Make EvalTask track resolved output paths

pkl-cli/src/main/kotlin/org/pkl/cli/CliEvaluator.kt

@@ -51,9 +51,10 @@ constructor(
   private val consoleWriter: Writer = System.out.writer(),
 ) : CliCommand(options.base) {
   /**
-   * Output files for the modules to be evaluated. Returns `null` if `options.outputPath` is `null`.
-   * Multiple modules may be mapped to the same output file, in which case their outputs are
-   * concatenated with [CliEvaluatorOptions.moduleOutputSeparator].
+   * Output files for the modules to be evaluated. Returns `null` if `options.outputPath` is `null`
+   * or if `options.multipleFileOutputPath` is not `null`. Multiple modules may be mapped to the
+   * same output file, in which case their outputs are concatenated with
+   * [CliEvaluatorOptions.moduleOutputSeparator].
    */
   @Suppress("MemberVisibilityCanBePrivate")
   val outputFiles: Set<File>? by lazy {

pkl-gradle/src/main/java/org/pkl/gradle/task/BasePklTask.java

@@ -28,15 +28,18 @@
 import java.util.function.Function;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
+import javax.inject.Inject;
 import org.gradle.api.DefaultTask;
 import org.gradle.api.InvalidUserDataException;
 import org.gradle.api.file.ConfigurableFileCollection;
 import org.gradle.api.file.DirectoryProperty;
 import org.gradle.api.file.FileSystemLocation;
+import org.gradle.api.model.ObjectFactory;
 import org.gradle.api.provider.ListProperty;
 import org.gradle.api.provider.MapProperty;
 import org.gradle.api.provider.Property;
 import org.gradle.api.provider.Provider;
+import org.gradle.api.provider.ProviderFactory;
 import org.gradle.api.tasks.Input;
 import org.gradle.api.tasks.InputFile;
 import org.gradle.api.tasks.InputFiles;
@@ -142,6 +145,7 @@ public void runTask() {
 
   @LateInit protected CliBaseOptions cachedOptions;
 
+  // Must be called during task execution time only.
   @Internal
   protected CliBaseOptions getCliBaseOptions() {
     if (cachedOptions == null) {
@@ -176,6 +180,12 @@ protected List<URI> getSourceModulesAsUris() {
     return Collections.emptyList();
   }
 
+  @Inject
+  protected abstract ObjectFactory getObjects();
+
+  @Inject
+  protected abstract ProviderFactory getProviders();
+
   protected List<Path> parseModulePath() {
     return getModulePath().getFiles().stream().map(File::toPath).collect(Collectors.toList());
   }

pkl-gradle/src/main/java/org/pkl/gradle/task/EvalTask.java

@@ -16,50 +16,82 @@
 package org.pkl.gradle.task;
 
 import java.io.File;
+import java.util.Collections;
+import java.util.Set;
+import javax.annotation.Nullable;
 import org.gradle.api.file.DirectoryProperty;
+import org.gradle.api.file.FileCollection;
 import org.gradle.api.file.RegularFileProperty;
 import org.gradle.api.provider.Property;
+import org.gradle.api.provider.Provider;
 import org.gradle.api.tasks.Input;
+import org.gradle.api.tasks.Internal;
 import org.gradle.api.tasks.Optional;
-import org.gradle.api.tasks.OutputDirectory;
-import org.gradle.api.tasks.OutputFile;
+import org.gradle.api.tasks.OutputDirectories;
+import org.gradle.api.tasks.OutputFiles;
 import org.pkl.cli.CliEvaluator;
 import org.pkl.cli.CliEvaluatorOptions;
 
 public abstract class EvalTask extends ModulesTask {
-  @OutputFile
-  @Optional
+
+  // not tracked because it might contain placeholders
+  // required
+  @Internal
   public abstract RegularFileProperty getOutputFile();
 
+  // not tracked because it might contain placeholders
+  // optional
+  @Internal
+  public abstract DirectoryProperty getMultipleFileOutputDir();
+
   @Input
-  @Optional
   public abstract Property<String> getOutputFormat();
 
   @Input
-  @Optional
   public abstract Property<String> getModuleOutputSeparator();
 
-  @OutputDirectory
+  @Input
+  public abstract Property<String> getExpression();
+
+  private final Provider<CliEvaluator> cliEvaluator =
+      getProviders()
+          .provider(
+              () ->
+                  new CliEvaluator(
+                      new CliEvaluatorOptions(
+                          getCliBaseOptions(),
+                          getOutputFile().get().getAsFile().getAbsolutePath(),
+                          getOutputFormat().get(),
+                          getModuleOutputSeparator().get(),
+                          mapAndGetOrNull(
+                              getMultipleFileOutputDir(), it -> it.getAsFile().getAbsolutePath()),
+                          getExpression().get())));
+
+  @SuppressWarnings("unused")
+  @OutputFiles
   @Optional
-  public abstract DirectoryProperty getMultipleFileOutputDir();
+  public FileCollection getEffectiveOutputFiles() {
+    return getObjects()
+        .fileCollection()
+        .from(cliEvaluator.map(e -> nullToEmpty(e.getOutputFiles())));
+  }
 
-  @Input
+  @OutputDirectories
   @Optional
-  public abstract Property<String> getExpression();
+  public FileCollection getEffectiveOutputDirs() {
+    return getObjects()
+        .fileCollection()
+        .from(cliEvaluator.map(e -> nullToEmpty(e.getOutputDirectories())));
+  }
+
+  private static <T> Set<T> nullToEmpty(@Nullable Set<T> set) {
+    return set == null ? Collections.emptySet() : set;
+  }
 
   @Override
   protected void doRunTask() {
     //noinspection ResultOfMethodCallIgnored
     getOutputs().getPreviousOutputFiles().forEach(File::delete);
-
-    new CliEvaluator(
-            new CliEvaluatorOptions(
-                getCliBaseOptions(),
-                getOutputFile().get().getAsFile().getAbsolutePath(),
-                getOutputFormat().get(),
-                getModuleOutputSeparator().get(),
-                mapAndGetOrNull(getMultipleFileOutputDir(), it -> it.getAsFile().getAbsolutePath()),
-                getExpression().get()))
-        .run();
+    cliEvaluator.get().run();
   }
 }

pkl-gradle/src/main/java/org/pkl/gradle/task/ModulesTask.java

@@ -128,12 +128,15 @@ private Pair<List<File>, List<URI>> splitFilesAndUris(List<Object> modules) {
   }
 
   /**
-   * Converts either a file or a URI to a URI. We convert a file to a URI via the {@link
+   * Converts either a file or a URI to a URI. We convert a relative file to a URI via the {@link
    * IoUtils#createUri(String)} because other ways of conversion can make relative paths into
    * absolute URIs, which may break module loading.
    */
   private URI parsedModuleNotationToUri(Object notation) {
     if (notation instanceof File file) {
+      if (file.isAbsolute()) {
+        return file.toPath().toUri();
+      }
       return IoUtils.createUri(IoUtils.toNormalizedPathString(file.toPath()));
     } else if (notation instanceof URI uri) {
       return uri;