Test javac problem matcher through Maven and Gradle builds

.github/workflows/javac-matcher-build-tools.yml

@@ -0,0 +1,155 @@
+name: javac problem matcher with Maven & Gradle
+
+# The javac problem matcher registered by setup-java (##[add-matcher] java.json)
+# only understands javac's *native* diagnostic format:
+#
+#     File.java:12: warning|error: message
+#
+# (matcher regex, owner=javac: ^([^:]+):(\d+): (warning|error): (.+?)$)
+#
+# This workflow demonstrates how the two major build tools interact with it:
+#
+#   * Gradle passes javac diagnostics through unchanged, so they DO match the
+#     matcher and show up as GitHub annotations.
+#   * The Maven compiler plugin reformats diagnostics to
+#         [WARNING] /path/File.java:[line,col] message
+#     which does NOT match the matcher, so Maven builds are NOT annotated even
+#     though the compiler reports the same warnings/errors.
+#
+# Each job captures the build log and asserts the number of matcher-format lines,
+# so the workflow is self-verifying (not just visual). Open a run and compare the
+# Gradle job's Annotations panel (populated) with the Maven job's (empty).
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+env:
+  # Exact javac matcher regex from actions/setup-java .github/java.json, as a
+  # POSIX ERE for grep. [^:]+ = file (no colon), then :line:, then severity.
+  MATCHER_RE: '^[^:]+:[0-9]+: (warning|error): .+$'
+
+jobs:
+  gradle-is-annotated:
+    name: 'Gradle build IS annotated - ${{ matrix.os }}'
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest]
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Java (registers the javac problem matcher)
+        uses: actions/setup-java@0f481fcb613427c0f801b606911222b5b6f3083a # v5.5.0
+        with:
+          distribution: temurin
+          java-version: '21'
+
+      - name: Gradle compile with warnings (matcher should annotate them)
+        working-directory: javac-matcher-gradle
+        shell: bash
+        run: |
+          set -euo pipefail
+          # compileJava emits warnings but succeeds; tee so the matcher sees the log too.
+          ./gradlew --no-daemon --console=plain clean compileJava 2>&1 | tee warn.log
+          hits=$(grep -Ec "$MATCHER_RE" warn.log || true)
+          echo "matcher-format lines: $hits"
+          if [ "$hits" -lt 1 ]; then
+            echo "::error::expected Gradle warnings in native javac format (matcher would annotate)"
+            exit 1
+          fi
+          echo "OK: $hits Gradle warning line(s) match the javac matcher -> annotated"
+
+      - name: Gradle compile with errors (matcher should annotate them)
+        id: compile
+        continue-on-error: true
+        working-directory: javac-matcher-gradle
+        shell: bash
+        run: ./gradlew --no-daemon --console=plain compileErrorsJava 2>&1 | tee err.log
+
+      - name: Confirm Gradle errors failed the build and match the matcher
+        working-directory: javac-matcher-gradle
+        shell: bash
+        run: |
+          set -euo pipefail
+          echo "compile outcome: ${{ steps.compile.outcome }}"
+          if [ "${{ steps.compile.outcome }}" != "failure" ]; then
+            echo "::error::expected Gradle compileErrorsJava to fail"
+            exit 1
+          fi
+          hits=$(grep -Ec "$MATCHER_RE" err.log || true)
+          echo "matcher-format lines: $hits"
+          if [ "$hits" -lt 1 ]; then
+            echo "::error::expected Gradle errors in native javac format (matcher would annotate)"
+            exit 1
+          fi
+          echo "OK: $hits Gradle error line(s) match the javac matcher -> annotated"
+
+  maven-is-not-annotated:
+    name: 'Maven build is NOT annotated - ${{ matrix.os }}'
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest]
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Java (registers the javac problem matcher)
+        uses: actions/setup-java@0f481fcb613427c0f801b606911222b5b6f3083a # v5.5.0
+        with:
+          distribution: temurin
+          java-version: '21'
+
+      - name: Maven compile with warnings (matcher must NOT annotate them)
+        working-directory: javac-matcher-maven
+        shell: bash
+        run: |
+          set -euo pipefail
+          mvn -B clean compile 2>&1 | tee warn.log
+          matcher=$(grep -Ec "$MATCHER_RE" warn.log || true)
+          diags=$(grep -Ec '\.java:\[[0-9]+,[0-9]+\]' warn.log || true)
+          echo "matcher-format lines: $matcher (expect 0), maven [line,col] diagnostics: $diags (expect >0)"
+          if [ "$diags" -lt 1 ]; then
+            echo "::error::expected the Maven compiler to report warnings ([WARNING] File.java:[l,c] ...)"
+            exit 1
+          fi
+          if [ "$matcher" -ne 0 ]; then
+            echo "::error::Maven output unexpectedly matched the javac matcher"
+            exit 1
+          fi
+          echo "OK: Maven reported $diags warning(s), but 0 lines match the matcher -> not annotated"
+
+      - name: Maven compile with errors (fails; matcher must NOT annotate them)
+        id: compile
+        continue-on-error: true
+        working-directory: javac-matcher-maven
+        shell: bash
+        run: mvn -B -Perrors clean compile 2>&1 | tee err.log
+
+      - name: Confirm Maven errors failed the build but were not matcher-annotated
+        working-directory: javac-matcher-maven
+        shell: bash
+        run: |
+          set -euo pipefail
+          echo "compile outcome: ${{ steps.compile.outcome }}"
+          if [ "${{ steps.compile.outcome }}" != "failure" ]; then
+            echo "::error::expected Maven -Perrors compile to fail"
+            exit 1
+          fi
+          matcher=$(grep -Ec "$MATCHER_RE" err.log || true)
+          diags=$(grep -Ec '\.java:\[[0-9]+,[0-9]+\]' err.log || true)
+          echo "matcher-format lines: $matcher (expect 0), maven [line,col] diagnostics: $diags (expect >0)"
+          if [ "$diags" -lt 1 ]; then
+            echo "::error::expected the Maven compiler to report errors ([ERROR] File.java:[l,c] ...)"
+            exit 1
+          fi
+          if [ "$matcher" -ne 0 ]; then
+            echo "::error::Maven error output unexpectedly matched the javac matcher"
+            exit 1
+          fi
+          echo "OK: Maven reported $diags error(s) in the log, but 0 lines match the matcher -> not annotated"

.gitignore

@@ -1,2 +1,5 @@
 target/
 *.class
+.gradle/
+build/
+*.log

README.md

@@ -35,7 +35,28 @@ Both are expected to pass: together they document exactly what changed.
 - `.github/workflows/` — one workflow per feature, each running on Ubuntu, Windows and macOS.
 - `maven-sample-project/` — a tiny Maven project with one external dependency, used by
   `maven-args.yml` to prove that transfer-progress logs are suppressed by default.
+- `javac-matcher/` — standalone `.java` sources (warnings + errors) compiled directly with
+  `javac` by `javac-problem-matcher.yml`.
+- `javac-matcher-maven/` / `javac-matcher-gradle/` — the same warning/error sources built
+  through Maven and Gradle, used by `javac-matcher-build-tools.yml` (below).
+
+## javac problem matcher vs build tools
+
+The `javac` problem matcher registered by setup-java only understands javac's **native**
+diagnostic format (`File.java:12: warning|error: message`). Whether your build gets
+annotated therefore depends on the build tool:
+
+| Build tool | Compiler output | Matched by `javac` matcher? |
+|------------|-----------------|-----------------------------|
+| Direct `javac` | `File.java:12: warning: …` | ✅ annotated |
+| **Gradle** | `File.java:12: warning: …` (passed through) | ✅ annotated |
+| **Maven** (compiler plugin) | `[WARNING] /path/File.java:[12,5] …` | ❌ not annotated |
+
+[`javac-matcher-build-tools.yml`](.github/workflows/javac-matcher-build-tools.yml) proves
+this by capturing each build log and asserting the number of matcher-format lines (0 for
+Maven, >0 for Gradle) — so it fails loudly if the behavior ever changes.
 
 ## Running
 
+
 Push to `main`, open a PR, or trigger any workflow manually via **workflow_dispatch**.

javac-matcher-gradle/build.gradle

@@ -0,0 +1,33 @@
+plugins {
+    id 'java'
+}
+
+// Exercises the javac problem matcher registered by setup-java when the build is
+// driven by Gradle. Gradle passes javac diagnostics through in their native form
+// "/path/File.java:line: warning|error: message", which the matcher regex
+// ^([^:]+):(\d+): (warning|error): (.+?)$ DOES match, so Gradle builds ARE
+// annotated. See .github/workflows/javac-matcher-build-tools.yml.
+//
+//   ./gradlew compileJava        -> compiles the warning sources (succeeds, warns)
+//   ./gradlew compileErrorsJava  -> compiles the failing sources (fails)
+
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
+sourceSets {
+    // Failing sources live in their own source set so they can be compiled in a
+    // dedicated step without breaking the (successful) warning compilation.
+    errors {
+        java {
+            srcDir 'src/errors/java'
+        }
+    }
+}
+
+tasks.withType(JavaCompile).configureEach {
+    options.compilerArgs += ['-Xlint:all']
+    options.deprecation = true
+}

javac-matcher-gradle/gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,9 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.1.0-bin.zip
+networkTimeout=10000
+retries=0
+retryBackOffMs=500
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists