Can't use `dockerfile` to custom env when there's no default image provided by cross

[Dirreke]

Describe your issue

I use cross to build for Tier3 target csky-unknown-linux-gnuabiv2hf and I write a Dockerfile.
I add the following to Cross.toml

[target.csky-unknown-linux-gnuabiv2hf]
dockerfile = "./path/to/docker/dockerfile"

However, when I run cross, it sait that

`cross` does not provide a Docker image for target csky-unknown-linux-gnuabiv2hf, specify a custom image in `Cross.toml`.

If I use the image in Cross.toml, I can run it successfully.

[target.csky-unknown-linux-gnuabiv2hf]
image = "csky"

Therefore, I want to know if it is desifned like this or it's a bug.

Which operating system is the host (e.g computer cross is on) running?

• Linux / BSD

What architecture is the host?

• x86_64

What container engine is cross using?

• docker

cross version

cross 0.2.5

[Emilgardis]

Hi! This was fixed recently with #1340

You can also just specify a dummy image, it won't use it unless you use it in the dockerfile

So either use cross which includes #1340 cargo install cross --git https://github.com/cross-rs/cross or specify

[target.csky-unknown-linux-gnuabiv2hf]
image = "csky-cross"
dockerfile = "./path/to/docker/dockerfile"