Derive Macro Error 

#[derive(Error)]
{
    // Attributes available to this derive:
    #[derail]
}

Generates an implementation of derail::Error and Display.

This macro can be applied to structs and enums. Unless otherwise noted, each struct and enum variant will be observed by a derail::Visitor, followed by its children if it has any.

Options

This derive macro accepts attributes of the form #[derail(..., ..., ...)], where each ... is an option. At least one option is required per attribute. Trailing commas are optional. Descriptions of each option follow.

child

• Applicable to: struct fields, enum variant fields.
• Optional.
• Conflicts with: children, skip_child, skip_self.

This option causes derail::Error::accept to be generated such that the field is visited as a single child. The field must be a derail::Error. For structs and enum variants with named fields, set the name of the field to child rather than using this attribute.

children

• Applicable to: struct fields, enum variant fields.
• Optional.
• Conflicts with: child, skip_child, skip_self.

This option causes derail::Error::accept to be generated such that the field is visited as a group of children. The field must be an ExactSizeIterator that yields derail::Errors. For structs and enum variants with named fields, set the name of the field to children rather than using this attribute.

skip_child

• Applicable to: struct fields, enum variant fields.
• Optional.
• Conflicts with: child, children, skip_self.

This option causes derail::Error::accept to be generated such that the field’s children are visited, but the field itself is skipped. The field must be a derail::Error. For structs and enum variants with named fields, set the name of the field to skip_child rather than using this attribute.

skip_self

• Applicable to: struct fields, enum variant fields.
• Optional.
• Conflicts with: child, children, skip_child, display(...).

This option causes derail::Error::accept to be generated such that the struct or enum variant containing this field is skipped, and the field is visited directly. It also causes Display::fmt to be generated for this struct or enum variant such that the field’s implementation of Display::fmt is called directly. The field must be a derail::Error. For structs and enum variants with named fields, set the name of the field to skip_self rather than using this attribute.

map_details = ...

• Applicable to: struct fields, enum variant fields; only where the chosen field also has one of the child, children, skip_child, or skip_self options set.
• Required if the parent and child have different concrete types for derail::Error::Details.

This option causes derail::Error::accept (and derail::Error::details in the case of skip_self) to be generated such that the function provided in place of ... is used to map the child’s derail::Error::Details into the parent’s. If = ... is omitted, From::from will be used.

This is primarily useful for enabling a derail::Error to contain child derail::Errors where the parent and children have different concrete types for derail::Error::Details. Where an identity function would be provided in place of ..., simply omit this option instead.

display(...)

• Applicable to: structs, enum variants.
• Required unless skip_self is used.
• Conflicts with: skip_self.

This option causes Display::fmt to be generated such that the tokens provided in place of ... are provided to write after $dst. Fields of structs and enum variants with named fields can be referred to by the same identifier. Fields of structs and enum variants with unnamed fields can be referred to by an identifier made by prefixing their index with an underscore.

See also the rules for implementing Display::fmt for Error implementors.

details

• Applicable to: struct fields, enum variant fields.
• Required if derail::Error::Details is not ().

This option chooses the field to return when derail::Error::details is called. For structs and enum variants with named fields, set the name of the field to details rather than using this attribute.

details = ...

• Applicable to: structs, enum variants.
• Required if derail::Error::Details is not () and there is no field named details or decorated with #[derail(details)].

This option causes derail::Error::details to be generated such that the expression provided in place of ... is evaluated and returned. Like with display(...), the expression can access named fields of the struct or enum variant using the same identifier, and unnamed fields using the index prefixed with an underscore.

type Details = ...

• Applicable to: structs, enums.
• Required.

This option sets the type to use for the derail::Error::Details associated type in the generated derail::Error implementation.

impl<...> Error where { ... }

• Applicable to: structs, enums.
• Optional.

This option allows for the generated derail::Error implementation to have its impl generics extended and its where clause set. Any generic parameters on the struct or enum definition will already be present in the generated impl generics. The <...> portion can be used to extend the set of impl generics (with or without predicates) and may be omitted if doing so is not required. Comma-separated where clause predicates can be specified within the curly brackets. No predicates will be automatically inferred from the struct or enum definition.

impl<...> Display where { ... }

• Applicable to: structs, enums.
• Optional.

This option allows for the generated Display implementation to have its impl generics extended and its where clause set. Any generic parameters on the struct or enum definition will already be present in the generated impl generics. The <...> portion can be used to extend the set of impl generics (with or without predicates) and may be omitted if doing so is not required. Comma-separated where clause predicates can be specified within the curly brackets. No predicates will be automatically inferred from the struct or enum definition.

crate = ...

• Applicable to: structs, enums.
• Optional.

This option can be used to change the path to the root of the derail crate used in macro expansion.