[SPARK-45132][SQL] Fix IDENTIFIER for function invocation

sql/api/src/main/antlr4/org/apache/spark/sql/catalyst/parser/SqlBaseParser.g4

@@ -967,7 +967,6 @@ primaryExpression
     | qualifiedName DOT ASTERISK                                                               #star
     | LEFT_PAREN namedExpression (COMMA namedExpression)+ RIGHT_PAREN                          #rowConstructor
     | LEFT_PAREN query RIGHT_PAREN                                                             #subqueryExpression
-    | IDENTIFIER_KW LEFT_PAREN expression RIGHT_PAREN                                          #identifierClause
     | functionName LEFT_PAREN (setQuantifier? argument+=functionArgument
        (COMMA argument+=functionArgument)*)? RIGHT_PAREN
        (FILTER LEFT_PAREN WHERE where=booleanExpression RIGHT_PAREN)?
@@ -1196,6 +1195,7 @@ qualifiedNameList
 
 functionName
     : IDENTIFIER_KW LEFT_PAREN expression RIGHT_PAREN
+    | identFunc=IDENTIFIER_KW   // IDENTIFIER itself is also a valid function name.
     | qualifiedName
     | FILTER
     | LEFT

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/parser/AstBuilder.scala

@@ -2246,13 +2246,6 @@ class AstBuilder extends DataTypeAstBuilder with SQLConfHelper with Logging {
     }
   }
 
-  /**
-   * Create an expression for the IDENTIFIER() clause.
-   */
-  override def visitIdentifierClause(ctx: IdentifierClauseContext): Expression = withOrigin(ctx) {
-    ExpressionWithUnresolvedIdentifier(expression(ctx.expression), UnresolvedAttribute(_))
-  }
-
   /**
    * Create a (windowed) Function expression.
    */
@@ -2274,19 +2267,31 @@ class AstBuilder extends DataTypeAstBuilder with SQLConfHelper with Logging {
     val filter = Option(ctx.where).map(expression(_))
     val ignoreNulls =
       Option(ctx.nullsOption).map(_.getType == SqlBaseParser.IGNORE).getOrElse(false)
-    val funcCtx = ctx.functionName
-    val func = withFuncIdentClause(
-      funcCtx,
-      ident => UnresolvedFunction(ident, arguments, isDistinct, filter, ignoreNulls)
-    )
 
-    // Check if the function is evaluated in a windowed context.
-    ctx.windowSpec match {
-      case spec: WindowRefContext =>
-        UnresolvedWindowExpression(func, visitWindowRef(spec))
-      case spec: WindowDefContext =>
-        WindowExpression(func, visitWindowDef(spec))
-      case _ => func
+    // Is this an IDENTIFIER clause instead of a function call?
+    if (ctx.functionName.identFunc != null &&
+      arguments.length == 1 && // One argument
+      ctx.setQuantifier == null && // No other clause
+      ctx.where == null &&
+      ctx.nullsOption == null &&
+      ctx.windowSpec == null) {
+      ExpressionWithUnresolvedIdentifier(arguments.head, UnresolvedAttribute(_))
+    } else {
+      // It's a function call
+      val funcCtx = ctx.functionName
+      val func = withFuncIdentClause(
+        funcCtx,
+        ident => UnresolvedFunction(ident, arguments, isDistinct, filter, ignoreNulls)
+      )
+
+      // Check if the function is evaluated in a windowed context.
+      ctx.windowSpec match {
+        case spec: WindowRefContext =>
+          UnresolvedWindowExpression(func, visitWindowRef(spec))
+        case spec: WindowDefContext =>
+          WindowExpression(func, visitWindowDef(spec))
+        case _ => func
+      }
     }
   }
 

sql/core/src/test/resources/sql-tests/analyzer-results/identifier-clause.sql.out

@@ -187,10 +187,11 @@ Project [coalesce(cast(null as int), 1) AS coalesce(NULL, 1)#x]
 
 
 -- !query
-SELECT IDENTIFIER('abs')(-1)
+SELECT IDENTIFIER('abs')(c1) FROM VALUES(-1) AS T(c1)
 -- !query analysis
-Project [abs(-1) AS abs(-1)#x]
-+- OneRowRelation
+Project [abs(c1#x) AS abs(c1)#x]
++- SubqueryAlias T
+   +- LocalRelation [c1#x]
 
 
 -- !query
@@ -708,6 +709,27 @@ org.apache.spark.sql.AnalysisException
 }
 
 
+-- !query
+SELECT `IDENTIFIER`('abs')(c1) FROM VALUES(-1) AS T(c1)
+-- !query analysis
+org.apache.spark.sql.AnalysisException
+{
+  "errorClass" : "UNRESOLVED_ROUTINE",
+  "sqlState" : "42883",
+  "messageParameters" : {
+    "routineName" : "`IDENTIFIER`",
+    "searchPath" : "[`system`.`builtin`, `system`.`session`, `spark_catalog`.`default`]"
+  },
+  "queryContext" : [ {
+    "objectType" : "",
+    "objectName" : "",
+    "startIndex" : 8,
+    "stopIndex" : 26,
+    "fragment" : "`IDENTIFIER`('abs')"
+  } ]
+}
+
+
 -- !query
 CREATE TABLE IDENTIFIER(1)(c1 INT)
 -- !query analysis

sql/core/src/test/resources/sql-tests/inputs/identifier-clause.sql

@@ -36,7 +36,7 @@ DROP SCHEMA s;
 
 -- Function reference
 SELECT IDENTIFIER('COAL' || 'ESCE')(NULL, 1);
-SELECT IDENTIFIER('abs')(-1);
+SELECT IDENTIFIER('abs')(c1) FROM VALUES(-1) AS T(c1);
 SELECT * FROM IDENTIFIER('ra' || 'nge')(0, 1);
 
 -- Table DDL
@@ -117,6 +117,7 @@ SELECT IDENTIFIER('') FROM VALUES(1) AS T(``);
 VALUES(IDENTIFIER(CAST(NULL AS STRING)));
 VALUES(IDENTIFIER(1));
 VALUES(IDENTIFIER(SUBSTR('HELLO', 1, RAND() + 1)));
+SELECT `IDENTIFIER`('abs')(c1) FROM VALUES(-1) AS T(c1);
 
 CREATE TABLE IDENTIFIER(1)(c1 INT);
 CREATE TABLE IDENTIFIER('a.b.c')(c1 INT);

sql/core/src/test/resources/sql-tests/results/identifier-clause.sql.out

@@ -205,9 +205,9 @@ struct<coalesce(NULL, 1):int>
 
 
 -- !query
-SELECT IDENTIFIER('abs')(-1)
+SELECT IDENTIFIER('abs')(c1) FROM VALUES(-1) AS T(c1)
 -- !query schema
-struct<abs(-1):int>
+struct<abs(c1):int>
 -- !query output
 1
 
@@ -818,6 +818,29 @@ org.apache.spark.sql.AnalysisException
 }
 
 
+-- !query
+SELECT `IDENTIFIER`('abs')(c1) FROM VALUES(-1) AS T(c1)
+-- !query schema
+struct<>
+-- !query output
+org.apache.spark.sql.AnalysisException
+{
+  "errorClass" : "UNRESOLVED_ROUTINE",
+  "sqlState" : "42883",
+  "messageParameters" : {
+    "routineName" : "`IDENTIFIER`",
+    "searchPath" : "[`system`.`builtin`, `system`.`session`, `spark_catalog`.`default`]"
+  },
+  "queryContext" : [ {
+    "objectType" : "",
+    "objectName" : "",
+    "startIndex" : 8,
+    "stopIndex" : 26,
+    "fragment" : "`IDENTIFIER`('abs')"
+  } ]
+}
+
+
 -- !query
 CREATE TABLE IDENTIFIER(1)(c1 INT)
 -- !query schema