit removes these two impls:
- `impl From<TokenTree> for TokenStream`
- `impl From<TokenTree> for TreeAndSpacing`
These were useful, but also resulted in code with many `.into()` calls
that was hard to read, particularly for anyone not highly familiar with
the relevant types. This commit makes some other changes to compensate:
- `TokenTree::token()` becomes `TokenTree::token_{alone,joint}()`.
- `TokenStream::token_{alone,joint}()` are added.
- `TokenStream::delimited` is added.
This results in things like this:
```rust
TokenTree::token(token::Semi, stmt.span).into()
```
changing to this:
```rust
TokenStream::token_alone(token::Semi, stmt.span)
```
This makes the type of the result, and its spacing, clearer.
These changes also simplifies `Cursor` and `CursorRef`, because they no longer
need to distinguish between `next` and `next_with_spacing`.
Implement `for<>` lifetime binder for closures
This PR implements RFC 3216 ([TI](https://github.com/rust-lang/rust/issues/97362)) and allows code like the following:
```rust
let _f = for<'a, 'b> |a: &'a A, b: &'b B| -> &'b C { b.c(a) };
// ^^^^^^^^^^^--- new!
```
cc ``@Aaron1011`` ``@cjgillot``
diagnostics: error messages when struct literals fail to parse
If an expression is supplied where a field is expected, the parser can become convinced that it's a shorthand field syntax when it's not.
This PR addresses it by explicitly recording the permitted `:` token immediately after the identifier, and also adds a suggestion to insert the name of the field if it looks like a complex expression.
Fixes#98917
Fix last `let_chains` blocker
In order to forbid things like `let x = (let y = 1);` or `if let a = 1 && { let x = let y = 1; } {}`, the parser **HAS** to know the context of `let`.
This context thing is not a surprise in the parser because you can see **a lot** of ad hoc fixes mixing parsing logic with validation logic creating code that looks more like spaghetti with tomato sauce.
To make things even greater, a new ad hoc fix was added to only allow `let`s in a valid `let_chains` context by checking the previously processed token. This was the only solution I could think of and believe me, I thought about it for a long time 👍
In the long term, it should be preferable to segregate different responsibilities or create a more robust and cleaner parser framework.
cc https://github.com/rust-lang/rust/pull/94927
cc https://github.com/rust-lang/rust/issues/53667
Use less string interning
This removes string interning in a couple of places where doing so won't result in perf improvements. I also switched one place to use pre-interned symbols.
Avoid some `&str` to `String` conversions with `MultiSpan::push_span_label`
This patch removes some`&str` to `String` conversions with `MultiSpan::push_span_label`.
The `rustc_lint_diagnostics` attribute is used by the diagnostic
translation/struct migration lints to identify calls where
non-translatable diagnostics or diagnostics outwith impls are being
created. Any function used in creating a diagnostic should be annotated
with this attribute so this commit adds the attribute to many more
functions.
Signed-off-by: David Wood <david.wood@huawei.com>
macros: use typed identifiers in diag and subdiag derive
Using typed identifiers instead of strings with the Fluent identifiers in the diagnostic and subdiagnostic derives - this enables the diagnostic derive to benefit from the compile-time validation that comes with typed identifiers, namely that use of a non-existent Fluent identifier will not compile.
r? `````@oli-obk`````
As in the diagnostic derive, using typed identifiers in the
subdiagnostic derive improves the diagnostics of using the subdiagnostic
derive as Fluent messages will be confirmed to exist at compile-time.
Signed-off-by: David Wood <david.wood@huawei.com>
Using typed identifiers instead of strings with the Fluent identifier
enables the diagnostic derive to benefit from the compile-time
validation that comes with typed identifiers - use of a non-existent
Fluent identifier will not compile.
Signed-off-by: David Wood <david.wood@huawei.com>
Fix pretty printing of empty bound lists in where-clause
Repro:
```rust
macro_rules! assert_item_stringify {
($item:item $expected:literal) => {
assert_eq!(stringify!($item), $expected);
};
}
fn main() {
assert_item_stringify! {
fn f<'a, T>() where 'a:, T: {}
"fn f<'a, T>() where 'a:, T: {}"
}
}
```
Previously this assertion would fail because rustc renders the where-clause as `where 'a, T` which is invalid syntax.
This PR makes the above assertion pass.
This bug also affects `-Zunpretty=expanded`. The intention is for that to emit syntactically valid code, but the buggy output is not valid Rust syntax.
```console
$ rustc <(echo "fn f<'a, T>() where 'a:, T: {}") -Zunpretty=expanded
#![feature(prelude_import)]
#![no_std]
#[prelude_import]
use ::std::prelude::rust_2015::*;
#[macro_use]
extern crate std;
fn f<'a, T>() where 'a, T {}
```
```console
$ rustc <(echo "fn f<'a, T>() where 'a:, T: {}") -Zunpretty=expanded | rustc -
error: expected `:`, found `,`
--> <anon>:7:23
|
7 | fn f<'a, T>() where 'a, T {}
| ^ expected `:`
```
Improve parser diagnostics
This pr fixes https://github.com/rust-lang/rust/issues/93867 and contains a couple of diagnostics related changes to the parser.
Here is a short list with some of the changes:
- don't suggest the same thing that is the current token
- suggest removing the current token if the following token is one of the suggestions (maybe incorrect)
- tell the user to put a type or lifetime after where if there is none (as a warning)
- reduce the amount of tokens suggested (via the new eat_noexpect and check_noexpect methods)
If any of these changes are undesirable, i can remove them, thanks!
Recover missing comma after match arm
If we're missing a comma after a match arm expression, try parsing another pattern and a following `=>`. If we find both of those, then recover by suggesting to insert a `,`.
Fixes#80112
Move conditions out of recover/report functions.
`Parser` has six recover/report functions that are passed a boolean, and
nothing is done if the boolean has a particular value.
This PR moves the tests outside the functions. This has the following effects.
- The number of lines of code goes down.
- Some `use` items become shorter.
- Avoids the strangeness whereby 11 out of 12 calls to
`maybe_recover_from_bad_qpath` pass `true` as the second argument.
- Makes it clear at the call site that only one of
`maybe_recover_from_bad_type_plus` and `maybe_report_ambiguous_plus` will be
run.
r? `@estebank`
Rollup of 6 pull requests
Successful merges:
- #89685 (refactor: VecDeques Iter fields to private)
- #97172 (Optimize the diagnostic generation for `extern unsafe`)
- #97395 (Miri call ABI check: ensure type size+align stay the same)
- #97431 (don't do `Sized` and other return type checks on RPIT's real type)
- #97555 (Source code page: line number click adds `NaN`)
- #97558 (Fix typos in comment)
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
Optimize the diagnostic generation for `extern unsafe`
This PR does the following about diagnostic generation when parsing foreign mod:
1. Fixes the FIXME about avoiding depending on the error message text.
2. Continue parsing when `unsafe` is followed by `{` (just like `unsafe extern {...}`).
3. Add test case.
To render the message of a Fluent attribute, the identifier of the
Fluent message must be known. `DiagnosticMessage::FluentIdentifier`
contains both the message's identifier and optionally the identifier of
an attribute. Generated constants for each attribute would therefore
need to be named uniquely (amongst all error messages) or be able to
refer to only the attribute identifier which will be combined with a
message identifier later. In this commit, the latter strategy is
implemented as part of the `Diagnostic` type's functions for adding
subdiagnostics of various kinds.
Signed-off-by: David Wood <david.wood@huawei.com>
Parse expression after `else` as a condition if followed by `{`
Fixes#49361.
Two things:
1. This wording needs help. I can never find a natural/intuitive phrasing when I write diagnostics 😅
2. Do we even want to show the "wrap in braces" case? I would assume most of the time the "add an `if`" case is the right one.
Remove hacks in `make_token_stream`.
`make_tokenstream` has three commented hacks, and a comment at the top
referring to #67062. These hacks have no observable effect, at least as judged
by running the test suite. The hacks were added in #82608, with an explanation
[here](https://github.com/rust-lang/rust/pull/82608#issuecomment-812877329). It
appears that one of the following is true: (a) they never did anything useful,
(b) they do something useful but we have no test coverage for them, or (c)
something has changed in the meantime that means they are no longer necessary.
This commit removes the hacks and the comments, in the hope that (b) is not
true.
r? `@Aaron1011`
Begin fixing all the broken doctests in `compiler/`
Begins to fix#95994.
All of them pass now but 24 of them I've marked with `ignore HELP (<explanation>)` (asking for help) as I'm unsure how to get them to work / if we should leave them as they are.
There are also a few that I marked `ignore` that could maybe be made to work but seem less important.
Each `ignore` has a rough "reason" for ignoring after it parentheses, with
- `(pseudo-rust)` meaning "mostly rust-like but contains foreign syntax"
- `(illustrative)` a somewhat catchall for either a fragment of rust that doesn't stand on its own (like a lone type), or abbreviated rust with ellipses and undeclared types that would get too cluttered if made compile-worthy.
- `(not-rust)` stuff that isn't rust but benefits from the syntax highlighting, like MIR.
- `(internal)` uses `rustc_*` code which would be difficult to make work with the testing setup.
Those reason notes are a bit inconsistently applied and messy though. If that's important I can go through them again and try a more principled approach. When I run `rg '```ignore \(' .` on the repo, there look to be lots of different conventions other people have used for this sort of thing. I could try unifying them all if that would be helpful.
I'm not sure if there was a better existing way to do this but I wrote my own script to help me run all the doctests and wade through the output. If that would be useful to anyone else, I put it here: https://github.com/Elliot-Roberts/rust_doctest_fixing_tool
Overhaul `MacArgs`
Motivation:
- Clarify some code that I found hard to understand.
- Eliminate one use of three places where `TokenKind::Interpolated` values are created.
r? `@petrochenkov`
The value in `MacArgs::Eq` is currently represented as a `Token`.
Because of `TokenKind::Interpolated`, `Token` can be either a token or
an arbitrary AST fragment. In practice, a `MacArgs::Eq` starts out as a
literal or macro call AST fragment, and then is later lowered to a
literal token. But this is very non-obvious. `Token` is a much more
general type than what is needed.
This commit restricts things, by introducing a new type `MacArgsEqKind`
that is either an AST expression (pre-lowering) or an AST literal
(post-lowering). The downside is that the code is a bit more verbose in
a few places. The benefit is that makes it much clearer what the
possibilities are (though also shorter in some other places). Also, it
removes one use of `TokenKind::Interpolated`, taking us a step closer to
removing that variant, which will let us make `Token` impl `Copy` and
remove many "handle Interpolated" code paths in the parser.
Things to note:
- Error messages have improved. Messages like this:
```
unexpected token: `"bug" + "found"`
```
now say "unexpected expression", which makes more sense. Although
arbitrary expressions can exist within tokens thanks to
`TokenKind::Interpolated`, that's not obvious to anyone who doesn't
know compiler internals.
- In `parse_mac_args_common`, we no longer need to collect tokens for
the value expression.
Using an obviously-placeholder syntax. An RFC would still be needed before this could have any chance at stabilization, and it might be removed at any point.
But I'd really like to have it in nightly at least to ensure it works well with try_trait_v2, especially as we refactor the traits.
`make_tokenstream` has three commented hacks, and a comment at the top
referring to #67062. These hacks have no observable effect, at least as judged
by running the test suite. The hacks were added in #82608, with an explanation
[here](https://github.com/rust-lang/rust/pull/82608#issuecomment-812877329). It
appears that one of the following is true: (a) they never did anything useful,
(b) they do something useful but we have no test coverage for them, or (c)
something has changed in the meantime that means they are no longer necessary.
This commit removes the hacks and the comments, in the hope that (b) is not
true.
Change `span_suggestion` (and variants) to take `impl ToString` rather
than `String` for the suggested code, as this simplifies the
requirements on the diagnostic derive.
Signed-off-by: David Wood <david.wood@huawei.com>
rustc_ast: Harmonize delimiter naming with `proc_macro::Delimiter`
Compiler cannot reuse `proc_macro::Delimiter` directly due to extra impls, but can at least use the same naming.
After this PR the only difference between these two enums is that `proc_macro::Delimiter::None` is turned into `token::Delimiter::Invisible`.
It's my mistake that the invisible delimiter is called `None` on stable, during the stabilization I audited the naming and wrote the docs, but missed the fact that the `None` naming gives a wrong and confusing impression about what this thing is.
cc https://github.com/rust-lang/rust/pull/96421
r? ``@nnethercote``
Less `NoDelim`
Currently there are several places where `NoDelim` (which really means "implicit delimiter" or "invisible delimiter") is used to mean "no delimiter". The name `NoDelim` is a bit misleading, and may be a cause.
This PR changes these places, e.g. by changing a `DelimToken` to `Option<DelimToken>` and then using `None` to mean "no delimiter". As a result, the *only* place where `NoDelim` values are now produced is within:
- `Delimiter::to_internal()`, when converting from `Delimiter::None`.
- `FlattenNonterminals::process_token()`, when converting `TokenKind::Interpolated`.
r? ````@petrochenkov````
This lets us clone just the parts within a `TokenTree` that need
cloning, rather than the entire thing. This is a surprisingly large
performance win, up to 4% on `async-std-1.10.0`.
This makes `CloseDelim` handling more like `OpenDelim` handling, which
produces `OpenDelim` and pushes the stack at the same time. It requires
some adjustment to `parse_token_tree` now that we don't remain within
the frame after getting the `CloseDelim`.
A Google search of the error message fails to return any relevant
resuts, suggesting this has never occurred in practice. And removeing it
reduces instruction counts by up to 2% on some benchmarks.
The loop is there to handle a `NoDelim` open/close token. This commit
changes `TokenCursor::inlined_next` so it never returns such a token.
This is a performance win because the conditional test in `bump()` is
removed.
If the parser needs changing in the future to handle `NoDelim` tokens,
then `inlined_next()` can easily be changed to return them.
The `DelimToken` here is `NoDelim`, which means the returned delim
tokens will just be ignored by `Parser::bump()`. This commit changes
things so the delim tokens won't be returned.
This will facilitate the change in the next commit.
`boolean` arguments aren't great, but the function is only used in three
places within this one file.
In particular, avoid wrapping a token within `TokenTree::Token` and then
immediately matching it and returning the token within. Just return the
token immediately.
Parse inner attributes on inline const block
According to https://github.com/rust-lang/rust/pull/84414#issuecomment-826150936, inner attributes are intended to be supported *"in all containers for statements (or some subset of statements)"*.
This PR adds inner attribute parsing and pretty-printing for inline const blocks (https://github.com/rust-lang/rust/issues/76001), which contain statements just like an unsafe block or a loop body.
```rust
let _ = const {
#![allow(...)]
let x = ();
x
};
```
By heap allocating the argument within `NtPath`, `NtVis`, and `NtStmt`.
This slightly reduces cumulative and peak allocation amounts, most
notably on `deep-vector`.
This commit updates the signatures of all diagnostic functions to accept
types that can be converted into a `DiagnosticMessage`. This enables
existing diagnostic calls to continue to work as before and Fluent
identifiers to be provided. The `SessionDiagnostic` derive just
generates normal diagnostic calls, so these APIs had to be modified to
accept Fluent identifiers.
In addition, loading of the "fallback" Fluent bundle, which contains the
built-in English messages, has been implemented.
Each diagnostic now has "arguments" which correspond to variables in the
Fluent messages (necessary to render a Fluent message) but no API for
adding arguments has been added yet. Therefore, diagnostics (that do not
require interpolation) can be converted to use Fluent identifiers and
will be output as before.
`MultiSpan` contains labels, which are more complicated with the
introduction of diagnostic translation and will use types from
`rustc_errors` - however, `rustc_errors` depends on `rustc_span` so
`rustc_span` cannot use types like `DiagnosticMessage` without
dependency cycles. Introduce a new `rustc_error_messages` crate that can
contain `DiagnosticMessage` and `MultiSpan`.
Signed-off-by: David Wood <david.wood@huawei.com>
Introduce a `DiagnosticMessage` type that will enable diagnostic
messages to be simple strings or Fluent identifiers.
`DiagnosticMessage` is now used in the implementation of the standard
`DiagnosticBuilder` APIs.
Signed-off-by: David Wood <david.wood@huawei.com>
Suggest `i += 1` when we see `i++` or `++i`
Closes#83502 (for `i++` and `++i`; `--i` should be covered by #82987, and `i--`
is tricky to handle).
This is a continuation of #83536.
r? `@estebank`
Fix multiline attributes handling in doctests
Fixes#55713.
I needed to have access to the `unclosed_delims` field in order to check that the attribute was completely parsed and didn't have missing parts, so I created a getter for it.
r? `@notriddle`
Remove `Nonterminal::NtTT`.
It's only needed for macro expansion, not as a general element in the
AST. This commit removes it, adds `NtOrTt` for the parser and macro
expansion cases, and renames the variants in `NamedMatch` to better
match the new type.
r? `@petrochenkov`
It's only needed for macro expansion, not as a general element in the
AST. This commit removes it, adds `NtOrTt` for the parser and macro
expansion cases, and renames the variants in `NamedMatch` to better
match the new type.
When encountering an inproperly terminated type parameter list, provide
a suggestion to close it after the last non-constraint type parameter
that was successfully parsed.
Fix#94058.
`run-rustfix` applies all suggestions regardless of their Applicability.
There's a flag, `rustfix-only-machine-applicable`, that does what it
says, but then the produced `.fixed` file would have invalid code from
the suggestions that weren't applied. So, I moved the cases of postfix
increment, in which case multiple suggestions are given, to the
`-notfixed` test, which does not run rustfix.
I also changed the Applicability to Unspecified since MaybeIncorrect
requires that the code be valid, even if it's incorrect.
Inline some parser functions
Some crates that do a lot of complex declarative macro expansion spend a lot of time parsing (and reparsing) tokens. These commits inline some functions for some minor speed wins.
r? `@ghost`
The call site within `Parser::bump` is hot.
Also add an inline annotation to `Parser::next_tok`. It was already
being inlined by the compiler; this just makes sure that continues.
suggest removing type ascription in bad parsing position
Not sure how to test this with the non-nightly suggestion. Didn't add a new UI test because it already manifests in an existing UI test.
Fixes#95014
Make ErrorReported impossible to construct outside `rustc_errors`
There are a few places were we have to construct it, though, and a few
places that are more invasive to change. To do this, we create a
constructor with a long obvious name.
cc #69426 `@varkor` `@eddyb` `@estebank`
I actually didn't see that I was assigned to this issue until now...
There are a few places were we have to construct it, though, and a few
places that are more invasive to change. To do this, we create a
constructor with a long obvious name.
More robust fallback for `use` suggestion
Our old way to suggest where to add `use`s would first look for pre-existing `use`s in the relevant crate/module, and if there are *no* uses, it would fallback on trying to use another item as the basis for the suggestion.
But this was fragile, as illustrated in issue #87613
This PR instead identifies span of the first token after any inner attributes, and uses *that* as the fallback for the `use` suggestion.
Fix#87613
then we just suggest the first legal position where you could inject a use.
To do this, I added `inject_use_span` field to `ModSpans`, and populate it in
parser (it is the span of the first token found after inner attributes, if any).
Then I rewrote the use-suggestion code to utilize it, and threw out some stuff
that is now unnecessary with this in place. (I think the result is easier to
understand.)
Then I added a test of issue 87613.
* Recover from invalid `'label: ` before block.
* Make suggestion to enclose statements in a block multipart.
* Point at `match`, `while`, `loop` and `unsafe` keywords when failing
to parse their expression.
* Do not suggest `{ ; }`.
* Do not suggest `|` when very unlikely to be what was wanted (in `let`
statements).
Adopt let else in more places
Continuation of #89933, #91018, #91481, #93046, #93590, #94011.
I have extended my clippy lint to also recognize tuple passing and match statements. The diff caused by fixing it is way above 1 thousand lines. Thus, I split it up into multiple pull requests to make reviewing easier. This is the biggest of these PRs and handles the changes outside of rustdoc, rustc_typeck, rustc_const_eval, rustc_trait_selection, which were handled in PRs #94139, #94142, #94143, #94144.
fix ICE when parsing lifetime as function argument
I don't really like this, but we basically need to emit an error instead of just delaying an bug, because there are too many places in the AST that aren't covered by my previous PRs...
cc: https://github.com/rust-lang/rust/issues/93282#issuecomment-1028052945
If an integer is entered with an upper-case base prefix (0Xbeef, 0O755, 0B1010), suggest to make it lowercase
The current error for this case isn't really great, it just complains about the whole thing past the `0` being an invalid suffix.
Incorporate distance limit from `find_best_match_for_name` directly into
Levenshtein distance computation.
Use the string size difference as a lower bound on the distance and exit
early when it exceeds the specified limit.
After finding a candidate within a limit, lower the limit further to
restrict the search space.
Let qpath contain NtTy: `<$:ty as $:ty>::…`
Example:
```rust
macro_rules! m {
(<$type:ty as $trait:ty>::$name:ident) => {
<$type as $trait>::$name
};
}
fn main() {
let _: m!(<str as ToOwned>::Owned);
}
```
Previous behavior:
```console
error: expected identifier, found `ToOwned`
--> src/main.rs:3:19
|
3 | <$type as $trait>::$name
| ^^^^^^ expected identifier
...
8 | let _: m!(<str as ToOwned>::Owned);
| ---------------------------
| |
| this macro call doesn't expand to a type
| in this macro invocation
```
The <code>expected identifier, found \`ToOwned\`</code> error is particularly silly. I think it should be fine to accept this code as long as $trait is of the form `TyKind::Path(None, path)`; if it is any other kind of `NtTy`, we'll keep the same behavior as before.
ProjectionPredicate should be able to handle both associated types and consts so this adds the
first step of that. It mainly just pipes types all the way down, not entirely sure how to handle
consts, but hopefully that'll come with time.
Fix suggesting turbofish with lifetime arguments
Now we suggest turbofish correctly given exprs like `foo<'_>`.
Also fix suggestion when we have `let x = foo<bar, baz>;` which was broken.
Parse `Ty?` as `Option<Ty>` and provide structured suggestion
Swift has specific syntax that desugars to `Option<T>` similar to our
`?` operator, which means that people might try to use it in Rust. Parse
it and gracefully recover.
Swift has specific syntax that desugars to `Option<T>` similar to our
`?` operator, which means that people might try to use it in Rust. Parse
it and gracefully recover.
Remove `SymbolStr`
This was originally proposed in https://github.com/rust-lang/rust/pull/74554#discussion_r466203544. As well as removing the icky `SymbolStr` type, it allows the removal of a lot of `&` and `*` occurrences.
Best reviewed one commit at a time.
r? `@oli-obk`
Fix suggestion of additional `pub` when using `pub pub fn ...`
Fix#87694.
Marked as draft to start with because I want to explore doing the same fix for `const const fn` and other repeated-but-valid keywords.
`@rustbot` label A-diagnostics D-invalid-suggestion T-compiler
By changing `as_str()` to take `&self` instead of `self`, we can just
return `&str`. We're still lying about lifetimes, but it's a smaller lie
than before, where `SymbolStr` contained a (fake) `&'static str`!
Recover on invalid operators `<>` and `<=>`
Thanks to #89871 for showing me how to do this.
Next, I think it'd be nice to recover on `<=>` too, like #89871 intended, if this even works.
Stabilise `feature(const_generics_defaults)`
`feature(const_generics_defaults)` is complete implementation wise and has a pretty extensive test suite so I think is ready for stabilisation.
needs stabilisation report and maybe an RFC 😅
r? `@lcnr`
cc `@rust-lang/project-const-generics`
Do not add `;` to expected tokens list when it's wrong
There's a few spots where semicolons are checked for to do error recovery, and should not be suggested (or checked for other stuff).
Fixes#87647
Also add a test case for inserting a semicolon on extern fns.
Without this fix, we got an error like this:
error: expected one of `->`, `where`, or `{`, found `}`
--> chk.rs:3:1
|
2 | fn foo()
| --- - expected one of `->`, `where`, or `{`
| |
| while parsing this `fn`
3 | }
| ^ unexpected token
Since this is inside an extern block, you're required to write function
prototypes with no body. This fixes a regression, and adds a test case
for it.
Improve diagnostic for missing half of binary operator in `if` condition
Fixes#91421. I've also changed it so that it doesn't consume the `else` token in the error case, because it will try to consume it again afterwards, leading to this incorrect error message (where the `else` reported as missing is actually there):
```
error: expected one of `.`, `;`, `?`, `else`, or an operator, found `{`
--> src/main.rs:4:12
|
4 | } else { 4 };
| ^ expected one of `.`, `;`, `?`, `else`, or an operator
```
r? `@lcnr`
expand: Turn `ast::Crate` into a first class expansion target
And stop creating a fake `mod` item for the crate root when expanding a crate, thus addressing FIXMEs left in https://github.com/rust-lang/rust/pull/82238, and making a step towards a proper support for crate-level macro attributes (cc #54726).
I haven't added token collection support for the whole crate in this PR, maybe later.
r? `@Aaron1011`
fix(doctest): detect extern crate items in statement doctests
This partially reverts #91026, because rustdoc needs to detect the extern statements, even when they appear inside implicit `main()`. It does not entirely revert it, so the old bug is still fixed, by duplicating some of the logic from `parse_mod` instead of trying to use it directly.
Fixes#91134
This partially reverts #91026, because rustdoc needs to detect the extern statements,
even when they appear inside implicit `main()`. It does not entirely revert it,
so the old bug is still fixed, by duplicating some of the logic from `parse_mod`
instead of trying to use it directly.
Fixes#91134
TraitKind -> Trait
TyAliasKind -> TyAlias
ImplKind -> Impl
FnKind -> Fn
All `*Kind`s in AST are supposed to be enums.
Tuple structs are converted to braced structs for the types above, and fields are reordered in syntactic order.
Also, mutable AST visitor now correctly visit spans in defaultness, unsafety, impl polarity and constness.
rustc_span: `Ident::invalid` -> `Ident::empty`
The equivalent for `Symbol`s was renamed some time ago (`kw::Invalid` -> `kw::Empty`), and it makes sense to do the same thing for `Ident`s as well.
Nicer error message if the user attempts to do let...else if
Gives a nice "conditional `else if` is not supported for `let...else`" error when encountering a `let...else if` pattern, as suggested in the [let...else tracking issue](https://github.com/rust-lang/rust/issues/87335#issuecomment-944846205).
"Fix" an overflow in byte position math
r? `@estebank`
help! I fixed the ICE only to brick the diagnostic.
I mean, it was wrong previously (using an already expanded macro span), but it is really bad now XD
Newcomers may write `{1, 2, 3}` for making arrays, and the current error
message is not informative enough to quickly convince them what is
needed to fix the error.
This PR implements a diagnostic for this case, and its output looks like
this:
```text
error: this code is interpreted as a block expression, not an array
--> src/lib.rs:1:22
|
1 | const FOO: [u8; 3] = {
| ______________________^
2 | | 1, 2, 3
3 | | };
| |_^
|
= note: to define an array, one would use square brackets instead of curly braces
help: try using [] instead of {}
|
1 | const FOO: [u8; 3] = [
2 | 1, 2, 3
3 | ];
|
```
Fix#87672
Recover from `Foo(a: 1, b: 2)`
Detect likely `struct` literal using parentheses as delimiters and emit
targeted suggestion instead of type ascription parse error.
Fix#61326.
Revert anon union parsing
Revert PR #84571 and #85515, which implemented anonymous union parsing in a manner that broke the context-sensitivity for the `union` keyword and thus broke stable Rust code.
Fix#88583.
Accept `m!{ .. }.method()` and `m!{ .. }?` statements.
This PR fixes something that I keep running into when using `quote!{}.into()` in a proc macro to convert the `proc_macro2::TokenStream` to a `proc_macro::TokenStream`:
Before:
```
error: expected expression, found `.`
--> src/lib.rs:6:6
|
4 | quote! {
5 | ...
6 | }.into()
| ^ expected expression
```
After:
```
```
(No output, compiles fine.)
---
Context:
For expressions like `{ 1 }` and `if true { 1 } else { 2 }`, we accept them as full statements without a trailing `;`, which means the following is not accepted:
```rust
{ 1 } - 1 // error
```
since that is parsed as two statements: `{ 1 }` and `-1`. Syntactically correct, but the type of `{ 1 }` should be `()` as there is no `;`.
However, for specifically `.` and `?` after the `}`, we do [continue parsing it as an expression](13db8440bb/compiler/rustc_parse/src/parser/expr.rs (L864-L876)):
```rust
{ "abc" }.len(); // ok
```
For braced macro invocations, we do not do this:
```rust
vec![1, 2, 3].len(); // ok
vec!{1, 2, 3}.len(); // error
```
(It parses `vec!{1, 2, 3}` as a full statement, and then complains about `.len()` not being a valid expression.)
This PR changes this to also look for a `.` and `?` after a braced macro invocation. We can be sure the macro is an expression and not a full statement in those cases, since no statement can start with a `.` or `?`.
Use smaller spans for some structured suggestions
Use more accurate suggestion spans for
* argument parse error
* fully qualified path
* missing code block type
* numeric casts
Change more x64 size checks to not apply to x32.
Commit 95e096d6 changed a bunch of size checks already, but more have
been added, so this fixes the new ones the same way: the various size
checks that are conditional on target_arch = "x86_64" were not intended
to apply to x86_64-unknown-linux-gnux32, so add
target_pointer_width = "64" to the conditions.
This commit focuses on emitting clean errors for the following syntax
error:
```
Some(42).map(|a|
dbg!(a);
a
);
```
Previous implementation tried to recover after parsing the closure body
(the `dbg` expression) by replacing the next `;` with a `,`, which made
the next expression belong to the next function argument. As such, the
following errors were emitted (among others):
- the semicolon token was not expected,
- a is not in scope,
- Option::map is supposed to take one argument, not two.
This commit allows us to gracefully handle this situation by adding
giving the parser the ability to remember when it has just parsed a
closure body inside a function call. When this happens, we can treat the
unexpected `;` specifically and try to parse as much statements as
possible in order to eat the whole block. When we can't parse statements
anymore, we generate a clean error indicating that the braces are
missing, and return an ExprKind::Err.
This reverts commit 059b68dd67.
Note that this was manually adjusted to retain some of the refactoring
introduced by commit 059b68dd67, so that it could
likewise retain the correction introduced in commit
5b4bc05fa5
Improve diagnostics for unary plus operators (#88276)
This pull request improves the diagnostics emitted on parsing a unary plus operator. See #88276.
Before:
```
error: expected expression, found `+`
--> src/main.rs:2:13
|
2 | let x = +1;
| ^ expected expression
```
After:
```
error: leading `+` is not supported
--> main.rs:2:13
|
2 | let x = +1;
| ^
| |
| unexpected `+`
| help: try removing the `+`
```
Commit 95e096d6 changed a bunch of size checks already, but more have
been added, so this fixes the new ones the same way: the various size
checks that are conditional on target_arch = "x86_64" were not intended
to apply to x86_64-unknown-linux-gnux32, so add
target_pointer_width = "64" to the conditions.
Detect bare blocks with type ascription that were meant to be a `struct` literal
Address part of #34255.
Potential improvement: silence the other knock down errors in `issue-34255-1.rs`.
Point at unclosed delimiters as part of the primary MultiSpan
Both the place where the parser encounters a needed closed delimiter and
the unclosed opening delimiter are important, so they should get the
same level of highlighting in the output.
_Context: https://twitter.com/mwk4/status/1430631546432675840_
Introduce `let...else`
Tracking issue: #87335
The trickiest part for me was enforcing the diverging else block with clear diagnostics. Perhaps the obvious solution is to expand to `let _: ! = ..`, but I decided against this because, when a "mismatched type" error is found in typeck, there is no way to trace where in the HIR the expected type originated, AFAICT. In order to pass down this information, I believe we should introduce `Expectation::LetElseNever(HirId)` or maybe add `HirId` to `Expectation::HasType`, but I left that as a future enhancement. For now, I simply assert that the block is `!` with a custom `ObligationCauseCode`, and I think this is clear enough, at least to start. The downside here is that the error points at the entire block rather than the specific expression with the wrong type. I left a todo to this effect.
Overall, I believe this PR is feature-complete with regard to the RFC.
Old error output:
3 | let _: usize = $f;
| ----- ^ expected `usize`, found struct `Baz`
| |
| expected due to this
New error output:
3 | let _: usize = $f;
| ----- ^^ expected `usize`, found struct `Baz`
| |
| expected due to this
Old error output:
= note: this warning originates in the macro `foo` (in Nightly builds, run with -Z macro-backtrace for more info)
help: wrap this expression in parentheses
|
4 | break '_l $f(;)
| ^ ^
New error output:
= note: this warning originates in the macro `foo` (in Nightly builds, run with -Z macro-backtrace for more info)
help: wrap this expression in parentheses
|
4 | break '_l ($f);
| ^ ^
Both the place where the parser encounters a needed closed delimiter and
the unclosed opening delimiter are important, so they should get the
same level of highlighting in the output.
- [x] Removed `?const` and change uses of `?const`
- [x] Added `~const` to the AST. It is gated behind const_trait_impl.
- [x] Validate `~const` in ast_validation.
- [ ] Add enum `BoundConstness` to the HIR. (With variants `NotConst` and
`ConstIfConst` allowing future extensions)
- [ ] Adjust trait selection and pre-existing code to use `BoundConstness`.
- [ ] Optional steps (*for this PR, obviously*)
- [ ] Fix#88155
- [ ] Do something with constness bounds in chalk
Allow labeled loops as value expressions for `break`
Fixes#86948. This is currently allowed:
```rust
return 'label: loop { break 'label 42; };
break ('label: loop { break 'label 42; });
break 1 + 'label: loop { break 'label 42; };
break 'outer 'inner: loop { break 'inner 42; };
```
But not this:
```rust
break 'label: loop { break 'label 42; };
```
I have fixed this, so that the above now parses as an unlabeled break with a labeled loop as its value expression.
Fix a parser ICE on invalid `fn` body
Fixes#87635
A better fix would add a check for `fn` body on `expected_one_of_not_found` but I haven't come up with a graceful way. Any idea?
r? ```@oli-obk``` ```@estebank```
After this commit, `unsafe async fn ...` now suggests the `async unsafe` fix
instead of misunderstanding the issue.
This is not perfect for repeated keywords (`const async const`) and for
keywords that are misplaced after `extern "some abi"` because of the way
`check_fn_font_matter` works, but changing it breaks so many tests and
diagnostics it has been judged too high a cost for this PR.
Add diagnostics for mistyped inclusive range
Inclusive ranges are correctly typed as `..=`. However, it's quite easy to think of it as being like `==`, and type `..==` instead. This PR adds helpful diagnostics for this case.
Resolves#86395 (there are some other cases there, but I think those should probably have separate issues).
r? `@estebank`
Stabilize "RangeFrom" patterns in 1.55
Implements a partial stabilization of #67264 and #37854.
Reference PR: https://github.com/rust-lang/reference/pull/900
# Stabilization Report
This stabilizes the `X..` pattern, shown as such, offering an exhaustive match for unsigned integers:
```rust
match x as u32 {
0 => println!("zero!"),
1.. => println!("positive number!"),
}
```
Currently if a Rust author wants to write such a match on an integer, they must use `1..={integer}::MAX` . By allowing a "RangeFrom" style pattern, this simplifies the match to not require the MAX path and thus not require specifically repeating the type inside the match, allowing for easier refactoring. This is particularly useful for instances like the above case, where different behavior on "0" vs. "1 or any positive number" is desired, and the actual MAX is unimportant.
Notably, this excepts slice patterns which include half-open ranges from stabilization, as the wisdom of those is still subject to some debate.
## Practical Applications
Instances of this specific usage have appeared in the compiler:
16143d1067/compiler/rustc_middle/src/ty/inhabitedness/mod.rs (L219)673d0db5e3/compiler/rustc_ty_utils/src/ty.rs (L524)
And I have noticed there are also a handful of "in the wild" users who have deployed it to similar effect, especially in the case of rejecting any value of a certain number or greater. It simply makes it much more ergonomic to write an irrefutable match, as done in Katholieke Universiteit Leuven's [SCALE and MAMBA project](05e5db00d5/WebAssembly/scale_std/src/fixed_point.rs (L685-L695)).
## Tests
There were already many tests in [src/test/ui/half-open-range/patterns](90a2e5e3fe/src/test/ui/half-open-range-patterns), as well as [generic pattern tests that test the `exclusive_range_pattern` feature](673d0db5e3/src/test/ui/pattern/usefulness/integer-ranges/reachability.rs), many dating back to the feature's introduction and remaining standing to this day. However, this stabilization comes with some additional tests to explore the... sometimes interesting behavior of interactions with other patterns. e.g. There is, at least, a mild diagnostic improvement in some edge cases, because before now, the pattern `0..=(5+1)` encounters the `half_open_range_patterns` feature gate and can thus emit the request to enable the feature flag, while also emitting the "inclusive range with no end" diagnostic. There is no intent to allow an `X..=` pattern that I am aware of, so removing the flag request is a strict improvement. The arrival of the `J | K` "or" pattern also enables some odd formations.
Some of the behavior tested for here is derived from experiments in this [Playground](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=58777b3c715c85165ac4a70d93efeefc) example, linked at https://github.com/rust-lang/rust/issues/67264#issuecomment-812770692, which may be useful to reference to observe the current behavior more closely.
In addition tests constituting an explanation of the "slicing range patterns" syntax issue are included in this PR.
## Desiderata
The exclusive range patterns and half-open range patterns are fairly strongly requested by many authors, as they make some patterns much more natural to write, but there is disagreement regarding the "closed" exclusive range pattern or the "RangeTo" pattern, especially where it creates "off by one" gaps in the presence of a "catch-all" wildcard case. Also, there are obviously no range analyses in place that will force diagnostics for e.g. highly overlapping matches. I believe these should be warned on, ideally, and I think it would be reasonable to consider such a blocker to stabilizing this feature, but there is no technical issue with the feature as-is from the purely syntactic perspective as such overlapping or missed matches can already be generated today with such a catch-all case. And part of the "point" of the feature, at least from my view, is to make it easier to omit wildcard matches: a pattern with such an "open" match produces an irrefutable match and does not need the wild card case, making it easier to benefit from exhaustiveness checking.
## History
- Implemented:
- Partially via exclusive ranges: https://github.com/rust-lang/rust/pull/35712
- Fully with half-open ranges: https://github.com/rust-lang/rust/pull/67258
- Unresolved Questions:
- The precedence concerns of https://github.com/rust-lang/rust/pull/48501 were considered as likely requiring adjustment but probably wanting a uniform consistent change across all pattern styles, given https://github.com/rust-lang/rust/issues/67264#issuecomment-720711656, but it is still unknown what changes might be desired
- How we want to handle slice patterns in ranges seems to be an open question still, as witnessed in the discussion of this PR!
I checked but I couldn't actually find an RFC for this, and given "approved provisionally by lang team without an RFC", I believe this might require an RFC before it can land? Unsure of procedure here, on account of this being stabilizing a subset of a feature of syntax.
r? `@scottmcm`
Fix ICE when misplaced visibility cannot be properly parsed
Fixes#86895
The issue was that a failure to parse the visibility was causing the original error to be dropped before being emitted.
The resulting error isn't quite as nice as when the visibility is parsed properly, but I'm not sure which error to prioritize here. Displaying both errors might be too confusing.
r? ```@estebank```
Re-add support for parsing (and pretty-printing) inner-attributes in match body
Re-add support for parsing (and pretty-printing) inner-attributes within body of a `match`.
In other words, we can do `match EXPR { #![inner_attr] ARM_1 ARM_2 ... }` again.
I believe this unbreaks the only four crates that crater flagged as broken by PR #83312.
(I am putting this up so that the lang-team can check it out and decide whether it changes their mind about what to do regarding PR #83312.)
Fix two ICEs in the parser
This pull request fixes#84104 and fixes#84148. The latter is caused by an invalid `assert_ne!()` in the parser, which I have simply removed because the error is then caught in another part of the parser.
#84104 is somewhat more subtle and has to do with a suggestion to remove extraneous `<` characters; for instance:
```rust
fn main() {
foo::<Ty<<<i32>();
}
```
currently leads to
```
error: unmatched angle brackets
--> unmatched-langle.rs:2:10
|
2 | foo::<Ty<<<i32>();
| ^^^ help: remove extra angle brackets
```
which is obviously wrong and stems from the fact that the code for issuing the above suggestion does not consider the possibility that there might be other tokens in between the opening angle brackets. In #84104, this has led to a span being generated that ends in the middle of a multi-byte character (because the code issuing the suggestion thought that it was only skipping over `<`, which are single-byte), causing an ICE.
# Stabilization report
## Summary
This stabilizes using macro expansion in key-value attributes, like so:
```rust
#[doc = include_str!("my_doc.md")]
struct S;
#[path = concat!(env!("OUT_DIR"), "/generated.rs")]
mod m;
```
See the changes to the reference for details on what macros are allowed;
see Petrochenkov's excellent blog post [on internals](https://internals.rust-lang.org/t/macro-expansion-points-in-attributes/11455)
for alternatives that were considered and rejected ("why accept no more
and no less?")
This has been available on nightly since 1.50 with no major issues.
## Notes
### Accepted syntax
The parser accepts arbitrary Rust expressions in this position, but any expression other than a macro invocation will ultimately lead to an error because it is not expected by the built-in expression forms (e.g., `#[doc]`). Note that decorators and the like may be able to observe other expression forms.
### Expansion ordering
Expansion of macro expressions in "inert" attributes occurs after decorators have executed, analogously to macro expressions appearing in the function body or other parts of decorator input.
There is currently no way for decorators to accept macros in key-value position if macro expansion must be performed before the decorator executes (if the macro can simply be copied into the output for later expansion, that can work).
## Test cases
- https://github.com/rust-lang/rust/blob/master/src/test/ui/attributes/key-value-expansion-on-mac.rs
- https://github.com/rust-lang/rust/blob/master/src/test/rustdoc/external-doc.rs
The feature has also been dogfooded extensively in the compiler and
standard library:
- https://github.com/rust-lang/rust/pull/83329
- https://github.com/rust-lang/rust/pull/83230
- https://github.com/rust-lang/rust/pull/82641
- https://github.com/rust-lang/rust/pull/80534
## Implementation history
- Initial proposal: https://github.com/rust-lang/rust/issues/55414#issuecomment-554005412
- Experiment to see how much code it would break: https://github.com/rust-lang/rust/pull/67121
- Preliminary work to restrict expansion that would conflict with this
feature: https://github.com/rust-lang/rust/pull/77271
- Initial implementation: https://github.com/rust-lang/rust/pull/78837
- Fix for an ICE: https://github.com/rust-lang/rust/pull/80563
## Unresolved Questions
~~https://github.com/rust-lang/rust/pull/83366#issuecomment-805180738 listed some concerns, but they have been resolved as of this final report.~~
## Additional Information
There are two workarounds that have a similar effect for `#[doc]`
attributes on nightly. One is to emulate this behavior by using a limited version of this feature that was stabilized for historical reasons:
```rust
macro_rules! forward_inner_docs {
($e:expr => $i:item) => {
#[doc = $e]
$i
};
}
forward_inner_docs!(include_str!("lib.rs") => struct S {});
```
This also works for other attributes (like `#[path = concat!(...)]`).
The other is to use `doc(include)`:
```rust
#![feature(external_doc)]
#[doc(include = "lib.rs")]
struct S {}
```
The first works, but is non-trivial for people to discover, and
difficult to read and maintain. The second is a strange special-case for
a particular use of the macro. This generalizes it to work for any use
case, not just including files.
I plan to remove `doc(include)` when this is stabilized. The
`forward_inner_docs` workaround will still compile without warnings, but
I expect it to be used less once it's no longer necessary.
Parse unsupported "default field const values":
```rust
struct S {
field: Type = const_val,
}
```
Recover from small `:` typo and provide suggestion:
```rust
struct S {
field; Type,
field2= Type,
}
```
In other words, we can do `match EXPR { #![inner_attr] ARM_1 ARM_2 ... }` again.
I believe this unbreaks the only four crates that crater flagged as broken by PR 83312.
(I am putting this up so that the lang-team can check it out and decide whether
it changes their mind about what to do regarding PR 83312.)
Improve diagnostics for functions in `struct` definitions
Tries to implement #76421.
This is probably going to need unit tests, but I wanted to hear from review all the cases tests should cover.
I'd like to follow up with the "mechanically applicable suggestion here that adds an impl block" step, but I'd need guidance. My idea for now would be to try to parse a function, and if that succeeds, create a dummy `ast::Item` impl block to then format it using `pprust`. Would that be a viable approach? Is there a better alternative?
r? `@matklad` cc `@estebank`
