Summary:
Implements based Rust-Python binding layer for error metadata propagation.
We introduce a new type, `TaggedExceptionData`, which carries CommonMetadata and the original (without metadata) error message for a Rust Anyhow error. This class is passed to RustError and can be accessed in Python (somewhat awkwardly) via indexing:
```
except error.RustError as e:
fault = e.args[0].fault()
typename = e.args[0].typename()
message = e.args[0].message()
```
As far as I can tell, due to limitations in cpython-rs, this can't be made more ergonomic without introducing a Python shim around the Rust binding layer, which could adapt the cpython-rs classes to use whatever API we'd like.
Currently, anyhow errors that are not otherwise special-cased will be converted into RustError, with both the original error message and any attached metadata printed as shown below
```
abort: intentional error for debugging with message 'intentional_error'
error has type name taggederror::IntentionalError and fault None
```
We can of course re-raise the error if desired to maintain the previous behavior for handling a RustError.
If we'd like other, specialized Rust Python Exception types to carry metadata (such as `IndexedLogError`), we'll need to modify them to accept a `TaggedExceptionData` like `RustError`.
Renamed the "cause an error in pure rust command" function to `debugcauserusterror`, and instead used the name `debugthrowrustexception` for a command which causes an error in rust which is converted to a Python exception across the binding layer.
Introduced a simple integration test which exercises `debugthrowrustexception`.
Added a basic handler for RustError to scmutil.py
Reviewed By: DurhamG
Differential Revision: D22517796
fbshipit-source-id: 0409489243fe739a26958aad48f608890eb93aa0
Summary:
Introduce new rust library, taggederror, which contains utilities for attaching metadata to errors. The library provides two main methods for attaching metadata to an error, the TaggedError wrapper type, and the AnyhowExt trait methods. Provides a struct, CommonMetadata, which contains all the metadata types introduced by taggederror (fault, transience, category, and typename), which can also be attached individually (and the same pattern can be used to attach other metadata).
Introduce a new native rust command, debugthrowrustexception, which causes the command to return an error, with some attached metadata.
Modify hg rust native command dispatch error handling to use debug formatter to print anyhow::Error errors. This will print out the source chain, contexts, and backtrace if available, which will cause the metadata we attach as a wrapper error or context to be printed.
Reviewed By: DurhamG
Differential Revision: D22420941
fbshipit-source-id: d38c5a10b686d86b69a2c0a19f5bcbf4ca24dff6
