Fix: Explicit handle null pattern and escape in like function. (#6894)

Summary:

When value at constant vector is null we shall not call valueAt().
This added check in ConstantVector and also make sure like function
handles null explicitly.

Differential Revision: D49917874

velox/functions/lib/Re2Functions.cpp

@@ -470,6 +470,18 @@ class OptimizedLikeWithMemcmp final : public VectorFunction {
   vector_size_t reducedPatternLength_;
 };
 
+// This functions is constructed when the input is a constant null.
+class AlwaysNull final : public VectorFunction {
+  void apply(
+      const SelectivityVector& rows,
+      std::vector<VectorPtr>& args,
+      const TypePtr& /* outputType */,
+      EvalCtx& context,
+      VectorPtr& resultRef) const final {
+    VELOX_UNREACHABLE("Not expected to be called.")
+  }
+};
+
 class LikeWithRe2 final : public VectorFunction {
  public:
   LikeWithRe2(StringView pattern, std::optional<char> escapeChar) {
@@ -947,6 +959,9 @@ std::shared_ptr<exec::VectorFunction> makeLike(
         inputArgs[2].type->toString());
 
     auto constantEscape = escape->as<ConstantVector<StringView>>();
+    if (constantEscape->isNullAt(0)) {
+      return std::make_shared<AlwaysNull>();
+    }
 
     try {
       VELOX_USER_CHECK_EQ(
@@ -966,6 +981,10 @@ std::shared_ptr<exec::VectorFunction> makeLike(
       "{} requires second argument to be a constant of type VARCHAR",
       name,
       inputArgs[1].type->toString());
+  if (constantPattern->isNullAt(0)) {
+    return std::make_shared<AlwaysNull>();
+  }
+
   auto pattern = constantPattern->as<ConstantVector<StringView>>()->valueAt(0);
   if (!escapeChar) {
     PatternKind patternKind;

velox/functions/lib/tests/Re2FunctionsTest.cpp

@@ -593,6 +593,16 @@ TEST_F(Re2FunctionsTest, likePatternSuffix) {
   EXPECT_TRUE(like(input, generateString(kAnyWildcardCharacter) + input));
 }
 
+TEST_F(Re2FunctionsTest, nullConstantPatternOrEscape) {
+  // Test null pattern.
+  ASSERT_TRUE(
+      !evaluateOnce<bool>("like('a', cast (null as varchar))").has_value());
+
+  // Test null escape.
+  ASSERT_TRUE(
+      !evaluateOnce<bool>("like('a', 'a', cast(null as varchar))").has_value());
+}
+
 TEST_F(Re2FunctionsTest, likePatternAndEscape) {
   auto like = ([&](std::optional<std::string> str,
                    std::optional<std::string> pattern,

velox/vector/ConstantVector.h

@@ -160,6 +160,7 @@ class ConstantVector final : public SimpleVector<T> {
   }
 
   virtual const T valueAt(vector_size_t /*idx*/) const override {
+    VELOX_DCHECK(!isNullAt(0));
     VELOX_DCHECK(initialized_);
     SimpleVector<T>::checkElementSize();
     return value();