dirstate: invalidate changes when parent-change fails When an error occurs during changing parents, we should invalidate all dirstate modifications and reload the dirstate. This is currently done by a `unlock` callback on the `wlock`. To fix this anomaly, we start dealing with the error directly in the context manager and its potential nesting. The "hard" part is to make sure that, when the parent-change context are nested, we and higher level nesting do not continue to use the invalidated dirstate. We introduce dedicated code to enforce that.

setup: Ensure target directory exists with building rust extension When the rust extension is the first to be build, the target directory may not exist so the copy fails.

filemerge: add union-other-first as internal merge tool See inline documentation for details.

rust: use `peek_mut` from the standard lib now that it's stable Just a little cleanup of a TODO found along the way.

clippy: actually fail if there are any warnings So far, only errors would trip the CI, this makes it so all warnings are elevated to errors, making it a CI fail if any warnings are present. This was the intended behavior, I just missed this when adding clippy.

rust-clippy: fix warning about nested ifs

debugshell: allow commands to be specified as a CLI argument Add a `--command` option to `hg debugshell` that allows the user to pass in Python code to evaluate directly from the command line. This was inspired by the `--command` option present in Facebook's Sapling fork of Mercurial, which in turn was inspired by the `-c` option of the Python interpreter itself. It is particularly useful for writing tests, especially for getting visibility into things that otherwise aren't exposed via debug commands.

heptapod-ci: add `clippy` to the CI This linter mostly makes our code more idiomatic, less surprising, has good suggestions and catches bugs. It's widely used in the Rust community and now part of the default toolchain when using `rustup`.

makefile: add `cargo clippy` to tests if cargo is available This linter mostly makes our code more idiomatic, less surprising, has good suggestions and catches bugs. It's widely used in the Rust community and now part of the default toolchain when using `rustup`.

rust-tests: run `cargo` tests inside the `rust` folder There is no reason to only run inside the `rust/hg-cpython` folder, even if the `cargo test --all` behavior ends up being the same.

rust-clippy: merge "revlog" module definition and struct implementation Module inception is confusing when looking for code and almost never the right choice.

rust-clippy: merge "config" module definition and struct implementation Module inception is confusing when looking for code and almost never the right choice.

rust-clippy: upgrade `bytes-cast` dependency I released a new version of `bytes-cast` to get rid of the clippy warning, and bump to edition 2021, so let's use it.

rust-clippy: remove redundant suffix from enum Same as last time, this makes the code clearer in this instance.

rust-clippy: fix remaining warnings in `hg-cpython`

rust-clippy: disable some lints crate-wide for `hg-cpython` `rust-cpython` creates some pretty funky code that also needs to be compatible with pretty old Rust. This makes clippy quite useless in `hg-cpython` unless you disable the lints that are always triggered by `py_class!` and related. Maybe `clippy` will allow one day to exclude a dependency from its linting, but this seems quite unlikely, so this is the best we've got at the moment.

rust-clippy: fix remaining warnings in `rhg` All of these are simple changes that for the most part are clear improvements and the rest are at most equivalent.

rust-clippy: fix most warnings in `hg-core` All of these are simple changes that for the most part are clear improvements and the rest are at most equivalent. The remaining warnings have to be fixed either with a bigger refactor like for the nested "revlog" module, or in the dependency `bytes-cast`, which we own. This will be done sometime in the future.

rust-utils: strip redundant prefix from enum This was highlighted by `clippy`, I think this makes the code cleaner.

rust-filepatterns: don't `Box` subincludes unnecessarily This was caught by `clippy`.

rust-nodemap: implement `PartialEq` without allocation This was caught by `clippy`. It's probable that this ends up optimized out by the compiler, but let's not rely on that.

rust-clippy: tell `clippy` we don't need to declare a default here This is a struct only useful for tests.

rust-clippy: refactor complex type This makes reading the signature a bit less tiring.

rust-clippy: simplify return type of debug function This makes the type a little bit more readable.

rust-clippy: add `is_empty` method to please the `clippy` gods I can see it being useful anyway.

rust: don't use a reference to a `Cow` This was caught by `clippy`.

rust-clippy: reassure `clippy` that 8 arguments is expected This API is a bit verbose, but refactoring it into a struct isn't better in this particular case IMO, and there is a lot of info to pass.

rust-clippy: use `write_all` since we're not expecting a partial write Clippy caught this. This is a good lint in general, but here this was not really a bug in this example code.

rust-clippy: tell clippy we want to keep those clauses separate This makes the cases more explicit, which is wanted in this specific instance.

rust-clippy: tell clippy we care about keeping those `if` clauses separate Thses were written this way because it spells out the logic in a more explicit manner.