In rare cases, Type.getEnclosingType() (or Type.toString()) may fail with a CompletionFailure. See this test:

---
diff --git a/test/langtools/tools/javac/processing/model/completionfailure/MissingClassFile.java b/test/langtools/tools/javac/processing/model/completionfailure/MissingClassFile.java
index 0d83b7b8ce1..c8c896de64b 100644
--- a/test/langtools/tools/javac/processing/model/completionfailure/MissingClassFile.java
+++ b/test/langtools/tools/javac/processing/model/completionfailure/MissingClassFile.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2018, 2021, 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
@@ -459,6 +459,64 @@ public class MissingClassFile {
         }
     }
 
+ void testGetEnclosingOnMissingType() throws Exception {
+ Path base = Paths.get(".");
+ Path libClasses = compileLib(base,
+ "package pkg;\n" +
+ "public class A<E> {\n" +
+ " public static class N<E> {}\n" +
+ "}\n",
+ "package pkg;\n" +
+ "public class T<E> {\n" +
+ " T<A<T>> n;\n" +
+ "}\n");
+ try (OutputStream out = Files.newOutputStream(libClasses.resolve("pkg/A.class"))) {
+ out.write(0);
+ }
+
+ Path testSrc = base.resolve("test-src");
+ tb.createDirectories(testSrc);
+ Path testClasses = base.resolve("test-classes");
+ tb.createDirectories(testClasses);
+
+ tb.writeJavaFiles(testSrc, "class Test { }");
+ tb.cleanDirectory(testClasses);
+
+ JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
+
+ List<Consumer<DeclaredType>> validators = Arrays.asList(
+ dt -> { if (dt.getEnclosingType().getKind() != TypeKind.NONE)
+ throw new AssertionError("Unexpected enclosing type: " +
+ dt.getEnclosingType());
+ },
+ dt -> { if (!"pkg.T<pkg.A<pkg.T>>".equals(dt.toString()))
+ throw new AssertionError("Unexpected toString: " +
+ dt.toString());
+ }
+ );
+
+ try (StandardJavaFileManager fm = compiler.getStandardFileManager(null, null, null)) {
+ for (Consumer<DeclaredType> validator : validators) {
+ com.sun.source.util.JavacTask task = (com.sun.source.util.JavacTask)
+ compiler.getTask(null,
+ null,
+ null,
+ Arrays.asList("-XDrawDiagnostics",
+ "-classpath",
+ libClasses.toString()),
+ null,
+ fm.getJavaFileObjects(tb.findJavaFiles(testSrc)));
+ task.analyze();
+ TypeElement a = task.getElements()
+ .getTypeElement(task.getElements()
+ .getModuleElement(""),
+ "pkg.T");
+ DeclaredType type = (DeclaredType) a.getEnclosedElements().get(0).asType();
+ validator.accept(type);
+ }
+ }
+ }
+
     private Path compileLib(Path base, String... sources) throws Exception {
---