8292625: jshell crash on "var a = a"

[blindpirate]

This commit adds the missing type assignment when attributing a variable's initial value. In some cases, this issue causes an NPE.

This issue has existed for a long time, but the NPE was swallowed until 4333942 stopped swallowing such exceptions.

---

Progress

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Issue

• JDK-8292625: jshell crash on "var a = a"

Reviewers

• Jim Laskey (@JimLaskey - Reviewer)
• Jan Lahoda (@lahodaj - Reviewer)

Reviewing

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[openjdk]

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[blindpirate]

@mcimadamore Can you please take a look?

[mlbridge]

Webrevs

• 03: Full - Incremental (0e1d8034)
• 02: Full - Incremental (8bb111b8)
• 01: Full - Incremental (5c58e847)
• 00: Full (dffd32b8)

[lahodaj]

Good catch, but I would personally prefer if attribExpr would set the type (as it does under normal circumstances), presumably here?

jdk/src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java

Line 4651 in 5c33454

return v.type = types.createErrorType(v.type);

Also, might be nice to have a (core javac) test that would not rely on JShell, if possible.

[blindpirate]

@lahodaj Done moving the assignment. However, this was not a problem with javac, probably due to different code path:

# zhb @ zhb in ~/Projects/jdk on git:jdk-8292625 x [7:03:45] C:1
$ cat Test.java
public class Test {
  public static void main() {
    var a = a;
  }
}

# zhb @ zhb in ~/Projects/jdk on git:jdk-8292625 x [7:03:48]
$ /Library/Java/JavaVirtualMachines/temurin-19.jdk/Contents/Home/bin/javac Test.java
Test.java:3: error: cannot infer type for local variable a
    var a = a;
        ^
  (cannot use 'var' on self-referencing variable)
1 error
printing javac parameters to: /Users/zhb/Projects/jdk/javac.20221122_070353.args

That's why I put the test into jshell tests.

[lahodaj]

@lahodaj Done moving the assignment. However, this was not a problem with javac, probably due to different code path:

# zhb @ zhb in ~/Projects/jdk on git:jdk-8292625 x [7:03:45] C:1
$ cat Test.java
public class Test {
  public static void main() {
    var a = a;
  }
}

# zhb @ zhb in ~/Projects/jdk on git:jdk-8292625 x [7:03:48]
$ /Library/Java/JavaVirtualMachines/temurin-19.jdk/Contents/Home/bin/javac Test.java
Test.java:3: error: cannot infer type for local variable a
    var a = a;
        ^
  (cannot use 'var' on self-referencing variable)
1 error
printing javac parameters to: /Users/zhb/Projects/jdk/javac.20221122_070353.args

That's why I put the test into jshell tests.

Thanks for moving the assignment. For tests, the test in JShell is fine, but there are other ways to the attributes in addition to that, like actually checking the type is assigned in the AST:

diff --git a/test/langtools/tools/javac/attr/AttrRecoveryTest.java b/test/langtools/tools/javac/attr/AttrRecoveryTest.java
index b364cc28001..f5589a8093f 100644
--- a/test/langtools/tools/javac/attr/AttrRecoveryTest.java
+++ b/test/langtools/tools/javac/attr/AttrRecoveryTest.java
@@ -36,6 +36,7 @@
 import com.sun.source.tree.AnnotationTree;
 import com.sun.source.tree.CompilationUnitTree;
 import com.sun.source.tree.ErroneousTree;
+import com.sun.source.tree.VariableTree;
 import com.sun.source.util.TaskEvent;
 import com.sun.source.util.TaskListener;
 import com.sun.source.util.TreePath;
@@ -45,7 +46,9 @@ import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.List;
+import java.util.concurrent.atomic.AtomicInteger;
 import javax.lang.model.element.Element;
+import javax.lang.model.type.TypeMirror;
 
 import toolbox.TestRunner;
 import toolbox.JavacTask;
@@ -162,4 +165,61 @@ public class AttrRecoveryTest extends TestRunner {
             throw new AssertionError();
         }
     }
+
+    @Test
+    public void testVarAssignment2Self(Path base) throws Exception {
+        Path current = base;
+        Path src = current.resolve("src");
+        Path classes = current.resolve("classes");
+        tb.writeJavaFiles(src,
+                          """
+                          public class Test {
+                              void t() {
+                                  var v = v;
+                              }
+                          }
+                          """);
+
+        Files.createDirectories(classes);
+
+        AtomicInteger seenVariables = new AtomicInteger();
+        TreePathScanner<Void, Trees> checkTypes = new TreePathScanner<>() {
+            @Override
+            public Void visitVariable(VariableTree node, Trees trees) {
+                if (node.getName().contentEquals("v")) {
+                    TypeMirror type = trees.getTypeMirror(getCurrentPath());
+                    if (type == null) {
+                        throw new AssertionError("Unexpected null type!");
+                    }
+                    seenVariables.incrementAndGet();
+                }
+                return super.visitVariable(node, trees);
+            }
+        };
+
+        new JavacTask(tb)
+            .options("-XDrawDiagnostics")
+            .outdir(classes)
+            .files(tb.findJavaFiles(src))
+            .callback(t -> {
+                t.addTaskListener(new TaskListener() {
+                    CompilationUnitTree parsed;
+                    @Override
+                    public void finished(TaskEvent e) {
+                        switch (e.getKind()) {
+                            case PARSE -> parsed = e.getCompilationUnit();
+                            case COMPILATION ->
+                                checkTypes.scan(parsed, Trees.instance(t));
+                        }
+                    }
+                });
+            })
+            .run(Task.Expect.FAIL)
+            .writeAll()
+            .getOutputLines(Task.OutputKind.DIRECT);
+
+        if (seenVariables.get() != 1) {
+            throw new AssertionError("Didn't see enough variables: " + seenVariables);
+        }
+    }
 }

I think the advantage of having the test in the javac tests (in addition to the JShell test) is that if someone modifies javac, and only runs javac tests, it would still fail.

[blindpirate]

Thanks for the guidance @lahodaj !

[openjdk]

@blindpirate This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8292625: jshell crash on "var a = a"

Reviewed-by: jlaskey, jlahoda

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 107 new commits pushed to the master branch:

• 05128c2: 8286185: The Java manpage can be more platform inclusive
• d450314: 8297276: Remove thread text from Subject.current
• cdf9ed0: 8297528: java/io/File/TempDirDoesNotExist.java test failing on windows-x64
• 105d9d7: 8295351: java/lang/Float/Binary16Conversion.java fails with "Unexpected result of converting"
• a80552e: 8236919: Refactor com.sun.tools.javac.main.CommandLine into a reusable module for other JDK tools
• a249a52: 8296754: AutoCreateSharedArchive in JDK 20 is not compatible with JDK 19
• 405b188: 8297570: jdk/jfr/threading/TestDeepVirtualStackTrace.java fails with -XX:-UseTLAB
• ba0a252: 8297717: Remove jdk/internal/misc/TerminatingThreadLocal/TestTerminatingThreadLocal.java from ProblemList
• c05dc80: 8297660: x86: Redundant test+jump in C1 allocateArray
• eff4c03: 8297343: TestStress*.java fail with "got different traces for the same seed"
• ... and 97 more: https://git.openjdk.org/jdk/compare/3ea89711e34639fef36b6cc143e37b5133aa80f8...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

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➡️ To flag this PR as ready for integration with the above commit message, type /integrate in a new comment. (Afterwards, your sponsor types /sponsor in a new comment to perform the integration).

[lahodaj]

Looks good to me!

[blindpirate]

/integrate

[blindpirate]

Thanks @lahodaj . Can you please sponsor this one?

[openjdk]

@blindpirate
Your change (at version 0e1d803) is now ready to be sponsored by a Committer.

[lahodaj]

/sponsor

[openjdk]

Going to push as commit 33587ff.
Since your change was applied there have been 120 commits pushed to the master branch:

• 2deb318: 8297065: DerOutputStream operations should not throw IOExceptions
• d83a07b: 8297200: java/net/httpclient/SpecialHeadersTest.java failed once in AssertionError due to selector thread remaining alive
• 5d2772a: 8297424: java/net/httpclient/AsyncExecutorShutdown.java fails in AssertionError due to misplaced assert
• 361b50e: 8292594: Use CSS custom properties for all fonts and colors
• 42b60ed: 8297030: Reduce Default Keep-Alive Timeout Value for httpclient
• 1301fb0: 8296470: Refactor VMError::report STEP macro to improve readability
• 48017b1: 8296804: Document HttpClient configuration properties in java.net.http module-info
• bd51b7e: 8296645: org.openjdk.bench.javax.tools.Javac leaves class files in current directory
• b27a61e: 8297216: Search results omit some methods
• 33dfc7d: 8296954: G1: Enable parallel scanning for heap region remset
• ... and 110 more: https://git.openjdk.org/jdk/compare/3ea89711e34639fef36b6cc143e37b5133aa80f8...master

Your commit was automatically rebased without conflicts.

[openjdk]

@lahodaj @blindpirate Pushed as commit 33587ff.

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