CI: use "$runs_on_pool", not "$jobname" to select packages & config

Change the setup hooks for the CI to use "$runs_on_pool" for the
"$regular" job. Now we won't need as much boilerplate when adding new
jobs to the "regular" matrix, see 956d2e4639 (tests: add a test mode
for SANITIZE=leak, run it in CI, 2021-09-23) for the last such commit.

I.e. now instead of needing to enumerate each jobname when we select
packages we can install things depending on the pool we're running
in.

That we didn't do this dates back to the now gone dependency on Travis
CI, but even if we add a new CI target in the future this'll be easier
to port over, since we can probably treat "ubuntu-latest" as a
stand-in for some recent Linux that can run "apt" commands.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.github/workflows/main.yml

@@ -227,12 +227,14 @@ jobs:
             pool: ubuntu-latest
           - jobname: linux-gcc
             cc: gcc
+            cc_package: gcc-8
             pool: ubuntu-latest
           - jobname: osx-clang
             cc: clang
             pool: macos-latest
           - jobname: osx-gcc
             cc: gcc
+            cc_package: gcc-9
             pool: macos-latest
           - jobname: linux-gcc-default
             cc: gcc
@@ -242,7 +244,9 @@ jobs:
             pool: ubuntu-latest
     env:
       CC: ${{matrix.vector.cc}}
+      CC_PACKAGE: ${{matrix.vector.cc_package}}
       jobname: ${{matrix.vector.jobname}}
+      runs_on_pool: ${{matrix.vector.pool}}
     runs-on: ${{matrix.vector.pool}}
     steps:
     - uses: actions/checkout@v2

ci/install-dependencies.sh

@@ -11,17 +11,11 @@ UBUNTU_COMMON_PKGS="make libssl-dev libcurl4-openssl-dev libexpat-dev
  tcl tk gettext zlib1g-dev perl-modules liberror-perl libauthen-sasl-perl
  libemail-valid-perl libio-socket-ssl-perl libnet-smtp-ssl-perl"
 
-case "$jobname" in
-linux-clang|linux-gcc|linux-leaks)
+case "$runs_on_pool" in
+ubuntu-latest)
 	sudo apt-get -q update
 	sudo apt-get -q -y install language-pack-is libsvn-perl apache2 \
-		$UBUNTU_COMMON_PKGS
-	case "$jobname" in
-	linux-gcc)
-		sudo apt-get -q -y install gcc-8
-		;;
-	esac
-
+		$UBUNTU_COMMON_PKGS $CC_PACKAGE
 	mkdir --parents "$P4_PATH"
 	pushd "$P4_PATH"
 		wget --quiet "$P4WHENCE/bin.linux26x86_64/p4d"
@@ -36,7 +30,7 @@ linux-clang|linux-gcc|linux-leaks)
 		cp git-lfs-$LINUX_GIT_LFS_VERSION/git-lfs .
 	popd
 	;;
-osx-clang|osx-gcc)
+macos-latest)
 	export HOMEBREW_NO_AUTO_UPDATE=1 HOMEBREW_NO_INSTALL_CLEANUP=1
 	# Uncomment this if you want to run perf tests:
 	# brew install gnu-time
@@ -50,15 +44,17 @@ osx-clang|osx-gcc)
 		brew install --cask --no-quarantine perforce
 	} ||
 	brew install homebrew/cask/perforce
-	case "$jobname" in
-	osx-gcc)
-		brew install gcc@9
-		# Just in case the image is updated to contain gcc@9
-		# pre-installed but not linked.
-		brew link gcc@9
-		;;
-	esac
+
+	if test -n "$CC_PACKAGE"
+	then
+		BREW_PACKAGE=${CC_PACKAGE/-/@}
+		brew install "$BREW_PACKAGE"
+		brew link "$BREW_PACKAGE"
+	fi
 	;;
+esac
+
+case "$jobname" in
 StaticAnalysis)
 	sudo apt-get -q update
 	sudo apt-get -q -y install coccinelle libcurl4-openssl-dev libssl-dev \

ci/lib.sh

@@ -156,11 +156,15 @@ export DEFAULT_TEST_TARGET=prove
 export GIT_TEST_CLONE_2GB=true
 export SKIP_DASHED_BUILT_INS=YesPlease
 
-case "$jobname" in
-linux-clang|linux-gcc|linux-leaks)
+case "$runs_on_pool" in
+ubuntu-latest)
+	if test "$jobname" = "linux-gcc-default"
+	then
+		break
+	fi
+
 	if [ "$jobname" = linux-gcc ]
 	then
-		export CC=gcc-8
 		MAKEFLAGS="$MAKEFLAGS PYTHON_PATH=/usr/bin/python3"
 	else
 		MAKEFLAGS="$MAKEFLAGS PYTHON_PATH=/usr/bin/python2"
@@ -180,17 +184,17 @@ linux-clang|linux-gcc|linux-leaks)
 	GIT_LFS_PATH="$HOME/custom/git-lfs"
 	export PATH="$GIT_LFS_PATH:$P4_PATH:$PATH"
 	;;
-osx-clang|osx-gcc)
+macos-latest)
 	if [ "$jobname" = osx-gcc ]
 	then
-		export CC=gcc-9
 		MAKEFLAGS="$MAKEFLAGS PYTHON_PATH=$(which python3)"
 	else
 		MAKEFLAGS="$MAKEFLAGS PYTHON_PATH=$(which python2)"
 	fi
 	;;
-linux-gcc-default)
-	;;
+esac
+
+case "$jobname" in
 linux32)
 	CC=gcc
 	;;
@@ -200,9 +204,6 @@ linux-musl)
 	MAKEFLAGS="$MAKEFLAGS NO_REGEX=Yes ICONV_OMITS_BOM=Yes"
 	MAKEFLAGS="$MAKEFLAGS GIT_TEST_UTF8_LOCALE=C.UTF-8"
 	;;
-esac
-
-case "$jobname" in
 linux-leaks)
 	export SANITIZE=leak
 	export GIT_TEST_PASSING_SANITIZE_LEAK=true