8309235: Unnamed Variables (_) can't be used in JShell

Co-authored-by: Jan Lahoda <jlahoda@openjdk.org>
Co-authored-by: Aggelos Biboudis <abimpoudis@openjdk.org>
Reviewed-by: asotona

Author: 2 people

src/jdk.jshell/share/classes/jdk/internal/jshell/tool/JShellTool.java

@@ -3350,7 +3350,8 @@ private boolean cmdVars(String arg) {
             String val = state.status(vk) == Status.VALID
                     ? feedback.truncateVarValue(state.varValue(vk))
                     : getResourceString("jshell.msg.vars.not.active");
-            hard("  %s %s = %s", vk.typeName(), vk.name(), val);
+            String varName = vk.name();
+            hard("  %s %s = %s", vk.typeName(), varName.isEmpty() ? "_" : varName, val);
         });
         return true;
     }

src/jdk.jshell/share/classes/jdk/jshell/Eval.java

@@ -385,21 +385,28 @@ private List<Snippet> processVariables(String userSource, List<? extends Tree> u
                 subkind = SubKind.VAR_DECLARATION_SUBKIND;
             }
             Wrap wname;
-            int nameStart = compileSource.lastIndexOf(name, nameMax);
-            if (nameStart < 0) {
-                // the name has been transformed (e.g. unicode).
-                // Use it directly
-                wname = Wrap.identityWrap(name);
+            String fieldName;
+            if (name.isEmpty()) {
+                fieldName = "$UNNAMED";
+                wname = Wrap.simpleWrap(fieldName);
             } else {
-                int nameEnd = nameStart + name.length();
-                Range rname = new Range(nameStart, nameEnd);
-                wname = new Wrap.RangeWrap(compileSource, rname);
+                fieldName = name;
+                int nameStart = compileSource.lastIndexOf(name, nameMax);
+                if (nameStart < 0) {
+                    // the name has been transformed (e.g. unicode).
+                    // Use it directly
+                    wname = Wrap.identityWrap(name);
+                } else {
+                    int nameEnd = nameStart + name.length();
+                    Range rname = new Range(nameStart, nameEnd);
+                    wname = new Wrap.RangeWrap(compileSource, rname);
+                }
             }
             Wrap guts = Wrap.varWrap(compileSource, typeWrap, sbBrackets.toString(), wname,
                                      winit, enhancedDesugaring, anonDeclareWrap);
             DiagList modDiag = modifierDiagnostics(vt.getModifiers(), dis, true);
             Snippet snip = new VarSnippet(state.keyMap.keyForVariable(name), userSource, guts,
-                    name, subkind, displayType, hasEnhancedType ? fullTypeName : null, anonymousClasses,
+                    name, fieldName, subkind, displayType, hasEnhancedType ? fullTypeName : null, anonymousClasses,
                     tds.declareReferences(), modDiag);
             snippets.add(snip);
         }
@@ -659,7 +666,7 @@ private List<Snippet> processExpression(String userSource, Tree tree, String com
                 }
                 Collection<String> declareReferences = null; //TODO
                 snip = new VarSnippet(state.keyMap.keyForVariable(name), userSource, guts,
-                        name, SubKind.TEMP_VAR_EXPRESSION_SUBKIND, displayTypeName, fullTypeName, anonymousClasses, declareReferences, null);
+                        name, name, SubKind.TEMP_VAR_EXPRESSION_SUBKIND, displayTypeName, fullTypeName, anonymousClasses, declareReferences, null);
             } else {
                 guts = Wrap.methodReturnWrap(compileSource);
                 snip = new ExpressionSnippet(state.keyMap.keyForExpression(name, typeName), userSource, guts,

src/jdk.jshell/share/classes/jdk/jshell/JShell.java

@@ -726,7 +726,7 @@ public String varValue(VarSnippet snippet) throws IllegalStateException {
         }
         String value;
         try {
-            value = executionControl().varValue(snippet.classFullName(), snippet.name());
+            value = executionControl().varValue(snippet.classFullName(), snippet.fieldName());
         } catch (EngineTerminationException ex) {
             throw new IllegalStateException(ex.getMessage());
         } catch (ExecutionControlException ex) {

src/jdk.jshell/share/classes/jdk/jshell/KeyMap.java

@@ -65,6 +65,10 @@ MethodKey keyForMethod(String name, String parameterTypes) {
     }
 
     VarKey keyForVariable(String name) {
+        if (name.isEmpty()) {
+            return new VarKey(state, name);
+        }
+
         return varMap.computeIfAbsent(name, k -> new VarKey(state, name));
     }
 

src/jdk.jshell/share/classes/jdk/jshell/ReplParser.java

@@ -229,7 +229,7 @@ List<? extends JCTree> replUnit(JCModifiers pmods, Comment dc) {
                     } else if ((isVoid || (lastmode & TYPE) != 0) && LAX_IDENTIFIER.test(token.kind)) {
                         // we have "Type Ident", so we can assume it is variable or method declaration
                         pos = token.pos;
-                        Name name = ident();
+                        Name name = identOrUnderscore();
                         if (token.kind == LPAREN) {
                         // method declaration
                             //mods.flags |= Flags.STATIC;

src/jdk.jshell/share/classes/jdk/jshell/SnippetMaps.java

@@ -101,7 +101,7 @@ String packageAndImportsExcept(Set<Key> except, Collection<Snippet> plus) {
         StringBuilder sb = new StringBuilder();
         sb.append("package ").append(REPL_PACKAGE).append(";\n");
         for (Snippet si : keyIndexToSnippet) {
-            if (si != null && si.status().isDefined() && (except == null || !except.contains(si.key()))) {
+            if (si != null && si.status().isDefined() && (except == null || !except.contains(si.key())) && si.name() != null && !si.name().isEmpty()) {
                 sb.append(si.importLine(state));
             }
         }

src/jdk.jshell/share/classes/jdk/jshell/VarSnippet.java

@@ -58,15 +58,22 @@ public class VarSnippet extends DeclarationSnippet {
      */
     final Set<String> anonymousClasses;
 
+    final String fieldName;
+
      VarSnippet(VarKey key, String userSource, Wrap guts,
-            String name, SubKind subkind, String typeName, String fullTypeName,
+            String name, String fieldName, SubKind subkind, String typeName, String fullTypeName,
             Set<String> anonymousClasses, Collection<String> declareReferences,
             DiagList syntheticDiags) {
         super(key, userSource, guts, name, subkind, null, declareReferences,
                 null, syntheticDiags);
         this.typeName = typeName;
         this.fullTypeName = fullTypeName;
         this.anonymousClasses = anonymousClasses;
+        this.fieldName = fieldName;
+    }
+
+    String fieldName() {
+        return fieldName;
     }
 
     /**

test/langtools/jdk/jshell/UnnamedTest.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2023, 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.
+ */
+
+/*
+ * @test
+ * @bug 9999999
+ * @summary Tests for unnamed variables
+ * @library /tools/lib
+ * @modules jdk.compiler/com.sun.tools.javac.api
+ *          jdk.compiler/com.sun.tools.javac.main
+ *          jdk.jshell
+ * @build Compiler KullaTesting TestingInputStream ExpectedDiagnostic
+ * @run testng UnnamedTest
+ */
+
+import java.util.function.Consumer;
+import jdk.jshell.VarSnippet;
+import org.testng.Assert;
+import org.testng.annotations.Test;
+
+import jdk.jshell.JShell;
+
+public class UnnamedTest extends KullaTesting {
+
+    @Test
+    public void unnamed() {
+        VarSnippet sn1 = varKey(assertEval("int _ = 0;"));
+        VarSnippet sn2 = varKey(assertEval("String _ = \"x\";"));
+        Assert.assertEquals(getState().varValue(sn1), "0");
+        Assert.assertEquals(getState().varValue(sn2), "\"x\"");
+    }
+
+    @Override
+    public void setUp(Consumer<JShell.Builder> bc) {
+        super.setUp(bc.andThen(b -> b.compilerOptions("--enable-preview", "--source", System.getProperty("java.specification.version"))));
+    }
+}