WIP: linq4j nullability

linq4j/build.gradle.kts

@@ -19,4 +19,5 @@ dependencies {
 
     implementation("com.google.guava:guava")
     implementation("org.apache.calcite.avatica:avatica-core")
+    implementation("org.checkerframework:checker-qual")
 }

linq4j/src/main/java/org/apache/calcite/linq4j/ModularInteger.java

@@ -18,6 +18,8 @@
 
 import com.google.common.base.Preconditions;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 /**
  * Represents an integer in modular arithmetic.
  * Its {@code value} is between 0 and {@code m - 1} for some modulus {@code m}.
@@ -35,7 +37,7 @@ class ModularInteger {
     this.modulus = modulus;
   }
 
-  @Override public boolean equals(Object obj) {
+  @Override public boolean equals(@Nullable Object obj) {
     return obj == this
         || obj instanceof ModularInteger
         && value == ((ModularInteger) obj).value

linq4j/src/main/java/org/apache/calcite/linq4j/tree/AbstractNode.java

@@ -16,6 +16,8 @@
  */
 package org.apache.calcite.linq4j.tree;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 import java.lang.reflect.Type;
 import java.util.Objects;
 
@@ -70,12 +72,12 @@ public Node accept(Shuttle shuttle) {
         "visit not supported: " + getClass() + ":" + nodeType);
   }
 
-  public Object evaluate(Evaluator evaluator) {
+  public @Nullable Object evaluate(Evaluator evaluator) {
     throw new RuntimeException(
         "evaluation not supported: " + getClass() + ":" + nodeType);
   }
 
-  @Override public boolean equals(Object o) {
+  @Override public boolean equals(@Nullable Object o) {
     if (this == o) {
       return true;
     }

linq4j/src/main/java/org/apache/calcite/linq4j/tree/ArrayLengthRecordField.java

@@ -16,6 +16,8 @@
  */
 package org.apache.calcite.linq4j.tree;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 import java.lang.reflect.Array;
 import java.lang.reflect.Type;
 import java.util.Objects;
@@ -58,7 +60,7 @@ public Type getDeclaringClass() {
     return clazz;
   }
 
-  @Override public boolean equals(Object o) {
+  @Override public boolean equals(@Nullable Object o) {
     if (this == o) {
       return true;
     }

linq4j/src/main/java/org/apache/calcite/linq4j/tree/BinaryExpression.java

@@ -16,6 +16,8 @@
  */
 package org.apache.calcite.linq4j.tree;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 import java.lang.reflect.Type;
 import java.util.Objects;
 
@@ -44,7 +46,7 @@ public class BinaryExpression extends Expression {
     return visitor.visit(this, expression0, expression1);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  public <@Nullable R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
@@ -88,8 +90,7 @@ public Object evaluate(Evaluator evaluator) {
         throw cannotEvaluate();
       }
     case Equal:
-      return expression0.evaluate(evaluator)
-          .equals(expression1.evaluate(evaluator));
+      return Objects.equals(expression0.evaluate(evaluator), expression1.evaluate(evaluator));
     case GreaterThan:
       switch (primitive) {
       case INT:
@@ -241,7 +242,7 @@ private double evaluateDouble(Expression expression, Evaluator evaluator) {
     return ((Number) expression.evaluate(evaluator)).doubleValue();
   }
 
-  @Override public boolean equals(Object o) {
+  @Override public boolean equals(@Nullable Object o) {
     if (this == o) {
       return true;
     }

linq4j/src/main/java/org/apache/calcite/linq4j/tree/BlockBuilder.java

@@ -16,6 +16,8 @@
  */
 package org.apache.calcite.linq4j.tree;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 import java.lang.reflect.Modifier;
 import java.lang.reflect.Type;
 import java.util.ArrayList;
@@ -41,7 +43,7 @@ public class BlockBuilder {
       new HashMap<>();
 
   private final boolean optimizing;
-  private final BlockBuilder parent;
+  private final @Nullable BlockBuilder parent;
 
   private static final Shuttle OPTIMIZE_SHUTTLE = new OptimizeShuttle();
 
@@ -66,7 +68,7 @@ public BlockBuilder(boolean optimizing) {
    *
    * @param optimizing Whether to eliminate common sub-expressions
    */
-  public BlockBuilder(boolean optimizing, BlockBuilder parent) {
+  public BlockBuilder(boolean optimizing, @Nullable BlockBuilder parent) {
     this.optimizing = optimizing;
     this.parent = parent;
   }
@@ -85,7 +87,7 @@ public void clear() {
    * (possibly a variable) that represents the result of the newly added
    * block.
    */
-  public Expression append(String name, BlockStatement block) {
+  public @Nullable Expression append(String name, BlockStatement block) {
     return append(name, block, true);
   }
 
@@ -99,7 +101,7 @@ public Expression append(String name, BlockStatement block) {
    * a variable. Do not do this if the expression has
    * side-effects or a time-dependent value.
    */
-  public Expression append(String name, BlockStatement block,
+  public @Nullable Expression append(String name, BlockStatement block,
       boolean optimize) {
     if (statements.size() > 0) {
       Statement lastStatement = statements.get(statements.size() - 1);
@@ -184,7 +186,7 @@ public Expression append(String name, Expression expression) {
   /**
    * Appends an expression to a list of statements, if it is not null.
    */
-  public Expression appendIfNotNull(String name, Expression expression) {
+  public @Nullable Expression appendIfNotNull(String name, @Nullable Expression expression) {
     if (expression == null) {
       return null;
     }
@@ -283,7 +285,7 @@ private Expression normalizeDeclaration(DeclarationStatement decl) {
    * @param expr expression to test
    * @return existing ParameterExpression or null
    */
-  public DeclarationStatement getComputedExpression(Expression expr) {
+  public @Nullable DeclarationStatement getComputedExpression(Expression expr) {
     if (parent != null) {
       DeclarationStatement decl = parent.getComputedExpression(expr);
       if (decl != null) {

linq4j/src/main/java/org/apache/calcite/linq4j/tree/BlockStatement.java

@@ -16,6 +16,8 @@
  */
 package org.apache.calcite.linq4j.tree;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 import java.lang.reflect.Type;
 import java.util.HashSet;
 import java.util.List;
@@ -61,7 +63,7 @@ private boolean distinctVariables(boolean fail) {
     return shuttle.visit(this, newStatements);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  public <@Nullable R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
@@ -77,15 +79,15 @@ public <R> R accept(Visitor<R> visitor) {
     writer.end("}\n");
   }
 
-  @Override public Object evaluate(Evaluator evaluator) {
+  @Override public @Nullable Object evaluate(Evaluator evaluator) {
     Object o = null;
     for (Statement statement : statements) {
       o = statement.evaluate(evaluator);
     }
     return o;
   }
 
-  @Override public boolean equals(Object o) {
+  @Override public boolean equals(@Nullable Object o) {
     if (this == o) {
       return true;
     }

linq4j/src/main/java/org/apache/calcite/linq4j/tree/CatchBlock.java

@@ -16,6 +16,8 @@
  */
 package org.apache.calcite.linq4j.tree;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 import java.util.Objects;
 
 /**
@@ -31,7 +33,7 @@ public CatchBlock(ParameterExpression parameter,
     this.body = body;
   }
 
-  @Override public boolean equals(Object o) {
+  @Override public boolean equals(@Nullable Object o) {
     if (this == o) {
       return true;
     }

linq4j/src/main/java/org/apache/calcite/linq4j/tree/ClassDeclaration.java

@@ -16,6 +16,8 @@
  */
 package org.apache.calcite.linq4j.tree;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 import java.lang.reflect.Modifier;
 import java.lang.reflect.Type;
 import java.util.List;
@@ -66,11 +68,11 @@ public ClassDeclaration accept(Shuttle shuttle) {
     return shuttle.visit(this, members1);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  public <@Nullable R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
-  @Override public boolean equals(Object o) {
+  @Override public boolean equals(@Nullable Object o) {
     if (this == o) {
       return true;
     }

linq4j/src/main/java/org/apache/calcite/linq4j/tree/ClassDeclarationFinder.java

@@ -18,6 +18,8 @@
 
 import org.apache.calcite.linq4j.function.Function1;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationTargetException;
 import java.util.ArrayList;
@@ -30,7 +32,7 @@
  * created for optimizing a new expression tree.
  */
 public class ClassDeclarationFinder extends Shuttle {
-  protected final ClassDeclarationFinder parent;
+  protected final @Nullable ClassDeclarationFinder parent;
 
   /**
    * The list of new final static fields to be added to the current class.
@@ -254,7 +256,7 @@ protected boolean isConstant(Iterable<? extends Expression> list) {
    * @param expression input expression
    * @return always returns null
    */
-  protected ParameterExpression findDeclaredExpression(Expression expression) {
+  protected @Nullable ParameterExpression findDeclaredExpression(Expression expression) {
     return null;
   }
 

linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConditionalExpression.java

@@ -16,6 +16,8 @@
  */
 package org.apache.calcite.linq4j.tree;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 import java.lang.reflect.Type;
 import java.util.List;
 import java.util.Objects;
@@ -41,7 +43,7 @@ public ConditionalExpression(List<Node> expressionList, Type type) {
     this.expressionList = expressionList;
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  public <@Nullable R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
@@ -59,7 +61,7 @@ public <R> R accept(Visitor<R> visitor) {
     }
   }
 
-  @Override public boolean equals(Object o) {
+  @Override public boolean equals(@Nullable Object o) {
     if (this == o) {
       return true;
     }

linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConditionalStatement.java

@@ -16,6 +16,8 @@
  */
 package org.apache.calcite.linq4j.tree;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 import java.util.List;
 import java.util.Objects;
 
@@ -46,7 +48,7 @@ public ConditionalStatement(List<Node> expressionList) {
     return shuttle.visit(this, list);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  public <@Nullable R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
@@ -72,7 +74,7 @@ private static <E> E last(List<E> collection) {
     return collection.get(collection.size() - 1);
   }
 
-  @Override public boolean equals(Object o) {
+  @Override public boolean equals(@Nullable Object o) {
     if (this == o) {
       return true;
     }

linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConstantExpression.java

@@ -16,6 +16,8 @@
  */
 package org.apache.calcite.linq4j.tree;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 import java.lang.reflect.Constructor;
 import java.lang.reflect.Field;
 import java.lang.reflect.Type;
@@ -32,9 +34,9 @@
  * Represents an expression that has a constant value.
  */
 public class ConstantExpression extends Expression {
-  public final Object value;
+  public final @Nullable Object value;
 
-  public ConstantExpression(Type type, Object value) {
+  public ConstantExpression(Type type, @Nullable Object value) {
     super(ExpressionType.Constant, type);
     this.value = value;
     if (value != null) {
@@ -54,15 +56,15 @@ public ConstantExpression(Type type, Object value) {
     }
   }
 
-  public Object evaluate(Evaluator evaluator) {
+  public @Nullable Object evaluate(Evaluator evaluator) {
     return value;
   }
 
   @Override public Expression accept(Shuttle shuttle) {
     return shuttle.visit(this);
   }
 
-  public <R> R accept(Visitor<R> visitor) {
+  public <@Nullable R> R accept(Visitor<R> visitor) {
     return visitor.visit(this);
   }
 
@@ -77,7 +79,7 @@ public <R> R accept(Visitor<R> visitor) {
   }
 
   private static ExpressionWriter write(ExpressionWriter writer,
-      final Object value, Type type) {
+      final Object value, @Nullable Type type) {
     if (value == null) {
       return writer.append("null");
     }
@@ -328,7 +330,7 @@ private static void escapeString(StringBuilder buf, String s) {
     buf.append('"');
   }
 
-  @Override public boolean equals(Object o) {
+  @Override public boolean equals(@Nullable Object o) {
     // REVIEW: Should constants with the same value and different type
     // (e.g. 3L and 3) be considered equal.
     if (this == o) {

linq4j/src/main/java/org/apache/calcite/linq4j/tree/ConstantUntypedNull.java

@@ -16,6 +16,8 @@
  */
 package org.apache.calcite.linq4j.tree;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 /**
  * Represents a constant null of unknown type
  * Java allows type inference for such nulls, thus "null" cannot always be
@@ -36,7 +38,7 @@ private ConstantUntypedNull() {
     writer.append("null");
   }
 
-  @Override public boolean equals(Object o) {
+  @Override public boolean equals(@Nullable Object o) {
     return o == INSTANCE;
   }