Allow javac plugin to infer targetroot from javac class output directory

Author: Win Wang

docs/manual-configuration.md

@@ -66,7 +66,9 @@ compiler plugin. To do this you need to explicitly configure two directories:
   It's important that all of the source files that should be index live under
   this directory.
 - `-targetroot:PATH`: the absolute path to the directory where to generate
-  SemanticDB file. This directory can be anywhere on your file system.
+  SemanticDB file. This directory can be anywhere on your file system.  
+  Alternatively, pass in `-targetroot:javac-classes-directory`
+  for the plugin to automatically use the `javac` output directory.
 
 If you're using Gradle.
 

semanticdb-javac/src/main/java/com/sourcegraph/semanticdb_javac/SemanticdbJavacOptions.java

@@ -3,18 +3,31 @@
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.ArrayList;
+import javax.tools.FileObject;
+import javax.tools.JavaFileManager;
+import javax.tools.JavaFileObject;
 
-/** Settings that can be configured alongside the -Xplugin compiler option. */
+import com.sun.tools.javac.util.Context;
+
+import static javax.tools.StandardLocation.CLASS_OUTPUT;
+
+/**
+ * Settings that can be configured alongside the -Xplugin compiler option.
+ */
 public class SemanticdbJavacOptions {
 
-  /** The directory to place */
+  /**
+   * The directory to place META-INF and its .semanticdb files
+   */
   public Path targetroot;
 
   public Path sourceroot;
   public boolean includeText = false;
   public boolean verboseEnabled = false;
   public final ArrayList<String> errors;
 
+  public static String stubClassName = "META-INF-stub";
+
   public SemanticdbJavacOptions() {
     errors = new ArrayList<>();
   }
@@ -26,11 +39,20 @@ public static String missingRequiredDirectoryOption(String option) {
         option, option);
   }
 
-  public static SemanticdbJavacOptions parse(String[] args) {
+  public static String JAVAC_CLASSES_DIR_ARG = "javac-classes-directory";
+
+  public static SemanticdbJavacOptions parse(String[] args, Context ctx) {
     SemanticdbJavacOptions result = new SemanticdbJavacOptions();
+    boolean useJavacClassesDir = false;
     for (String arg : args) {
       if (arg.startsWith("-targetroot:")) {
-        result.targetroot = Paths.get(arg.substring("-targetroot:".length()));
+        String argValue = arg.substring("-targetroot:".length());
+        if (argValue.equals(JAVAC_CLASSES_DIR_ARG)) {
+          useJavacClassesDir = true;
+          result.targetroot = getJavacClassesDir(result, ctx);
+        } else {
+          result.targetroot = Paths.get(argValue);
+        }
       } else if (arg.startsWith("-sourceroot:")) {
         result.sourceroot = Paths.get(arg.substring("-sourceroot:".length())).normalize();
       } else if (arg.equals("-text:on")) {
@@ -47,12 +69,32 @@ public static SemanticdbJavacOptions parse(String[] args) {
         result.errors.add(String.format("unknown flag '%s'\n", arg));
       }
     }
-    if (result.targetroot == null) {
+    if (result.targetroot == null && !useJavacClassesDir) {
       result.errors.add(missingRequiredDirectoryOption("targetroot"));
     }
     if (result.sourceroot == null) {
       result.errors.add(missingRequiredDirectoryOption("sourceroot"));
     }
     return result;
   }
+
+  private static Path getJavacClassesDir(SemanticdbJavacOptions result, Context ctx) {
+    // I'm not aware of a better way to get the class output directory from javac
+    Path outputDir = null;
+    try {
+      JavaFileManager fm = ctx.get(JavaFileManager.class);
+      FileObject outputDirStub =
+          fm.getJavaFileForOutput(CLASS_OUTPUT, stubClassName, JavaFileObject.Kind.CLASS, null);
+      outputDir = Paths.get(outputDirStub.toUri()).toAbsolutePath().getParent();
+    } catch (Exception e) {
+      String errorMsg =
+          String.format(
+              "-targetroot:%s passed but could not get the class output directory: %s",
+              JAVAC_CLASSES_DIR_ARG,
+              e.getMessage()
+          );
+      result.errors.add(errorMsg);
+    }
+    return outputDir;
+  }
 }

semanticdb-javac/src/main/java/com/sourcegraph/semanticdb_javac/SemanticdbPlugin.java

@@ -1,8 +1,10 @@
 package com.sourcegraph.semanticdb_javac;
 
-import com.sun.source.util.*;
+import com.sun.source.util.JavacTask;
+import com.sun.source.util.Plugin;
 import com.sun.tools.javac.api.BasicJavacTask;
 import com.sun.tools.javac.model.JavacTypes;
+import com.sun.tools.javac.util.Context;
 
 /** Entrypoint of the semanticdb-javac compiler plugin. */
 public class SemanticdbPlugin implements Plugin {
@@ -14,10 +16,12 @@ public String getName() {
 
   @Override
   public void init(JavacTask task, String... args) {
+    Context ctx = ((BasicJavacTask) task).getContext();
+
     SemanticdbReporter reporter = new SemanticdbReporter();
-    SemanticdbJavacOptions options = SemanticdbJavacOptions.parse(args);
+    SemanticdbJavacOptions options = SemanticdbJavacOptions.parse(args, ctx);
     GlobalSymbolsCache globals = new GlobalSymbolsCache(options);
-    JavacTypes javacTypes = JavacTypes.instance(((BasicJavacTask) task).getContext());
+    JavacTypes javacTypes = JavacTypes.instance(ctx);
     if (!options.errors.isEmpty()) {
       for (String error : options.errors) {
         reporter.error(error);

tests/unit/src/main/scala/tests/SimpleFileManager.java

@@ -1,31 +1,36 @@
 package tests;
 
+import java.net.URI;
+import java.util.ArrayList;
+import java.util.List;
 import javax.tools.FileObject;
 import javax.tools.ForwardingJavaFileManager;
 import javax.tools.JavaFileObject;
 import javax.tools.StandardJavaFileManager;
-import java.net.URI;
-import java.util.ArrayList;
-import java.util.List;
+
+import com.sourcegraph.semanticdb_javac.SemanticdbJavacOptions;
 
 public class SimpleFileManager
-        extends ForwardingJavaFileManager<StandardJavaFileManager> {
+    extends ForwardingJavaFileManager<StandardJavaFileManager> {
 
-    public List<SimpleClassFile> compiled = new ArrayList<>();
-    protected SimpleFileManager(StandardJavaFileManager fileManager) {
-        super(fileManager);
-    }
+  public List<SimpleClassFile> compiled = new ArrayList<>();
+
+  protected SimpleFileManager(StandardJavaFileManager fileManager) {
+    super(fileManager);
+  }
 
-    // standard constructors/getters
+  // standard constructors/getters
 
-    @Override
-    public JavaFileObject getJavaFileForOutput(Location location,
-                                               String className, JavaFileObject.Kind kind, FileObject sibling) {
-        SimpleClassFile result = new SimpleClassFile(
-                URI.create("string://" + className));
-        compiled.add(result);
-        return result;
+  @Override
+  public JavaFileObject getJavaFileForOutput(Location location,
+                                             String className, JavaFileObject.Kind kind, FileObject sibling) {
+    SimpleClassFile result = new SimpleClassFile(
+        URI.create("string://" + className));
+    if (!className.equals(SemanticdbJavacOptions.stubClassName)) {
+      compiled.add(result);
     }
+    return result;
+  }
 
 }