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Global error explanations improvements

This commit is contained in:
ggomez 2016-02-15 17:57:21 +01:00
parent 4b7245047b
commit 1c8766761e
4 changed files with 221 additions and 134 deletions
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243
src/librustc/diagnostics.rs
View File

@ -20,8 +20,8 @@ This error suggests that the expression arm corresponding to the noted pattern
will never be reached as for all possible values of the expression being
matched, one of the preceding patterns will match.
This means that perhaps some of the preceding patterns are too general, this one
is too specific or the ordering is incorrect.
This means that perhaps some of the preceding patterns are too general, this
one is too specific or the ordering is incorrect.
For example, the following `match` block has too many arms:
@ -104,28 +104,86 @@ E0004: r##"
This error indicates that the compiler cannot guarantee a matching pattern for
one or more possible inputs to a match expression. Guaranteed matches are
required in order to assign values to match expressions, or alternatively,
determine the flow of execution.
determine the flow of execution. Erroneous code example:
```compile_fail
enum Terminator {
HastaLaVistaBaby,
TalkToMyHand,
}
let x = Terminator::HastaLaVistaBaby;
match x { // error: non-exhaustive patterns: `HastaLaVistaBaby` not covered
Terminator::TalkToMyHand => {}
}
```
If you encounter this error you must alter your patterns so that every possible
value of the input type is matched. For types with a small number of variants
(like enums) you should probably cover all cases explicitly. Alternatively, the
underscore `_` wildcard pattern can be added after all other patterns to match
"anything else".
"anything else". Example:
```
enum Terminator {
HastaLaVistaBaby,
TalkToMyHand,
}
let x = Terminator::HastaLaVistaBaby;
match x {
Terminator::TalkToMyHand => {}
Terminator::HastaLaVistaBaby => {}
}
// or:
match x {
Terminator::TalkToMyHand => {}
_ => {}
}
```
"##,
E0005: r##"
Patterns used to bind names must be irrefutable, that is, they must guarantee
that a name will be extracted in all cases. If you encounter this error you
probably need to use a `match` or `if let` to deal with the possibility of
failure.
that a name will be extracted in all cases. Erroneous code example:
```compile_fail
let x = Some(1);
let Some(y) = x;
// error: refutable pattern in local binding: `None` not covered
```
If you encounter this error you probably need to use a `match` or `if let` to
deal with the possibility of failure. Example:
```compile_fail
let x = Some(1);
match x {
Some(y) => {
// do something
},
None => {}
}
// or:
if let Some(y) = x {
// do something
}
```
"##,
E0007: r##"
This error indicates that the bindings in a match arm would require a value to
be moved into more than one location, thus violating unique ownership. Code like
the following is invalid as it requires the entire `Option<String>` to be moved
into a variable called `op_string` while simultaneously requiring the inner
String to be moved into a variable called `s`.
be moved into more than one location, thus violating unique ownership. Code
like the following is invalid as it requires the entire `Option<String>` to be
moved into a variable called `op_string` while simultaneously requiring the
inner `String` to be moved into a variable called `s`.
```compile_fail
let x = Some("s".to_string());
@ -180,7 +238,7 @@ by-ref.
This limitation may be removed in a future version of Rust.
Wrong example:
Erroneous code example:
```compile_fail
struct X { x: (), }
@ -264,7 +322,7 @@ trait Foo where Self: Sized {
}
```
we cannot create an object of type `Box<Foo>` or `&Foo` since in this case
We cannot create an object of type `Box<Foo>` or `&Foo` since in this case
`Self` would not be `Sized`.
Generally, `Self : Sized` is used to indicate that the trait should not be used
@ -294,7 +352,7 @@ impl Trait for u8 {
```
(Note that `&self` and `&mut self` are okay, it's additional `Self` types which
cause this problem)
cause this problem.)
In such a case, the compiler cannot predict the return type of `foo()` in a
situation like the following:
@ -573,15 +631,15 @@ type X = u32; // ok!
"##,
E0133: r##"
Using unsafe functionality, is potentially dangerous and disallowed
by safety checks. Examples:
Using unsafe functionality is potentially dangerous and disallowed by safety
checks. Examples:
- Dereferencing raw pointers
- Calling functions via FFI
- Calling functions marked unsafe
* Dereferencing raw pointers
* Calling functions via FFI
* Calling functions marked unsafe
These safety checks can be relaxed for a section of the code
by wrapping the unsafe instructions with an `unsafe` block. For instance:
These safety checks can be relaxed for a section of the code by wrapping the
unsafe instructions with an `unsafe` block. For instance:
```
unsafe fn f() { return; }
@ -1039,14 +1097,16 @@ let y = match x {
println!("{}", y);
```
In the previous example, the print statement was never reached when the wildcard
match arm was hit, so we were okay with `foo()` not returning an integer that we
could set to `y`. But in this example, `foo()` actually does return control, so
the print statement will be executed with an uninitialized value.
In the previous example, the print statement was never reached when the
wildcard match arm was hit, so we were okay with `foo()` not returning an
integer that we could set to `y`. But in this example, `foo()` actually does
return control, so the print statement will be executed with an uninitialized
value.
Obviously we cannot have functions which are allowed to be used in such
positions and yet can return control. So, if you are defining a function that
returns `!`, make sure that there is no way for it to actually finish executing.
returns `!`, make sure that there is no way for it to actually finish
executing.
"##,
E0271: r##"
@ -1206,19 +1266,19 @@ trait Index<Idx> { ... }
foo(true); // `bool` does not implement `Index<u8>`
```
there will be an error about `bool` not implementing `Index<u8>`, followed by a
There will be an error about `bool` not implementing `Index<u8>`, followed by a
note saying "the type `bool` cannot be indexed by `u8`".
As you can see, you can specify type parameters in curly braces for substitution
with the actual types (using the regular format string syntax) in a given
situation. Furthermore, `{Self}` will substitute to the type (in this case,
`bool`) that we tried to use.
As you can see, you can specify type parameters in curly braces for
substitution with the actual types (using the regular format string syntax) in
a given situation. Furthermore, `{Self}` will substitute to the type (in this
case, `bool`) that we tried to use.
This error appears when the curly braces contain an identifier which doesn't
match with any of the type parameters or the string `Self`. This might happen if
you misspelled a type parameter, or if you intended to use literal curly braces.
If it is the latter, escape the curly braces with a second curly brace of the
same type; e.g. a literal `{` is `{{`
match with any of the type parameters or the string `Self`. This might happen
if you misspelled a type parameter, or if you intended to use literal curly
braces. If it is the latter, escape the curly braces with a second curly brace
of the same type; e.g. a literal `{` is `{{`.
"##,
E0273: r##"
@ -1239,10 +1299,10 @@ foo(true); // `bool` does not implement `Index<u8>`
there will be an error about `bool` not implementing `Index<u8>`, followed by a
note saying "the type `bool` cannot be indexed by `u8`".
As you can see, you can specify type parameters in curly braces for substitution
with the actual types (using the regular format string syntax) in a given
situation. Furthermore, `{Self}` will substitute to the type (in this case,
`bool`) that we tried to use.
As you can see, you can specify type parameters in curly braces for
substitution with the actual types (using the regular format string syntax) in
a given situation. Furthermore, `{Self}` will substitute to the type (in this
case, `bool`) that we tried to use.
This error appears when the curly braces do not contain an identifier. Please
add one of the same name as a type parameter. If you intended to use literal
@ -1274,8 +1334,8 @@ trait.
E0275: r##"
This error occurs when there was a recursive trait requirement that overflowed
before it could be evaluated. Often this means that there is unbounded recursion
in resolving some type bounds.
before it could be evaluated. Often this means that there is unbounded
recursion in resolving some type bounds.
For example, in the following code:
@ -1288,9 +1348,9 @@ impl<T> Foo for T where Bar<T>: Foo {}
```
To determine if a `T` is `Foo`, we need to check if `Bar<T>` is `Foo`. However,
to do this check, we need to determine that `Bar<Bar<T>>` is `Foo`. To determine
this, we check if `Bar<Bar<Bar<T>>>` is `Foo`, and so on. This is clearly a
recursive requirement that can't be resolved directly.
to do this check, we need to determine that `Bar<Bar<T>>` is `Foo`. To
determine this, we check if `Bar<Bar<Bar<T>>>` is `Foo`, and so on. This is
clearly a recursive requirement that can't be resolved directly.
Consider changing your trait bounds so that they're less self-referential.
"##,
@ -1336,7 +1396,7 @@ fn main() {
// we now call the method with the i32 type, which doesn't implement
// the Foo trait
some_func(5i32); // error: the trait `Foo` is not implemented for the
// type `i32`
// type `i32`
}
```
@ -1564,7 +1624,9 @@ borrows were allowed:
```compile_fail
match Some(()) {
None => { },
option if option.take().is_none() => { /* impossible, option is `Some` */ },
option if option.take().is_none() => {
/* impossible, option is `Some` */
},
Some(_) => { } // When the previous match failed, the option became `None`.
}
```
@ -1615,12 +1677,29 @@ See also https://github.com/rust-lang/rust/issues/14587
E0306: r##"
In an array literal `[x; N]`, `N` is the number of elements in the array. This
number cannot be negative.
must be an unsigned integer. Erroneous code example:
```compile_fail
let x = [0i32; true]; // error: expected positive integer for repeat count,
// found boolean
```
Working example:
```
let x = [0i32; 2];
```
"##,
E0307: r##"
The length of an array is part of its type. For this reason, this length must be
a compile-time constant.
The length of an array is part of its type. For this reason, this length must
be a compile-time constant. Erroneous code example:
```compile_fail
let len = 10;
let x = [0i32; len]; // error: expected constant integer for repeat count,
// found variable
```
"##,
E0308: r##"
@ -1713,24 +1792,22 @@ struct Foo<T: 'static> {
"##,
E0398: r##"
In Rust 1.3, the default object lifetime bounds are expected to
change, as described in RFC #1156 [1]. You are getting a warning
because the compiler thinks it is possible that this change will cause
a compilation error in your code. It is possible, though unlikely,
that this is a false alarm.
In Rust 1.3, the default object lifetime bounds are expected to change, as
described in RFC #1156 [1]. You are getting a warning because the compiler
thinks it is possible that this change will cause a compilation error in your
code. It is possible, though unlikely, that this is a false alarm.
The heart of the change is that where `&'a Box<SomeTrait>` used to
default to `&'a Box<SomeTrait+'a>`, it now defaults to `&'a
Box<SomeTrait+'static>` (here, `SomeTrait` is the name of some trait
type). Note that the only types which are affected are references to
boxes, like `&Box<SomeTrait>` or `&[Box<SomeTrait>]`. More common
types like `&SomeTrait` or `Box<SomeTrait>` are unaffected.
The heart of the change is that where `&'a Box<SomeTrait>` used to default to
`&'a Box<SomeTrait+'a>`, it now defaults to `&'a Box<SomeTrait+'static>` (here,
`SomeTrait` is the name of some trait type). Note that the only types which are
affected are references to boxes, like `&Box<SomeTrait>` or
`&[Box<SomeTrait>]`. More common types like `&SomeTrait` or `Box<SomeTrait>`
are unaffected.
To silence this warning, edit your code to use an explicit bound.
Most of the time, this means that you will want to change the
signature of a function that you are calling. For example, if
the error is reported on a call like `foo(x)`, and `foo` is
defined as follows:
To silence this warning, edit your code to use an explicit bound. Most of the
time, this means that you will want to change the signature of a function that
you are calling. For example, if the error is reported on a call like `foo(x)`,
and `foo` is defined as follows:
```ignore
fn foo(arg: &Box<SomeTrait>) { ... }
@ -1742,8 +1819,8 @@ You might change it to:
fn foo<'a>(arg: &Box<SomeTrait+'a>) { ... }
```
This explicitly states that you expect the trait object `SomeTrait` to
contain references (with a maximum lifetime of `'a`).
This explicitly states that you expect the trait object `SomeTrait` to contain
references (with a maximum lifetime of `'a`).
[1]: https://github.com/rust-lang/rfcs/pull/1156
"##,
@ -1812,8 +1889,8 @@ Also, for now, it is not possible to write deprecation messages either.
"##,
E0517: r##"
This error indicates that a `#[repr(..)]` attribute was placed on an unsupported
item.
This error indicates that a `#[repr(..)]` attribute was placed on an
unsupported item.
Examples of erroneous code:
@ -1829,29 +1906,29 @@ struct Foo {bar: bool, baz: bool}
#[repr(C)]
impl Foo {
...
// ...
}
```
- The `#[repr(C)]` attribute can only be placed on structs and enums
- The `#[repr(packed)]` and `#[repr(simd)]` attributes only work on structs
- The `#[repr(u8)]`, `#[repr(i16)]`, etc attributes only work on enums
* The `#[repr(C)]` attribute can only be placed on structs and enums.
* The `#[repr(packed)]` and `#[repr(simd)]` attributes only work on structs.
* The `#[repr(u8)]`, `#[repr(i16)]`, etc attributes only work on enums.
These attributes do not work on typedefs, since typedefs are just aliases.
Representations like `#[repr(u8)]`, `#[repr(i64)]` are for selecting the
discriminant size for C-like enums (when there is no associated data, e.g. `enum
Color {Red, Blue, Green}`), effectively setting the size of the enum to the size
of the provided type. Such an enum can be cast to a value of the same type as
well. In short, `#[repr(u8)]` makes the enum behave like an integer with a
constrained set of allowed values.
discriminant size for C-like enums (when there is no associated data, e.g.
`enum Color {Red, Blue, Green}`), effectively setting the size of the enum to
the size of the provided type. Such an enum can be cast to a value of the same
type as well. In short, `#[repr(u8)]` makes the enum behave like an integer
with a constrained set of allowed values.
Only C-like enums can be cast to numerical primitives, so this attribute will
not apply to structs.
`#[repr(packed)]` reduces padding to make the struct size smaller. The
representation of enums isn't strictly defined in Rust, and this attribute won't
work on enums.
representation of enums isn't strictly defined in Rust, and this attribute
won't work on enums.
`#[repr(simd)]` will give a struct consisting of a homogenous series of machine
types (i.e. `u8`, `i32`, etc) a representation that permits vectorization via
@ -1860,8 +1937,8 @@ single list of data.
"##,
E0518: r##"
This error indicates that an `#[inline(..)]` attribute was incorrectly placed on
something other than a function or method.
This error indicates that an `#[inline(..)]` attribute was incorrectly placed
on something other than a function or method.
Examples of erroneous code:
@ -1871,7 +1948,7 @@ struct Foo;
#[inline(never)]
impl Foo {
...
// ...
}
```

20
src/librustc_borrowck/diagnostics.rs
View File

@ -26,7 +26,8 @@ fn foo() -> Box<Fn(u32) -> u32> {
Notice that `x` is stack-allocated by `foo()`. By default, Rust captures
closed-over data by reference. This means that once `foo()` returns, `x` no
longer exists. An attempt to access `x` within the closure would thus be unsafe.
longer exists. An attempt to access `x` within the closure would thus be
unsafe.
Another situation where this might be encountered is when spawning threads:
@ -73,7 +74,14 @@ fn main() {
```
To fix this, ensure that any declared variables are initialized before being
used.
used. Example:
```
fn main() {
let x: i32 = 0;
let y = x; // ok!
}
```
"##,
E0382: r##"
@ -210,8 +218,8 @@ let mut y: Box<_> = Box::new(&mut x);
**y = 2;
```
It can also be fixed by using a type with interior mutability, such as `Cell` or
`RefCell`:
It can also be fixed by using a type with interior mutability, such as `Cell`
or `RefCell`:
```
use std::cell::Cell;
@ -259,8 +267,8 @@ fn foo<F: FnMut()>(f: F) { }
```
Alternatively, we can consider using the `Cell` and `RefCell` types to achieve
interior mutability through a shared reference. Our example's `mutable` function
could be redefined as below:
interior mutability through a shared reference. Our example's `mutable`
function could be redefined as below:
```
use std::cell::Cell;

10
src/librustc_privacy/diagnostics.rs
View File

@ -27,8 +27,8 @@ pub fn foo<T: Foo> (t: T) {} // same error
```
To solve this error, please ensure that the trait is also public. The trait
can be made inaccessible if necessary by placing it into a private inner module,
but it still has to be marked with `pub`. Example:
can be made inaccessible if necessary by placing it into a private inner
module, but it still has to be marked with `pub`. Example:
```ignore
pub trait Foo { // we set the Foo trait public
@ -55,8 +55,8 @@ mod Foo {
```
To solve this error, please ensure that the type is also public. The type
can be made inaccessible if necessary by placing it into a private inner module,
but it still has to be marked with `pub`.
can be made inaccessible if necessary by placing it into a private inner
module, but it still has to be marked with `pub`.
Example:
```
@ -165,7 +165,7 @@ let f = Bar::Foo(0); // error: cannot invoke tuple struct constructor with
```
To solve this issue, please ensure that all of the fields of the tuple struct
are public. Alternatively, provide a new() method to the tuple struct to
are public. Alternatively, provide a `new()` method to the tuple struct to
construct it from a given inner value. Example:
```

82
src/librustc_resolve/diagnostics.rs
View File

@ -94,8 +94,8 @@ mod bar {
"##,
E0253: r##"
Attempt was made to import an unimportable value. This can happen when
trying to import a method from a trait. An example of this error:
Attempt was made to import an unimportable value. This can happen when trying
to import a method from a trait. An example of this error:
```compile_fail
mod foo {
@ -149,10 +149,10 @@ fn main() {}
"##,
E0259: r##"
The name chosen for an external crate conflicts with another external crate that
has been imported into the current module.
The name chosen for an external crate conflicts with another external crate
that has been imported into the current module.
Wrong example:
Erroneous code example:
```compile_fail
extern crate a;
@ -251,8 +251,8 @@ https://doc.rust-lang.org/reference.html#types
"##,
E0364: r##"
Private items cannot be publicly re-exported. This error indicates that
you attempted to `pub use` a type or value that was not itself public.
Private items cannot be publicly re-exported. This error indicates that you
attempted to `pub use` a type or value that was not itself public.
Here is an example that demonstrates the error:
@ -275,15 +275,15 @@ mod foo {
pub use foo::X;
```
See the 'Use Declarations' section of the reference for more information
on this topic:
See the 'Use Declarations' section of the reference for more information on
this topic:
https://doc.rust-lang.org/reference.html#use-declarations
"##,
E0365: r##"
Private modules cannot be publicly re-exported. This error indicates
that you attempted to `pub use` a module that was not itself public.
Private modules cannot be publicly re-exported. This error indicates that you
attempted to `pub use` a module that was not itself public.
Here is an example that demonstrates the error:
@ -313,8 +313,8 @@ https://doc.rust-lang.org/reference.html#use-declarations
"##,
E0401: r##"
Inner items do not inherit type parameters from the functions they are
embedded in. For example, this will not compile:
Inner items do not inherit type parameters from the functions they are embedded
in. For example, this will not compile:
```compile_fail
fn foo<T>(x: T) {
@ -543,16 +543,15 @@ impl Bar {
"##,
E0411: r##"
The `Self` keyword was used outside an impl or a trait. Erroneous
code example:
The `Self` keyword was used outside an impl or a trait. Erroneous code example:
```compile_fail
<Self>::foo; // error: use of `Self` outside of an impl or trait
```
The `Self` keyword represents the current type, which explains why it
can only be used inside an impl or a trait. It gives access to the
associated items of a type:
The `Self` keyword represents the current type, which explains why it can only
be used inside an impl or a trait. It gives access to the associated items of a
type:
```
trait Foo {
@ -564,7 +563,7 @@ trait Baz : Foo {
}
```
However, be careful when two types has a common associated type:
However, be careful when two types have a common associated type:
```compile_fail
trait Foo {
@ -581,8 +580,8 @@ trait Baz : Foo + Foo2 {
}
```
This problem can be solved by specifying from which trait we want
to use the `Bar` type:
This problem can be solved by specifying from which trait we want to use the
`Bar` type:
```
trait Foo {
@ -604,16 +603,20 @@ An undeclared type name was used. Example of erroneous codes:
```compile_fail
impl Something {} // error: use of undeclared type name `Something`
// or:
trait Foo {
fn bar(N); // error: use of undeclared type name `N`
}
// or:
fn foo(x: T) {} // error: use of undeclared type name `T`
```
To fix this error, please verify you didn't misspell the type name,
you did declare it or imported it into the scope. Examples:
To fix this error, please verify you didn't misspell the type name, you did
declare it or imported it into the scope. Examples:
```
struct Something;
@ -635,8 +638,8 @@ fn foo<T>(x: T) {} // ok!
"##,
E0413: r##"
A declaration shadows an enum variant or unit-like struct in scope.
Example of erroneous code:
A declaration shadows an enum variant or unit-like struct in scope. Example of
erroneous code:
```compile_fail
struct Foo;
@ -666,8 +669,7 @@ The goal here is to avoid a conflict of names.
"##,
E0415: r##"
More than one function parameter have the same name. Example of erroneous
code:
More than one function parameter have the same name. Example of erroneous code:
```compile_fail
fn foo(f: i32, f: i32) {} // error: identifier `f` is bound more than
@ -682,8 +684,7 @@ fn foo(f: i32, g: i32) {} // ok!
"##,
E0416: r##"
An identifier is bound more than once in a pattern. Example of erroneous
code:
An identifier is bound more than once in a pattern. Example of erroneous code:
```compile_fail
match (1, 2) {
@ -739,8 +740,7 @@ match 0 {
"##,
E0419: r##"
An unknown enum variant, struct or const was used. Example of
erroneous code:
An unknown enum variant, struct or const was used. Example of erroneous code:
```compile_fail
match 0 {
@ -766,8 +766,8 @@ match Something::NotFoo {
"##,
E0422: r##"
You are trying to use an identifier that is either undefined or not a
struct. For instance:
You are trying to use an identifier that is either undefined or not a struct.
For instance:
``` compile_fail
fn main () {
@ -785,13 +785,13 @@ fn main () {
}
```
In this case, `foo` is defined, but is not a struct, so Rust can't use
it as one.
In this case, `foo` is defined, but is not a struct, so Rust can't use it as
one.
"##,
E0423: r##"
A `struct` variant name was used like a function name. Example of
erroneous code:
A `struct` variant name was used like a function name. Example of erroneous
code:
```compile_fail
struct Foo { a: bool};
@ -801,8 +801,8 @@ let f = Foo();
// it like a function name
```
Please verify you didn't misspell the name of what you actually wanted
to use here. Example:
Please verify you didn't misspell the name of what you actually wanted to use
here. Example:
```
fn Foo() -> u32 { 0 }
@ -851,6 +851,7 @@ something_that_doesnt_exist::foo;
// error: unresolved name `something_that_doesnt_exist::foo`
// or:
trait Foo {
fn bar() {
Self; // error: unresolved name `Self`
@ -858,6 +859,7 @@ trait Foo {
}
// or:
let x = unknown_variable; // error: unresolved name `unknown_variable`
```
@ -941,7 +943,7 @@ use something::self; // ok!
"##,
E0431: r##"
`self` import was made. Erroneous code example:
An invalid `self` import was made. Erroneous code example:
```compile_fail
use {self}; // error: `self` import can only appear in an import list with a