Pre-built image not used as-is

[chrmarti]

Apologies if this is the wrong place to ask, but would the proposal above address the fact that running devcontainer build followed by devcontainer open opens VS Code but then in the output one of the first things it does is start building stuff again?

[1690 ms] Start: Run: docker events --format {{json .}} --filter event=start
[1692 ms] Start: Run: docker-compose --project-name myproject -f /Users/username/Projects/myproject/docker-compose.yml build

It makes for a very slow startup experience since I cannot interact with the editor until the build completes. What is also non-intuitive for me is that even though it rebuilds after opening the dev container, I am sometimes still prompted that e.g. docker-compose.yml has changed and may need to be rebuilt. How many times does it need to build before VS Code is content that everything is in working shape and can let me get to work?

Originally posted by @jsma in devcontainers/spec#21 (comment)

[jsma]

I just tried the devcontainer build && devcontainer open on a clean checkout of a bare bones docker-compose/dev container setup WITHOUT any features and everything works as I'd expect. VS Code terminal output shows a straightforward docker-compose up without any additional prompts.

As a test, I shut down VS Code and added the "github-cli": "latest", as the one and only feature using a text editor. I ran devcontainer build which shows docker doing its thing followed by devcontainer open. The VS Code terminal output shows a normal docker-compose up but then I get this prompt:

Clicking "Rebuild" does trigger the docker-compose build again of course:

[1462 ms] Start: Run: docker events --format {{json .}} --filter event=start
[1463 ms] Start: Run: docker-compose --project-name wagtail-vs-code-demo -f /Users/username/Projects/wagtail-vs-code-demo/docker-compose.debug.yml -f /Users/username/Projects/wagtail-vs-code-demo/.devcontainer/docker-compose.yml build

I was under the impression that devcontainer build would do whatever it would normally do had I simply used devcontainer open and then used the command palette to rebuild the dev container. As a VS Code newbie, I found it confusing that the command line build step is followed by a prompt in the UI to "Rebuild".

[chrmarti]

devcontainer build doesn't have access to the checksum we use in the extension to see if the configuration changed. One option might be to store a checksum on / in the container.