Auto merge of #423 - ecstatic-morse:windows-docs, r=pietroalbini

Add steps for provisioning a Windows box to run `crater`

This adds detailed set-up instructions for running `crater` on a Windows box. Obviously this depends on #399. I also tried to explain some of the complexity around Docker image compatibility.

docs/agent-machine-setup-windows.md

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+# Setting up a new Crater Windows agent machine
+
+## Operating System
+
+The agent machine should run Windows Server build 1803 (Windows 10 build 1803
+will **not** work, see below). The machine should have Hyper-V enabled (images
+ending in `v3` on Azure DevOps), although this may not be necessary since we
+only use process isolation. Testing has been done on a server with a GUI, but
+all installation steps can be done at the command line with the exception of
+configuring Docker Desktop. It may be possible to use a headless server if
+Docker is already properly configured. The following paragraphs contain the
+rationale for choosing this particular build of Windows. If this does not
+interest you, skip to the next section.
+
+Docker on Windows supports two different ways to run containers, process
+isolation and Hyper-V isolation. Hyper-V isolation is more secure and more
+flexible, but it is too slow for our purposes; it essentially spins up a VM for
+each container. In order to run process isolation, the build number of the
+agent machine and the docker image [need to match][ver-compat]. You can use
+`winver` to print the version of Windows from the command line. Windows Server
+2016 additionally requires that the **revision number** of the agent machine
+and container image match as well. VMs based on a particular revision of
+Windows can be hard to find, so we want to use a build later than Server 2016.
+
+The `rustops/crates-build-env-windows` image is built on Azure Pipelines CI
+infrastructure, which provides a Windows 1803 host with docker pre-installed
+(the latest Windows version available on AppVeyor is Server 2016). Therefore we
+use this same build of Windows to do `crater` runs. Note that process isolation
+is [disabled on Windows 10 prior to build 1809][win-10], so you **must** use
+Windows Server. Additionally, running containers on Windows 10 requires a
+Professional or Enterprise license. It's possible to run `crater` on other
+builds of Windows as long as you understand these constraints, but you'll need
+to build your own `crates-build-env-windows` image based on a compatible
+version, as the `rustops` one is based on Windows 1803.
+
+[ver-compat]: https://docs.microsoft.com/en-us/virtualization/windowscontainers/deploy-containers/version-compatibility
+[win-10]: https://docs.microsoft.com/en-us/virtualization/windowscontainers/about/faq#can-i-run-windows-containers-in-process-isolated-mode-on-windows-10-enterprise-or-professional
+
+## Install [**Docker Desktop for Windows**][docker-desktop]
+
+[docker-desktop]: https://hub.docker.com/editions/community/docker-ce-desktop-windows
+
+- Download and run the [**Docker Desktop for Windows**][docker-desktop] installer (*not* Docker Toolbox):
+  ```powershell
+  (New-Object System.Net.WebClient).DownloadFile("https://download.docker.com/win/stable/Docker%20for%20Windows%20Installer.exe", ".\DockerInstaller.exe"); `
+  .\DockerInstaller.exe
+  ```
+
+- Check "Use Windows containers instead of Linux containers" during
+  installation. Once installed, double check that Windows containers are indeed
+  enabled by right-clicking the Docker icon in the dock.
+
+- Docker will then detect whether the "Containerization" and "Hyper-V" OS
+  features are enabled. If they are disabled, Docker will try to enable them
+  for you. Alternatively, run the following commands and then reboot.
+
+  ```powershell
+  Enable-WindowsOptionalFeature -Online -FeatureName Microsoft-Hyper-V -All
+  Enable-WindowsOptionalFeature -Online -FeatureName Containers -All
+  ```
+
+## Install [`chocolatey`][] and `git`
+
+[`chocolatey`]: https://chocolatey.org/install
+
+Chocolately is a 3rd-party package manager for Windows. We'll use it to install a
+version of `git` which can be used directly from `PowerShell`, as well as some
+other useful things:
+
+```Powershell
+Set-ExecutionPolicy Bypass -Scope Process -Force; iex ((New-Object System.Net.WebClient).DownloadString('https://chocolatey.org/install.ps1'))
+```
+Then we can install `git`:
+
+```Powershell
+choco install git
+```
+
+## Install the Visual Studio VC++ tools
+
+We could use the commands from the Dockerfile, but since we already installed `chocolatey`:
+
+```powershell
+choco install -y visualstudio2017-workload-vctools
+```
+
+## Install rust locally
+
+Follow the normal procedure, but note that `rustup-init.exe` cannot be
+[downloaded from the command line using normal Windows
+utilities][rustup-download]. Instead, use `curl.exe` (the suffix is important),
+which is installed by default on newer versions of Windows or available via
+`chocolately`:
+
+```powershell
+curl.exe -o rustup-init.exe https://win.rustup.rs/x86_64
+.\rustup-init.exe
+```
+
+[rustup-download]: https://github.com/rust-lang/rustup.rs/issues/829
+["Trusted Sites"]: https://www.itg.ias.edu/content/how-add-trusted-sites-internet-explorer
+
+Disabling "Real-time Protection" in "Settings > Update & Security > Windows
+Defender" may speed up [the installation of `rust-docs`][rust-docs].
+
+[rust-docs]: https://github.com/rust-lang/rustup.rs/issues/1540
+
+## Build crater
+
+The next step is to download and build `crater` just like on a [Linux
+agent](./agent-machine-setup.md):
+
+```powershell
+git clone https://github.com/rust-lang-nursery/crater
+cd crater
+cargo build --release
+
+# This is going to take a while to complete
+cargo run --release -- prepare-local
+```
+
+Running `minicrater` tests require that the `*.expected.json` files match the
+output of crater exactly. However, when installed via `chocolately`, `git` has
+config `core.autocrlf` set to `true` by default. This will override the
+preferences in `crater`'s `.gitattributes` file and cause the JSON files to
+have the wrong line endings (CRLF). Make sure you set `core.autocrlf = false`
+before cloning the repo.
+
+If you've already cloned the repo, simply run the following from inside of it
+to replace the JSON files:
+
+```powershell
+git config core.autocrlf false
+rm -r tests/
+git checkout -- tests/
+```
+
+Remember to run `cargo run -- create-lists` before running the tests.