[SPARK-50990][SQL] Refactor UpCast resolution out of the Analyzer

### What changes were proposed in this pull request?

Refactor `UpCast` resolution out of the `Analyzer`.

### Why are the changes needed?

To reuse this code in single-pass `Resolver`.

### Does this PR introduce _any_ user-facing change?

No, just a refactoring.

### How was this patch tested?

Existing tests.

### Was this patch authored or co-authored using generative AI tooling?

Copilot.nvim.

Closes #49669 from vladimirg-db/vladimirg-db/refactor-upcast-resolution-out.

Authored-by: Vladimir Golubev <[email protected]>
Signed-off-by: Max Gekk <[email protected]>

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala

@@ -3727,45 +3727,16 @@ class Analyzer(override val catalogManager: CatalogManager) extends RuleExecutor
    * Replace the [[UpCast]] expression by [[Cast]], and throw exceptions if the cast may truncate.
    */
   object ResolveUpCast extends Rule[LogicalPlan] {
-    private def fail(from: Expression, to: DataType, walkedTypePath: Seq[String]) = {
-      val fromStr = from match {
-        case l: LambdaVariable => "array element"
-        case e => e.sql
-      }
-      throw QueryCompilationErrors.upCastFailureError(fromStr, from, to, walkedTypePath)
-    }
-
     def apply(plan: LogicalPlan): LogicalPlan = plan.resolveOperatorsUpWithPruning(
       _.containsPattern(UP_CAST), ruleId) {
       case p if !p.childrenResolved => p
       case p if p.resolved => p
 
       case p => p.transformExpressionsWithPruning(_.containsPattern(UP_CAST), ruleId) {
-        case u @ UpCast(child, _, _) if !child.resolved => u
-
-        case UpCast(_, target, _) if target != DecimalType && !target.isInstanceOf[DataType] =>
-          throw SparkException.internalError(
-            s"UpCast only supports DecimalType as AbstractDataType yet, but got: $target")
-
-        case UpCast(child, target, walkedTypePath) if target == DecimalType
-          && child.dataType.isInstanceOf[DecimalType] =>
-          assert(walkedTypePath.nonEmpty,
-            "object DecimalType should only be used inside ExpressionEncoder")
-
-          // SPARK-31750: if we want to upcast to the general decimal type, and the `child` is
-          // already decimal type, we can remove the `Upcast` and accept any precision/scale.
-          // This can happen for cases like `spark.read.parquet("/tmp/file").as[BigDecimal]`.
-          child
-
-        case UpCast(child, target: AtomicType, _)
-            if conf.getConf(SQLConf.LEGACY_LOOSE_UPCAST) &&
-              child.dataType == StringType =>
-          Cast(child, target.asNullable)
-
-        case u @ UpCast(child, _, walkedTypePath) if !Cast.canUpCast(child.dataType, u.dataType) =>
-          fail(child, u.dataType, walkedTypePath)
-
-        case u @ UpCast(child, _, _) => Cast(child, u.dataType)
+        case unresolvedUpCast @ UpCast(child, _, _) if !child.resolved =>
+          unresolvedUpCast
+        case unresolvedUpCast: UpCast =>
+          UpCastResolution.resolve(unresolvedUpCast)
       }
     }
   }

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/UpCastResolution.scala

@@ -0,0 +1,69 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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 org.apache.spark.sql.catalyst.analysis
+
+import org.apache.spark.SparkException
+import org.apache.spark.sql.catalyst.SQLConfHelper
+import org.apache.spark.sql.catalyst.expressions.{Cast, Expression, UpCast}
+import org.apache.spark.sql.catalyst.expressions.objects.LambdaVariable
+import org.apache.spark.sql.errors.QueryCompilationErrors
+import org.apache.spark.sql.internal.SQLConf
+import org.apache.spark.sql.types.{AtomicType, DataType, DecimalType, StringType}
+
+object UpCastResolution extends SQLConfHelper {
+  def resolve(unresolvedUpCast: UpCast): Expression = unresolvedUpCast match {
+    case UpCast(_, target, _) if target != DecimalType && !target.isInstanceOf[DataType] =>
+      throw SparkException.internalError(
+        s"UpCast only supports DecimalType as AbstractDataType yet, but got: $target"
+      )
+
+    case UpCast(child, target, walkedTypePath)
+        if target == DecimalType
+        && child.dataType.isInstanceOf[DecimalType] =>
+      assert(
+        walkedTypePath.nonEmpty,
+        "object DecimalType should only be used inside ExpressionEncoder"
+      )
+
+      // SPARK-31750: if we want to upcast to the general decimal type, and the `child` is
+      // already decimal type, we can remove the `Upcast` and accept any precision/scale.
+      // This can happen for cases like `spark.read.parquet("/tmp/file").as[BigDecimal]`.
+      child
+
+    case UpCast(child, target: AtomicType, _)
+        if conf.getConf(SQLConf.LEGACY_LOOSE_UPCAST) &&
+        child.dataType == StringType =>
+      Cast(child, target.asNullable)
+
+    case unresolvedUpCast @ UpCast(child, _, walkedTypePath)
+        if !Cast.canUpCast(child.dataType, unresolvedUpCast.dataType) =>
+      fail(child, unresolvedUpCast.dataType, walkedTypePath)
+
+    case unresolvedUpCast @ UpCast(child, _, _) =>
+      Cast(child, unresolvedUpCast.dataType)
+  }
+
+  private def fail(from: Expression, to: DataType, walkedTypePath: Seq[String]) = {
+    val fromStr = from match {
+      case l: LambdaVariable => "array element"
+      case e => e.sql
+    }
+
+    throw QueryCompilationErrors.upCastFailureError(fromStr, from, to, walkedTypePath)
+  }
+}