Annotate javac warnings from the build job only

setup-java's problem matcher turns javac's warnings, Error Prone's
among them, into annotations on the diff, and it is on by default. It
was on in every job that compiles the same sources: build, the three
newer JDKs, the five native platforms and both CodeQL analyses. Windows
never annotated, because the matcher's pattern takes no path with a
colon in it.

GitHub keeps only the first ten warnings of a step. The build prints
188, and as it runs in parallel, each job prints them in its own order
and keeps its own ten. So on #98 one warning showed up to ten times,
the one next to it once, and most not at all.

build keeps the matcher, now explicitly and with a comment saying why;
every other setup-java step on a pull request passes
problem-matcher: false. Each warning shows at most once, though still
only the first ten the build prints.

Author: abashev

.github/workflows/ci.yml

@@ -22,11 +22,16 @@ jobs:
         with:
           persist-credentials: false
 
+      # setup-java's problem matcher turns javac's warnings, Error Prone's among them, into annotations on
+      # the diff. This is the one job that keeps it: every other job compiles the same sources, and with
+      # the matcher on there too each warning showed once per job. GitHub keeps only the first ten
+      # warnings of a step, so the annotations are the first ten warnings the parallel build prints.
       - name: Install JDK 21
         uses: actions/setup-java@de7274f081f381c8f8158605e0321c36c376e2e6 # v6.0.1
         with:
           distribution: temurin
           java-version: '21'
+          problem-matcher: true
 
       - name: Build
         run: ./gradlew test
@@ -68,19 +73,22 @@ jobs:
         with:
           persist-credentials: false
 
+      # No problem matcher in this job: `build` annotates the warnings.
       - name: Install JDK ${{ matrix.jdk }} for the tests
         id: test-jdk
         uses: actions/setup-java@de7274f081f381c8f8158605e0321c36c376e2e6 # v6.0.1
         with:
           distribution: temurin
           java-version: ${{ matrix.jdk }}
+          problem-matcher: false
 
       # Installed last, so that it is the JAVA_HOME Gradle runs and compiles on.
       - name: Install JDK 21
         uses: actions/setup-java@de7274f081f381c8f8158605e0321c36c376e2e6 # v6.0.1
         with:
           distribution: temurin
           java-version: '21'
+          problem-matcher: false
 
       - name: Explain the extra Gradle arguments
         if: ${{ matrix.gradle_args != '' }}
@@ -138,13 +146,15 @@ jobs:
 
       # The jars compile with a Java 21 toolchain, which gradle.properties looks up in JDK21_HOME. On
       # Linux and macOS Gradle also finds the runner's own JDK 21 by its location, on Windows it does not.
-      # Installed before GraalVM, so that Gradle itself still runs on GraalVM.
+      # Installed before GraalVM, so that Gradle itself still runs on GraalVM. No problem matcher: `build`
+      # annotates the warnings.
       - name: Install JDK 21 for the jars
         id: jdk21
         uses: actions/setup-java@de7274f081f381c8f8158605e0321c36c376e2e6 # v6.0.1
         with:
           distribution: temurin
           java-version: '21'
+          problem-matcher: false
 
       - name: Install GraalVM 25 for the image
         uses: graalvm/setup-graalvm@0426e2e191540e8514dff98dc52a5f5146a2a276 # v1.6.6

.github/workflows/codeql-analysis.yml

@@ -30,11 +30,13 @@ jobs:
         with:
           persist-credentials: false
 
+      # No problem matcher: the javac warnings are annotated by CI's `build` job.
       - name: Set up JDK 21
         uses: actions/setup-java@de7274f081f381c8f8158605e0321c36c376e2e6 # v6.0.1
         with:
           distribution: temurin
           java-version: '21'
+          problem-matcher: false
 
       - name: Initialize CodeQL
         uses: github/codeql-action/init@1c5b675653bb5c22dbe9b12b556ec555138e09fd # v4.38.1