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This attempts to bring better error messages to invalid method calls, by applying some heuristics to identify common mistakes.
The algorithm is inspired by Levenshtein distance and longest common sub-sequence. In essence, we treat the types of the function, and the types of the arguments you provided as two "words" and compute the edits to get from one to the other.
We then modify that algorithm to detect 4 cases:
- A function input is missing
- An extra argument was provided
- The type of an argument is straight up invalid
- Two arguments have been swapped
- A subset of the arguments have been shuffled
(We detect the last two as separate cases so that we can detect two swaps, instead of 4 parameters permuted.)
It helps to understand this argument by paying special attention to terminology: "inputs" refers to the inputs being *expected* by the function, and "arguments" refers to what has been provided at the call site.
The basic sketch of the algorithm is as follows:
- Construct a boolean grid, with a row for each argument, and a column for each input. The cell [i, j] is true if the i'th argument could satisfy the j'th input.
- If we find an argument that could satisfy no inputs, provided for an input that can't be satisfied by any other argument, we consider this an "invalid type".
- Extra arguments are those that can't satisfy any input, provided for an input that *could* be satisfied by another argument.
- Missing inputs are inputs that can't be satisfied by any argument, where the provided argument could satisfy another input
- Swapped / Permuted arguments are identified with a cycle detection algorithm.
As each issue is found, we remove the relevant inputs / arguments and check for more issues. If we find no issues, we match up any "valid" arguments, and start again.
Note that there's a lot of extra complexity:
- We try to stay efficient on the happy path, only computing the diagonal until we find a problem, and then filling in the rest of the matrix.
- Closure arguments are wrapped in a tuple and need to be unwrapped
- We need to resolve closure types after the rest, to allow the most specific type constraints
- We need to handle imported C functions that might be variadic in their inputs.
I tried to document a lot of this in comments in the code and keep the naming clear.
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When encountering an unsatisfied trait bound, if there are no other
suggestions, mention all the types that *do* implement that trait:
```
error[E0277]: the trait bound `f32: Foo` is not satisfied
--> $DIR/impl_wf.rs:22:6
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LL | impl Baz<f32> for f32 { }
| ^^^^^^^^ the trait `Foo` is not implemented for `f32`
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= help: the following other types implement trait `Foo`:
Option<T>
i32
str
note: required by a bound in `Baz`
--> $DIR/impl_wf.rs:18:31
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LL | trait Baz<U: ?Sized> where U: Foo { }
| ^^^ required by this bound in `Baz`
```
Mention implementers of traits in `ImplObligation`s.
Do not mention other `impl`s for closures, ranges and `?`.
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Stabilize `#[cfg(panic = "...")]`
[Stabilization PR](https://rustc-dev-guide.rust-lang.org/stabilization_guide.html#stabilization-pr) for #77443
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It should only include the identifier, or misspelling suggestions will be wrong.
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Rebase commit
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Don't allow {} to refer to implicit captures in format_args.
Fixes #93378
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Accommodate yield points in the format_args expansion
Fixes #93274.
For the case `println!("{} {:?}", "", async {}.await)` in the issue, the expansion before:
```rust
::std::io::_print(
::core::fmt::Arguments::new_v1(
&["", " ", "\n"],
&[
::core::fmt::ArgumentV1::new(&"", ::core::fmt::Display::fmt),
::core::fmt::ArgumentV1::new(&async {}.await, ::core::fmt::Debug::fmt),
],
),
);
```
After:
```rust
::std::io::_print(
::core::fmt::Arguments::new_v1(
&["", " ", "\n"],
&match (&"", &async {}.await) {
_args => [
::core::fmt::ArgumentV1::new(_args.0, ::core::fmt::Display::fmt),
::core::fmt::ArgumentV1::new(_args.1, ::core::fmt::Debug::fmt),
],
},
),
);
```
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Currently fails with:
error: future cannot be sent between threads safely
--> $DIR/src/test/ui/fmt/format-with-yield-point.rs:21:17
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LL | assert_send(with_await());
| ^^^^^^^^^^^^ future returned by `with_await` is not `Send`
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= help: the trait `Sync` is not implemented for `core::fmt::Opaque`
note: future is not `Send` as this value is used across an await
--> $DIR/src/test/ui/fmt/format-with-yield-point.rs:11:37
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LL | println!("{} {:?}", "", async {}.await);
| --------------------------------^^^^^^-
| | |
| | await occurs here, with `$crate::format_args_nl!($($arg)*)` maybe used later
| has type `ArgumentV1<'_>` which is not `Send`
| `$crate::format_args_nl!($($arg)*)` is later dropped here
note: required by a bound in `assert_send`
--> $DIR/src/test/ui/fmt/format-with-yield-point.rs:18:24
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LL | fn assert_send(_: impl Send) {}
| ^^^^ required by this bound in `assert_send`
error: future cannot be sent between threads safely
--> $DIR/src/test/ui/fmt/format-with-yield-point.rs:22:17
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LL | assert_send(with_macro_call());
| ^^^^^^^^^^^^^^^^^ future returned by `with_macro_call` is not `Send`
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= help: the trait `Sync` is not implemented for `core::fmt::Opaque`
note: future is not `Send` as this value is used across an await
--> $DIR/src/test/ui/fmt/format-with-yield-point.rs:6:17
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LL | async {}.await
| ^^^^^^ await occurs here, with `$crate::format_args_nl!($($arg)*)` maybe used later
...
LL | println!("{} {:?}", "", m!());
| -----------------------------
| | |
| | in this macro invocation
| has type `ArgumentV1<'_>` which is not `Send`
| `$crate::format_args_nl!($($arg)*)` is later dropped here
note: required by a bound in `assert_send`
--> $DIR/src/test/ui/fmt/format-with-yield-point.rs:18:24
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LL | fn assert_send(_: impl Send) {}
| ^^^^ required by this bound in `assert_send`
= note: this error originates in the macro `m` (in Nightly builds, run with -Z macro-backtrace for more info)
error: aborting due to 2 previous errors
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Works as expected, and there are widespread reports of success with it,
as well as interest in it.
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Warn when an escaped newline skips multiple lines
Resolves #87319
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* On suggestions that include deletions, use a diff inspired output format
* When suggesting addition, use `+` as underline
* Color highlight modified span
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From what I can tell, the goal of the tests is to ensure that the error
formatting is correct. I think this is still being tested as intended
after this change.
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* Always point at macros, including derive macros
* Point at non-local items that introduce a trait requirement
* On private associated item, point at definition
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When there are multiple macros in use, it can be difficult to tell
which one was responsible for producing an error.
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This extends the `panic_fmt` lint to warn for all cases where the first
argument cannot be interpreted as a format string, as will happen in
Rust 2021.
It suggests to add `"{}", ` to format the message as a string. In the
case of `std::panic!()`, it also suggests the recently stabilized
`std::panic::panic_any()` function as an alternative.
It renames the lint to `non_fmt_panic` to match the lint naming
guidelines.
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of whole format string
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diagnostics: shorten paths of unique symbols
This is a step towards implementing a fix for #50310, and continuation of the discussion in [Pre-RFC: Nicer Types In Diagnostics - compiler - Rust Internals](https://internals.rust-lang.org/t/pre-rfc-nicer-types-in-diagnostics/11139). Impressed upon me from previous discussion in #21934 that an RFC for this is not needed, and I should just come up with code.
The recent improvements to `use` suggestions that I've contributed have given rise to this implementation. Contrary to previous suggestions, it's rather simple logic, and I believe it only reduces the amount of cognitive load that a developer would need when reading type errors.
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If a symbol name can only be imported from one place, and as long as it was not glob-imported anywhere in the current crate, we can trim its printed path to the last component.
This has wide implications on error messages with types, for example, shortening `std::vec::Vec` to just `Vec`, as long as there is no other `Vec` importable from anywhere.
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If a symbol name can only be imported from one place for a type, and
as long as it was not glob-imported anywhere in the current crate, we
can trim its printed path and print only the name.
This has wide implications on error messages with types, for example,
shortening `std::vec::Vec` to just `Vec`, as long as there is no other
`Vec` importable anywhere.
This adds a new '-Z trim-diagnostic-paths=false' option to control this
feature.
On the good path, with no diagnosis printed, we should try to avoid
issuing this query, so we need to prevent trimmed_def_paths query on
several cases.
This change also relies on a previous commit that differentiates
between `Debug` and `Display` on various rustc types, where the latter
is trimmed and presented to the user and the former is not.
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If a comma in a format call is replaced with a similar token, then we
emit an error and continue parsing, instead of stopping at this point.
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Previous implementation used the `Parser::parse_expr` function in order
to extract the format expression. If the first comma following the
format expression was mistakenly replaced with a dot, then the next
format expression was eaten by the function, because it looked as a
syntactically valid expression, which resulted in incorrectly spanned
error messages.
The way the format expression is exctracted is changed: we first look at
the first available token in the first argument supplied to the
`format!` macro call. If it is a string literal, then it is promoted as
a format expression immediatly, otherwise we fall back to the original
`parse_expr`-related method.
This allows us to ensure that the parser won't consume too much tokens
when a typo is made.
A test has been created so that it is ensured that the issue is properly
fixed.
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Apply suggestion from varkor
Co-authored-by: varkor <github@varkor.com>
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This prevents accidental dereferences and so forth of the Void type, as well as
cleaning up the error message to reference Opaque rather than the more
complicated PhantomData type.
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Previously:
error: invalid format string: invalid argument name `_x`
--> src/main.rs:2:16
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2 | println!("{_x}", a=0);
| ^^ invalid argument name in format string
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= note: argument names cannot start with an underscore
Not supporting identifiers starting with underscore appears to have been
an arbitrary limitation from 2013 in code that was most likely never
reviewed:
https://github.com/rust-lang/rust/pull/8245/files#diff-0347868ef389c805e97636623e4a4ea6R277
The error message was dutifully improved in #50610 but is there any
reason that leading underscore would be a special case?
This commit updates the format_args parser to accept identifiers with
leading underscores.
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Add secondary span labels with no text to make it clear when there's a
mismatch bewteen the positional arguments in a format string and the
arguments to the macro. This shouldn't affect experienced users, but it
should make it easier for newcomers to more clearly understand how
`format!()` and `println!()` are supposed to be used.
```
error: 2 positional arguments in format string, but there is 1 argument
--> file8.rs:2:14
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2 | format!("{} {}", 1);
| ^^ ^^ -
```
instead of
```
error: 2 positional arguments in format string, but there is 1 argument
--> file8.rs:2:14
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2 | format!("{} {}", 1);
| ^^ ^^
```
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