8015809: More user friendly compile-time errors for uncaught exceptions in lambda expression

Summary: Producing individual errors for uncaught undeclared exceptions inside lambda expressions, rather than one error for the whole lambda
Reviewed-by: mcimadamore

src/share/classes/com/sun/tools/javac/code/Type.java

@@ -1161,7 +1161,7 @@ public abstract class Type implements TypeMirror {
         }
 
         public boolean contains(Type elem) {
-            return elem == this || contains(argtypes, elem) || restype.contains(elem);
+            return elem == this || contains(argtypes, elem) || restype.contains(elem) || contains(thrown, elem);
         }
 
         public MethodType asMethodType() { return this; }

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

@@ -2607,8 +2607,7 @@ public class Attr extends JCTree.Visitor {
         * are compatible with the expected functional interface descriptor. This means that:
         * (i) parameter types must be identical to those of the target descriptor; (ii) return
         * types must be compatible with the return type of the expected descriptor;
-        * (iii) thrown types must be 'included' in the thrown types list of the expected
-        * descriptor.
+        * (iii) finish inference of thrown types if required.
         */
         private void checkLambdaCompatible(JCLambda tree, Type descriptor, CheckContext checkContext, boolean speculativeAttr) {
             Type returnType = checkContext.inferenceContext().asFree(descriptor.getReturnType());
@@ -2630,9 +2629,7 @@ public class Attr extends JCTree.Visitor {
 
             if (!speculativeAttr) {
                 List<Type> thrownTypes = checkContext.inferenceContext().asFree(descriptor.getThrownTypes());
-                if (chk.unhandled(tree.inferredThrownTypes == null ? List.<Type>nil() : tree.inferredThrownTypes, thrownTypes).nonEmpty()) {
-                    log.error(tree, "incompatible.thrown.types.in.lambda", tree.inferredThrownTypes);
-                }
+                chk.unhandled(tree.inferredThrownTypes == null ? List.<Type>nil() : tree.inferredThrownTypes, thrownTypes);
             }
         }
 

src/share/classes/com/sun/tools/javac/comp/Flow.java

@@ -224,7 +224,7 @@ public class Flow {
         }
         try {
             new AliveAnalyzer().analyzeTree(env, that, make);
-            new FlowAnalyzer().analyzeTree(env, that, make);
+            new LambdaFlowAnalyzer().analyzeTree(env, that, make);
         } finally {
             if (!speculative) {
                 log.popDiagnosticHandler(diagHandler);
@@ -1259,12 +1259,24 @@ public class Flow {
             ListBuffer<FlowPendingExit> prevPending = pendingExits;
             try {
                 pendingExits = ListBuffer.lb();
-                caught = List.of(syms.throwableType); //inhibit exception checking
+                caught = tree.getDescriptorType(types).getThrownTypes();
                 thrown = List.nil();
                 scan(tree.body);
-                tree.inferredThrownTypes = thrown;
-            }
-            finally {
+                List<FlowPendingExit> exits = pendingExits.toList();
+                pendingExits = new ListBuffer<FlowPendingExit>();
+                while (exits.nonEmpty()) {
+                    FlowPendingExit exit = exits.head;
+                    exits = exits.tail;
+                    if (exit.thrown == null) {
+                        Assert.check(exit.tree.hasTag(RETURN));
+                    } else {
+                        // uncaught throws will be reported later
+                        pendingExits.append(exit);
+                    }
+                }
+
+                errorUncaught();
+            } finally {
                 pendingExits = prevPending;
                 caught = prevCaught;
                 thrown = prevThrown;
@@ -1302,6 +1314,33 @@ public class Flow {
         }
     }
 
+    /**
+     * Specialized pass that performs inference of thrown types for lambdas.
+     */
+    class LambdaFlowAnalyzer extends FlowAnalyzer {
+        @Override
+        public void visitLambda(JCLambda tree) {
+            if (tree.type != null &&
+                    tree.type.isErroneous()) {
+                return;
+            }
+            List<Type> prevCaught = caught;
+            List<Type> prevThrown = thrown;
+            ListBuffer<FlowPendingExit> prevPending = pendingExits;
+            try {
+                pendingExits = ListBuffer.lb();
+                caught = List.of(syms.throwableType);
+                thrown = List.nil();
+                scan(tree.body);
+                tree.inferredThrownTypes = thrown;
+            } finally {
+                pendingExits = prevPending;
+                caught = prevCaught;
+                thrown = prevThrown;
+            }
+        }
+    }
+
     /**
      * This pass implements (i) definite assignment analysis, which ensures that
      * each variable is assigned when used and (ii) definite unassignment analysis,

src/share/classes/com/sun/tools/javac/resources/compiler.properties

@@ -732,10 +732,6 @@ compiler.misc.incompatible.ret.type.in.mref=\
     bad return type in method reference\n\
     {0}
 
-# 0: list of type
-compiler.err.incompatible.thrown.types.in.lambda=\
-    incompatible thrown types {0} in lambda expression
-
 # 0: list of type
 compiler.err.incompatible.thrown.types.in.mref=\
     incompatible thrown types {0} in method reference

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

@@ -645,7 +645,7 @@ public abstract class JCTree implements Tree, Cloneable, DiagnosticPosition {
         public List<Type> targets;
 
         public Type getDescriptorType(Types types) {
-            return types.findDescriptorType(targets.head);
+            return targets.nonEmpty() ? types.findDescriptorType(targets.head) : types.createErrorType(null);
         }
     }
 

test/tools/javac/diags/examples/IncompatibleThrownTypesInLambda.java → test/tools/javac/lambda/ExceptionsInLambda.java

 /*
- * Copyright (c) 2012, Oracle and/or its affiliates. All rights reserved.
+ * 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
@@ -21,12 +21,41 @@
  * questions.
  */
 
-// key: compiler.err.incompatible.thrown.types.in.lambda
+/*
+ * @test
+ * @bug 8015809
+ * @summary Producing individual errors for uncaught undeclared exceptions inside lambda expressions, instead of one error for whole lambda
+ * @compile/fail/ref=ExceptionsInLambda.out -XDrawDiagnostics ExceptionsInLambda.java
+ */
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileReader;
+import java.io.InputStream;
+import java.io.Reader;
+
+public class ExceptionsInLambda {
+
+    public static void main(Runnable p, File f) {
+        main(() -> {
+            StringBuilder sb = new StringBuilder();
 
-class IncompatibleThrownTypesInLambda {
-    interface SAM {
-        void m();
+            Reader in = new FileReader(f);
+            int r;
+
+            while ((r = in.read()) != (-1)) {
+                sb.append((char) r);
+            }
+        }, f);
+
+        doOpen(() -> new FileInputStream(f));
     }
 
-    SAM s = ()-> { throw new Exception(); };
+    public static InputStream doOpen(Open open) {
+        return open.open();
+    }
+
+    public interface Open {
+        public InputStream open();
+    }
 }

test/tools/javac/lambda/ExceptionsInLambda.out

+ExceptionsInLambda.java:43:25: compiler.err.unreported.exception.need.to.catch.or.throw: java.io.FileNotFoundException
+ExceptionsInLambda.java:46:32: compiler.err.unreported.exception.need.to.catch.or.throw: java.io.IOException
+ExceptionsInLambda.java:51:22: compiler.err.unreported.exception.need.to.catch.or.throw: java.io.FileNotFoundException
+3 errors

test/tools/javac/lambda/TargetType21.out

 TargetType21.java:28:9: compiler.err.ref.ambiguous: call, kindname.method, call(TargetType21.SAM2), TargetType21, kindname.method, <R,A>call(TargetType21.SAM3<R,A>), TargetType21
-TargetType21.java:28:14: compiler.err.incompatible.thrown.types.in.lambda: java.lang.Exception
 TargetType21.java:29:9: compiler.err.ref.ambiguous: call, kindname.method, call(TargetType21.SAM2), TargetType21, kindname.method, <R,A>call(TargetType21.SAM3<R,A>), TargetType21
 TargetType21.java:30:13: compiler.err.prob.found.req: (compiler.misc.cyclic.inference: A)
 TargetType21.java:31:9: compiler.err.ref.ambiguous: call, kindname.method, call(TargetType21.SAM1), TargetType21, kindname.method, <R,A>call(TargetType21.SAM3<R,A>), TargetType21
-5 errors
+4 errors