Dynamically builds docker build matrix

.github/workflows/docker-tests.yml

@@ -8,12 +8,25 @@ on:
       - master
 
 jobs:
-  build-on-linux:
-    strategy:
-      matrix:
-        project: [armeria, dropwizard, ratpack, webmvc25-jetty, webmvc3-jetty, webmvc4-boot, webmvc4-jetty]
+  discover-projects:
+    name: Build project matrix
     runs-on: ubuntu-latest
+    outputs:
+      matrix: ${{ steps.set-matrix.outputs.matrix }}
+    steps:
+      - name: Checkout Sources
+        uses: actions/checkout@v2
+        with:
+          fetch-depth: 1
+      - id: set-matrix
+        name: Generate outputs.matrix from pom.xml listing
+        run: echo "::set-output name=matrix::{\"include\":$(.github/workflows/projects-as-json)}"
+  build-and-verify-docker:
     name: Build and verify Docker images
+    needs: discover-projects
+    runs-on: ubuntu-latest
+    strategy:
+      matrix: ${{ fromJson(needs.discover-projects.outputs.matrix) }}
     steps:
       - name: Install Docker
         uses: docker-practice/actions-setup-docker@master

.github/workflows/projects-as-json

@@ -0,0 +1,6 @@
+#!/bin/sh
+
+set -ue
+
+# Make a string like: [{"project":"armeria"},{"project":"dropwizard"}]
+ls */pom.xml|sed 's~\(.*\)/pom.xml~{"project":"\1"}~g'|tr '\n' ','|sed 's/\(.*\),$/[\1]/'

docker/hooks/build

@@ -1,4 +1,6 @@
-#!/bin/sh -v
+#!/bin/sh -x
+
+set -ue
 
 # This hook is called with the current directory set to the same as the Dockerfile, so we go back
 # to top level.

docker/hooks/push

@@ -1,4 +1,6 @@
-#!/bin/sh -v
+#!/bin/sh -x
+
+set -ue
 
 # Override push to avoid pushing a latest tag. We use tags for each example.
 if [ "$DOCKER_REPO" = "index.docker.io/openzipkin/example-brave" ]; then