LET/SET values cannot be used in parallel commands such as BUILD

[idodod]

What went wrong?

Trying to defined the name of the target in a LET statement, the name of the target is not properly expanded and the target cannot be built.

VERSION 0.8

FROM alpine

foo:
    LET target=+bar
    BUILD $target

bar:
    RUN echo hello from bar

earthly +foo

What should have happened?

The command should succeed in eventually building +bar.
chan

Other Helpful Information

Changing the LET command to an ARG allows the target to be built.

It appears LET/SET do not block parallel commands, thus BUILD is executed before LET is evaluated.

[idodod]

This also fixes a bug where a BUILD might get executed twice with different values of an arg.
Consider the folliwing:

FROM alpine

foo:
   LET my_val=abc
   BUILD +bar --my_arg=$my_val
   
bar:
  ARG my_arg="123"
  RUN echo $my_arg   

earthly +foo would result in +bar getting executed twice - once with my_arg="" and once with my_arg="abc", where the latter is the intended behavior.

[idodod]

will be included in next releases (v0.8.8)