Subject: Re: [PATCH v1 2/2] travis-ci: skip a branch build if equal tag is present

From: SZEDER Gábor <[email-masked]>
Date: Mon, 11 Sep 2017 16:52:41 +0200

> If we push a branch and a tag pointing to the HEAD of this branch,

s/the HEAD of//, perhaps?
There is no such thing as "HEAD" (all capital!) of a branch, is it?

> then Travis CI would run the build twice. This wastes resources and

Nit: s/run the build/build and test the same tree/, to further stress
that the two builds are redundant.

> slows the testing.
> 
> Add a function to detect this situation and skip the build the branch

s/skip the build/skip building/ ?

> if appropriate. Invoke this function on every build.
> 
> Helped-by: Junio C Hamano <[email-masked]>
> Signed-off-by: Lars Schneider <[email-masked]>
> ---
>  ci/lib-travisci.sh | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
> 
> diff --git a/ci/lib-travisci.sh b/ci/lib-travisci.sh
> index 44d6ba2dd2..9c4ae9bdd0 100755
> --- a/ci/lib-travisci.sh
> +++ b/ci/lib-travisci.sh
> @@ -1,5 +1,28 @@
>  # Library of functions shared by all CI scripts
>  
> +skip_branch_tip_with_tag () {
> +	# Sometimes, a branch is pushed at the same time the tag that points
> +	# at the same commit as the tip of the branch is pushed, and building
> +	# both at the same time is a waste.
> +	#
> +	# Travis gives a tagname e.g. v2.14.0 in $TRAVIS_BRANCH when
> +	# the build is triggered by a push to a tag.  Let's see if
> +	# $TRAVIS_BRANCH is exactly at a tag, and if so, if it is
> +	# different from $TRAVIS_BRANCH.  That way, we can tell if
> +	# we are building the tip of a branch that is tagged and
> +	# we can skip the build because we won't be skipping a build
> +	# of a tag.
> +
> +	if TAG=$(git describe --exact-match "$TRAVIS_BRANCH" 2>/dev/null) &&
> +		$TAG != $TRAVIS_BRANCH

This must be

    [ $TAG != $TRAVIS_BRANCH ]

otherwise the shell will rightfully complain:

  $ TRAVIS_BRANCH=v2.14.0 ./ci/lib-travisci.sh 
  ./ci/lib-travisci.sh: line 17: v2.14.0: command not found

Furthermore, I would prefer quotes around $TAG and $TRAVIS_BRANCH.  If
either one of those two variables were empty (or contain multiple
words) at that point, the shell would complain.  Now, I don't think
that either can end up being empty, so quotes are not necessary, but
having quotes around them would save future readers from spending
brain cycles on this unnecessarily.

> +	then
> +		echo "Tip of $TRAVIS_BRANCH is exactly at $TAG"
> +		exit 0
> +	fi
> +}
> +
>  # Set 'exit on error' for all CI scripts to let the caller know that
>  # something went wrong
>  set -e
> +
> +skip_branch_tip_with_tag
> -- 
> 2.14.1
> 
>