[CMake] Only build `clad` plugin if requested

[guitargeek]

Building clad should not depend on the result of the connectivity check, but whether it is enabled.

[github-actions[bot]]

Test Results

    10 files      10 suites   1d 16h 47m 10s :stopwatch:  2 631 tests  2 631 :white_check_mark: 0 :zzz: 0 :x: 24 812 runs  24 812 :white_check_mark: 0 :zzz: 0 :x:

Results for commit 9b63c980.

[guitargeek]

LGTM. The related error message and disabling is done (correctly in regard to this fix) on CMakeLists.txt line 99 to 106

That is correct! I should have maybe explained it in the PR description. Thank you very much for double-checking.

[ynikitenko]

I faced the following problem when compiling ROOT from source,

[ 73%] Performing download step (git clone) for 'clad'

however, I was offline, and the whole build process interrupted.

I think that building from source assumes you have downloaded everything and you can safely compile in an isolated environment. At least it must be specified somewhere beforehand that one needs a connection or those modules.

Does your commit fix that in future versions?

[guitargeek]

Hi! The PR that fixes the problem you report is this one:

• https://github.com/root-project/root/pull/15488

[ynikitenko]

Thank you. Not exactly: in my case I was online, and then went offline. The build process for ROOT takes several hours on my laptop.

I wouldn't call that check reliable. Ideally, it could download the files during that check or in the beginning of the build process.