8371309: Diagnostic.getEndPosition can throw an NPE with typical broken code

src/jdk.compiler/share/classes/com/sun/tools/javac/tree/JCTree.java

@@ -505,7 +505,7 @@ public JCTree getTree() {
 
     // for default DiagnosticPosition
     public int getStartPosition() {
-        return TreeInfo.getStartPos(this);
+        return noNoPos(TreeInfo.getStartPos(this));
     }
 
     // for default DiagnosticPosition
@@ -515,7 +515,14 @@ public int getPreferredPosition() {
 
     // for default DiagnosticPosition
     public int getEndPosition(EndPosTable endPosTable) {
-        return TreeInfo.getEndPos(this, endPosTable);
+        return noNoPos(TreeInfo.getEndPos(this, endPosTable));
+    }
+
+    private int noNoPos(int position) {
+        if (position == JCDiagnostic.NOPOS) {
+            return pos;
+        }
+        return position;
     }
 
     /**

src/jdk.compiler/share/classes/com/sun/tools/javac/tree/TreeInfo.java

@@ -651,6 +651,11 @@ public static int getEndPos(JCTree tree, EndPosTable endPosTable) {
         if (tree == null)
             return Position.NOPOS;
 
+        if (endPosTable == null) {
+            // fall back on limited info in the tree
+            return endPos(tree);
+        }
+
         int mapPos = endPosTable.getEndPos(tree);
         if (mapPos != Position.NOPOS)
             return mapPos;

test/langtools/tools/javac/diags/DiagnosticGetEndPosition.java

@@ -0,0 +1,217 @@
+/*
+ * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/**
+ * @test
+ * @bug 8371309
+ * @summary Verify that Diagnostic.getEndPosition works reasonably
+ * @library /tools/lib
+ * @modules jdk.compiler/com.sun.tools.javac.api
+ *          jdk.compiler/com.sun.tools.javac.main
+ * @run junit DiagnosticGetEndPosition
+ */
+import java.net.URI;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.List;
+import javax.tools.JavaCompiler;
+import javax.tools.JavaFileObject;
+import javax.tools.SimpleJavaFileObject;
+import javax.tools.ToolProvider;
+
+import com.sun.source.util.JavacTask;
+
+import org.junit.jupiter.api.Test;
+
+import toolbox.ToolBox;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class DiagnosticGetEndPosition {
+    final JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
+    final ToolBox tb = new ToolBox();
+
+    @Test
+    public void testGetEndPositionDuringParsing() {
+        JavaFileObject testFile =
+                SimpleJavaFileObject.forSource(URI.create("mem:///Test.java"),
+                                               """
+                                               public class Test extends {}
+                                               """);
+        compiler.getTask(
+            null,
+            null,
+            diagnostic -> assertEquals(26, diagnostic.getEndPosition()),
+            null,
+            null,
+            List.of(testFile)
+        ).call();
+    }
+
+    @Test
+    public void testNoErrorsFromInternalParses() throws Exception {
+        Path base = Paths.get(".");
+        Path src = base.resolve("src");
+        tb.writeJavaFiles(src,
+                          """
+                          module m {
+                             exports test;
+                          }
+                          """,
+                          """
+                          package test;
+                          public class Test extends {}
+                          """);
+
+        try (var fm = compiler.getStandardFileManager(null, null, null)) {
+            compiler.getTask(
+                null,
+                null,
+                d -> fail(d.toString()),
+                List.of("-sourcepath", src.toString()),
+                null,
+                fm.getJavaFileObjects(src.resolve("module-info.java"))
+            ).call();
+        }
+    }
+
+    @Test
+    public void testGetEndPositionWorkForImplicitParse() throws Exception {
+        Path base = Paths.get(".");
+        Path src = base.resolve("src");
+        String implCode = """
+                          package test;
+                          public class Impl {
+                              public static final int C = 1 / 0;
+                          }
+                          """;
+        tb.writeJavaFiles(src,
+                          implCode,
+                          """
+                          package test;
+                          public class Test {
+                              Impl i; //force parsing of Impl
+                          }
+                          """);
+
+        try (var fm = compiler.getStandardFileManager(null, null, null)) {
+            compiler.getTask(
+                null,
+                null,
+                d -> assertEquals("", //ideally would be "0", but the positions are not fully set yet
+                                  implCode.substring((int) d.getStartPosition(),
+                                                     (int) d.getEndPosition())),
+                List.of("-sourcepath", src.toString(), "-Xlint:divzero"),
+                null,
+                fm.getJavaFileObjects(src.resolve("test").resolve("Test.java"))
+            ).call();
+        }
+    }
+
+    @Test
+    public void testWronglyNamedClass() throws Exception {
+        Path base = Paths.get(".");
+        Path src = base.resolve("src");
+        tb.writeFile(src.resolve("test").resolve("WronglyNamed.java"),
+                     """
+                     package test;
+                     class SomeOtherName {}
+                     """);
+        tb.writeJavaFiles(src,
+                          """
+                          package test;
+                          public class Test {
+                              WronglyNamed l; //parse WronglyNamed.java
+                          }
+                          """);
+
+        try (var fm = compiler.getStandardFileManager(null, null, null)) {
+            compiler.getTask(
+                null,
+                null,
+                null,
+                List.of("-sourcepath", src.toString()),
+                null,
+                fm.getJavaFileObjects(tb.findJavaFiles(src))
+            ).call();
+        }
+    }
+
+    @Test
+    public void testWronglyNamedPackageInfo() throws Exception {
+        Path base = Paths.get(".");
+        Path src = base.resolve("src");
+        tb.writeFile(src.resolve("test").resolve("package-info.java"),
+                     """
+                     package wrongpackage;
+                     """);
+        tb.writeJavaFiles(src,
+                          """
+                          package test;
+                          public class Test {
+                          }
+                          """);
+
+        try (var fm = compiler.getStandardFileManager(null, null, null)) {
+            JavacTask task = (JavacTask) compiler.getTask(
+                null,
+                null,
+                null,
+                List.of("-sourcepath", src.toString()),
+                null,
+                fm.getJavaFileObjects(src.resolve("test").resolve("Test.java"))
+            );
+            task.analyze();
+            task.getElements().getPackageElement("test").getAnnotationMirrors();
+        }
+    }
+
+    @Test
+    public void testGetEndPositionSyntheticTree() throws Exception {
+        Path base = Paths.get(".");
+        Path src = base.resolve("src");
+        String testCode = """
+                          package test;
+                          public class Test extends Base {
+                          }
+                          class Base {
+                              Base(int i) {}
+                          }
+                          """;
+
+        tb.writeJavaFiles(src, testCode);
+
+        try (var fm = compiler.getStandardFileManager(null, null, null)) {
+            compiler.getTask(
+                null,
+                null,
+                d -> assertEquals("",
+                                  testCode.substring((int) d.getStartPosition(),
+                                                     (int) d.getEndPosition())),
+                List.of("-sourcepath", src.toString(), "-Xlint:divzero"),
+                null,
+                fm.getJavaFileObjects(src.resolve("test").resolve("Test.java"))
+            ).call();
+        }
+    }
+}