feat: log inner error in additon to the context

[hanabi1224]

Summary of changes

anyhow::Context provides a convenient way of wrapping the error with some context text, and the inner text is present in stack trace when the final error is unwrapped. However, In a long-running service like forest, most of the errors are logged with tracing instead of being unwrapped. In this case, unless the debug formatting("{error:?}") is specified, the inner errors which are quite helpful for troubleshooting in many cases are not present in the log text. To fix the issue, we could

1. specify debug formatting
2. make a simple wrapper of .map_err.

This PR tries to implement the 2nd solution above.

Changes introduced in this pull request:

• Introduce crate::error::Context2 as a drop-in replacement of anyhow::Context

Reference issue to close (if applicable)

Closes

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

[aatifsyed]

I don't think we should do this (or I don't understand the problem enough).

let e: anyhow::Result;
tracing::error(?e, "error doing foo");

This gives us the desired formatting:
https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=b139670fd7096276d92c0da257608a86

If you really want to do it this way, I would have a shim around anyhow::Error that just changed the formatting params

[LesnyRumcajs]

How it's done is a detail. The fact that we need to use the Debug to get the full trace is non-intuitive, making the current error messages difficult to reason about.

Either this change needs to be implemented, one way or another, or all error messages should use the ?e or a variant of that. If we do the latter, it should be enforced in CI. As discussed with @hanabi1224 in Slack, our expectation is that the Display of an error is a sum of its errors, not just the top-level context, which is rarely useful on its own.

[aatifsyed]

The fact that we need to use the Debug to get the full trace is non-intuitive, making the current error messages difficult to reason about.
...
As discussed with @hanabi1224 in Slack, our expectation is that the Display of an error is a sum of its errors, not just the top-level context, which is rarely useful on its own.

Anyhow is correctly following the documentation on std::error::Error:

Error messages are typically concise lowercase sentences without trailing punctuation

A motivator for anyhow::Error's Debug implementation is that it gives the chain when used with std::process::Termination

I don't think the error is in any of the APIs we use, so I don't in-principle agree with (either)

• duplicating anyhow::Context in this PR
• (or) wrapping anyhow::Error to change its formatting

I can bear it as an interim measure, but the real fix is to use tracing's structured logging machinery #4143

[aatifsyed]

Fine with this as an interim measure, but prefer #4143

[hanabi1224]

Superseded by #4174