Add initial codespaces support for dotnet/runtime (dotnet#59723)

* Add initial codespaces support for dotnet/runtime

* Enable codespaces-prebuild

.devcontainer/Dockerfile

@@ -0,0 +1,12 @@
+# See here for image contents: https://github.com/microsoft/vscode-dev-containers/tree/v0.192.0/containers/dotnet/.devcontainer/base.Dockerfile
+
+# [Choice] .NET version: 5.0, 3.1, 2.1
+ARG VARIANT="5.0"
+FROM mcr.microsoft.com/vscode/devcontainers/dotnet:0-${VARIANT}
+
+# Set up machine requirements to build the repo
+RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
+    && apt-get -y install --no-install-recommends cmake llvm-9 clang-9 \
+        build-essential python curl git lldb-6.0 liblldb-6.0-dev \
+        libunwind8 libunwind8-dev gettext libicu-dev liblttng-ust-dev \
+        libssl-dev libnuma-dev libkrb5-dev zlib1g-dev ninja-build

.devcontainer/devcontainer.json

@@ -0,0 +1,35 @@
+// For format details, see https://aka.ms/devcontainer.json. For config options, see the README at:
+// https://github.com/microsoft/vscode-dev-containers/tree/v0.192.0/containers/dotnet
+{
+	"name": "C# (.NET)",
+	"build": {
+		"dockerfile": "Dockerfile",
+		"args": { 
+			// Update 'VARIANT' to pick a .NET Core version: 2.1, 3.1, 5.0
+			"VARIANT": "5.0",
+		}
+	},
+
+	"settings": {
+		// Loading projects on demand is better for larger codebases
+		"omnisharp.enableMsBuildLoadProjectsOnDemand": true
+	},
+
+	// Add the IDs of extensions you want installed when the container is created.
+	"extensions": [
+		"ms-dotnettools.csharp"
+	],
+
+	// Use 'onCreateCommand' to run pre-build commands inside the codespace
+	"onCreateCommand": "${containerWorkspaceFolder}/.devcontainer/scripts/onCreateCommand.sh",
+
+	// Add the locally installed dotnet to the path to ensure that it is activated
+	// This allows developers to just use 'dotnet build' on the command-line, and the local dotnet version will be used.
+	"remoteEnv": {
+		"PATH": "${containerWorkspaceFolder}/.dotnet:${containerEnv:PATH}",
+		"DOTNET_MULTILEVEL_LOOKUP": "0"
+	},
+
+	// Comment out connect as root instead. More info: https://aka.ms/vscode-remote/containers/non-root.
+	"remoteUser": "vscode"
+}

.devcontainer/scripts/onCreateCommand.sh

@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+set -e
+
+# prebuild the repo, so it is ready for development
+./build.sh libs+clr -rc Release

.github/workflows/create-codespaces-prebuild.yml

@@ -0,0 +1,17 @@
+name: Create Codespaces Prebuild
+on:
+  schedule:
+    # Run at 06:00 am UTC every day
+    - cron:  '0 6 * * *'
+  workflow_dispatch:
+jobs:
+  createPrebuild:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: github/codespaces-precache@v1.0.1
+        with:
+          regions: WestUs2
+          sku_name: standardLinux32gb
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

.gitignore

@@ -279,7 +279,6 @@ Session.vim
 
 # Visual Studio Code
 .vscode/
-.devcontainer/
 
 # Private test configuration and binaries.
 config.ps1