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pub use paste::paste;
/**
`define_error!` is the main macro that implements a mini DSL to
define error types using `flex-error`. The DSL syntax
is as follows:
```ignore
define_error! {
ErrorName {
SubErrorWithFieldsAndErrorSource
{ field1: Type1, field2: Type2, ... }
[ ErrorSource ]
| e | { format_args!(
"format error message with field1: {}, field2: {}, source: {}",
e.field1, e.field2, e.source)
},
SubErrorWithFieldsOnly
{ field1: Type1, field2: Type2, ... }
| e | { format_args!(
"format error message with field1: {}, field2: {}",
e.field1, e.field2)
},
SubErrorWithSourceOnly
[ ErrorSource ]
| e | { format_args!(
"format error message with source: {}",
e.source)
},
SubError
| e | { format_args!(
"only suberror message")
},
}
}
```
## Macro Expansion
Behind the scene, for an error named `MyError`, `define_error!`
does the following:
- Define a struct in the form
```ignore
pub struct MyError(pub MyErrorDetail, pub flex_error::DefaultTracer)
```
- Define an enum in the form
```ignore
pub enum MyError { ... }
```
For each suberror named `MySubError`, does the following:
- Define a variant in `MyError` in the form
```ignore
pub enum MyError { ..., MySubError(MySubErrorSubdetail) ,... }
```
- Implement [`core::fmt::Debug`] and [`core::fmt::Display`]
for `MyError`.
- If the `"std"` feature is enabled on the `flex-error` crate,
it will generate an `impl` block for [`std::error::Error`].
- Implement [`ErrorSource<DefaultTracer>`](crate::ErrorSource)
for `MyError`, with `MyErrorDetail` being the `Detail` type,
and `MyError` being the `Source` type.
- Implement the following helper methods in `impl MyError {...}`:
- `pub fn detail(&self) -> &MyErrorDetail`
- `pub fn trace(&self) -> flex_error::DefaultTracer`
- `pub fn add_trace<E: Display>(self, e: &E) -> MyError`
- Define a struct in the form
```ignore
pub struct MySubErrorSubdetail { ... }
```
- For each field named `my_field: MyFieldType`, define a struct
field in the form
```ignore
struct MySubErrorSubdetail { ..., pub my_field: MyFieldType, ... }
```
- If the sub-error has an error source `MySource` implementing
[`ErrorSource<DefaultTracer>`](crate::ErrorSource), define a `source` field
in the form
```ignore
struct MySubErrorSubdetail { ..., pub source: MySource::Detail }
```
- Implement [`core::fmt::Display`] in the form
```ignore
impl Display for MySubErrorSubdetail { ... }
```
- Define a snake-cased error constructor method in `MyError` in the form
```ignore
impl MyError { pub fn my_sub_error(...) -> MyError { ... } }
```
- For each field named `my_field: MyFieldType`, define a
function argument in the form
```ignore
fn my_sub_error(..., my_field: MyFieldType, ...)
```
- If the sub-error has an error source `MySource` implementing
[`ErrorSource`](crate::ErrorSource), define a `source` field in the form
```ignore
fn my_sub_error(..., source: MySource::Detail)
```
## Formatter
For each sub-error definition, a formatter needs to be provided using the
closure syntax. For example, the following definition:
```ignore
MyError {
MySubError
{ code: u32 }
[ MySource ]
| e | { format_args!("error with code {}", e.code) },
...
}
```
will include the following expansion:
```
impl ::core::fmt::Display for MySubErrorSubdetail {
fn fmt(&self, f: &mut ::core::fmt::Formatter<'_>) -> ::core::fmt::Result {
let e = self;
write!(f, "{}", format_args!("error with code {}", e.code))
}
}
```
Note that there is no need to manually display the error source, as the
source is already automatically traced by the error tracer.
If a sub-error do not have any field, we can write a simpler form of the
formatter like:
```ignore
MyError {
MySubError
| _ | { "something went wrong" },
...
}
```
## Example Definition
We can demonstrate the macro expansion of `define_error!` with the following example:
```ignore
// An external error type implementing Display
use external_crate::ExternalError;
define_error! {
FooError {
Bar
{ code: u32 }
[ DisplayError<ExternalError> ]
| e | { format_args!("Bar error with code {}", e.code) },
Baz
{ extra: String }
| e | { format_args!("General Baz error with extra detail: {}", e.extra) }
}
}
```
The above code will be expanded into something like follows:
```ignore
pub struct FooError(pub FooErrorDetail, pub flex_error::DefaultTracer);
#[derive(Debug)]
pub enum FooErrorDetail {
Bar(BarSubdetail),
Baz(BazSubdetail),
}
#[derive(Debug)]
pub struct BarSubdetail {
pub code: u32,
pub source: ExternalError
}
#[derive(Debug)]
pub struct BazSubdetail {
pub extra: String
}
fn bar_error(code: u32, source: ExternalError) -> FooError { ... }
fn baz_error(extra: String) -> FooError { ... }
impl ::core::fmt::Display for BarSubdetail {
fn fmt(&self, f: &mut ::core::fmt::Formatter<'_>) -> ::core::fmt::Result {
let e = self;
write!(f, "{}", format_args!("Bar error with code {}", e.code))
}
}
impl ::core::fmt::Display for BazSubdetail {
fn fmt(&self, f: &mut ::core::fmt::Formatter<'_>) -> ::core::fmt::Result {
let e = self;
write!(f, "{}", format_args!("General Baz error with extra detail: {}", e.code))
}
}
impl Display for FooErrorDetail { ... }
```
For the detailed macro expansion, you can use [cargo-expand](https://github.com/dtolnay/cargo-expand)
to expand the Rust module that uses `define_error!` to see how the error definition
gets expanded.
Since `FooError` implements [`ErrorSource`](crate::ErrorSource), it can be used
directly as a error source in other error definitions. For example:
```ignore
define_error! {
QuuxError {
Foo
{ action: String }
[ FooError ]
| e | { format_args!("error arised from Foo when performing action {}", e.action) },
...
}
}
```
Would be expanded to include the following definitions:
```ignore
pub struct FooSubdetail {
pub action: String,
pub source: FooErrorDetail
}
pub fn foo_error(action: String, source: FooError) { ... }
```
In the formatter for `QuuxErrorDetail::Foo`, we can also see that it does not
need to include the error string from `FooError`. This is because the error
tracer already takes care of the source error trace, so the full trace is
automatically tracked inside `foo_error`. The outer error only need to
add additional detail about what caused the source error to be raised.
## Attributes
`define_error!` supports adding attributes to the generated error types.
### First `doc` Attribute
If the first attribute is a [`doc`](https://doc.rust-lang.org/rustdoc/the-doc-attribute.html)
attribute, it is attached to the main error struct. For example:
```ignore
define_error! {
/// Documentation for MyError
MyError { ... }
}
```
will include the following expansion:
```ignore
#[doc = "Documentation for MyError"]
pub struct MyError(pub MyErrorDetail, pub flex_error::DefaultTracer);
```
## Common Attributes
For all other attributes defined on the main error type,
they are defined on the _error detail_ and _sub-errors type. For example:
```ignore
define_error! {
#[derive(Debug, Clone)]
MyError {
Foo
{ ... }
| _ | { "foo error" },
Bar
{ ... }
| _ | { "bar error" },
}
}
```
will include the following expansion:
```ignore
pub struct MyError(pub MyErrorDetail, pub flex_error::DefaultTracer);
#[derive(Debug, Clone)]
pub enum MyErrorDetail { ... }
#[derive(Debug, Clone)]
pub struct FooSubdetail { ... }
#[derive(Debug, Clone)]
pub struct BarSubdetail { ... }
```
Note that we do not add the `derive` attribute to the main error struct
`MyError`. This is because the [`DefaultTracer`](crate::DefaultTracer)
type is opaque, and auto deriving traits like `Clone` on it is
generally not supported.
If you need the main error type to implement certain traits,
you can instead define your own custom `impl` definition for it.
## Sub Attributes
We can also define custom attributes for only the sub-error.
In that case, the attribute is given to the sub-detail type.
For example:
```ignore
define_error! {
MyError {
/// Documentation for Foo
#[derive(Clone)]
Foo
{ ... }
| _ | { "foo error" },
...
}
}
```
will include the following expansion:
```ignore
#[doc = "Documentation for Foo"]
#[derive(Clone)]
pub struct FooSubdetail { ... }
```
Note that if no attribute is given to the main error,
the `#[derive(Debug)]` trait is added by default.
So there is no need to derive it again in the
sub-errors.
**/
#[macro_export]
macro_rules! define_error {
( $name:ident
{ $($suberrors:tt)* }
) => {
$crate::define_error_with_tracer![
@tracer( $crate::DefaultTracer ),
@attr[ derive(Debug) ],
@name( $name ),
@suberrors{ $($suberrors)* }
];
};
( #[doc = $doc:literal] $( #[$attr:meta] )*
$name:ident
{ $($suberrors:tt)* }
) => {
$crate::define_error_with_tracer![
@tracer( $crate::DefaultTracer ),
@doc( $doc ),
@attr[ $( $attr ),* ],
@name( $name ),
@suberrors{ $($suberrors)* }
];
};
( $( #[$attr:meta] )*
$name:ident
{ $($suberrors:tt)* }
) => {
$crate::define_error_with_tracer![
@tracer( $crate::DefaultTracer ),
@attr[ $( $attr ),* ],
@name( $name ),
@suberrors{ $($suberrors)* }
];
};
( @with_tracer[ $tracer:ty ]
$name:ident,
{ $($suberrors:tt)* }
) => {
$crate::define_error_with_tracer![
@tracer( $tracer ),
@attr[ derive(Debug) ],
@name( $name ),
@suberrors{ $($suberrors)* }
];
};
( @with_tracer[ $tracer:ty ]
$( #[$attr:meta] )*
$name:ident,
@suberrors{ $($suberrors:tt)* }
) => {
$crate::define_error_with_tracer![
@tracer( $tracer ),
@attr[ $( $attr ),* ],
@name( $name ),
@suberrors{ $($suberrors)* }
];
};
}
/// This macro allows error types to be defined with custom error tracer types
/// other than [`DefaultTracer`](crate::DefaultTracer). Behind the scene,
/// a macro call to `define_error!{ ... } really expands to
/// `define_error_with_tracer!{ flex_error::DefaultTracer; ... }`
#[macro_export]
#[doc(hidden)]
macro_rules! define_error_with_tracer {
( @tracer( $tracer:ty ),
$( @doc($doc:literal), )?
@attr[ $( $attr:meta ),* ],
@name($name:ident),
@suberrors{ $($suberrors:tt)* } $(,)?
) => {
$crate::macros::paste![
$crate::define_main_error!(
@tracer( $tracer ),
$( @doc( $doc ), )?
@name( $name )
);
$crate::define_error_detail!(
@attr[ $( $attr ),* ] ,
@name( $name ),
@suberrors{ $($suberrors)* });
$crate::define_suberrors! {
@tracer($tracer),
@attr[ $( $attr ),* ],
@name($name),
{ $( $suberrors )* }
}
];
};
}
#[macro_export]
#[doc(hidden)]
macro_rules! define_main_error {
( @tracer( $tracer:ty ),
$( @doc( $doc:literal ), )?
@name( $name:ident ) $(,)?
) => {
$crate::macros::paste![
$crate::define_main_error_struct!(
@tracer( $tracer ),
$( @doc($doc), )?
@name( $name )
);
impl $crate::ErrorSource<$tracer> for $name {
type Source = Self;
type Detail = [< $name Detail >];
fn error_details($name(detail, trace): Self) -> ([< $name Detail >], Option<$tracer>) {
(detail, Some(trace))
}
}
impl ::core::fmt::Debug for $name
where
$tracer: ::core::fmt::Debug,
{
fn fmt(&self, f: &mut ::core::fmt::Formatter<'_>) -> ::core::fmt::Result {
::core::fmt::Debug::fmt(self.trace(), f)
}
}
impl ::core::fmt::Display for $name
where
$tracer: ::core::fmt::Debug,
{
fn fmt(&self, f: &mut ::core::fmt::Formatter<'_>)
-> ::core::fmt::Result
{
// Always use `Debug` to format error traces, as eyre do not
// include full back trace information in normal Display mode.
::core::fmt::Debug::fmt(self.trace(), f)
}
}
$crate::define_std_err_impl!(
@tracer( $tracer ),
@name( $name )
);
impl $name {
pub fn detail(&self) -> &[< $name Detail >] {
&self.0
}
pub fn into_detail(self) -> [< $name Detail >] {
self.0
}
pub fn trace(&self) -> &$tracer {
&self.1
}
pub fn into_trace(self) -> $tracer {
self.1
}
pub fn add_trace<E: ::core::fmt::Display>(self, message: &E) -> Self
where
$tracer: $crate::ErrorMessageTracer,
{
let detail = self.0;
let trace = $crate::ErrorMessageTracer::add_message(self.1, message);
$name(detail, trace)
}
pub fn trace_from<E, Cont>(source: E::Source, cont: Cont) -> Self
where
E: $crate::ErrorSource<$tracer>,
$tracer: $crate::ErrorMessageTracer,
Cont: FnOnce(E::Detail) -> [< $name Detail >],
{
let (detail1, m_trace1) = E::error_details(source);
let detail2 = cont(detail1);
match m_trace1 {
Some(trace1) => {
let trace2 = $crate::ErrorMessageTracer::add_message(trace1, &detail2);
$name(detail2, trace2)
}
None => {
let trace2 = $crate::ErrorMessageTracer::new_message(&detail2);
$name(detail2, trace2)
}
}
}
}
];
}
}
// define the impl for `std::error::Error` only in std mode
#[cfg(feature = "std")]
#[macro_export]
#[doc(hidden)]
macro_rules! define_std_err_impl {
( @tracer( $tracer:ty ),
@name( $name:ident ) $(,)?
) => {
$crate::macros::paste![
impl $crate::StdError for $name
where
[< $name Detail >]: ::core::fmt::Display,
$tracer: ::core::fmt::Debug + ::core::fmt::Display,
$tracer: $crate::ErrorMessageTracer,
{
fn source(&self) -> ::core::option::Option<&(dyn $crate::StdError + 'static)> {
$crate::ErrorMessageTracer::as_error(self.trace())
}
}
];
}
}
// do not define the impl for `std::error::Error` when in no_std mode
#[cfg(not(feature = "std"))]
#[macro_export]
#[doc(hidden)]
macro_rules! define_std_err_impl {
( @tracer( $tracer:ty ),
@name( $name:ident ) $(,)?
) => {};
}
#[macro_export]
#[doc(hidden)]
macro_rules! define_main_error_struct {
( @tracer( $tracer:ty ),
$( @doc( $doc:literal ), )?
@name( $name:ident ) $(,)?
) => {
$crate::macros::paste![
$( #[doc = $doc] )?
pub struct $name (pub [< $name Detail >], pub $tracer);
];
}
}
#[macro_export]
#[doc(hidden)]
macro_rules! with_suberrors {
( @cont($cont:path),
@ctx[ $($args:tt)* ],
@suberrors{
$(
$( #[$sub_attr:meta] )*
$suberror:ident
$( { $( $arg_name:ident : $arg_type:ty ),* $(,)? } )?
$( [ $source:ty ] )?
| $formatter_arg:pat | $formatter:expr
),* $(,)?
} $(,)?
) => {
$cont!( @ctx[ $( $args )* ], @suberrors{ $( $suberror ),* } );
}
}
#[macro_export]
#[doc(hidden)]
macro_rules! define_error_detail {
( @attr[ $( $attr:meta ),* ],
@name( $name:ident ),
@suberrors{ $($suberrors:tt)* } $(,)?
) => {
$crate::with_suberrors!(
@cont($crate::define_error_detail_enum),
@ctx[
@attr[ $( $attr ),* ],
@name($name)
],
@suberrors{ $( $suberrors )* }
);
$crate::with_suberrors!(
@cont($crate::define_error_detail_display),
@ctx[
@name($name)
],
@suberrors{ $( $suberrors )* }
);
}
}
#[macro_export]
#[doc(hidden)]
macro_rules! define_error_detail_enum {
( @ctx[
@attr[ $( $attr:meta ),* ],
@name($name:ident)
],
@suberrors{ $( $suberror:ident ),* } $(,)?
) => {
$crate::macros::paste! [
$( #[$attr] )*
pub enum [< $name Detail >] {
$(
$suberror (
[< $suberror Subdetail >]
)
),*
}
];
}
}
#[macro_export]
#[doc(hidden)]
macro_rules! define_error_detail_display {
( @ctx[
@name( $name:ident )
],
@suberrors{ $( $suberror:ident ),* } $(,)?
) => {
$crate::macros::paste! [
impl ::core::fmt::Display for [< $name Detail >] {
fn fmt(&self, f: &mut ::core::fmt::Formatter<'_>)
-> ::core::fmt::Result
{
match self {
$(
Self::$suberror( suberror ) => {
::core::write!( f, "{}", suberror )
}
),*
}
}
}
];
}
}
#[macro_export]
#[doc(hidden)]
macro_rules! define_suberrors {
( @tracer($tracer:ty),
@attr[ $( $attr:meta ),* ],
@name($name:ident),
{} $(,)?
) => { };
( @tracer($tracer:ty),
@attr[ $( $attr:meta ),* ],
@name($name:ident),
{
$( #[$sub_attr:meta] )*
$suberror:ident
$( { $( $arg_name:ident : $arg_type:ty ),* $(,)? } )?
$( [ $source:ty ] )?
| $formatter_arg:pat | $formatter:expr
$( , $($tail:tt)* )?
}
) => {
$crate::macros::paste![
$crate::define_suberror! {
@tracer( $tracer ),
@attr[ $( $attr ),* ],
@sub_attr[ $( $sub_attr ),* ],
@name( $name ),
@suberror( $suberror ),
@args( $( $( $arg_name : $arg_type ),* )? )
$( @source[ $source ] )?
}
impl ::core::fmt::Display for [< $suberror Subdetail >] {
fn fmt(&self, f: &mut ::core::fmt::Formatter<'_>) -> ::core::fmt::Result {
use ::core::format_args;
let $formatter_arg = self;
::core::write!(f, "{}", $formatter)
}
}
impl $name {
$crate::define_error_constructor! {
@tracer( $tracer ),
@name( $name ),
@suberror( $suberror ),
@args( $( $( $arg_name : $arg_type ),* )? )
$( @source[ $source ] )?
}
}
];
$crate::define_suberrors! {
@tracer($tracer),
@attr[ $( $attr ),* ],
@name($name),
{ $( $( $tail )* )? }
}
};
}
/// Internal macro used to define suberror structs
#[macro_export]
#[doc(hidden)]
macro_rules! define_suberror {
( @tracer( $tracer:ty ),
@attr[ $( $attr:meta ),* ],
@sub_attr[ $( $sub_attr:meta ),* ],
@name( $name:ident ),
@suberror( $suberror:ident ),
@args( $( $arg_name:ident: $arg_type:ty ),* )
@source[ Self ]
) => {
$crate::macros::paste! [
$( #[ $attr ] )*
$( #[ $sub_attr ] )*
pub struct [< $suberror Subdetail >] {
$( pub $arg_name: $arg_type, )*
pub source: $crate::alloc::boxed::Box< [< $name Detail >] >
}
];
};
( @tracer( $tracer:ty ),
@attr[ $( $attr:meta ),* ],
@sub_attr[ $( $sub_attr:meta ),* ],
@name( $name:ident ),
@suberror( $suberror:ident ),
@args( $( $arg_name:ident: $arg_type:ty ),* )
$( @source[ $source:ty ] )?
) => {
$crate::macros::paste! [
$( #[ $attr ] )*
$( #[ $sub_attr ] )*
pub struct [< $suberror Subdetail >] {
$( pub $arg_name: $arg_type, )*
$( pub source: $crate::AsErrorDetail<$source, $tracer> )?
}
];
};
}
/// Internal macro used to define suberror constructor functions
#[macro_export]
#[doc(hidden)]
macro_rules! define_error_constructor {
( @tracer( $tracer:ty ),
@name( $name:ident ),
@suberror( $suberror:ident ),
@args( $( $arg_name:ident: $arg_type:ty ),* ) $(,)?
) => {
$crate::macros::paste! [
pub fn [< $suberror:snake >](
$( $arg_name: $arg_type, )*
) -> $name
{
let detail = [< $name Detail >]::$suberror([< $suberror Subdetail >] {
$( $arg_name, )*
});
let trace = < $tracer as $crate::ErrorMessageTracer >::new_message(&detail);
$name(detail, trace)
}
];
};
( @tracer( $tracer:ty ),
@name( $name:ident ),
@suberror( $suberror:ident ),
@args( $( $arg_name:ident: $arg_type:ty ),* )
@source[ Self ]
) => {
$crate::macros::paste! [
pub fn [< $suberror:snake >](
$( $arg_name: $arg_type, )*
source: $name
) -> $name
{
let detail = [< $name Detail >]::$suberror([< $suberror Subdetail >] {
$( $arg_name, )*
source: Box::new(source.0),
});
let trace = source.1.add_message(&detail);
$name(detail, trace)
}
];
};
( @tracer( $tracer:ty ),
@name( $name:ident ),
@suberror( $suberror:ident ),
@args( $( $arg_name:ident: $arg_type:ty ),* )
@source[ $source:ty ]
) => {
$crate::macros::paste! [
pub fn [< $suberror:snake >](
$( $arg_name: $arg_type, )*
source: $crate::AsErrorSource< $source, $tracer >
) -> $name
{
$name::trace_from::<$source, _>(source,
| source_detail | {
[< $name Detail >]::$suberror([< $suberror Subdetail >] {
$( $arg_name, )*
source: source_detail,
})
})
}
];
};
}