[PATCH 1/2] ci: don't update Homebrew

Lately our GCC macOS build job on Travis CI has been erroring out while installing dependencies with:

  +brew link gcc@8
  Error: No such keg: /usr/local/Cellar/gcc@8
  The command "ci/install-dependencies.sh" failed and exited with 1 during .

Now, while gcc@8 is still pre-installed (but not linked) and would be perfectly usable in the Travis CI macOS image we use [1], it's at version 8.2. However, when installing dependencies we first explicitly run 'brew update', which spends over two minutes to update itself and information about the available packages, and it learns about GCC 8.3. After that point gcc@8 exclusively refers to v8.3, and, unfortunately, 'brew' is just too dumb to be able to do anything with the still installed 8.2 package, and the subsequent 'brew link gcc@8' fails. (Even 'brew uninstall gcc@8' fails with the same error!)

Don't run 'brew update' to keep the already installed GCC 8.2 'brew link'-able. Note that in addition we have to 'export HOMEBREW_NO_AUTO_UPDATE=1' first, because 'brew' is so very helpful that it would implicitly run update for us on the next 'brew install <pkg>' otherwise.

Disabling 'brew update' has additional benefits:

  - It shaves off 2-3mins from the ~4mins currently spent on
    installing dependencies, and the macOS build jobs have always been
    prone to exceeding the time limit on Travis CI.

  - Our builds won't suddenly break because of the occasional Homebrew
    breakages [2].

The drawback is that we'll be stuck with slightly older versions of the packages that we install via Homebrew (Git-LFS 2.5.2 and Perforce 2018.1; they are currently at 2.7.2 and 2019.1, respectively). We might want to reconsider this decision as time goes on and/or switch to a more recent macOS image as they become available.

[1] 2000ac9fbf (travis-ci: switch to Xcode 10.1 macOS image,
    2019-01-17)

[2] See e.g. a1ccaedd62 (travis-ci: make the OSX build jobs' 'brew
    update' more quiet, 2019-02-02) or

    https://public-inbox.org/git/20180907032002.23366-1-szeder.dev@gmail.com/T/#+u

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
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 ci/install-dependencies.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)