Add tests for Bazel sourceroot inference

scip-javac/build.gradle.kts

@@ -22,6 +22,13 @@ tasks.named<JavaCompile>("compileJava") {
     }
 }
 
+tasks.named<JavaCompile>("compileTestJava") {
+    // Tests use `@ClientCodeWrapper.Trusted` (an internal javac API) to construct file objects
+    // that mimic Bazel's compiler. `--add-exports` is incompatible with `--release`.
+    options.release.set(null as Int?)
+    options.compilerArgs.addAll(JavacInternals.jvmOptions(rootDir))
+}
+
 tasks.named<Test>("test") {
     jvmArgs(JavacInternals.jvmOptions(rootDir))
 }

scip-javac/src/main/java/org/scip_code/scip_java/javac/ScipTaskListener.java

@@ -177,7 +177,6 @@ public static Path absolutePathFromUri(ScipJavacOptions options, JavaFileObject
   }
 
   // Infers the `-sourceroot:` flag from the provided file.
-  // FIXME: add unit tests https://github.com/scip-code/scip-java/issues/444
   private void inferBazelSourceroot(JavaFileObject file) {
     if (options.uriScheme != UriScheme.BAZEL || options.sourceroot != null) return;
     Path absolutePath = absolutePathFromUri(options, file);
@@ -195,6 +194,13 @@ private void inferBazelSourceroot(JavaFileObject file) {
       if (!uriName.equals(pathName)) break;
       relativePathDepth++;
     }
+    if (relativePathDepth == absolutePathDepth) {
+      // Every name of absolutePath is a suffix of uriPath (for example, when both paths are
+      // identical because the file object's toString() didn't match a known Bazel pattern).
+      // There is no prefix left to use as the sourceroot, so fall back to the filesystem root.
+      options.sourceroot = absolutePath.getRoot();
+      return;
+    }
     options.sourceroot =
         absolutePath
             .getRoot()

scip-javac/src/test/java/org/scip_code/scip_java/javac/BazelSourcerootTest.java

@@ -0,0 +1,155 @@
+package org.scip_code.scip_java.javac;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import com.sun.tools.javac.api.ClientCodeWrapper;
+import java.io.File;
+import java.io.IOException;
+import java.io.StringWriter;
+import java.io.UncheckedIOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import javax.tools.JavaCompiler;
+import javax.tools.JavaFileObject;
+import javax.tools.SimpleJavaFileObject;
+import javax.tools.ToolProvider;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+import org.scip_code.scip.Document;
+import org.scip_code.scip.Index;
+
+/**
+ * Tests the automatic sourceroot inference of {@code -build-tool:bazel} compilations (see {@code
+ * ScipTaskListener.inferBazelSourceroot}) by driving the real compiler with file objects that mimic
+ * the ones constructed by Bazel's Java compiler.
+ */
+class BazelSourcerootTest {
+
+  /**
+   * Mimics the {@code com.sun.tools.javac.file.PathFileObject.SimpleFileObject} instances that the
+   * plugin sees under Bazel: {@code toUri()} points to the file in a sandbox/temporary directory
+   * while {@code toString()} renders a "human-readable" path pointing to the original source file.
+   *
+   * <p>The {@link ClientCodeWrapper.Trusted} annotation stops javac from wrapping this file object
+   * in a {@code WrappedJavaFileObject}, which would change the result of {@code toString()}.
+   * Bazel's file objects are never wrapped because javac-internal classes are trusted.
+   */
+  @ClientCodeWrapper.Trusted
+  private static final class BazelSourceFile extends SimpleJavaFileObject {
+    private final Path humanReadablePath;
+    private final String content;
+
+    BazelSourceFile(Path sandboxPath, Path humanReadablePath, String content) {
+      super(sandboxPath.toUri(), Kind.SOURCE);
+      this.humanReadablePath = humanReadablePath;
+      this.content = content;
+    }
+
+    @Override
+    public CharSequence getCharContent(boolean ignoreEncodingErrors) {
+      return content;
+    }
+
+    @Override
+    public String toString() {
+      return "SimpleFileObject[" + humanReadablePath + "]";
+    }
+  }
+
+  private static void compile(Path targetroot, List<JavaFileObject> compilationUnits) {
+    JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
+    SimpleFileManager fileManager =
+        new SimpleFileManager(compiler.getStandardFileManager(null, null, null), targetroot);
+    StringWriter output = new StringWriter();
+    List<String> arguments =
+        Arrays.asList(
+            "-processorpath",
+            TestCompiler.PROCESSOR_PATH,
+            "-classpath",
+            TestCompiler.PROCESSOR_PATH,
+            "-Xplugin:scip -build-tool:bazel");
+    JavaCompiler.CompilationTask task =
+        compiler.getTask(output, fileManager, null, arguments, null, compilationUnits);
+    boolean isSuccess = task.call();
+    assertTrue(isSuccess, () -> "compilation should succeed, compiler output:\n" + output);
+  }
+
+  private static Document readShardDocument(Path shardPath) {
+    assertTrue(Files.isRegularFile(shardPath), () -> "expected SCIP shard at " + shardPath);
+    try {
+      Index shard = Index.parseFrom(Files.readAllBytes(shardPath));
+      assertEquals(1, shard.getDocumentsCount());
+      return shard.getDocuments(0);
+    } catch (IOException e) {
+      throw new UncheckedIOException(e);
+    }
+  }
+
+  @Test
+  void sandboxedCompilation(
+      @TempDir Path workspace, @TempDir Path sandbox, @TempDir Path targetroot) {
+    // The typical case: javac sees the source files in a sandbox directory while their
+    // human-readable paths point into the workspace. The sourceroot is inferred from the
+    // first compilation unit (the longest common suffix of the two paths is
+    // src/com/example/Hello.java, what remains is the workspace directory) and shards are
+    // written under the workspace-relative path of each source file.
+    Path execroot = sandbox.resolve("execroot").resolve("_main");
+    compile(
+        targetroot,
+        Arrays.asList(
+            new BazelSourceFile(
+                execroot.resolve("src/com/example/Hello.java"),
+                workspace.resolve("src/com/example/Hello.java"),
+                "package com.example;\npublic class Hello {}"),
+            new BazelSourceFile(
+                execroot.resolve("src/com/example/inner/World.java"),
+                workspace.resolve("src/com/example/inner/World.java"),
+                "package com.example.inner;\npublic class World {}")));
+    Path scipRoot = targetroot.resolve("META-INF").resolve("scip");
+    Document hello = readShardDocument(scipRoot.resolve("src/com/example/Hello.java.scip"));
+    assertEquals("src/com/example/Hello.java", hello.getRelativePath());
+    Document world = readShardDocument(scipRoot.resolve("src/com/example/inner/World.java.scip"));
+    assertEquals("src/com/example/inner/World.java", world.getRelativePath());
+  }
+
+  @Test
+  void onlyFileNameInCommon(
+      @TempDir Path workspace, @TempDir Path sandbox, @TempDir Path targetroot) {
+    // When the sandbox layout shares nothing with the workspace layout except the file
+    // name, the inferred sourceroot is the parent directory of the source file.
+    compile(
+        targetroot,
+        Collections.singletonList(
+            new BazelSourceFile(
+                sandbox.resolve("Hello.java"),
+                workspace.resolve("nested/dir/Hello.java"),
+                "public class Hello {}")));
+    Document document =
+        readShardDocument(
+            targetroot.resolve("META-INF").resolve("scip").resolve("Hello.java.scip"));
+    assertEquals("Hello.java", document.getRelativePath());
+  }
+
+  @Test
+  void unrecognizedFileObjectsFallBackToFilesystemRoot(
+      @TempDir Path sandbox, @TempDir Path targetroot) {
+    // SimpleSourceFile's toString() doesn't match any of the known Bazel file object
+    // patterns, so the plugin falls back to using the URI path as the human-readable path.
+    // The two paths are then identical and the inferred sourceroot degenerates to the
+    // filesystem root: shards are written under the full path of each source file.
+    Path source = sandbox.resolve("com/example/Hello.java");
+    compile(
+        targetroot,
+        Collections.singletonList(
+            new SimpleSourceFile(source, "package com.example;\npublic class Hello {}")));
+    Path relative = source.getRoot().relativize(source);
+    Document document =
+        readShardDocument(
+            targetroot.resolve("META-INF").resolve("scip").resolve(relative + ".scip"));
+    assertEquals(relative.toString().replace(File.separatorChar, '/'), document.getRelativePath());
+  }
+}