Gradle task executes is Configuration phase but not in Execution phase - gradle

Question

I have a Gradle task which simply copies the files from one folder to another.
When the copy 'from' 'into' methods are called during configuration phase it works but when they are called in the execution phase it doesn't.
Doing it this way it works
task copyServerConfig(type:Copy) {
from "${projectDir}" + File.separator + 'server_config'
into localServer
}
gradle copyServerConfig
:copyServerConfig
BUILD SUCCESSFUL
Total time: 0.686 secs
With the '<<' it doesn't show any error but the files are not copied:
task copyServerConfig(type:Copy) << {
from "${projectDir}" + File.separator + 'server_config'
into localServer
}
gradle copyServerConfig
:copyServerConfig UP-TO-DATE
BUILD SUCCESSFUL
Total time: 0.654 secs
Same thing happen if I put it inside a doFirst{} block.
Another thing I don't understand is the following:
If I execute this task:
task task1(type:Exec) << {
commandLine 'echo', ' TEST'
}
I get this error:
gradle task1
:task1 FAILED
FAILURE: Build failed with an exception.
What went wrong:
Execution failed for task ':task1'.
execCommand == null!
But if I change to this:
task task1(type:Exec) {
commandLine 'echo', ' TEST'
}
gradle task1
:task1
TEST
BUILD SUCCESSFUL
Total time: 0.655 secs
I read in the documentation about the about build lifecycle and I understand commands inside doFirst{} and doLast{} blocks execute during the Execution phase and commands outside those blocks execute in the Configuration phase.
But I think there is some important concept I am missing here. Why is this happening ? What is the difference of having a command being executed in the Configuration phase vs Execution phase ?

Answer 1

The first variant is a correct way to declare a Copy task
task copyServerConfig(type:Copy) {
from "${projectDir}" + File.separator + 'server_config'
into localServer
}
Here you say "this is a task of type Copy with name copyServerConfig, this is from param and this is into param". The code inside the brackets is used to configure a task.
<< operator adds a doAfter closure to the task, that is executed after it.
task copyServerConfig(type:Copy) << {
from "${projectDir}" + File.separator + 'server_config'
into localServer
}
This declaration means "create empty (not configured) Copy task and execute these two lines after it is done. Here you did not configure a task, it does nothing and is always UP-TO-DATE. The two lines in doAfter closure do nothing as well, because they are not related to Copy task, so from and into keywords have no effect.
The similar thing happens with Exec task
task task1(type:Exec) << {
commandLine 'echo', ' TEST'
}
Here you have empty Exec task that fails because it is not configured.