GitHub Actions workflow improvements (#11507)

* Checkout merged branches for pull requests
* Add support for incremental add-on builds to speed up PR builds
* Echo the mvn command used for builds

Signed-off-by: Wouter Born <github@maindrain.net>

.github/scripts/maven-build

@@ -1,7 +1,11 @@
 #!/bin/bash
 
 BUILD_LOG=build.log
-DEFAULT_ARGUMENTS="clean verify -B -T 1.5C -U"
+
+ARGUMENTS="clean verify -B -T 1.5C -U"
+if [ $# -ge 1 ]; then
+    ARGUMENTS=$@
+fi
 
 function print_reactor_summary() {
     local start_end=$(grep -anE "\[INFO\] \\-{70,}" "$BUILD_LOG" | tail -n4 | cut -f1 -d: | sed -e 1b -e '$!d' | xargs)
@@ -22,22 +26,78 @@ function mvnp() {
         stdbuf -o0 sed -e :a -e "s/^.\{1,${padding}\}|/ &/;ta" # right align progress with padding
 }
 
+function build_all() {
+    echo
+    echo "Building all projects"
+    echo
+    echo "+ mvn $ARGUMENTS"
+    echo
+
+    mvnp $ARGUMENTS
+
+    status=$?
+    echo
+
+    if [ $status -eq 0 ]; then
+        print_reactor_summary
+    else
+        tail -n 2000 "$BUILD_LOG"
+    fi
+
+    exit $status
+}
+
+function changed_files() {
+    sed 's#,#\n#g' <<< $CHANGED_FILES
+}
+
+function addon_unrelated_changed_files() {
+    local addon="$1"
+    changed_files | \
+        grep -Ev "^(bundles/|itests/)$addon([/.].*)?$" | \
+        grep -Ev "^(CODEOWNERS|bom/openhab-addons/pom.xml|bundles/pom.xml|itests/pom.xml)$"
+}
+
+function changed_addons() {
+    changed_files | grep -E '(bundles/|itests/)org\.openhab\.' | sed -E 's#.+/(org\.openhab\.[a-z0-9]+\.[a-z0-9]+).*#\1#g' | sort -u
+}
+
+function addon_projects() {
+    local addon="$1"
+
+    # include add-on projects
+    local projects=":$(find . -mindepth 2 -maxdepth 2 -type d -regextype egrep -regex "./(bundles|itests)/$addon(\..*)?$" | grep -Ev 'org.openhab.binding.mqtt.homeassistant.tests|org.openhab.binding.mqtt.homie.tests' | sort | sed -E 's#./(bundles|itests)/##g' | xargs | sed 's# #,:#g')"
+
+    # include BOMs
+    projects="$projects,:org.openhab.addons.bom.openhab-core-index,:org.openhab.addons.bom.runtime-index,:org.openhab.addons.bom.test-index"
+
+    # exclude features
+    projects="$projects,-:org.openhab.addons.reactor.features.karaf,-:org.openhab.addons.features.karaf.openhab-addons,-:org.openhab.addons.features.karaf.openhab-addons-external"
+
+    echo $projects
+}
+
+function build_addon() {
+    local addon="$1"
+    local mvn_command="mvn $ARGUMENTS -am -amd -pl $(addon_projects $addon)"
+
+    echo
+    echo "Building add-on: $addon"
+    echo
+    echo "+ $mvn_command"
+    echo
+
+    $mvn_command 2>&1 | tee "$BUILD_LOG"
+}
+
+function build_based_on_changes() {
+    local changed_addon=$(changed_addons | xargs)
+    if [ $(echo $changed_addon | wc -w) -eq 1 ] && [ $(addon_unrelated_changed_files $changed_addon | wc -l) -eq 0 ]; then
+        build_addon $changed_addon
+    else
+        build_all
+    fi
+}
+
 mvn -v
-echo
-
-if [ $# -ge 1 ]; then
-    mvnp $@
-else
-    mvnp $DEFAULT_ARGUMENTS
-fi
-
-status=$?
-echo
-
-if [ $status -eq 0 ]; then
-    print_reactor_summary
-else
-    tail -n 2000 "$BUILD_LOG"
-fi
-
-exit $status
+build_based_on_changes