core: give SetGlobalDefaultError a useful Debug impl
#2250
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## Motivation
When a global default dispatcher has already been set, the
`dispatch::set_global_default` function fails with a
`SetGlobalDefaultError`. The `fmt::Display` impl for this type includes
a message explaining that the error indicates that a global default has
already been set, but the `fmt::Debug` impl is derived, and just looks
like this:
```
SetGlobalDefaultError { _no_construct: () }
```
which isn't particularly helpful.
Unfortunately, when `unwrap()`ping or `expect()`ing a `Result`, the
`fmt::Debug` implementation for the error type is used, rather than
`fmt::Display`. This means that the error message will not explain to
the user why setting the global default dispatcher failed, which is a
bummer.
## Solution
This branch replaces the derived `Debug` impl with a manually
implemented one that prints the same message as the `Display` impl, but
formatted like a tuple struct with a single string field. This avoids
emitting `Debug` output that's *just* a textual human-readable message,
rather than looking like Rust code, but ensures the message is visible
to the user when writing code like
```rust
tracing::dispatch::set_global_default(foo).unwrap();
```
The mesasge now looks like:
```
SetGlobalDefaultError("a global default trace dispatcher has already been set")
```
which should be a bit easier to debug.
hawkw
added a commit
that referenced
this pull request
Jul 29, 2022
## Motivation
When a global default dispatcher has already been set, the
`dispatch::set_global_default` function fails with a
`SetGlobalDefaultError`. The `fmt::Display` impl for this type includes
a message explaining that the error indicates that a global default has
already been set, but the `fmt::Debug` impl is derived, and just looks
like this:
```
SetGlobalDefaultError { _no_construct: () }
```
which isn't particularly helpful.
Unfortunately, when `unwrap()`ping or `expect()`ing a `Result`, the
`fmt::Debug` implementation for the error type is used, rather than
`fmt::Display`. This means that the error message will not explain to
the user why setting the global default dispatcher failed, which is a
bummer.
## Solution
This branch replaces the derived `Debug` impl with a manually
implemented one that prints the same message as the `Display` impl, but
formatted like a tuple struct with a single string field. This avoids
emitting `Debug` output that's *just* a textual human-readable message,
rather than looking like Rust code, but ensures the message is visible
to the user when writing code like
```rust
tracing::dispatch::set_global_default(foo).unwrap();
```
The mesasge now looks like:
```
SetGlobalDefaultError("a global default trace dispatcher has already been set")
```
which should be a bit easier to debug.
hawkw
added a commit
that referenced
this pull request
Jul 29, 2022
## Motivation
When a global default dispatcher has already been set, the
`dispatch::set_global_default` function fails with a
`SetGlobalDefaultError`. The `fmt::Display` impl for this type includes
a message explaining that the error indicates that a global default has
already been set, but the `fmt::Debug` impl is derived, and just looks
like this:
```
SetGlobalDefaultError { _no_construct: () }
```
which isn't particularly helpful.
Unfortunately, when `unwrap()`ping or `expect()`ing a `Result`, the
`fmt::Debug` implementation for the error type is used, rather than
`fmt::Display`. This means that the error message will not explain to
the user why setting the global default dispatcher failed, which is a
bummer.
## Solution
This branch replaces the derived `Debug` impl with a manually
implemented one that prints the same message as the `Display` impl, but
formatted like a tuple struct with a single string field. This avoids
emitting `Debug` output that's *just* a textual human-readable message,
rather than looking like Rust code, but ensures the message is visible
to the user when writing code like
```rust
tracing::dispatch::set_global_default(foo).unwrap();
```
The mesasge now looks like:
```
SetGlobalDefaultError("a global default trace dispatcher has already been set")
```
which should be a bit easier to debug.
hawkw
added a commit
that referenced
this pull request
Jul 29, 2022
## Motivation
When a global default dispatcher has already been set, the
`dispatch::set_global_default` function fails with a
`SetGlobalDefaultError`. The `fmt::Display` impl for this type includes
a message explaining that the error indicates that a global default has
already been set, but the `fmt::Debug` impl is derived, and just looks
like this:
```
SetGlobalDefaultError { _no_construct: () }
```
which isn't particularly helpful.
Unfortunately, when `unwrap()`ping or `expect()`ing a `Result`, the
`fmt::Debug` implementation for the error type is used, rather than
`fmt::Display`. This means that the error message will not explain to
the user why setting the global default dispatcher failed, which is a
bummer.
## Solution
This branch replaces the derived `Debug` impl with a manually
implemented one that prints the same message as the `Display` impl, but
formatted like a tuple struct with a single string field. This avoids
emitting `Debug` output that's *just* a textual human-readable message,
rather than looking like Rust code, but ensures the message is visible
to the user when writing code like
```rust
tracing::dispatch::set_global_default(foo).unwrap();
```
The mesasge now looks like:
```
SetGlobalDefaultError("a global default trace dispatcher has already been set")
```
which should be a bit easier to debug.
hawkw
added a commit
that referenced
this pull request
Jul 29, 2022
# 0.1.29 (July 29, 2022) This release of `tracing-core` adds `PartialEq` and `Eq` implementations for metadata types, and improves error messages when setting the global default subscriber fails. ### Added - `PartialEq` and `Eq` implementations for `Metadata` ([#2229]) - `PartialEq` and `Eq` implementations for `FieldSet` ([#2229]) ### Fixed - Fixed unhelpful `fmt::Debug` output for `dispatcher::SetGlobalDefaultError` ([#2250]) - Fixed compilation with `-Z minimal-versions` ([#2246]) Thanks to @jswrenn and @CAD97 for contributing to this release! [#2229]: #2229 [#2246]: #2246 [#2250]: #2250
hawkw
added a commit
that referenced
this pull request
Jul 29, 2022
# 0.1.29 (July 29, 2022) This release of `tracing-core` adds `PartialEq` and `Eq` implementations for metadata types, and improves error messages when setting the global default subscriber fails. ### Added - `PartialEq` and `Eq` implementations for `Metadata` ([#2229]) - `PartialEq` and `Eq` implementations for `FieldSet` ([#2229]) ### Fixed - Fixed unhelpful `fmt::Debug` output for `dispatcher::SetGlobalDefaultError` ([#2250]) - Fixed compilation with `-Z minimal-versions` ([#2246]) Thanks to @jswrenn and @CAD97 for contributing to this release! [#2229]: #2229 [#2246]: #2246 [#2250]: #2250
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Motivation
When a global default dispatcher has already been set, the
dispatch::set_global_defaultfunction fails with aSetGlobalDefaultError. Thefmt::Displayimpl for this type includesa message explaining that the error indicates that a global default has
already been set, but the
fmt::Debugimpl is derived, and just lookslike this:
which isn't particularly helpful.
Unfortunately, when
unwrap()ping orexpect()ing aResult, thefmt::Debugimplementation for the error type is used, rather thanfmt::Display. This means that the error message will not explain tothe user why setting the global default dispatcher failed, which is a
bummer.
Solution
This branch replaces the derived
Debugimpl with a manuallyimplemented one that prints the same message as the
Displayimpl, butformatted like a tuple struct with a single string field. This avoids
emitting
Debugoutput that's just a textual human-readable message,rather than looking like Rust code, but ensures the message is visible
to the user when writing code like
The mesasge now looks like:
which should be a bit easier to debug.