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Refine when invalid prefix case error arises
Fix cases where the "invalid base prefix for number literal" error arises with suffixes that look erroneously capitalized but which are actually invalid.
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Fix cases where the "invalid base prefix for number literal" error arises with
suffixes that look erroneously capitalized but which are in fact invalid.
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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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hkmatsumoto:suggest-inexisting-field-for-unmentioned-field, r=estebank
Suggest replacing an inexisting field for an unmentioned field
Fix #87938
This PR adds a suggestion to replace an inexisting field for an
unmentioned field. Given the following code:
```rust
enum Foo {
Bar { alpha: u8, bravo: u8, charlie: u8 },
}
fn foo(foo: Foo) {
match foo {
Foo::Bar {
alpha,
beta, // `bravo` miswritten as `beta` here.
charlie,
} => todo!(),
}
}
```
the compiler now emits the error messages below.
```text
error[E0026]: variant `Foo::Bar` does not have a field named `beta`
--> src/lib.rs:9:13
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9 | beta, // `bravo` miswritten as `beta` here.
| ^^^^
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| variant `Foo::Bar` does not have this field
| help: `Foo::Bar` has a field named `bravo`: `bravo`
```
Note that this suggestion is available iff the number of inexisting
fields and unmentioned fields are both 1.
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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
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This PR adds a suggestion to replace an inexisting field for an
unmentioned field. Given the following code:
```rust
enum Foo {
Bar { alpha: u8, bravo: u8, charlie: u8 },
}
fn foo(foo: Foo) {
match foo {
Foo::Bar {
alpha,
beta, // `bravo` miswritten as `beta` here.
charlie,
} => todo!(),
}
}
```
the compiler now emits the error messages below.
```text
error[E0026]: variant `Foo::Bar` does not have a field named `beta`
--> src/lib.rs:9:13
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9 | beta, // `bravo` miswritten as `beta` here.
| ^^^^
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| variant `Foo::Bar` does not have this field
| help: `Foo::Bar` has a field named `bravo`: `bravo`
```
Note that this suggestion is available iff the number of inexisting
fields and unmentioned fields are both 1.
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For two reasons:
1. Now that the suggestion span has been corrected, the output is a bit
cluttered and hard to read. Putting the suggestion its own window
creates more space.
2. It's easier to see what's being suggested, since now the version
after the suggestion is applied is shown.
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(And same for tuple variants.)
Previously, the span was just for the constructor name, which meant it
would result in syntactically-invalid code when applied. Now, the span
is for the entire expression.
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Use more accurate suggestion spans for
* argument parse error
* fully qualified path
* missing code block type
* numeric casts
* E0212
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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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And tuple variant syntax, but that didn't fit in the subject :)
Now the fact that these are suggestions is exposed both to the layout
engine and to IDEs and rustfix for automatic application.
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Also added missing backtick in "you can cast" message.
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Before it always used `an`; now it uses the correct article for the type.
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re https://github.com/rust-lang/rust/pull/72380#discussion_r438289385
Given the toy code
```rust
fn is_positive(n: usize) {
n > -1_isize;
}
```
We currently get a type mismatch error like the following:
```
error[E0308]: mismatched types
--> src/main.rs:2:9
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2 | n > -1_isize;
| ^^^^^^^^ expected `usize`, found `isize`
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help: you can convert an `isize` to `usize` and panic if the converted value wouldn't fit
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2 | n > (-1_isize).try_into().unwrap();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```
But clearly, `-1` can never fit into a `usize`, so the suggestion will
always panic. A more useful message would tell the user that the value
can never fit in the expected type:
```
error[E0308]: mismatched types
--> test.rs:2:9
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2 | n > -1_isize;
| ^^^^^^^^ expected `usize`, found `isize`
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note: `-1_isize` can never fit into `usize`
--> test.rs:2:9
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2 | n > -1_isize;
| ^^^^^^^^
```
Which is what this commit implements.
I only added this check for negative literals because
- Currently we can only perform such a check for literals (constant
value propagation is outside the scope of the typechecker at this
point)
- A lint error for out-of-range numeric literals is already emitted
IMO it makes more sense to put this check in librustc_lint, but as far
as I can tell the typecheck pass happens before the lint pass, so I've
added it here.
r? @estebank
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Given a code
```rust
fn foo(x: u8, y: u32) -> bool {
x > y
}
fn main() {}
```
it could be more helpful to provide a suggestion to do "u32::from(x)"
rather than "y.try_into().unwrap()", since the latter may panic.
We do this by passing the LHS of a binary expression up the stack into
the coercion checker.
Closes #73145
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Remove `integer-into.rs` since the numeric-cast tests already cover
these cases.
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Make the spacing between the code snippet and verbose structured
suggestions consistent with note and help messages.
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