add initial dotnet support

[rkm]

Hello hello.

This PR adds 2nd class support for dotnet tools by using dotnet pack and dotnet tool install.

I've also tested a "real world" hook:

$ cd /tmp
$ rm -rf ./foo
$ dotnet new console --name foo
The template "Console Application" was created successfully.

Processing post-creation actions...
Running 'dotnet restore' on foo/foo.csproj...
  Determining projects to restore...
  Restored /tmp/foo/foo.csproj (in 190 ms).

Restore succeeded.

$ cd foo
$ git init
Initialized empty Git repository in /tmp/foo/.git/
$ sed -i 's/Console/    Console/g' Program.cs
$ pre-commit try-repo https://github.com/rkm/format --ref af89478 --files=foo.csproj
[INFO] Initializing environment for https://github.com/rkm/format.
===============================================================================
Using config:
===============================================================================
repos:
-   repo: https://github.com/rkm/format
    rev: af89478
    hooks:
    -   id: dotnet-format
===============================================================================
[INFO] Installing environment for https://github.com/rkm/format.
[INFO] Once installed this environment will be reused.
[INFO] This may take a few minutes...
dotnet format............................................................Failed
- hook id: dotnet-format
- files were modified by this hook

  Formatting code files in workspace '/tmp/foo/foo.csproj'.
  Warnings were encountered while loading the workspace. Set the verbosity option to the 'diagnostic' level to log warnings.
  Formatted code file '/tmp/foo/Program.cs'.
  Format complete in 3530ms.

One of the issues I found was that nuget doesn't play nicely when some env vars are not set. In particular the Windows build was failing until I added the tox.ini changes below. If you don't want to carry that addition, then I can probably investigate a workaround using get_env_patch.

Looking forward to your review!

[asottile]

looks great for a first pass, I'm excited about seeing this land!

[asottile]

(I should really just write a formatter for this) -- generally blank lines at the top of blocks make it harder to read, I can go through and remove these if you want

[asottile]

could this be fixed by using a temporary directory to build and then just copy the products into the envdir?

[rkm]

Yeah I'm not sure if/how this is done for other languages -- it seems like the hook repo is already cloned before install_environment is called so there's no chance by that point to clone/build in a temp dir.

I had a minimal version before which removed just the bin, obj, and pre-commit-build dirs since those are the ones we know will exist. I can revert to that if you'd prefer? Or we could skip any cleanup completely. The main reason I added this was that the format repo I used in the example above is chunky, and all we need after install is the envdir.

[asottile]

I think go does a similar thing and build a temporary build directory and then copies the binaries out of it -- maybe that can be some inspiration?

[rkm]

With go we seem to specify where the build artefacts will be placed. I'm not sure we can easily do here without doing bota a dotnet build cmd and then a dotnet pack --no-build and somehow finding the build output (which can be anywhere really depending on the project layout).

Could we do a git clean and exclude the final tool directory?

[asottile]

a git clean would unfortunately preclude doing 1st class in the future so we should avoid that (multiple language_versions end up in the same clone directory)

[rkm]

Think I've addressed all your comments now. I've spotted this issue though, so will check if we need to handle that here.

[asottile]

looks good! just a few little things and I think this is done (assuming you're happy with it)

[rkm]

Heyo. I think I'm happy with this now if you are!

There will probably be some rough edges found once this starts being used in the wild. Happy for you to ping me in any issues though.

[asottile]

[asottile]

would you like to update docs for this? the _new in_ should be 2.8.0

[rkm]

Sure, will do.