explicit caching broken since 0.6.3, when SAVE IMAGE used without explicitly setting image name

[andyli]

FROM busybox

file-a:
    RUN touch file-a
    SAVE IMAGE --cache-hint

file-b:
    RUN touch file-b
    SAVE IMAGE --cache-hint

build:
    BUILD +file-a
    BUILD +file-b

Build the +build target with enabled read-write caches:

vscode ➜ /workspace$ earthly --version
earthly version v0.6.3 linux/amd64; Ubuntu 20.04
vscode ➜ /workspace$ earthly --ci --push --remote-cache ghcr.io/andyli/test:cache +build

 1. Init 🚀
————————————————————————————————————————————————————————————————————————————————

           buildkitd | Found buildkit daemon as docker container (earthly-buildkitd)
           buildkitd | Updated image available. Restarting buildkit daemon...
           buildkitd | ...Done


 2. Build 🔧
————————————————————————————————————————————————————————————————————————————————

             busybox | --> Load metadata linux/amd64
Error: build target: build main: bkClient.Build: failed to solve: image  is defined multiple times for the same default platform

It seems to work with earthly 0.6.2, but I haven't tested throughly.

[alexcb]

Does this occur if you add VERSION 0.6 to the top line of the Earthfile, or is it specific only when VERSION 0.5 is being used (which is the default when no version is specified)

[andyli]

Got the same error with VERSION 0.6 added to the top.

[alexcb]

It looks like it's failing due to SAVE IMAGE omitting the name (which should be fine, but obviously isn't).

As a work-around, I was able to get this to work:

VERSION 0.6
FROM busybox

file-a:
    RUN touch file-a
    SAVE IMAGE --cache-hint file-a

file-b:
    RUN touch file-b
    SAVE IMAGE --cache-hint file-b

build:
    BUILD +file-a
    BUILD +file-b

Thanks for the bug report.