Ceyhun Can Ulker f515e9d35c attributes: add err(Debug) meta to use Debug impl (#1631) ...

## Motivation

This PR attempts to solve #1630 by introducing `err(Debug)` meta to
`intrument` attribute macro. As `err` meta causes the error (`e`)
returned by instrumented function to be passed to `tracing::error!(error
= %e)` i.e. makes it use the `Display` implementation of `e`, the newly
added `err(Debug)` makes expands to `tracing::error!(error = ?e)` which
makes the `error!` macro to use `Debug` implementation for `e`. `err`
and `err(Debug)` are mutually exclusive, adding both will create a
compilation error.

`err(Display)` is also supported to specify `Display` explicitly.

As tried to describe, for some types implementing `Error` it might be
more suitable to use `Debug` implementation as in the case of
`eyre::Result`. This frees us to manually go over the error chain and
print them all, so that `instrument` attribute macro would do it for us.

## Solution

- Added a custom keyword `err(Debug)` similar to `err`,
- Add `err(Debug)` field to `InstrumentArgs`,
- Add parsing for `err(Debug)` arg and check for conflicts with `err`,
- Generate `tracing::error!(error = ?e)` when `err(Debug)` is `true` and
  `tracing::error!(error = %e)` when `err(Display)` or `err` is `true`,
- Interpolate generated `err_block` into `Err` branches in both async
  and sync return positions, if `err` or `err(Debug)` is `true`.

2021-10-22 13:26:09 -07:00

..

lib.rs

attributes: add err(Debug) meta to use Debug impl (#1631)

2021-10-22 13:26:09 -07:00