8024437: Inferring the exception thrown: sometimes fails to compile

Reviewed-by: jjg

langtools/src/share/classes/com/sun/tools/javac/code/Flags.java

@@ -261,7 +261,7 @@ public class Flags {
     public static final long SIGNATURE_POLYMORPHIC = 1L<<46;
 
     /**
-     * Flag that marks inference variables used in a 'throws' clause
+     * Flag that indicates that an inference variable is used in a 'throws' clause.
      */
     public static final long THROWS = 1L<<47;
 

langtools/src/share/classes/com/sun/tools/javac/jvm/ClassReader.java

@@ -56,6 +56,7 @@ import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;
 import static com.sun.tools.javac.code.Flags.*;
 import static com.sun.tools.javac.code.Kinds.*;
 import static com.sun.tools.javac.code.TypeTag.CLASS;
+import static com.sun.tools.javac.code.TypeTag.TYPEVAR;
 import static com.sun.tools.javac.jvm.ClassFile.*;
 import static com.sun.tools.javac.jvm.ClassFile.Version.*;
 
@@ -703,6 +704,12 @@ public class ClassReader {
                 sigp++;
                 thrown = thrown.prepend(sigToType());
             }
+            // if there is a typevar in the throws clause we should state it.
+            for (List<Type> l = thrown; l.nonEmpty(); l = l.tail) {
+                if (l.head.hasTag(TYPEVAR)) {
+                    l.head.tsym.flags_field |= THROWS;
+                }
+            }
             return new MethodType(argtypes,
                                   restype,
                                   thrown.reverse(),

langtools/test/tools/javac/T8024437/ExceptionInferenceFromClassFileTest.java

@@ -0,0 +1,74 @@
+/*
+ * Copyright (c) 2013, 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.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * 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 8024437
+ * @summary Inferring the exception thrown by a lambda: sometimes fails to compile
+ * @library /tools/javac/lib
+ * @build ToolBox
+ * @run main ExceptionInferenceFromClassFileTest
+ */
+
+import java.nio.file.Files;
+import java.nio.file.Paths;
+
+public class ExceptionInferenceFromClassFileTest {
+
+    static final String ABSrc =
+            "class B {\n" +
+            "    public static <E extends Throwable> void t(A<E> a) throws E {\n" +
+            "        a.run();\n" +
+            "    }\n" +
+            "}\n" +
+
+            "interface A<E extends Throwable> {\n" +
+            "    void run() throws E;\n" +
+            "}";
+
+    static final String CSrc =
+            "class C {\n" +
+            "    public void d() {\n" +
+            "        B.t(null);\n" +
+            "    }\n" +
+            "}";
+
+    public static void main(String[] args) throws Exception {
+        Files.createDirectory(Paths.get("out"));
+
+        ToolBox.JavaToolArgs compileABParams =
+                new ToolBox.JavaToolArgs()
+                .setOptions("-d", "out")
+                .setSources(ABSrc);
+        ToolBox.javac(compileABParams);
+
+        ToolBox.JavaToolArgs compileCParams =
+                new ToolBox.JavaToolArgs()
+                .setOptions("-d", "out", "-cp", "out")
+                .setSources(CSrc);
+        ToolBox.javac(compileCParams);
+    }
+
+}