feat: Implement TSQL specific function call mapper

  - Implements the mapper and tests for transformation rules on TSQL specific
    functions.

TODO: Manually test translations in Databricks workspace

core/src/main/scala/com/databricks/labs/remorph/generators/sql/ExpressionGenerator.scala

@@ -39,11 +39,28 @@ class ExpressionGenerator(val callMapper: ir.CallMapper = new ir.CallMapper())
       case ua: ir.UpdateAction => updateAction(ctx, ua)
       case a: ir.Assign => assign(ctx, a)
       case opts: ir.Options => options(ctx, opts)
+      case i: ir.KnownInterval => interval(ctx, i)
 
       case x => throw TranspileException(s"Unsupported expression: $x")
     }
   }
 
+  private def interval(ctx: GeneratorContext, interval: ir.KnownInterval): String = {
+    val iType = interval.iType match {
+      case ir.YEAR_INTERVAL => "YEAR"
+      case ir.MONTH_INTERVAL => "MONTH"
+      case ir.WEEK_INTERVAL => "WEEK"
+      case ir.DAY_INTERVAL => "DAY"
+      case ir.HOUR_INTERVAL => "HOUR"
+      case ir.MINUTE_INTERVAL => "MINUTE"
+      case ir.SECOND_INTERVAL => "SECOND"
+      case ir.MILLISECOND_INTERVAL => "MILLISECOND"
+      case ir.MICROSECOND_INTERVAL => "MICROSECOND"
+      case ir.NANOSECOND_INTERVAL => "NANOSECOND"
+    }
+    s"INTERVAL ${generate(ctx, interval.value)} ${iType}"
+  }
+
   private def options(ctx: GeneratorContext, opts: ir.Options): String = {
     // First gather the options that are set by expressions
     val exprOptions = opts.expressionOpts.map { case (key, expression) =>
@@ -154,6 +171,9 @@ class ExpressionGenerator(val callMapper: ir.CallMapper = new ir.CallMapper())
     call match {
       case r: RLike => rlike(ctx, r)
       case fn: ir.Fn => s"${fn.prettyName}(${fn.children.map(expression(ctx, _)).mkString(", ")})"
+
+      // Certain functions can be translated to SQL functions directly
+      case e: ir.Expression => expression(ctx, e)
       case _ => throw TranspileException("not implemented")
     }
 

core/src/main/scala/com/databricks/labs/remorph/parsers/intermediate/extensions.scala

@@ -195,3 +195,26 @@ case class WithOptions(input: LogicalPlan, options: Expression) extends UnaryNod
   override def child: LogicalPlan = input
   override def output: Seq[Attribute] = input.output
 }
+
+// Though at least TSQL only needs the time based intervals, we are including all the interval types
+// supported by Spark SQL for completeness and future proofing
+sealed trait KnownIntervalType
+case object NANOSECOND_INTERVAL extends KnownIntervalType
+case object MICROSECOND_INTERVAL extends KnownIntervalType
+case object MILLISECOND_INTERVAL extends KnownIntervalType
+case object SECOND_INTERVAL extends KnownIntervalType
+case object MINUTE_INTERVAL extends KnownIntervalType
+case object HOUR_INTERVAL extends KnownIntervalType
+case object DAY_INTERVAL extends KnownIntervalType
+case object WEEK_INTERVAL extends KnownIntervalType
+case object MONTH_INTERVAL extends KnownIntervalType
+case object YEAR_INTERVAL extends KnownIntervalType
+
+// TSQL - For translation purposes, we cannot use teh standard Catalyst CalendarInterval as it is not
+// meant for code generation and converts everything to microseconds. It is much easier to use an extension
+// to the AST to represent the interval as it is required in TSQL, where we need to know if we were dealing with
+// MONTHS, HOURS, etc.
+case class KnownInterval(value: Expression, iType: KnownIntervalType) extends Expression {
+  override def children: Seq[Expression] = Seq(value)
+  override def dataType: DataType = UnresolvedType
+}

core/src/main/scala/com/databricks/labs/remorph/parsers/tsql/rules/TSqlCallMapper.scala

@@ -0,0 +1,83 @@
+package com.databricks.labs.remorph.parsers.tsql.rules
+
+import com.databricks.labs.remorph.parsers.intermediate._
+
+class TSqlCallMapper extends CallMapper {
+
+  override def convert(call: Fn): Expression = {
+    call match {
+      case CallFunction("DATEADD", args) =>
+        processDateAdd(args)
+      case x: CallFunction => super.convert(x)
+    }
+  }
+
+  private def processDateAdd(args: Seq[Expression]): Expression = {
+
+    // The first argument of the TSQL DATEADD function is the interval type, which is one of way too
+    // many strings and aliases for "day", "month", "year", etc. We need to extract this string and
+    // perform the translation based on what we get
+    val interval = args.head match {
+      case Column(_, id) => id.id.toLowerCase()
+      case _ =>
+        throw new IllegalArgumentException("DATEADD interval type is not valid. Should be 'day', 'month', 'year', etc.")
+    }
+
+    // The value is how many units, type indicated by interval, to add to the date
+    val value = args(1)
+
+    // And this is the thing we are going to add the value to
+    val objectReference = args(2)
+
+    // The interval type names are all over the place in TSQL, some of them having names that
+    // belie their actual function.
+    interval match {
+
+      // Days are all that Spark DATE_ADD operates on, but the arguments are transposed from TSQL
+      // despite the fact that 'dayofyear' implies the number of the day in the year, it is in fact the
+      // same as day, as is `weekday`
+      case "day" | "dayofyear" | "dd" | "d" | "dy" | "y" | "weekday" | "dw" | "w" =>
+        DateAdd(objectReference, value)
+
+      // Months are handled by the MonthAdd function, with arguments transposed from TSQL
+      case "month" | "mm" | "m" => AddMonths(objectReference, value)
+
+      // There is no equivalent to quarter in Spark, so we have to use the MonthAdd function and multiply by 3
+      case "quarter" | "qq" | "q" => AddMonths(objectReference, Multiply(value, Literal(3)))
+
+      // There is no equivalent to year in Spark SQL, but we use months and multiply by 12
+      case "year" | "yyyy" | "yy" => AddMonths(objectReference, Multiply(value, Literal(12)))
+
+      // Weeks are not supported in Spark SQL, but we can multiply by 7 to get the same effect with DATE_ADD
+      case "week" | "wk" | "ww" => DateAdd(objectReference, Multiply(value, Literal(7)))
+
+      // Hours are not supported in Spark SQL, but we can use the number of hours to create an INTERVAL
+      // and add it to the object reference
+      case "hour" | "hh" => Add(objectReference, KnownInterval(value, HOUR_INTERVAL))
+
+      // Minutes are not supported in Spark SQL, but we can use the number of minutes to create an INTERVAL
+      // and add it to the object reference
+      case "minute" | "mi" | "n" => Add(objectReference, KnownInterval(value, MINUTE_INTERVAL))
+
+      // Seconds are not supported in Spark SQL, but we can use the number of seconds to create an INTERVAL
+      // and add it to the object reference
+      case "second" | "ss" | "s" => Add(objectReference, KnownInterval(value, SECOND_INTERVAL))
+
+      // Milliseconds are not supported in Spark SQL, but we can use the number of milliseconds to create an INTERVAL
+      // and add it to the object reference
+      case "millisecond" | "ms" => Add(objectReference, KnownInterval(value, MILLISECOND_INTERVAL))
+
+      // Microseconds are not supported in Spark SQL, but we can use the number of microseconds to create an INTERVAL
+      // and add it to the object reference
+      case "microsecond" | "mcs" => Add(objectReference, KnownInterval(value, MICROSECOND_INTERVAL))
+
+      // Nanoseconds are not supported in Spark SQL, but we can use the number of nanoseconds to create an INTERVAL
+      // and add it to the object reference
+      case "nanosecond" | "ns" => Add(objectReference, KnownInterval(value, NANOSECOND_INTERVAL))
+
+      case _ =>
+        throw new IllegalArgumentException(
+          s"DATEADD interval type '${interval}' is not valid. Should be 'day', 'month', 'year', etc.")
+    }
+  }
+}

core/src/main/scala/com/databricks/labs/remorph/transpilers/TSqlToDatabricksTranspiler.scala

@@ -2,15 +2,15 @@ package com.databricks.labs.remorph.transpilers
 
 import com.databricks.labs.remorph.generators.GeneratorContext
 import com.databricks.labs.remorph.generators.sql.{ExpressionGenerator, LogicalPlanGenerator}
-import com.databricks.labs.remorph.parsers.tsql.rules.{PullLimitUpwards, TopPercentToLimitSubquery, TrapInsertDefaultsAction}
+import com.databricks.labs.remorph.parsers.tsql.rules.{PullLimitUpwards, TSqlCallMapper, TopPercentToLimitSubquery, TrapInsertDefaultsAction}
 import com.databricks.labs.remorph.parsers.tsql.{TSqlAstBuilder, TSqlErrorStrategy, TSqlLexer, TSqlParser}
 import com.databricks.labs.remorph.parsers.{ProductionErrorCollector, intermediate => ir}
 import org.antlr.v4.runtime.{CharStreams, CommonTokenStream}
 
 class TSqlToDatabricksTranspiler extends BaseTranspiler {
   private val astBuilder = new TSqlAstBuilder()
   private val optimizer = ir.Rules(PullLimitUpwards, new TopPercentToLimitSubquery, TrapInsertDefaultsAction)
-  private val generator = new LogicalPlanGenerator(new ExpressionGenerator())
+  private val generator = new LogicalPlanGenerator(new ExpressionGenerator(new TSqlCallMapper()))
 
   override def parse(input: String): ir.LogicalPlan = {
     val inputString = CharStreams.fromString(input)

core/src/test/scala/com/databricks/labs/remorph/parsers/tsql/TSqlExpressionGeneratorTest.scala

@@ -0,0 +1,96 @@
+package com.databricks.labs.remorph.parsers.tsql
+
+import com.databricks.labs.remorph.generators.sql.{ExpressionGenerator, GeneratorTestCommon}
+import com.databricks.labs.remorph.parsers.intermediate.IRHelpers
+import com.databricks.labs.remorph.parsers.tsql.rules.TSqlCallMapper
+import com.databricks.labs.remorph.parsers.{intermediate => ir}
+import org.scalatest.wordspec.AnyWordSpec
+import org.scalatestplus.mockito.MockitoSugar
+
+// Only add tests here that require the TSqlCallMapper, or in the future any other transformer/rule
+// that is specific to T-SQL. Otherwise they belong in ExpressionGeneratorTest.
+
+class TSqlExpressionGeneratorTest
+    extends AnyWordSpec
+    with GeneratorTestCommon[ir.Expression]
+    with MockitoSugar
+    with IRHelpers {
+
+  override protected val generator = new ExpressionGenerator(new TSqlCallMapper)
+
+  "DATEADD" should {
+    "transpile to DATE_ADD" in {
+      ir.CallFunction(
+        "DATEADD",
+        Seq(simplyNamedColumn("day"), ir.Literal(42.toShort), simplyNamedColumn("col1"))) generates "DATE_ADD(col1, 42)"
+
+      ir.CallFunction(
+        "DATEADD",
+        Seq(
+          simplyNamedColumn("week"),
+          ir.Literal(42.toShort),
+          simplyNamedColumn("col1"))) generates "DATE_ADD(col1, 42 * 7)"
+    }
+
+    "transpile to ADD_MONTHS" in {
+      ir.CallFunction(
+        "DATEADD",
+        Seq(
+          simplyNamedColumn("Month"),
+          ir.Literal(42.toShort),
+          simplyNamedColumn("col1"))) generates "ADD_MONTHS(col1, 42)"
+
+      ir.CallFunction(
+        "DATEADD",
+        Seq(
+          simplyNamedColumn("qq"),
+          ir.Literal(42.toShort),
+          simplyNamedColumn("col1"))) generates "ADD_MONTHS(col1, 42 * 3)"
+    }
+
+    "transpile to INTERVAL" in {
+      ir.CallFunction(
+        "DATEADD",
+        Seq(
+          simplyNamedColumn("hour"),
+          ir.Literal(42.toShort),
+          simplyNamedColumn("col1"))) generates "col1 + INTERVAL 42 HOUR"
+
+      ir.CallFunction(
+        "DATEADD",
+        Seq(
+          simplyNamedColumn("minute"),
+          ir.Literal(42.toShort),
+          simplyNamedColumn("col1"))) generates "col1 + INTERVAL 42 MINUTE"
+
+      ir.CallFunction(
+        "DATEADD",
+        Seq(
+          simplyNamedColumn("second"),
+          ir.Literal(42.toShort),
+          simplyNamedColumn("col1"))) generates "col1 + INTERVAL 42 SECOND"
+
+      ir.CallFunction(
+        "DATEADD",
+        Seq(
+          simplyNamedColumn("millisecond"),
+          ir.Literal(42.toShort),
+          simplyNamedColumn("col1"))) generates "col1 + INTERVAL 42 MILLISECOND"
+
+      ir.CallFunction(
+        "DATEADD",
+        Seq(
+          simplyNamedColumn("mcs"),
+          ir.Literal(42.toShort),
+          simplyNamedColumn("col1"))) generates "col1 + INTERVAL 42 MICROSECOND"
+
+      ir.CallFunction(
+        "DATEADD",
+        Seq(
+          simplyNamedColumn("ns"),
+          ir.Literal(42.toShort),
+          simplyNamedColumn("col1"))) generates "col1 + INTERVAL 42 NANOSECOND"
+    }
+  }
+
+}

tests/resources/functional/tsql/functions/test_dateadd_hour_1.sql

@@ -7,4 +7,4 @@
 SELECT DATEADD(hour, 7, col1) AS add_hours_col1 FROM tabl;
 
 -- databricks sql:
-SELECT (col1 + INTERVAL 7 HOUR) AS add_hours_col1 FROM tabl;
+SELECT col1 + INTERVAL 7 HOUR AS add_hours_col1 FROM tabl;

tests/resources/functional/tsql/functions/test_dateadd_hour_2.sql

@@ -7,4 +7,4 @@
 SELECT DATEADD(hh, 7, col1) AS add_hours_col1 FROM tabl;
 
 -- databricks sql:
-SELECT (col1 + INTERVAL 7 HOUR) AS add_hours_col1 FROM tabl;
+SELECT col1 + INTERVAL 7 HOUR AS add_hours_col1 FROM tabl;

tests/resources/functional/tsql/functions/test_dateadd_microsecond_1.sql

@@ -7,4 +7,4 @@
 SELECT DATEADD(MICROSECOND, 7, col1) AS add_microsecond_col1 FROM tabl;
 
 -- databricks sql:
-SELECT (col1 + INTERVAL 7 MICROSECOND) AS add_microsecond_col1 FROM tabl;
+SELECT col1 + INTERVAL 7 MICROSECOND AS add_microsecond_col1 FROM tabl;

tests/resources/functional/tsql/functions/test_dateadd_microsecond_2.sql

@@ -7,4 +7,4 @@
 SELECT DATEADD(mcs, 7, col1) AS add_microsecond_col1 FROM tabl;
 
 -- databricks sql:
-SELECT (col1 + INTERVAL 7 MICROSECOND) AS add_microsecond_col1 FROM tabl;
+SELECT col1 + INTERVAL 7 MICROSECOND) AS add_microsecond_col1 FROM tabl;

tests/resources/functional/tsql/functions/test_dateadd_millisecond_1.sql

@@ -7,4 +7,4 @@
 SELECT DATEADD(millisecond, 7, col1) AS add_minutes_col1 FROM tabl;
 
 -- databricks sql:
-SELECT (col1 + INTERVAL 7 MILLISECOND) AS add_minutes_col1 FROM tabl;
+SELECT col1 + INTERVAL 7 MILLISECOND) AS add_minutes_col1 FROM tabl;

tests/resources/functional/tsql/functions/test_dateadd_millisecond_2.sql

@@ -7,4 +7,4 @@
 SELECT DATEADD(ms, 7, col1) AS add_milliseconds_col1 FROM tabl;
 
 -- databricks sql:
-SELECT (col1 + INTERVAL 7 MILLISECOND) AS add_milliseconds_col1 FROM tabl;
+SELECT col1 + INTERVAL 7 MILLISECOND) AS add_milliseconds_col1 FROM tabl;

tests/resources/functional/tsql/functions/test_dateadd_minute_1.sql

@@ -7,4 +7,4 @@
 SELECT DATEADD(minute, 7, col1) AS add_minutes_col1 FROM tabl;
 
 -- databricks sql:
-SELECT (col1 + INTERVAL 7 MINUTE) AS add_minutes_col1 FROM tabl;
+SELECT col1 + INTERVAL 7 MINUTE AS add_minutes_col1 FROM tabl;

tests/resources/functional/tsql/functions/test_dateadd_minute_2.sql

@@ -7,4 +7,4 @@
 SELECT DATEADD(mi, 7, col1) AS add_minutes_col1 FROM tabl;
 
 -- databricks sql:
-SELECT (col1 + INTERVAL 7 MINUTE) AS add_minutes_col1 FROM tabl;
+SELECT col1 + INTERVAL 7 MINUTE) AS add_minutes_col1 FROM tabl;

tests/resources/functional/tsql/functions/test_dateadd_minute_3.sql

@@ -7,4 +7,4 @@
 SELECT DATEADD(n, 7, col1) AS add_minutes_col1 FROM tabl;
 
 -- databricks sql:
-SELECT (col1 + INTERVAL 7 MINUTE) AS add_minutes_col1 FROM tabl;
+SELECT col1 + INTERVAL 7 MINUTE) AS add_minutes_col1 FROM tabl;

tests/resources/functional/tsql/functions/test_dateadd_nanosecond_1.sql

@@ -7,4 +7,4 @@
 SELECT DATEADD(NANOSECOND, 7, col1) AS add_nanoseconds_col1 FROM tabl;
 
 -- databricks sql:
-SELECT (col1 + INTERVAL 7 NANOSECOND) AS add_nanoseconds_col1 FROM tabl;
+SELECT col1 + INTERVAL 7 NANOSECOND) AS add_nanoseconds_col1 FROM tabl;

tests/resources/functional/tsql/functions/test_dateadd_nanosecond_2.sql

@@ -7,4 +7,4 @@
 SELECT DATEADD(NS, 7, col1) AS add_minutes_col1 FROM tabl;
 
 -- databricks sql:
-SELECT (col1 + INTERVAL 7 NANOSECOND) AS add_minutes_col1 FROM tabl;
+SELECT col1 + INTERVAL 7 NANOSECOND) AS add_minutes_col1 FROM tabl;

tests/resources/functional/tsql/functions/test_dateadd_second_1.sql

@@ -7,4 +7,4 @@
 SELECT DATEADD(second, 7, col1) AS add_seconds_col1 FROM tabl;
 
 -- databricks sql:
-SELECT (col1 + INTERVAL 7 SECOND) AS add_seconds_col1 FROM tabl;
+SELECT col1 + INTERVAL 7 SECOND) AS add_seconds_col1 FROM tabl;

tests/resources/functional/tsql/functions/test_dateadd_second_2.sql

@@ -7,4 +7,4 @@
 SELECT DATEADD(ss, 7, col1) AS add_seconds_col1 FROM tabl;
 
 -- databricks sql:
-SELECT (col1 + INTERVAL 7 SECOND) AS add_seconds_col1 FROM tabl;
+SELECT col1 + INTERVAL 7 SECOND) AS add_seconds_col1 FROM tabl;

tests/resources/functional/tsql/functions/test_dateadd_second_3.sql

@@ -7,4 +7,4 @@
 SELECT DATEADD(s, 7, col1) AS add_minutes_col1 FROM tabl;
 
 -- databricks sql:
-SELECT (col1 + INTERVAL 7 SECOND) AS add_minutes_col1 FROM tabl;
+SELECT col1 + INTERVAL 7 SECOND) AS add_minutes_col1 FROM tabl;