8226510: No compilation error when switch expression has no result expressions

Ensure a compile-time error is produced when there are no result expressions in an switch expression.

Reviewed-by: vromero

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

@@ -1447,6 +1447,9 @@ public class Attr extends JCTree.Visitor {
         if (tree.cases.isEmpty()) {
             log.error(tree.pos(),
                       Errors.SwitchExpressionEmpty);
+        } else if (caseTypes.isEmpty()) {
+            log.error(tree.pos(),
+                      Errors.SwitchExpressionNoResultExpressions);
         }
 
         Type owntype = (tree.polyKind == PolyKind.STANDALONE) ? condType(caseTypePositions.toList(), caseTypes.toList()) : pt();

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

@@ -223,6 +223,9 @@ compiler.warn.invalid.yield=\
 compiler.err.switch.expression.empty=\
     switch expression does not have any case clauses
 
+compiler.err.switch.expression.no.result.expressions=\
+    switch expression does not have any result expressions
+
 # 0: name
 compiler.err.call.must.be.first.stmt.in.ctor=\
     call to {0} must be first statement in constructor

test/langtools/tools/javac/diags/examples/BreakOutsideSwitchExpression.java

@@ -30,7 +30,8 @@ class BreakOutsideSwitchExpression {
     int t(int i) {
         OUT: while (true) {
             return switch (i) {
-                default: break OUT;
+                case 0: break OUT;
+                default: yield 0;
             };
         }
         return -1;

test/langtools/tools/javac/diags/examples/ContinueOutsideSwitchExpression.java

@@ -30,7 +30,8 @@ class ContinueOutsideSwitchExpression {
     int t(int i) {
         OUT: while (true) {
             return switch (i) {
-                default: continue OUT;
+                case 0: continue OUT;
+                default: yield 0;
             };
         }
     }

test/langtools/tools/javac/diags/examples/ReturnOutsideSwitchExpression.java

@@ -29,7 +29,8 @@
 class ReturnOutsideSwitchExpression {
     int t(int i) {
         return switch (i) {
-            default: return -1;
+            case 0: return -1;
+            default: yield 0;
         };
     }
 }

test/langtools/tools/javac/diags/examples/RuleCompletesNormally.java

@@ -29,7 +29,8 @@
 class RuleCompletesNormally {
     public String convert(int i) {
         return switch (i) {
-            default -> {}
+            case 0 -> {}
+            default -> "";
         };
     }
 }

test/langtools/tools/javac/diags/examples/SwitchExpressionCompletesNormally.java

@@ -29,6 +29,7 @@
 class SwitchExpressionCompletesNormally {
     public String convert(int i) {
         return switch (i) {
+            case 0: yield "";
             default:
         };
     }

test/langtools/tools/javac/diags/examples/SwitchExpressionNoResultExpressions.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2019, 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.
+ */
+
+// key: compiler.err.switch.expression.no.result.expressions
+// key: compiler.note.preview.filename
+// key: compiler.note.preview.recompile
+// options: --enable-preview -source ${jdk.version}
+
+class SwitchExpressionCompletesNormally {
+    public String convert(int i) {
+        return switch (i) {
+            default -> throw new AssertionError();
+        };
+    }
+}

test/langtools/tools/javac/switchexpr/EmptySwitch.java

@@ -23,15 +23,29 @@
 
 /*
  * @test
- * @bug 8206986
+ * @bug 8206986 8226510
- * @summary Verify than an empty switch expression is rejected.
+ * @summary Verify than a switch that does not yield a value is rejected.
- * @compile/fail/ref=EmptySwitch.out --enable-preview -source ${jdk.version} -XDrawDiagnostics EmptySwitch.java
+ * @compile/fail/ref=EmptySwitch.out --enable-preview -source ${jdk.version} -XDrawDiagnostics -XDshould-stop.at=FLOW EmptySwitch.java
  */
 
 public class EmptySwitch {
     private void print(EmptySwitchEnum t) {
         (switch (t) {
         }).toString();
+        (switch (t) {
+            default -> throw new IllegalStateException();
+        }).toString();
+        (switch (t) {
+            default: throw new IllegalStateException();
+        }).toString();
+        (switch (0) {
+            case 0: yield "";
+            default:
+        }).toString();
+        (switch (0) {
+            case 0 -> { yield ""; }
+            default -> { }
+        }).toString();
     }
 
     enum EmptySwitchEnum {

test/langtools/tools/javac/switchexpr/EmptySwitch.out

@@ -1,4 +1,8 @@
 EmptySwitch.java:33:10: compiler.err.switch.expression.empty
+EmptySwitch.java:35:10: compiler.err.switch.expression.no.result.expressions
+EmptySwitch.java:38:10: compiler.err.switch.expression.no.result.expressions
+EmptySwitch.java:44:9: compiler.err.switch.expression.completes.normally
+EmptySwitch.java:47:26: compiler.err.rule.completes.normally
 - compiler.note.preview.filename: EmptySwitch.java
 - compiler.note.preview.recompile
-1 error
+5 errors

test/langtools/tools/javac/switchexpr/ExpressionSwitchBreaks2.java

@@ -41,9 +41,11 @@ public class ExpressionSwitchBreaks2 {
         }
         }
         j: print(switch (i) {
+            case 0: yield 0;
             default: break j;
         }, 0);
         j2: print(switch (i) {
+            case 0: yield 0;
             default: break j2;
         }, 0);
         return null;

test/langtools/tools/javac/switchexpr/ExpressionSwitchBreaks2.out

@@ -5,8 +5,8 @@ ExpressionSwitchBreaks2.java:29:29: compiler.err.continue.outside.switch.express
 ExpressionSwitchBreaks2.java:30:29: compiler.err.undef.label: UNKNOWN
 ExpressionSwitchBreaks2.java:40:17: compiler.err.no.switch.expression
 ExpressionSwitchBreaks2.java:40:29: compiler.err.cant.resolve.location: kindname.variable, undef, , , (compiler.misc.location: kindname.class, ExpressionSwitchBreaks2, null)
-ExpressionSwitchBreaks2.java:44:22: compiler.err.break.outside.switch.expression
+ExpressionSwitchBreaks2.java:45:22: compiler.err.break.outside.switch.expression
-ExpressionSwitchBreaks2.java:47:22: compiler.err.break.outside.switch.expression
+ExpressionSwitchBreaks2.java:49:22: compiler.err.break.outside.switch.expression
 - compiler.note.preview.filename: ExpressionSwitchBreaks2.java
 - compiler.note.preview.recompile
-9 errors
+9 errors

test/langtools/tools/javac/switchexpr/ExpressionSwitchFlow.java

@@ -22,6 +22,7 @@ public class ExpressionSwitchFlow {
     private String test3(int i) {
         return switch (i) {
             case 0 -> {}
+            case 1 -> "";
             default -> throw new IllegalStateException();
         };
     }
@@ -40,17 +41,20 @@ public class ExpressionSwitchFlow {
     private String test6(int i) {
         return switch (i) {
             case 0 -> throw new IllegalStateException();
+            case 1 -> "";
             default -> {}
         };
     }
     private String test7(int i) {
         return switch (i) {
             case 0: throw new IllegalStateException();
+            case 1: yield "";
             default:
         };
     }
     private String test8(int i) {
         return switch (i) {
+            case 1: yield "";
             case 0: i++;
             default: {
             }
@@ -58,6 +62,7 @@ public class ExpressionSwitchFlow {
     }
     private String test9(int i) {
         return switch (i) {
+            case 1: yield "";
             case 0:
             default:
                 System.err.println();

test/langtools/tools/javac/switchexpr/ExpressionSwitchFlow.out

@@ -1,12 +1,12 @@
 ExpressionSwitchFlow.java:11:24: compiler.err.rule.completes.normally
 ExpressionSwitchFlow.java:18:13: compiler.err.rule.completes.normally
 ExpressionSwitchFlow.java:24:24: compiler.err.rule.completes.normally
-ExpressionSwitchFlow.java:31:25: compiler.err.rule.completes.normally
+ExpressionSwitchFlow.java:32:25: compiler.err.rule.completes.normally
-ExpressionSwitchFlow.java:37:25: compiler.err.rule.completes.normally
+ExpressionSwitchFlow.java:38:25: compiler.err.rule.completes.normally
-ExpressionSwitchFlow.java:43:25: compiler.err.rule.completes.normally
+ExpressionSwitchFlow.java:45:25: compiler.err.rule.completes.normally
-ExpressionSwitchFlow.java:50:9: compiler.err.switch.expression.completes.normally
+ExpressionSwitchFlow.java:53:9: compiler.err.switch.expression.completes.normally
-ExpressionSwitchFlow.java:57:9: compiler.err.switch.expression.completes.normally
+ExpressionSwitchFlow.java:61:9: compiler.err.switch.expression.completes.normally
-ExpressionSwitchFlow.java:64:9: compiler.err.switch.expression.completes.normally
+ExpressionSwitchFlow.java:69:9: compiler.err.switch.expression.completes.normally
 - compiler.note.preview.filename: ExpressionSwitchFlow.java
 - compiler.note.preview.recompile
 9 errors

test/langtools/tools/javac/switchexpr/WrongBreakTest.out

@@ -1,8 +1,9 @@
 WrongBreakTest.java:36:41: compiler.err.illegal.start.of.expr
 WrongBreakTest.java:35:39: compiler.err.break.outside.switch.expression
+WrongBreakTest.java:35:17: compiler.err.switch.expression.no.result.expressions
 WrongBreakTest.java:36:9: compiler.err.ref.ambiguous: test, kindname.method, test(int), WrongBreakTest, kindname.method, test(java.lang.Object), WrongBreakTest
 WrongBreakTest.java:38:13: compiler.err.no.switch.expression
 WrongBreakTest.java:41:13: compiler.err.no.switch.expression
 - compiler.note.preview.filename: WrongBreakTest.java
 - compiler.note.preview.recompile
-5 errors
+6 errors