From 66a48bf4bbf68750c3a6ca5c6da28098c33cadf4 Mon Sep 17 00:00:00 2001
From: Joseph <jdhsoc@gmail.com>
Date: Thu, 11 Jun 2026 11:13:46 +0100
Subject: [PATCH] Add CollectionIsEmptyRefactor (java:S1155)

Implements SonarQube rule java:S1155 - rewrites size comparisons on
Collection types to use isEmpty()/!isEmpty() instead.

Classes placed in the sonar.s1155 package convention:
- CollectionIsEmptyRefactor (main operation)
- TestCollectionIsEmptyRefactor and test fixtures

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 .../s1155/CollectionIsEmptyRefactor.java      | 168 ++++++++++++++++++
 .../sonar/s1155/CollectionIsEmptyExample.java |  27 +++
 .../s1155/CollectionIsEmptyExampleAfter.java  |  27 +++
 ...CollectionIsEmptyNonCollectionExample.java |  26 +++
 ...ctionIsEmptyNonCollectionExampleAfter.java |  26 +++
 .../sonar/s1155/NonCollectionWithSize.java    |   6 +
 .../s1155/TestCollectionIsEmptyRefactor.java  |  30 ++++
 7 files changed, 310 insertions(+)
 create mode 100644 astra-core/src/main/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyRefactor.java
 create mode 100644 astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyExample.java
 create mode 100644 astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyExampleAfter.java
 create mode 100644 astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyNonCollectionExample.java
 create mode 100644 astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyNonCollectionExampleAfter.java
 create mode 100644 astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/NonCollectionWithSize.java
 create mode 100644 astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/TestCollectionIsEmptyRefactor.java

diff --git a/astra-core/src/main/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyRefactor.java b/astra-core/src/main/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyRefactor.java
new file mode 100644
index 0000000..6367493
--- /dev/null
+++ b/astra-core/src/main/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyRefactor.java
@@ -0,0 +1,168 @@
+package org.alfasoftware.astra.core.refactoring.operations.sonar.s1155;
+
+import java.io.IOException;
+
+import org.alfasoftware.astra.core.utils.ASTOperation;
+import org.eclipse.jdt.core.dom.AST;
+import org.eclipse.jdt.core.dom.ASTNode;
+import org.eclipse.jdt.core.dom.CompilationUnit;
+import org.eclipse.jdt.core.dom.Expression;
+import org.eclipse.jdt.core.dom.ITypeBinding;
+import org.eclipse.jdt.core.dom.InfixExpression;
+import org.eclipse.jdt.core.dom.MethodInvocation;
+import org.eclipse.jdt.core.dom.NumberLiteral;
+import org.eclipse.jdt.core.dom.PrefixExpression;
+import org.eclipse.jdt.core.dom.rewrite.ASTRewrite;
+import org.eclipse.jface.text.BadLocationException;
+import org.eclipse.text.edits.MalformedTreeException;
+
+/**
+ * Implements SonarQube rule java:S1155 — {@code Collection.isEmpty()} should be used to test for emptiness.
+ *
+ * <p>Replaces {@code size()} comparisons against 0 or 1 with the semantically equivalent
+ * {@code isEmpty()} call. Both operand orderings are supported.
+ *
+ * <pre>
+ *   col.size() == 0   →  col.isEmpty()
+ *   col.size() != 0   →  !col.isEmpty()
+ *   col.size() &gt; 0    →  !col.isEmpty()
+ *   col.size() &gt;= 1   →  !col.isEmpty()
+ *   col.size() &lt; 1    →  col.isEmpty()
+ *   col.size() &lt;= 0   →  col.isEmpty()
+ *   0 == col.size()   →  col.isEmpty()
+ *   0 != col.size()   →  !col.isEmpty()
+ * </pre>
+ *
+ * <p>Binding resolution is used to confirm the receiver is a {@code java.util.Collection} subtype
+ * before rewriting. Expressions where the type cannot be resolved are left unchanged.
+ */
+public class CollectionIsEmptyRefactor implements ASTOperation {
+
+  private static final String COLLECTION_FQN = "java.util.Collection";
+
+  @Override
+  public void run(CompilationUnit compilationUnit, ASTNode node, ASTRewrite rewriter)
+      throws IOException, MalformedTreeException, BadLocationException {
+    if (!(node instanceof InfixExpression)) {
+      return;
+    }
+    InfixExpression infix = (InfixExpression) node;
+
+    // Extended operands occur on chains like a + b + c; comparisons never have them.
+    // Guard anyway to keep the logic below simple.
+    if (!infix.extendedOperands().isEmpty()) {
+      return;
+    }
+
+    Expression left = infix.getLeftOperand();
+    Expression right = infix.getRightOperand();
+    InfixExpression.Operator op = infix.getOperator();
+
+    // size() on left, literal on right
+    if (isSizeInvocation(left) && isZeroOrOne(right)) {
+      Boolean negate = shouldNegate(op, literalValue(right), false);
+      if (negate != null && isCollectionReceiver((MethodInvocation) left)) {
+        rewrite(rewriter, infix, (MethodInvocation) left, negate);
+      }
+      return;
+    }
+
+    // literal on left, size() on right (reversed operand ordering)
+    if (isZeroOrOne(left) && isSizeInvocation(right)) {
+      Boolean negate = shouldNegate(op, literalValue(left), true);
+      if (negate != null && isCollectionReceiver((MethodInvocation) right)) {
+        rewrite(rewriter, infix, (MethodInvocation) right, negate);
+      }
+    }
+  }
+
+
+  private boolean isSizeInvocation(Expression expr) {
+    if (!(expr instanceof MethodInvocation)) return false;
+    MethodInvocation mi = (MethodInvocation) expr;
+    return "size".equals(mi.getName().getIdentifier())
+        && mi.arguments().isEmpty()
+        && mi.getExpression() != null;
+  }
+
+
+  private boolean isZeroOrOne(Expression expr) {
+    if (!(expr instanceof NumberLiteral)) return false;
+    String token = ((NumberLiteral) expr).getToken();
+    return "0".equals(token) || "1".equals(token);
+  }
+
+
+  private int literalValue(Expression expr) {
+    return Integer.parseInt(((NumberLiteral) expr).getToken());
+  }
+
+
+  /**
+   * Returns {@code true} when the replacement should be {@code !isEmpty()}, {@code false} for
+   * {@code isEmpty()}, or {@code null} when the operator/literal combination is not a recognised
+   * S1155 pattern.
+   *
+   * @param op            the infix operator
+   * @param value         the numeric literal value (0 or 1)
+   * @param sizeOnRight   whether {@code size()} is the right operand (reversed ordering)
+   */
+  private Boolean shouldNegate(InfixExpression.Operator op, int value, boolean sizeOnRight) {
+    InfixExpression.Operator normalized = sizeOnRight ? flip(op) : op;
+
+    if (normalized == InfixExpression.Operator.EQUALS && value == 0) return false;
+    if (normalized == InfixExpression.Operator.NOT_EQUALS && value == 0) return true;
+    if (normalized == InfixExpression.Operator.GREATER && value == 0) return true;
+    if (normalized == InfixExpression.Operator.GREATER_EQUALS && value == 1) return true;
+    if (normalized == InfixExpression.Operator.LESS && value == 1) return false;
+    if (normalized == InfixExpression.Operator.LESS_EQUALS && value == 0) return false;
+    return null;
+  }
+
+
+  private InfixExpression.Operator flip(InfixExpression.Operator op) {
+    if (op == InfixExpression.Operator.GREATER) return InfixExpression.Operator.LESS;
+    if (op == InfixExpression.Operator.LESS) return InfixExpression.Operator.GREATER;
+    if (op == InfixExpression.Operator.GREATER_EQUALS) return InfixExpression.Operator.LESS_EQUALS;
+    if (op == InfixExpression.Operator.LESS_EQUALS) return InfixExpression.Operator.GREATER_EQUALS;
+    return op; // == and != are symmetric
+  }
+
+
+  private boolean isCollectionReceiver(MethodInvocation sizeCall) {
+    Expression receiver = sizeCall.getExpression();
+    ITypeBinding binding = receiver.resolveTypeBinding();
+    if (binding == null || binding.isRecovered()) {
+      return false;
+    }
+    return implementsCollection(binding);
+  }
+
+
+  private boolean implementsCollection(ITypeBinding binding) {
+    if (binding == null) return false;
+    if (COLLECTION_FQN.equals(binding.getErasure().getQualifiedName())) return true;
+    for (ITypeBinding iface : binding.getInterfaces()) {
+      if (implementsCollection(iface)) return true;
+    }
+    return implementsCollection(binding.getSuperclass());
+  }
+
+
+  private void rewrite(ASTRewrite rewriter, InfixExpression infix, MethodInvocation sizeCall, boolean negate) {
+    AST ast = infix.getAST();
+
+    MethodInvocation isEmptyCall = ast.newMethodInvocation();
+    isEmptyCall.setName(ast.newSimpleName("isEmpty"));
+    isEmptyCall.setExpression((Expression) ASTNode.copySubtree(ast, sizeCall.getExpression()));
+
+    if (negate) {
+      PrefixExpression prefix = ast.newPrefixExpression();
+      prefix.setOperator(PrefixExpression.Operator.NOT);
+      prefix.setOperand(isEmptyCall);
+      rewriter.replace(infix, prefix, null);
+    } else {
+      rewriter.replace(infix, isEmptyCall, null);
+    }
+  }
+}
diff --git a/astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyExample.java b/astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyExample.java
new file mode 100644
index 0000000..f789cdb
--- /dev/null
+++ b/astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyExample.java
@@ -0,0 +1,27 @@
+package org.alfasoftware.astra.core.refactoring.operations.sonar.s1155;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class CollectionIsEmptyExample {
+
+  private final List<String> list = new ArrayList<>();
+
+  void sizeOnLeft() {
+    boolean a = list.size() == 0;
+    boolean b = list.size() != 0;
+    boolean c = list.size() > 0;
+    boolean d = list.size() >= 1;
+    boolean e = list.size() < 1;
+    boolean f = list.size() <= 0;
+  }
+
+  void reversedOperands() {
+    boolean a = 0 == list.size();
+    boolean b = 0 != list.size();
+    boolean c = 0 < list.size();
+    boolean d = 1 <= list.size();
+    boolean e = 1 > list.size();
+    boolean f = 0 >= list.size();
+  }
+}
diff --git a/astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyExampleAfter.java b/astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyExampleAfter.java
new file mode 100644
index 0000000..27a3fb2
--- /dev/null
+++ b/astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyExampleAfter.java
@@ -0,0 +1,27 @@
+package org.alfasoftware.astra.core.refactoring.operations.sonar.s1155;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class CollectionIsEmptyExampleAfter {
+
+  private final List<String> list = new ArrayList<>();
+
+  void sizeOnLeft() {
+    boolean a = list.isEmpty();
+    boolean b = ! list.isEmpty();
+    boolean c = ! list.isEmpty();
+    boolean d = ! list.isEmpty();
+    boolean e = list.isEmpty();
+    boolean f = list.isEmpty();
+  }
+
+  void reversedOperands() {
+    boolean a = list.isEmpty();
+    boolean b = ! list.isEmpty();
+    boolean c = ! list.isEmpty();
+    boolean d = ! list.isEmpty();
+    boolean e = list.isEmpty();
+    boolean f = list.isEmpty();
+  }
+}
diff --git a/astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyNonCollectionExample.java b/astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyNonCollectionExample.java
new file mode 100644
index 0000000..b4c9dcf
--- /dev/null
+++ b/astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyNonCollectionExample.java
@@ -0,0 +1,26 @@
+package org.alfasoftware.astra.core.refactoring.operations.sonar.s1155;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class CollectionIsEmptyNonCollectionExample {
+
+  private final NonCollectionWithSize custom = new NonCollectionWithSize();
+  private final List<String> list = new ArrayList<>();
+
+  void nonCollectionShouldNotChange() {
+    boolean a = custom.size() == 0;
+    boolean b = custom.size() != 0;
+    boolean c = custom.size() > 0;
+  }
+
+  void alreadyUsingIsEmpty() {
+    boolean a = list.isEmpty();
+    boolean b = !list.isEmpty();
+  }
+
+  void unsupportedLiteralShouldNotChange() {
+    boolean a = list.size() == 2;
+    boolean b = list.size() > 5;
+  }
+}
diff --git a/astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyNonCollectionExampleAfter.java b/astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyNonCollectionExampleAfter.java
new file mode 100644
index 0000000..4c7d095
--- /dev/null
+++ b/astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/CollectionIsEmptyNonCollectionExampleAfter.java
@@ -0,0 +1,26 @@
+package org.alfasoftware.astra.core.refactoring.operations.sonar.s1155;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class CollectionIsEmptyNonCollectionExampleAfter {
+
+  private final NonCollectionWithSize custom = new NonCollectionWithSize();
+  private final List<String> list = new ArrayList<>();
+
+  void nonCollectionShouldNotChange() {
+    boolean a = custom.size() == 0;
+    boolean b = custom.size() != 0;
+    boolean c = custom.size() > 0;
+  }
+
+  void alreadyUsingIsEmpty() {
+    boolean a = list.isEmpty();
+    boolean b = !list.isEmpty();
+  }
+
+  void unsupportedLiteralShouldNotChange() {
+    boolean a = list.size() == 2;
+    boolean b = list.size() > 5;
+  }
+}
diff --git a/astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/NonCollectionWithSize.java b/astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/NonCollectionWithSize.java
new file mode 100644
index 0000000..3480db6
--- /dev/null
+++ b/astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/NonCollectionWithSize.java
@@ -0,0 +1,6 @@
+package org.alfasoftware.astra.core.refactoring.operations.sonar.s1155;
+
+/** Helper type used by tests — has {@code size()} but does NOT implement {@code java.util.Collection}. */
+class NonCollectionWithSize {
+  public int size() { return 0; }
+}
diff --git a/astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/TestCollectionIsEmptyRefactor.java b/astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/TestCollectionIsEmptyRefactor.java
new file mode 100644
index 0000000..b4382d2
--- /dev/null
+++ b/astra-core/src/test/java/org/alfasoftware/astra/core/refactoring/operations/sonar/s1155/TestCollectionIsEmptyRefactor.java
@@ -0,0 +1,30 @@
+package org.alfasoftware.astra.core.refactoring.operations.sonar.s1155;
+
+import java.util.Collections;
+
+import org.alfasoftware.astra.core.refactoring.AbstractRefactorTest;
+import org.alfasoftware.astra.core.refactoring.operations.sonar.s1155.CollectionIsEmptyRefactor;
+import org.junit.Test;
+
+public class TestCollectionIsEmptyRefactor extends AbstractRefactorTest {
+
+  /**
+   * All six size()-comparison forms in both normal and reversed operand order
+   * are replaced with isEmpty() or !isEmpty() as appropriate.
+   */
+  @Test
+  public void testAllForms() {
+    assertRefactor(CollectionIsEmptyExample.class,
+        Collections.singleton(new CollectionIsEmptyRefactor()));
+  }
+
+  /**
+   * Non-Collection.size() calls, already-correct isEmpty() calls, and
+   * size() comparisons against literals other than 0/1 are left unchanged.
+   */
+  @Test
+  public void testNoOpCases() {
+    assertRefactor(CollectionIsEmptyNonCollectionExample.class,
+        Collections.singleton(new CollectionIsEmptyRefactor()));
+  }
+}