# Upgrading from previous releases
- [Version 0.5 → 0.6](#version-05--06)
- [Version 0.4 → 0.5](#version-04--05)
- [Version 0.3 → 0.4](#version-03--04)
- [Version 0.2 → 0.3](#version-02--03)
- [Version 0.1 → 0.2](#version-01--02)
## Version 0.5 → 0.6
### Minimum supported version of Rust is now 1.31
If you are writing a library, you will need to increase your minimum
supported version of Rust to 1.31 or better. If you are writing an
application, you should be able to upgrade your installed compiler by
the same mechanism that you installed it.
### Backtraces
The `Backtrace` type is now always available, so it is encouraged to
make liberal use of it in your errors. If you are writing an
application that displays backtraces, make sure to enable the
[`backtrace` feature flag](crate::guide::feature_flags) so that
backtraces are populated when they are created.
Implementations of `Backtrace::default` and `Backtrace::new` have been
removed and replaced with `GenerateBacktrace::generate`.
The `backtrace-crate` feature flag has been renamed to
`backtraces-impl-backtrace-crate`. The backtrace returned by
`ErrorCompat::backtrace` is now the `backtrace::Backtrace` type when
this flag is enabled, so the implementation of `AsRef` has been
removed..
### Futures
Support for the standard library features has been stabilized, so the
feature flag has been renamed from `unstable-futures` to `futures`.
## Version 0.4 → 0.5
### `backtrace(delegate)` replaced with `backtrace`
Previously, if you wanted to delegate backtrace creation to
another error, you would specify `#[snafu(backtrace(delegate))]`
on the source field that references the other error.
Now, you specify the simpler `#[snafu(backtrace)]`. Since source
fields must be error types, and backtrace fields must be
`Backtrace` types, this is unambiguous and simplifies the API.
#### Before
```rust,ignore
#[derive(Debug, Snafu)]
enum Error {
MyVariant {
#[snafu(backtrace(delegate))]
source: OtherError,
},
}
```
#### After
```rust,ignore
#[derive(Debug, Snafu)]
enum Error {
MyVariant {
#[snafu(backtrace)]
source: OtherError,
},
}
```
### `source(from)` implies `source`
Previously, if you had wanted to treat a field that wasn't named
"source" as a source field, *and* you wanted to transform the
field from another type, you had to specify both
`#[snafu(source)]` and `#[snafu(source(from(...)))]`.
Now, `#[snafu(source(from(...)))]` implies `#[snafu(source)]` --
it automatically treats the field as a source field regardless of
its name, so you can remove the `#[snafu(source)]` attribute.
#### Before
```rust,ignore
#[derive(Debug, Snafu)]
enum Error {
CauseIsAnError {
#[snafu(source)]
#[snafu(source(from(Error, Box::new)))]
cause: Box<Error>,
},
}
```
#### After
```rust,ignore
#[derive(Debug, Snafu)]
enum Error {
CauseIsAnError {
#[snafu(source(from(Error, Box::new)))]
cause: Box<Error>,
},
}
```
### New errors for attribute misuse and duplication
Previously, SNAFU would ignore `#[snafu(...)]` attributes that
were used in invalid locations. If attributes were duplicated,
either the first or last would apply (depending on the attribute)
and the rest would be ignored.
One example is specifying `#[snafu(source(from(...)))]` on an
enum variant instead of the source field in that variant:
```rust,ignore
#[derive(Debug, Snafu)]
enum Error {
// This used to be ignored, and will now cause an error:
#[snafu(source(from(Error, Box::new)))]
MyVariant {
source: Box<Error>,
},
}
```
Now, compiler errors will be emitted that point to any misused or
duplicated attributes.
## Version 0.3 → 0.4
### `Context` vs. `IntoError`
The `Context` type and related `From` implementations have been
removed in favor of the [`IntoError`](crate::IntoError) trait. If
you were making use of this for custom conversions, you will need
to update your trait bounds:
#### Before
```rust,ignore
fn example<C, E>(context: C) -> MyType<E>
where
snafu::Context<SomeError, C>: Into<E>;
```
#### After
```rust,ignore
fn example<C, E>(context: C) -> MyType<E>
where
C: snafu::IntoError<E, Source = SomeError>,
E: std::error::Error + snafu::ErrorCompat;
```
### `Borrow<std::error::Error>`
SNAFU no longer generates `Borrow<std::error::Error>`
implementations for SNAFU error types (sorry for the whiplash if
you were affected by this when upgrading to 0.3).
## Version 0.2 → 0.3
Minimal changes should be required: if you previously implemented
`Borrow<std::error::Error>` for a SNAFU error type, you should
remove that implementation and allow SNAFU to implement it for
you.
## Version 0.1 → 0.2
Support for the `snafu::display` attribute was removed as this
type of attribute was [never intended to be
supported][oops]. Since this required a SemVer-incompatible
version, the attribute format has also been updated and
normalized.
1. Attributes have been renamed
- `snafu_display` and `snafu::display` became `snafu(display)`.
- `snafu_visibility` became `snafu(visibility)`
- `snafu_backtrace` became `snafu(backtrace)`
1. Support for `snafu_display` with individually-quoted format
arguments was removed. Migrate to either the "clean" or "all
one string" styles, depending on what version of Rust you are
targeting.
[oops]: https://github.com/rust-lang/rust/pull/58899
### Before
```rust,ignore
#[derive(Debug, Snafu)]
enum DisplayUpdate {
#[snafu::display("Format and {}", argument)]
CleanStyle { argument: i32 },
#[snafu_display("Format and {}", "argument")]
QuotedArgumentStyle { argument: i32 },
#[snafu_display = r#"("Format and {}", argument)"#]
AllOneStringStyle { argument: i32 },
}
```
```rust,ignore
#[derive(Debug, Snafu)]
enum VisibilityUpdate {
#[snafu_visibility(pub(crate))]
CleanStyle,
#[snafu_visibility = "pub(crate)"]
AllOneStringStyle,
}
```
### After
```rust,ignore
# use snafu::Snafu;
#[derive(Debug, Snafu)]
enum DisplayUpdate {
#[snafu(display("Format and {}", argument))]
CleanStyle { argument: i32 },
#[snafu(display = r#"("Format and {}", argument)"#)]
QuotedArgumentStyle { argument: i32 },
#[snafu(display = r#"("Format and {}", argument)"#)]
AllOneStringStyle { argument: i32 },
}
```
```rust,ignore
# use snafu::Snafu;
#[derive(Debug, Snafu)]
enum VisibilityUpdate {
#[snafu(visibility(pub(crate)))]
CleanStyle,
#[snafu(visibility = "pub(crate)")]
AllOneStringStyle,
}
```