8367530: The exhaustiveness errors could be improved

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

@@ -50,6 +50,7 @@
 import static com.sun.tools.javac.code.Kinds.Kind.*;
 import static com.sun.tools.javac.code.TypeTag.BOOLEAN;
 import static com.sun.tools.javac.code.TypeTag.VOID;
+import com.sun.tools.javac.comp.ExhaustivenessComputer.ExhaustivenessResult;
 import com.sun.tools.javac.resources.CompilerProperties.Fragments;
 import static com.sun.tools.javac.tree.JCTree.Tag.*;
 import com.sun.tools.javac.util.JCDiagnostic.Fragment;
@@ -696,9 +697,20 @@ public void visitSwitch(JCSwitch tree) {
             tree.isExhaustive = tree.hasUnconditionalPattern ||
                                 TreeInfo.isErrorEnumSwitch(tree.selector, tree.cases);
             if (exhaustiveSwitch) {
-                tree.isExhaustive |= exhaustiveness.exhausts(tree.selector, tree.cases);
                 if (!tree.isExhaustive) {
-                    log.error(tree, Errors.NotExhaustiveStatement);
+                    ExhaustivenessResult exhaustivenessResult = exhaustiveness.exhausts(tree.selector, tree.cases);
+
+                    tree.isExhaustive = exhaustivenessResult.exhaustive();
+
+                    if (!tree.isExhaustive) {
+                        if (exhaustivenessResult.notExhaustiveDetails().isEmpty()) {
+                            log.error(tree, Errors.NotExhaustiveStatement);
+                        } else {
+                            List<JCDiagnostic> details =
+                                    convertNotExhaustiveDetails(exhaustivenessResult);
+                            log.error(tree, Errors.NotExhaustiveStatementDetails(details));
+                        }
+                    }
                 }
             }
             if (!tree.hasUnconditionalPattern && !exhaustiveSwitch) {
@@ -735,16 +747,33 @@ public void visitSwitchExpression(JCSwitchExpression tree) {
                 TreeInfo.isErrorEnumSwitch(tree.selector, tree.cases)) {
                 tree.isExhaustive = true;
             } else {
-                tree.isExhaustive = exhaustiveness.exhausts(tree.selector, tree.cases);
-            }
+                ExhaustivenessResult exhaustivenessResult = exhaustiveness.exhausts(tree.selector, tree.cases);
+
+                tree.isExhaustive = exhaustivenessResult.exhaustive();
 
-            if (!tree.isExhaustive) {
-                log.error(tree, Errors.NotExhaustive);
+                if (!tree.isExhaustive) {
+                    if (exhaustivenessResult.notExhaustiveDetails().isEmpty()) {
+                        log.error(tree, Errors.NotExhaustive);
+                    } else {
+                        List<JCDiagnostic> details =
+                                convertNotExhaustiveDetails(exhaustivenessResult);
+                        log.error(tree, Errors.NotExhaustiveDetails(details));
+                    }
+                }
             }
+
             alive = prevAlive;
             alive = alive.or(resolveYields(tree, prevPendingExits));
         }
 
+        private List<JCDiagnostic> convertNotExhaustiveDetails(ExhaustivenessResult exhaustivenessResult) {
+            return exhaustivenessResult.notExhaustiveDetails()
+                                       .stream()
+                                       .sorted()
+                                       .map(detail -> diags.fragment(Fragments.NotExhaustiveDetail(detail)))
+                                       .collect(List.collector());
+        }
+
         public void visitTry(JCTry tree) {
             ListBuffer<PendingExit> prevPendingExits = pendingExits;
             pendingExits = new ListBuffer<>();

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

@@ -1473,6 +1473,20 @@ compiler.err.not.exhaustive=\
 compiler.err.not.exhaustive.statement=\
     the switch statement does not cover all possible input values
 
+# 0: list of diagnostic
+compiler.err.not.exhaustive.details=\
+    the switch expression does not cover all possible input values\n\
+    missing patterns: {0}
+
+# 0: list of diagnostic
+compiler.err.not.exhaustive.statement.details=\
+    the switch statement does not cover all possible input values\n\
+    missing patterns: {0}
+
+# 0: string
+compiler.misc.not.exhaustive.detail=\
+    \n{0}
+
 compiler.err.initializer.must.be.able.to.complete.normally=\
     initializer must be able to complete normally
 

test/langtools/tools/javac/diags/Example.java

@@ -602,9 +602,13 @@ boolean run(PrintWriter out, Set<String> keys, boolean raw, List<String> opts, L
          */
         private static void scanForKeys(JCDiagnostic d, Set<String> keys) {
             keys.add(d.getCode());
-            for (Object o: d.getArgs()) {
-                if (o instanceof JCDiagnostic) {
-                    scanForKeys((JCDiagnostic) o, keys);
+            List<Object> todoArgs = new ArrayList<>(Arrays.asList(d.getArgs()));
+            while (!todoArgs.isEmpty()) {
+                Object o = todoArgs.removeLast();
+                if (o instanceof JCDiagnostic sd) {
+                    scanForKeys(sd, keys);
+                } else if (o instanceof List l) {
+                    todoArgs.addAll(l);
                 }
             }
             for (JCDiagnostic sd: d.getSubdiagnostics())

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2018, 2025, 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
@@ -22,6 +22,7 @@
  */
 
 // key: compiler.err.not.exhaustive
+// options: -XDexhaustivityTimeout=0
 
 class NotExhaustive {
     int t(int i) {

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

@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2025, 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.not.exhaustive.details
+// key: compiler.misc.not.exhaustive.detail
+// options: -XDexhaustivityTimeout=-1
+
+class NotExhaustiveDetails {
+    int t(int i) {
+        return switch (i) {
+            case 0 -> -1;
+        };
+    }
+}

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2021, 2025, 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
@@ -22,6 +22,7 @@
  */
 
 // key: compiler.err.not.exhaustive.statement
+// options: -XDexhaustivityTimeout=0
 
 class NotExhaustive {
     void t(Object o) {

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

@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2025, 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.not.exhaustive.statement.details
+// key: compiler.misc.not.exhaustive.detail
+// options: -XDexhaustivityTimeout=-1
+
+class NotExhaustiveDetails {
+    void t(Object o) {
+        switch (o) {
+            case String s -> System.err.println("String of length: " + s.length());
+        };
+    }
+}

test/langtools/tools/javac/patterns/Exhaustiveness.java

@@ -2393,6 +2393,7 @@ private void doTest(Path base, String[] libraryCode, String testCode, boolean st
                              "-Xlint:-preview",
                              "--class-path", libClasses.toString(),
                              "-XDshould-stop.at=FLOW",
+                             "-XDexhaustivityTimeout=0",
                              stopAtFlow ? "-XDshould-stop.ifNoError=FLOW"
                                         : "-XDnoop")
                     .outdir(classes)