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</pre><pre class="rust ">
<span class="doccomment">//! An experimental new error-handling library.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! The primary items exported by this library are:</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! - `Fail`: a new trait for custom error types in Rust.</span>
<span class="doccomment">//! - `Error`: a wrapper around `Fail` types to make it easy to coalesce them</span>
<span class="doccomment">//! at higher levels.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! As a general rule, library authors should create their own error types and</span>
<span class="doccomment">//! implement `Fail` for them, whereas application authors should primarily</span>
<span class="doccomment">//! deal with the `Error` type. There are exceptions to this rule, though, in</span>
<span class="doccomment">//! both directions, and users should do whatever seems most appropriate to</span>
<span class="doccomment">//! their situation.</span>
<span class="attribute">#![<span class="ident">cfg_attr</span>(<span class="ident">not</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"std"</span>), <span class="ident">no_std</span>)]</span>
<span class="attribute">#![<span class="ident">deny</span>(<span class="ident">missing_docs</span>)]</span>
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">with_std</span> { ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">i</span>:<span class="ident">item</span>)<span class="kw-2">*</span>) <span class="op">=></span> ($(<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"std"</span>)]</span><span class="macro-nonterminal">$</span><span class="macro-nonterminal">i</span>)<span class="kw-2">*</span>) }
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">without_std</span> { ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">i</span>:<span class="ident">item</span>)<span class="kw-2">*</span>) <span class="op">=></span> ($(<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">not</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"std"</span>))]</span><span class="macro-nonterminal">$</span><span class="macro-nonterminal">i</span>)<span class="kw-2">*</span>) }
<span class="kw">mod</span> <span class="ident">backtrace</span>;
<span class="kw">mod</span> <span class="ident">compat</span>;
<span class="kw">mod</span> <span class="ident">context</span>;
<span class="kw">mod</span> <span class="ident">result_ext</span>;
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">any</span>::<span class="ident">TypeId</span>;
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">fmt</span>::{<span class="ident">Debug</span>, <span class="ident">Display</span>};
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">backtrace</span>::<span class="ident">Backtrace</span>;
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">compat</span>::<span class="ident">Compat</span>;
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">context</span>::<span class="ident">Context</span>;
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">result_ext</span>::<span class="ident">ResultExt</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"derive"</span>)]</span>
<span class="attribute">#[<span class="ident">allow</span>(<span class="ident">unused_imports</span>)]</span>
<span class="attribute">#[<span class="ident">macro_use</span>]</span>
<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">failure_derive</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"derive"</span>)]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">hidden</span>)]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">failure_derive</span>::<span class="kw-2">*</span>;
<span class="macro">with_std</span><span class="macro">!</span> {
<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">core</span>;
<span class="kw">mod</span> <span class="ident">sync_failure</span>;
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">sync_failure</span>::<span class="ident">SyncFailure</span>;
<span class="kw">mod</span> <span class="ident">error</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">error</span>::<span class="ident">Error</span> <span class="kw">as</span> <span class="ident">StdError</span>;
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">error</span>::<span class="ident">Error</span>;
<span class="kw">mod</span> <span class="ident">macros</span>;
<span class="kw">mod</span> <span class="ident">error_message</span>;
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">error_message</span>::<span class="ident">err_msg</span>;
}
<span class="doccomment">/// The `Fail` trait.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Implementors of this trait are called 'failures'.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// All error types should implement `Fail`, which provides a baseline of</span>
<span class="doccomment">/// functionality that they all share.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// `Fail` has no required methods, but it does require that your type</span>
<span class="doccomment">/// implement several other traits:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// - `Display`: to print a user-friendly representation of the error.</span>
<span class="doccomment">/// - `Debug`: to print a verbose, developer-focused representation of the</span>
<span class="doccomment">/// error.</span>
<span class="doccomment">/// - `Send + Sync`: Your error type is required to be safe to transfer to and</span>
<span class="doccomment">/// reference from another thread</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Additionally, all failures must be `'static`. This enables downcasting.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// `Fail` provides several methods with default implementations. Two of these</span>
<span class="doccomment">/// may be appropriate to override depending on the definition of your</span>
<span class="doccomment">/// particular failure: the `cause` and `backtrace` methods.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The `failure_derive` crate provides a way to derive the `Fail` trait for</span>
<span class="doccomment">/// your type. Additionally, all types that already implement</span>
<span class="doccomment">/// `std::error::Error`, and are also `Send`, `Sync`, and `'static`, implement</span>
<span class="doccomment">/// `Fail` by a blanket impl.</span>
<span class="kw">pub</span> <span class="kw">trait</span> <span class="ident">Fail</span>: <span class="ident">Display</span> <span class="op">+</span> <span class="ident">Debug</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</span> <span class="op">+</span> <span class="lifetime">'static</span> {
<span class="doccomment">/// Returns a reference to the underlying cause of this failure, if it</span>
<span class="doccomment">/// is an error that wraps other errors.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returns `None` if this failure does not have another error as its</span>
<span class="doccomment">/// underlying cause. By default, this returns `None`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This should **never** return a reference to `self`, but only return</span>
<span class="doccomment">/// `Some` when it can return a **different** failure. Users may loop</span>
<span class="doccomment">/// over the cause chain, and returning `self` would result in an infinite</span>
<span class="doccomment">/// loop.</span>
<span class="kw">fn</span> <span class="ident">cause</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">Fail</span><span class="op">></span> {
<span class="prelude-val">None</span>
}
<span class="doccomment">/// Returns a reference to the `Backtrace` carried by this failure, if it</span>
<span class="doccomment">/// carries one.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returns `None` if this failure does not carry a backtrace. By</span>
<span class="doccomment">/// default, this returns `None`.</span>
<span class="kw">fn</span> <span class="ident">backtrace</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">Backtrace</span><span class="op">></span> {
<span class="prelude-val">None</span>
}
<span class="doccomment">/// Provides context for this failure.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This can provide additional information about this error, appropriate</span>
<span class="doccomment">/// to the semantics of the current layer. That is, if you have a</span>
<span class="doccomment">/// lower-level error, such as an IO error, you can provide additional context</span>
<span class="doccomment">/// about what that error means in the context of your function. This</span>
<span class="doccomment">/// gives users of this function more information about what has gone</span>
<span class="doccomment">/// wrong.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This takes any type that implements `Display`, as well as</span>
<span class="doccomment">/// `Send`/`Sync`/`'static`. In practice, this means it can take a `String`</span>
<span class="doccomment">/// or a string literal, or another failure, or some other custom context-carrying</span>
<span class="doccomment">/// type.</span>
<span class="kw">fn</span> <span class="ident">context</span><span class="op"><</span><span class="ident">D</span><span class="op">></span>(<span class="self">self</span>, <span class="ident">context</span>: <span class="ident">D</span>) <span class="op">-></span> <span class="ident">Context</span><span class="op"><</span><span class="ident">D</span><span class="op">></span> <span class="kw">where</span>
<span class="ident">D</span>: <span class="ident">Display</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</span> <span class="op">+</span> <span class="lifetime">'static</span>,
<span class="self">Self</span>: <span class="ident">Sized</span>,
{
<span class="ident">Context</span>::<span class="ident">with_err</span>(<span class="ident">context</span>, <span class="self">self</span>)
}
<span class="doccomment">/// Wraps this failure in a compatibility wrapper that implements</span>
<span class="doccomment">/// `std::error::Error`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This allows failures to be compatible with older crates that</span>
<span class="doccomment">/// expect types that implement the `Error` trait from `std::error`.</span>
<span class="kw">fn</span> <span class="ident">compat</span>(<span class="self">self</span>) <span class="op">-></span> <span class="ident">Compat</span><span class="op"><</span><span class="self">Self</span><span class="op">></span> <span class="kw">where</span>
<span class="self">Self</span>: <span class="ident">Sized</span>,
{
<span class="ident">Compat</span> { <span class="ident">error</span>: <span class="self">self</span> }
}
<span class="doccomment">/// Returns a iterator over the causes of this `Fail` with itself</span>
<span class="doccomment">/// as the first item and the `root_cause` as the final item.</span>
<span class="kw">fn</span> <span class="ident">causes</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">Causes</span> <span class="kw">where</span> <span class="self">Self</span>: <span class="ident">Sized</span> {
<span class="ident">Causes</span> { <span class="ident">fail</span>: <span class="prelude-val">Some</span>(<span class="self">self</span>) }
}
<span class="doccomment">/// Returns the "root cause" of this `Fail` - the last value in the</span>
<span class="doccomment">/// cause chain which does not return an underlying `cause`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If this type does not have a cause, `self` is returned, because</span>
<span class="doccomment">/// it is its own root cause.</span>
<span class="kw">fn</span> <span class="ident">root_cause</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">Fail</span> <span class="kw">where</span>
<span class="self">Self</span>: <span class="ident">Sized</span>,
{
<span class="ident">find_root_cause</span>(<span class="self">self</span>)
}
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">hidden</span>)]</span>
<span class="kw">fn</span> <span class="ident">__private_get_type_id__</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">TypeId</span> {
<span class="ident">TypeId</span>::<span class="ident">of</span>::<span class="op"><</span><span class="self">Self</span><span class="op">></span>()
}
}
<span class="kw">impl</span> <span class="ident">Fail</span> {
<span class="doccomment">/// Attempts to downcast this failure to a concrete type by reference.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If the underlying error is not of type `T`, this will return `None`.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">downcast_ref</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Fail</span><span class="op">></span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">__private_get_type_id__</span>() <span class="op">==</span> <span class="ident">TypeId</span>::<span class="ident">of</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>() {
<span class="kw">unsafe</span> { <span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="kw-2">*</span>(<span class="self">self</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Fail</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">T</span>)) }
} <span class="kw">else</span> {
<span class="prelude-val">None</span>
}
}
<span class="doccomment">/// Attempts to downcast this failure to a concrete type by mutable</span>
<span class="doccomment">/// reference.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If the underlying error is not of type `T`, this will return `None`.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">downcast_mut</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Fail</span><span class="op">></span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">T</span><span class="op">></span> {
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">__private_get_type_id__</span>() <span class="op">==</span> <span class="ident">TypeId</span>::<span class="ident">of</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>() {
<span class="kw">unsafe</span> { <span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span>(<span class="self">self</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">Fail</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">T</span>)) }
} <span class="kw">else</span> {
<span class="prelude-val">None</span>
}
}
<span class="doccomment">/// Returns the "root cause" of this `Fail` - the last value in the</span>
<span class="doccomment">/// cause chain which does not return an underlying `cause`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If this type does not have a cause, `self` is returned, because</span>
<span class="doccomment">/// it is its own root cause.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">root_cause</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">Fail</span> {
<span class="ident">find_root_cause</span>(<span class="self">self</span>)
}
<span class="doccomment">/// Returns a iterator over the causes of this `Fail` with itself</span>
<span class="doccomment">/// as the first item and the `root_cause` as the final item.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">causes</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">Causes</span> {
<span class="ident">Causes</span> { <span class="ident">fail</span>: <span class="prelude-val">Some</span>(<span class="self">self</span>) }
}
}
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"std"</span>)]</span>
<span class="kw">impl</span><span class="op"><</span><span class="ident">E</span>: <span class="ident">StdError</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</span> <span class="op">+</span> <span class="lifetime">'static</span><span class="op">></span> <span class="ident">Fail</span> <span class="kw">for</span> <span class="ident">E</span> {}
<span class="doccomment">/// A iterator over the causes of a `Fail`</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Causes</span><span class="op"><</span><span class="lifetime">'f</span><span class="op">></span> {
<span class="ident">fail</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="lifetime">'f</span> <span class="ident">Fail</span><span class="op">></span>,
}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'f</span><span class="op">></span> <span class="ident">Iterator</span> <span class="kw">for</span> <span class="ident">Causes</span><span class="op"><</span><span class="lifetime">'f</span><span class="op">></span> {
<span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="kw-2">&</span><span class="lifetime">'f</span> <span class="ident">Fail</span>;
<span class="kw">fn</span> <span class="ident">next</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="lifetime">'f</span> <span class="ident">Fail</span><span class="op">></span> {
<span class="self">self</span>.<span class="ident">fail</span>.<span class="ident">map</span>(<span class="op">|</span><span class="ident">fail</span><span class="op">|</span> {
<span class="self">self</span>.<span class="ident">fail</span> <span class="op">=</span> <span class="ident">fail</span>.<span class="ident">cause</span>();
<span class="ident">fail</span>
})
}
}
<span class="kw">fn</span> <span class="ident">find_root_cause</span>(<span class="kw-2">mut</span> <span class="ident">fail</span>: <span class="kw-2">&</span><span class="ident">Fail</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">Fail</span> {
<span class="kw">while</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">cause</span>) <span class="op">=</span> <span class="ident">fail</span>.<span class="ident">cause</span>() {
<span class="ident">fail</span> <span class="op">=</span> <span class="ident">cause</span>;
}
<span class="ident">fail</span>
}
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