JEP 456: Unnamed Variables & Patterns (#1410)

JEP 456: Unnamed Variables & Patterns

Author: crogoz

palantir-java-format/src/main/java/com/palantir/javaformat/java/JavaInputAstVisitor.java

@@ -30,9 +30,7 @@
 import static com.palantir.javaformat.java.Trees.precedence;
 import static com.palantir.javaformat.java.Trees.skipParen;
 import static com.sun.source.tree.Tree.Kind.ANNOTATION;
-import static com.sun.source.tree.Tree.Kind.BLOCK;
 import static com.sun.source.tree.Tree.Kind.EXTENDS_WILDCARD;
-import static com.sun.source.tree.Tree.Kind.METHOD_INVOCATION;
 import static com.sun.source.tree.Tree.Kind.STRING_LITERAL;
 import static java.util.stream.Collectors.toList;
 
@@ -3462,7 +3460,7 @@ int declareOne(
                     if (receiverExpression.isPresent()) {
                         scan(receiverExpression.get(), null);
                     } else {
-                        visit(name);
+                        variableName(name);
                     }
                     builder.op(op);
                 }
@@ -3512,6 +3510,10 @@ int declareOne(
         return baseDims;
     }
 
+    protected void variableName(Name name) {
+        visit(name);
+    }
+
     private void maybeAddDims(Deque<List<? extends AnnotationTree>> annotations) {
         maybeAddDims(new ArrayDeque<>(), annotations);
     }
@@ -3600,7 +3602,7 @@ private void declareMany(List<VariableTree> fragments, Direction annotationDirec
             builder.breakOp(" ");
             builder.open(ZERO);
             maybeAddDims(dims);
-            visit(fragment.getName());
+            variableName(fragment.getName());
             maybeAddDims(dims);
             ExpressionTree initializer = fragment.getInitializer();
             if (initializer != null) {

palantir-java-format/src/main/java/com/palantir/javaformat/java/java21/Java21InputAstVisitor.java

@@ -25,6 +25,7 @@
 import com.sun.source.tree.ExpressionTree;
 import com.sun.source.tree.PatternCaseLabelTree;
 import com.sun.source.tree.PatternTree;
+import javax.lang.model.element.Name;
 
 /**
  * Extends {@link Java14InputAstVisitor} with support for AST nodes that were added or modified in
@@ -78,4 +79,13 @@ public Void visitDeconstructionPattern(DeconstructionPatternTree node, Void unus
         token(")");
         return null;
     }
+
+    @Override
+    protected void variableName(Name name) {
+        if (name.isEmpty()) {
+            token("_");
+        } else {
+            visit(name);
+        }
+    }
 }

palantir-java-format/src/test/java/com/palantir/javaformat/java/FileBasedTests.java

@@ -58,7 +58,8 @@ public final class FileBasedTests {
                             "SwitchDouble",
                             "SwitchUnderscore",
                             "I880",
-                            "I1309")
+                            "I1309",
+                            "Unnamed")
                     .build();
 
     private final Class<?> testClass;

palantir-java-format/src/test/resources/com/palantir/javaformat/java/testdata/Unnamed.input

@@ -0,0 +1,46 @@
+class Unnamed {
+  {
+    int acc = 0;
+    for (Order _ : orders) {
+      if (acc < LIMIT) {
+        acc++;
+      }
+    }
+
+    
+
+    for (int i = 0, _ = sideEffect(); i < 10; i++) { }
+
+    Queue<Integer> q = null;
+    while (q.size() >= 3) {
+      var x = q.remove();
+      var y = q.remove();
+      var _ = q.remove();
+      new Point(x, y);
+    }
+
+    while (q.size() >= 3) {
+      var x = q.remove();
+      var _ = q.remove();
+      var _ = q.remove();
+      new Point(x, 0) ;
+    }
+
+    String s = null;
+    try {
+      int i = Integer.parseInt(s);
+    } catch (NumberFormatException _) {
+      System.out.println("Bad number: " + s);
+    }
+
+    try { doSomething(); }
+    catch (Exception _) { doSomething(); }
+    catch (Throwable _) { doSomething(); }
+
+    try (var _ = ScopedContext.acquire()) {
+      doSomething();
+    }
+
+    stream.collect(Collectors.toMap(String::toUpperCase, _ -> "NODATA"));
+  }
+}

palantir-java-format/src/test/resources/com/palantir/javaformat/java/testdata/Unnamed.output

@@ -0,0 +1,48 @@
+class Unnamed {
+    {
+        int acc = 0;
+        for (Order _ : orders) {
+            if (acc < LIMIT) {
+                acc++;
+            }
+        }
+
+        for (int i = 0, _ = sideEffect(); i < 10; i++) {}
+
+        Queue<Integer> q = null;
+        while (q.size() >= 3) {
+            var x = q.remove();
+            var y = q.remove();
+            var _ = q.remove();
+            new Point(x, y);
+        }
+
+        while (q.size() >= 3) {
+            var x = q.remove();
+            var _ = q.remove();
+            var _ = q.remove();
+            new Point(x, 0);
+        }
+
+        String s = null;
+        try {
+            int i = Integer.parseInt(s);
+        } catch (NumberFormatException _) {
+            System.out.println("Bad number: " + s);
+        }
+
+        try {
+            doSomething();
+        } catch (Exception _) {
+            doSomething();
+        } catch (Throwable _) {
+            doSomething();
+        }
+
+        try (var _ = ScopedContext.acquire()) {
+            doSomething();
+        }
+
+        stream.collect(Collectors.toMap(String::toUpperCase, _ -> "NODATA"));
+    }
+}