Commit the Maven wrapper jar and cache the wrapper's Maven distribution in CI

The .gitignore negation for the wrapper jar came before *.jar, so the jar was
never committed and every CI job downloaded it from Maven Central; a 429 from
Central failed the errorprone job on 03e4dea. The negation now follows *.jar.
CI jobs also cache ~/.m2/wrapper, which setup-java's maven cache does not
cover, so the Maven 3.8.6 distribution is not fetched on every run.

Author: Mark Pollack

.github/workflows/ci.yml

@@ -27,6 +27,11 @@ jobs:
           java-version: '17'
           distribution: 'temurin'
           cache: maven
+      - name: Cache the Maven distribution the wrapper uses
+        uses: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830 # v4
+        with:
+          path: ~/.m2/wrapper
+          key: maven-wrapper-${{ hashFiles('.mvn/wrapper/maven-wrapper.properties') }}
 
       - name: Build with Maven
         run: ./mvnw clean verify -B
@@ -55,6 +60,11 @@ jobs:
           java-version: '21'
           distribution: 'temurin'
           cache: maven
+      - name: Cache the Maven distribution the wrapper uses
+        uses: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830 # v4
+        with:
+          path: ~/.m2/wrapper
+          key: maven-wrapper-${{ hashFiles('.mvn/wrapper/maven-wrapper.properties') }}
 
       - name: Build with Maven (Error Prone and NullAway enforced)
         run: ./mvnw -B clean verify
@@ -75,6 +85,11 @@ jobs:
           java-version: '17'
           distribution: 'temurin'
           cache: maven
+      - name: Cache the Maven distribution the wrapper uses
+        uses: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830 # v4
+        with:
+          path: ~/.m2/wrapper
+          key: maven-wrapper-${{ hashFiles('.mvn/wrapper/maven-wrapper.properties') }}
 
       - name: Contention tests pinned to one CPU
         run: taskset -c 0 ./mvnw -B -pl acp-core -am test -Dtest='MultiPromptSyncSessionTest,AcpAgentSessionPromptLockTest' -Dsurefire.failIfNoSpecifiedTests=false
@@ -97,6 +112,11 @@ jobs:
           java-version: '17'
           distribution: 'temurin'
           cache: maven
+      - name: Cache the Maven distribution the wrapper uses
+        uses: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830 # v4
+        with:
+          path: ~/.m2/wrapper
+          key: maven-wrapper-${{ hashFiles('.mvn/wrapper/maven-wrapper.properties') }}
 
       # Install first rather than -am: a -Dtest filter would also reach the JSON modules,
       # which scan acp-core's test-jar for their contract tests.

.gitignore

@@ -1,7 +1,6 @@
 ### Maven/Gradle Builds ###
 target/
 .m2repo/
-!.mvn/wrapper/maven-wrapper.jar
 !**/src/main/**/target/
 !**/src/test/**/target/
 build/
@@ -58,6 +57,8 @@ derby.log
 
 ### Package Files ###
 *.jar
+# The Maven wrapper jar is committed so mvnw needs no download; this must follow *.jar to win.
+!.mvn/wrapper/maven-wrapper.jar
 *.war
 *.nar
 *.ear