Refresh the GitHub Actions CI (#632)

This change:

* Builds the library with Go 1.14, too.
* Builds the non-legacy tests with Ubuntu Focal (20.04).
* Adds testing for system-wide libraries, both static and dynamic
  versions.
* Fixes a typo in the README.

3 files changed, 88 insertions, 23 deletions

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5472f22..88e6c57 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -46,10 +46,10 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        go: [ '1.11', '1.12', '1.13' ]
+        go: [ '1.11', '1.12', '1.13', '1.14' ]
     name: Go ${{ matrix.go }}
 
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
 
     steps:
     - name: Set up Go
@@ -71,13 +71,13 @@ jobs:
       fail-fast: false
     name: Go (dynamic)
 
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
 
     steps:
     - name: Set up Go
       uses: actions/setup-go@v1
       with:
-        go-version: '1.13'
+        go-version: '1.14'
       id: go
     - name: Check out code into the Go module directory
       uses: actions/checkout@v1
@@ -87,3 +87,47 @@ jobs:
         make build-libgit2-dynamic
     - name: Test
       run: make test-dynamic
+
+  build-system-dynamic:
+    strategy:
+      fail-fast: false
+    name: Go (system-wide, dynamic)
+
+    runs-on: ubuntu-20.04
+
+    steps:
+    - name: Set up Go
+      uses: actions/setup-go@v1
+      with:
+        go-version: '1.14'
+      id: go
+    - name: Check out code into the Go module directory
+      uses: actions/checkout@v1
+    - name: Build libgit2
+      run: |
+        git submodule update --init
+        sudo ./script/build-libgit2.sh --dynamic --system
+    - name: Test
+      run: make test
+
+  build-system-static:
+    strategy:
+      fail-fast: false
+    name: Go (system-wide, static)
+
+    runs-on: ubuntu-20.04
+
+    steps:
+    - name: Set up Go
+      uses: actions/setup-go@v1
+      with:
+        go-version: '1.14'
+      id: go
+    - name: Check out code into the Go module directory
+      uses: actions/checkout@v1
+    - name: Build libgit2
+      run: |
+        git submodule update --init
+        sudo ./script/build-libgit2.sh --static --system
+    - name: Test
+      run: go test --count=1 --tags "static,system_libgit2" ./...
diff --git a/README.md b/README.md
index 05dddec..79a96e9 100644
--- a/README.md
+++ b/README.md
@@ -31,7 +31,7 @@ The `master` branch follows the tip of libgit2 itself (with some lag) and as suc
 
 ### Which branch to send Pull requests to
 
-If there's something version-specific that you'd want to contribute to, you can send them to the `release-${MAJOR}-${MINOR}` branches, which follow libgit2's releases.
+If there's something version-specific that you'd want to contribute to, you can send them to the `release-${MAJOR}.${MINOR}` branches, which follow libgit2's releases.
 
 Installing
 ----------
diff --git a/script/build-libgit2.sh b/script/build-libgit2.sh
index 7398cd9..98ff78b 100755
--- a/script/build-libgit2.sh
+++ b/script/build-libgit2.sh
@@ -6,33 +6,54 @@
 
 set -e
 
-if [ "$#" -eq "0" ]; then
-	echo "Usage: $0 <--dynamic|--static>">&2
+usage() {
+	echo "Usage: $0 <--dynamic|--static> [--system]">&2
 	exit 1
+}
+
+if [ "$#" -eq "0" ]; then
+	usage
 fi
 
 ROOT="$(cd "$(dirname "$0")/.." && echo "${PWD}")"
 VENDORED_PATH="${ROOT}/vendor/libgit2"
+BUILD_SYSTEM=OFF
+
+while [ $# -gt 0 ]; do
+	case "$1" in
+		--static)
+			BUILD_PATH="${ROOT}/static-build"
+			BUILD_SHARED_LIBS=OFF
+			;;
 
-case "$1" in
-	--static)
-		BUILD_PATH="${ROOT}/static-build"
-		BUILD_SHARED_LIBS=OFF
-		;;
+		--dynamic)
+			BUILD_PATH="${ROOT}/dynamic-build"
+			BUILD_SHARED_LIBS=ON
+			;;
 
-	--dynamic)
-		BUILD_PATH="${ROOT}/dynamic-build"
-		BUILD_SHARED_LIBS=ON
-		;;
+		--system)
+			BUILD_SYSTEM=ON
+			;;
 
-	*)
-		echo "Usage: $0 <--dynamic|--static>">&2
-		exit 1
-		;;
-esac
+		*)
+			usage
+			;;
+	esac
+	shift
+done
 
-mkdir -p "${BUILD_PATH}/build" "${BUILD_PATH}/install/lib"
+if [ -z "${BUILD_SHARED_LIBS}" ]; then
+	usage
+fi
+
+if [ "${BUILD_SYSTEM}" = "ON" ]; then
+	BUILD_INSTALL_PREFIX="/usr"
+else
+	BUILD_INSTALL_PREFIX="${BUILD_PATH}/install"
+	mkdir -p "${BUILD_PATH}/install/lib"
+fi
 
+mkdir -p "${BUILD_PATH}/build" &&
 cd "${BUILD_PATH}/build" &&
 cmake -DTHREADSAFE=ON \
       -DBUILD_CLAR=OFF \
@@ -40,7 +61,7 @@ cmake -DTHREADSAFE=ON \
       -DREGEX_BACKEND=builtin \
       -DCMAKE_C_FLAGS=-fPIC \
       -DCMAKE_BUILD_TYPE="RelWithDebInfo" \
-      -DCMAKE_INSTALL_PREFIX="${BUILD_PATH}/install" \
+      -DCMAKE_INSTALL_PREFIX="${BUILD_INSTALL_PREFIX}" \
       -DCMAKE_INSTALL_LIBDIR="lib" \
       "${VENDORED_PATH}" &&