Add support for collated strings in OpConverter

PROTOCOL.md

@@ -3261,6 +3261,7 @@ children | The child operations for the op. This allows us to represent a predic
 name | Specifies the name of a column. This is only applicable to column ops.
 value | Specifies the value of a literal. This is only applicable to literal ops.
 valueType | Specifies the value type of a column or a literal op. This is only applicate to column and literal ops.
+exprCtx | Optional field that provides additional expression context.
 
 The supported Ops:
 
@@ -3291,6 +3292,14 @@ ValueType | Description
 "double" | Represents a Double type.
 "timestamp" | Represents a timestamp in [Timestamp Format](#timestamp-format).
 
+The exprCtx structure:
+
+When present, the `exprCtx` field is a JSON object that may contain the following fields:
+
+Field Name | Description
+-|-
+collationIdentifier | Optional string that specifies the collation to use for string comparisons. The format is `provider.collationName.version`. The provider is either `icu` for ICU-based collations (e.g., UNICODE_CI) or `spark` for Spark-specific collations (e.g., UTF8_LCASE). The version specifies the version of collation used (e.g. ICU version "75.1"). Example: "icu.UNICODE_CI.75.1" or "spark.UTF8_LCASE.75.1". When collationIdentifier field is absent, the default UTF8_BINARY collation is used. For more information about collations in Delta, see the [collations protocol RFC](https://github.com/delta-io/delta/issues/2894).
+
 
 Examples
 
@@ -3346,6 +3355,21 @@ Examples
 }
 ```
 
+4. Collated string comparison.
+
+```json
+{
+  "op": "equal",
+  "children": [
+    {"op": "column", "name": "name", "valueType": "string"},
+    {"op": "literal", "value": "TestValue", "valueType": "string"}
+  ],
+  "exprCtx": {
+    "collationIdentifier": "icu.UNICODE_CI.75.1"
+  }
+}
+```
+
 ## Delta Sharing Streaming Specs
 Delta Sharing Streaming is supported starting from delta-sharing-spark 0.6.0. As it's implemented
 based on spark structured streaming, it leverages a pull model to consume the new data of the shared

client/src/main/scala-2.12/io/delta/sharing/filters/CollationExtractor.scala

@@ -0,0 +1,35 @@
+/*
+ * Copyright (2021) The Delta Lake Project Authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.delta.sharing.filters
+
+import org.apache.spark.sql.catalyst.expressions.{Expression => SqlExpression}
+import org.apache.spark.sql.types.{StringType => SqlStringType}
+
+object CollationExtractor {
+  // Extracts collation identifier from two expressions if both are strings
+  // with the same collation.
+  def extractCollationIdentifier(
+      left: SqlExpression,
+      right: SqlExpression): Option[String] = {
+    // The 2.12 client depends on Spark 3.5, which does not support collations.
+    // This means we cannot extract the collation identifier. In this case, we
+    // return None to default to UTF8 binary comparisons, as collations are just a
+    // writer feature in Delta and Spark 3.5 does not support them but should still
+    // be able to read the table.
+    None
+  }
+}

client/src/main/scala-2.13/io/delta/sharing/filters/CollationExtractor.scala

@@ -0,0 +1,53 @@
+/*
+ * Copyright (2021) The Delta Lake Project Authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.delta.sharing.filters
+
+import com.ibm.icu.util.VersionInfo.ICU_VERSION
+import org.apache.spark.sql.catalyst.expressions.{Expression => SqlExpression}
+import org.apache.spark.sql.types.{StringType => SqlStringType}
+
+object CollationExtractor {
+  // Extracts collation identifier from two expressions if both are strings
+  // with the same collation.
+  def extractCollationIdentifier(
+      left: SqlExpression,
+      right: SqlExpression): Option[String] = {
+    (left.dataType, right.dataType) match {
+      case (leftStr: SqlStringType, rightStr: SqlStringType) =>
+        // Spark needs to make sure to only compare strings of the same collation.
+        if (leftStr != rightStr) {
+          throw new IllegalArgumentException(
+            s"Cannot compare strings with different collations: " +
+            s"'${leftStr.typeName}' vs '${rightStr.typeName}'"
+          )
+        }
+
+        val typeName = leftStr.typeName
+        if (typeName.startsWith("string collate")) {
+          val collationName = typeName.stripPrefix("string collate").trim
+          val provider = if (collationName.equalsIgnoreCase("UTF8_LCASE")) "spark" else "icu"
+          val version = s"${ICU_VERSION.getMajor}.${ICU_VERSION.getMinor}"
+          Some(s"$provider.$collationName.$version")
+        } else {
+          None
+        }
+
+      case _ =>
+        None
+    }
+  }
+}

client/src/main/scala/io/delta/sharing/filters/JsonPredicates.scala

@@ -27,6 +27,13 @@ import com.fasterxml.jackson.annotation.{JsonSubTypes, JsonTypeInfo}
  */
 case class EvalContext(partitionValues: Map[String, String])
 
+/**
+ * The expression context containing metadata about the operation.
+ *
+ * @param collationIdentifier The collation identifier for string comparisons, if applicable.
+ */
+case class ExprContext(collationIdentifier: Option[String] = None)
+
 /**
  * The data types supported by the filtering operations.
  */
@@ -243,33 +250,38 @@ case class IsNullOp(children: Seq[LeafOp]) extends NonLeafOp with UnaryOp {
  * @param children Expected size is 2.
  */
 
-case class EqualOp(children: Seq[LeafOp]) extends NonLeafOp with BinaryOp {
+case class EqualOp(children: Seq[LeafOp], exprCtx: Option[ExprContext] = None)
+    extends NonLeafOp with BinaryOp {
   override def validate(forV2: Boolean = false): Unit = validateChildren(children, forV2)
 
   override def eval(ctx: EvalContext): Any = EvalHelper.equal(children, ctx)
 }
 
-case class LessThanOp(children: Seq[LeafOp]) extends NonLeafOp with BinaryOp {
+case class LessThanOp(children: Seq[LeafOp], exprCtx: Option[ExprContext] = None)
+    extends NonLeafOp with BinaryOp {
   override def validate(forV2: Boolean = false): Unit = validateChildren(children, forV2)
 
   override def eval(ctx: EvalContext): Any = EvalHelper.lessThan(children, ctx)
 }
 
-case class LessThanOrEqualOp(children: Seq[LeafOp]) extends NonLeafOp with BinaryOp {
+case class LessThanOrEqualOp(children: Seq[LeafOp], exprCtx: Option[ExprContext] = None)
+    extends NonLeafOp with BinaryOp {
   override def validate(forV2: Boolean = false): Unit = validateChildren(children, forV2)
 
   override def eval(ctx: EvalContext): Any =
     EvalHelper.lessThan(children, ctx) || EvalHelper.equal(children, ctx)
 }
 
-case class GreaterThanOp(children: Seq[LeafOp]) extends NonLeafOp with BinaryOp {
+case class GreaterThanOp(children: Seq[LeafOp], exprCtx: Option[ExprContext] = None)
+    extends NonLeafOp with BinaryOp {
   override def validate(forV2: Boolean = false): Unit = validateChildren(children, forV2)
 
   override def eval(ctx: EvalContext): Any =
     !EvalHelper.lessThan(children, ctx) && !EvalHelper.equal(children, ctx)
 }
 
-case class GreaterThanOrEqualOp(children: Seq[LeafOp]) extends NonLeafOp with BinaryOp {
+case class GreaterThanOrEqualOp(children: Seq[LeafOp], exprCtx: Option[ExprContext] = None)
+    extends NonLeafOp with BinaryOp {
   override def validate(forV2: Boolean = false): Unit = validateChildren(children, forV2)
 
   override def eval(ctx: EvalContext): Any = !EvalHelper.lessThan(children, ctx)

client/src/main/scala/io/delta/sharing/filters/OpConverter.scala

@@ -93,15 +93,30 @@ object OpConverter {
 
       // Convert comparison operators.
       case SqlEqualTo(left, right) =>
-        EqualOp(Seq(convertAsLeaf(left), convertAsLeaf(right)))
+        EqualOp(
+          Seq(convertAsLeaf(left), convertAsLeaf(right)),
+          extractExprContext(left, right)
+        )
       case SqlLessThan(left, right) =>
-        LessThanOp(Seq(convertAsLeaf(left), convertAsLeaf(right)))
+        LessThanOp(
+          Seq(convertAsLeaf(left), convertAsLeaf(right)),
+          extractExprContext(left, right)
+        )
       case SqlLessThanOrEqual(left, right) =>
-        LessThanOrEqualOp(Seq(convertAsLeaf(left), convertAsLeaf(right)))
+        LessThanOrEqualOp(
+          Seq(convertAsLeaf(left), convertAsLeaf(right)),
+          extractExprContext(left, right)
+        )
       case SqlGreaterThan(left, right) =>
-        GreaterThanOp(Seq(convertAsLeaf(left), convertAsLeaf(right)))
+        GreaterThanOp(
+          Seq(convertAsLeaf(left), convertAsLeaf(right)),
+          extractExprContext(left, right)
+        )
       case SqlGreaterThanOrEqual(left, right) =>
-        GreaterThanOrEqualOp(Seq(convertAsLeaf(left), convertAsLeaf(right)))
+        GreaterThanOrEqualOp(
+          Seq(convertAsLeaf(left), convertAsLeaf(right)),
+          extractExprContext(left, right)
+        )
 
       // Convert null operations.
       case SqlIsNull(child) =>
@@ -118,7 +133,9 @@ object OpConverter {
           )
         }
         val leafOp = convertAsLeaf(value)
-        list.map(e => EqualOp(Seq(leafOp, convertAsLeaf(e)))) match {
+        list.map(e =>
+          EqualOp(Seq(leafOp, convertAsLeaf(e)), extractExprContext(value, e))
+        ) match {
           case Seq() =>
             throw new IllegalArgumentException("The In predicate must have at least one entry")
           case Seq(child) => child
@@ -131,13 +148,14 @@ object OpConverter {
         val rightOp = convertAsLeaf(right)
         val leftIsNullOp = IsNullOp(Seq(leftOp))
         val rightIsNullOp = IsNullOp(Seq(rightOp))
+        val exprCtx = extractExprContext(left, right)
         // Either both are null, or none is null and they are equal.
         OrOp(Seq(
           AndOp(Seq(leftIsNullOp, rightIsNullOp)),
           AndOp(Seq(
             NotOp(Seq(leftIsNullOp)),
             NotOp(Seq(rightIsNullOp)),
-            EqualOp(Seq(leftOp, rightOp))))
+            EqualOp(Seq(leftOp, rightOp), exprCtx)))
         ))
 
       // Unsupported expressions.
@@ -186,7 +204,9 @@ object OpConverter {
       case SqlBooleanType => OpDataTypes.BoolType
       case SqlIntegerType => OpDataTypes.IntType
       case SqlLongType => OpDataTypes.LongType
-      case SqlStringType => OpDataTypes.StringType
+      // We need to match all string types (with different collations),
+      // and not just the case object which is UTF8_BINARY collated.
+      case _: SqlStringType => OpDataTypes.StringType
       case SqlDateType => OpDataTypes.DateType
       case SqlDoubleType => OpDataTypes.DoubleType
       case SqlFloatType => OpDataTypes.FloatType
@@ -207,4 +227,21 @@ object OpConverter {
       case _ => lit.toString
     }
   }
+
+  // Extracts expression context from two expressions, including collation information
+  // if both are strings with the same collation. This is a generic function that can be
+  // extended to extract other dimensions of context in the future.
+  private def extractExprContext(
+      left: SqlExpression,
+      right: SqlExpression): Option[ExprContext] = {
+    val collationId = CollationExtractor.extractCollationIdentifier(left, right)
+
+    // If we have any context information, return an ExprContext
+    if (collationId.isDefined) {
+      Some(ExprContext(collationIdentifier = collationId))
+    } else {
+      None
+    }
+  }
+
 }

client/src/test/scala-2.12/io/delta/sharing/filters/OpConverterCollationSuite.scala

@@ -0,0 +1,53 @@
+/*
+ * Copyright (2021) The Delta Lake Project Authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.delta.sharing.filters
+
+import org.apache.spark.SparkFunSuite
+import org.apache.spark.sql.catalyst.expressions.{
+  AttributeReference => SqlAttributeReference,
+  EqualTo => SqlEqualTo,
+  Literal => SqlLiteral
+}
+import org.apache.spark.sql.types.{
+  StringType => SqlStringType
+}
+
+class OpConverterCollationSuite extends SparkFunSuite {
+
+  test("UTF8_BINARY collation test") {
+    val defaultStringType = SqlStringType
+    val sqlColumn = SqlAttributeReference("email", defaultStringType)()
+    val sqlLiteral = SqlLiteral("[email protected]")
+    val sqlEq = SqlEqualTo(sqlColumn, sqlLiteral)
+
+    val op = OpConverter.convert(Seq(sqlEq)).get.asInstanceOf[EqualOp]
+    op.validate()
+
+    val columnOp = op.children(0).asInstanceOf[ColumnOp]
+    val literalOp = op.children(1).asInstanceOf[LiteralOp]
+    assert(columnOp.valueType == OpDataTypes.StringType)
+    assert(literalOp.valueType == OpDataTypes.StringType)
+
+    // UTF8_BINARY (default) should work fine on Scala 2.12
+    assert(op.exprCtx.isEmpty)
+  }
+
+  // Note: Collated string types (SqlStringType with collation parameter) don't exist in
+  // Spark 3.5 (Scala 2.12). They were added in Spark 4.0 (Scala 2.13).
+  // Therefore, we cannot test collation behavior in the Scala 2.12 version of this suite.
+  // All collation-specific tests are in the Scala 2.13 version of this suite.
+}