baseline-java-versions: javaCompiler property to compile Java code with a certain JDK version (#3342)

baseline-java-versions: Introduce an optional javaCompiler property to javaVersions which will determine which JDK is used to run the Java compiler. In this mode, --release is now used to target lower Java language versions/class file bytecode than the compiler.

Author: CRogers

README.md

@@ -21,7 +21,6 @@ _Baseline is a family of Gradle plugins for configuring Java projects with sensi
 | `com.palantir.baseline-reproducibility`            | Sensible defaults to ensure Jar, Tar and Zip tasks can be reproduced
 | `com.palantir.baseline-exact-dependencies`         | Ensures projects explicitly declare all the dependencies they rely on, no more and no less
 | `com.palantir.baseline-encoding`                   | Ensures projects use the UTF-8 encoding in compile tasks.
-| `com.palantir.baseline-release-compatibility`      | Ensures projects targeting older JREs only compile against classes and methods available in those JREs.
 | `com.palantir.baseline-testing`                    | Configures test tasks to dump heap dumps (hprof files) for convenient debugging
 | `com.palantir.baseline-test-heap`                  | Increases the default Test task heap from 512m to 2g.
 | `com.palantir.baseline-java-compiler-diagnostics`  | Applies the `-Xmaxwarns` and `-Xmaxwarns` compiler options with a very large limit to avoid truncating failure info.
@@ -242,12 +241,6 @@ checkImplicitDependencies {
 
 This plugin sets the encoding for JavaCompile tasks to `UTF-8`.
 
-## com.palantir.baseline-release-compatibility
-
-This plugin adds the `--release <number>` flag to JavaCompile tasks (when the compiler [supports it](https://openjdk.java.net/jeps/247)), so that published jars will only use methods available in the target JRE.  Relying on `sourceCompatibility = 1.8` and `targetCompatibility = 1.8` is insufficient because you run the risk of using method that have been added in newer JREs, e.g. `Optional#isEmpty`.
-
-This plugin may become redundant if this functionality is implemented upstream [in Gradle](https://github.com/gradle/gradle/issues/2510).
-
 ## com.palantir.baseline-testing
 
 Configures some sensible defaults:
@@ -289,15 +282,17 @@ The plugin is currently used on an opt-in basis. To use it, apply the plugin and
 apply plugin: 'com.palantir.baseline-java-versions'
 
 javaVersions {
+    javaCompiler = 25
     libraryTarget = 11
     distributionTarget = 17
     runtime = 21
 }
 ```
 
 The configurable fields of the `javaVersions` extension are:
-* `libraryTarget`: (required) The Java version used for compilation of libraries that are published.
-* `distributionTarget`: (optional) The Java version used for compilation of code used within distributions, but not published externally. Defaults to the `libraryTarget` version.
+* `javaCompiler`: (optional) The version of the Java compiler used. If not set, the appropriate `target` will be used. The `--release`, `--target` and `--source` compiler args are used to enable compiling code at a lower target than the compiler used. However, if `baseline-module-jvm-args`/`moduleJvmArgs` are used, `--release` will not be set as it is not compatible with exporting/opening system modules, meaning compilation will not fail if JDK APIs are used which are higher than the requested target.
+* `libraryTarget`: (required) The Java version targeted for compilation of libraries that are published.
+* `distributionTarget`: (optional) The Java version targeted for compilation of code used within distributions, but not published externally. Defaults to the `libraryTarget` version.
 * `runtime`: (optional) Runtime Java version for testing and packaging distributions. Defaults to the `distributionTarget` version.
 
 The configured Java versions are used as defaults for all projects.
@@ -326,12 +321,14 @@ A sub-project can also explicitly override the default Java versions, but doing
 ```gradle
 // In a sub-project's build.gradle
 javaVersion {
+    javaCompiler = 17
     target = 11
     runtime = 11
 }
 ```
 
 The optionally configurable fields of the `javaVersion` extension are:
+* `javaCompiler`: The version of the Java compiler used. If not set, `target` will be used. See note in above `javaVersions` extension regarding `javaCompiler`.
 * `target`: The target version used for compilation.
 * `runtime`: The runtime version used for testing and distributions.
 

gradle-baseline-java/build.gradle

@@ -69,6 +69,8 @@ dependencies {
     compileOnly 'org.immutables:value::annotations'
 }
 
+// Used in BaselineJavaVersionIntegrationTest
+tasks.test.dependsOn ':gradle-baseline-java:test-compiler-plugins:publishToMavenLocal'
 // Used in BaselineConfigIntegrationTest
 tasks.test.dependsOn ':gradle-baseline-java-config:publishToMavenLocal'
 tasks.test.dependsOn tasks.named('publishToMavenLocal')
@@ -79,6 +81,8 @@ tasks.checkJUnitDependencies.enabled = false
 test {
     environment 'CIRCLE_ARTIFACTS', "${buildDir}/artifacts"
     environment 'CIRCLE_TEST_REPORTS', "${buildDir}/circle-reports"
+
+    environment 'ORG_GRADLE_PROJECT_baselineTestCompilerPluginsVersion', project.version
     // TEMPHACK(okelvin): remove this to decouple baseline-error-prone
     environment 'ORG_GRADLE_PROJECT_baselineErrorProneVersion', "0.2.0"
 
@@ -146,13 +150,6 @@ gradlePlugin {
             description = 'Baseline Java is a collection of Gradle plugins for configuring code quality tools in builds.'
             tags.set(['java', 'checkstyle', 'code quality'])
         }
-        baselineReleaseCompatibility {
-            id = 'com.palantir.baseline-release-compatibility'
-            displayName = 'Palantir Baseline Release Compatibility Plugin'
-            implementationClass = 'com.palantir.baseline.plugins.BaselineReleaseCompatibility'
-            description = 'Baseline Java is a collection of Gradle plugins for configuring code quality tools in builds.'
-            tags.set(['java', 'checkstyle', 'code quality'])
-        }
         baselinePreferProjectModules {
             id = 'com.palantir.baseline-prefer-project-modules'
             displayName = 'Palantir Baseline Prefer Project Modules Plugin'

gradle-baseline-java/src/main/java/com/palantir/baseline/plugins/Baseline.java

@@ -57,7 +57,6 @@ public void apply(Project project) {
             proj.getPluginManager().apply(BaselineReproducibility.class);
             proj.getPluginManager().apply(BaselineClassUniquenessPlugin.class);
             proj.getPluginManager().apply(BaselineExactDependencies.class);
-            proj.getPluginManager().apply(BaselineReleaseCompatibility.class);
             proj.getPluginManager().apply(BaselineTesting.class);
             proj.getPluginManager().apply(BaselineTestHeap.class);
             proj.getPluginManager().apply(BaselineJavaCompilerDiagnostics.class);