errloc_macros 0.1.0

Error location utility macros
Documentation 
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/*
 * Copyright 2017, https://github.com/rustytools
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

//! Utility macros (and a function) to use with `std::panic::catch_unwind`

/// Macro that returns current source file name with a line number.
///
/// This macro returns "filename:linenumber" `&str`.
/// It can be used to include error location information
/// into panic payload like this: `foo().except(errloc!())`
#[macro_export]
macro_rules! errloc {
    () => {
        concat!(file!(), ':', line!())
    }
}

/// Macro that creates a message, concatenating current source file name
/// and a line number with the specified `&str`.
///
/// This macro return "<msg> (at filename:linenumber)" `&str`.
/// It can be used to include error location information
/// into panic payload like this: `panic!(errlocm!("Fatal error"))`
#[macro_export]
macro_rules! errlocm {
    ($e:expr) => {
        concat!($e, " (at ", file!(), ':', line!(), ')')
    }
}

/// This function extracts message from the panic payload, that
/// is obtained from `std::panic::catch_unwind`
///
/// This function extracts `&str` or `std::string::String` message
/// that was provided as a payload to `panic!` macro.
/// Result is returned as a `&str` and has the same lifetime
/// as an input payload.
///
/// Usage example:
///
/// ```
///std::panic::catch_unwind(|| {
///    panic!("Forty two");
///}).unwrap_or_else(|e| {
///    assert_eq!("Forty two", errloc_macros::msg(&e));
///});
/// ```
pub fn msg<'a>(e: &'a std::boxed::Box<std::any::Any + std::marker::Send + 'static>) -> &'a str {
    match e.downcast_ref::<&str>() {
        Some(st) => st,
        None => {
            match e.downcast_ref::<std::string::String>() {
                Some(stw) => stw.as_str(),
                None => "()",
            }
        },
    }
}