Add instructions for using Codespaces (#60996)

* Add instructions for using Codespaces

* Automate resetting the HEAD to the same commit ID used to build the pre-built container

* - Add notes about testing changes.

- Add 4-core machines

* Revert 4-core change since prebuild doesn't support multiple sku_names.

3 files changed, 12 insertions, 0 deletions

diff --git a/.devcontainer/devcontainer.json b/.devcontainer/devcontainer.json
index b3dfd99aebd..baf0b306f73 100644
--- a/.devcontainer/devcontainer.json
+++ b/.devcontainer/devcontainer.json
@@ -23,6 +23,9 @@
 	// Use 'onCreateCommand' to run pre-build commands inside the codespace
 	"onCreateCommand": "${containerWorkspaceFolder}/.devcontainer/scripts/onCreateCommand.sh",
 
+	// Use 'postCreateCommand' to run commands after the container is created.
+	"postCreateCommand": "${containerWorkspaceFolder}/.devcontainer/scripts/postCreateCommand.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": {
diff --git a/.devcontainer/scripts/onCreateCommand.sh b/.devcontainer/scripts/onCreateCommand.sh
index dc0154c619b..983db183068 100755
--- a/.devcontainer/scripts/onCreateCommand.sh
+++ b/.devcontainer/scripts/onCreateCommand.sh
@@ -4,3 +4,6 @@ set -e
 
 # prebuild the repo, so it is ready for development
 ./build.sh libs+clr -rc Release
+
+# save the commit hash of the currently built assemblies, so developers know which version was built
+git rev-parse HEAD > ./artifacts/prebuild.sha
diff --git a/.devcontainer/scripts/postCreateCommand.sh b/.devcontainer/scripts/postCreateCommand.sh
new file mode 100755
index 00000000000..8086037ab9a
--- /dev/null
+++ b/.devcontainer/scripts/postCreateCommand.sh
@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+set -e
+
+# reset the repo to the commit hash that was used to build the prebuilt Codespace
+git reset --hard $(cat ./artifacts/prebuild.sha)