refactor!: Column type safety (#2027)

This commit adds type safety in the overridden functions of the interface `IColumnType`, which will reduce the number of checks in those functions. This change propagates to other classes and interfaces that extend and use `IColumnType`.

The following are affected:

1. Custom column types
2. Custom functions extending `CustomFunction`
3. Custom operators extending `CustomOperator`
4. Custom expressions extending `ExpressionWithColumnType`
5. Usages of `CurrentTimestamp` function (class to object)

exposed-core/src/main/kotlin/org/jetbrains/exposed/dao/id/EntityID.kt

@@ -18,16 +18,17 @@ open class EntityID<T : Comparable<T>> protected constructor(val table: IdTable<
     var _value: Any? = id
 
     /** The identity value of type [T] wrapped by this [EntityID] instance. */
-    val value: T get() {
-        if (_value == null) {
-            invokeOnNoValue()
-            check(_value != null) { "Entity must be inserted" }
+    val value: T
+        get() {
+            if (_value == null) {
+                invokeOnNoValue()
+                check(_value != null) { "Entity must be inserted" }
+            }
+
+            @Suppress("UNCHECKED_CAST")
+            return _value!! as T
         }
 
-        @Suppress("UNCHECKED_CAST")
-        return _value!! as T
-    }
-
     /** Performs steps when the internal [_value] is accessed without first being initialized. */
     protected open fun invokeOnNoValue() {}
 

exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/Alias.kt

@@ -8,7 +8,7 @@ class Alias<out T : Table>(val delegate: T, val alias: String) : Table() {
     /** The table name along with its [alias]. */
     val tableNameWithAlias: String = "${delegate.tableName} $alias"
 
-    private fun <T : Any?> Column<T>.clone() = Column<T>(this@Alias, name, columnType)
+    private fun <T> Column<T>.clone() = Column<T>(this@Alias, name, columnType)
 
     /**
      * Returns the original column from the [delegate] table, or `null` if the [column] is not associated
@@ -111,7 +111,7 @@ class QueryAlias(val query: AbstractQuery<*>, val alias: String) : ColumnSet() {
 
     override infix fun crossJoin(otherTable: ColumnSet): Join = Join(this, otherTable, JoinType.CROSS)
 
-    private fun <T : Any?> Column<T>.clone() = Column<T>(table.alias(alias), name, columnType)
+    private fun <T> Column<T>.clone() = Column<T>(table.alias(alias), name, columnType)
 }
 
 /**

exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/Column.kt

@@ -21,7 +21,7 @@ class Column<T>(
     /** Name of the column. */
     val name: String,
     /** Data type of the column. */
-    override val columnType: IColumnType
+    override val columnType: IColumnType<T & Any>
 ) : ExpressionWithColumnType<T>(), DdlAware, Comparable<Column<*>> {
     /** The foreign key constraint on this column, or `null` if the column is not referencing. */
     var foreignKey: ForeignKeyConstraint? = null
@@ -63,12 +63,13 @@ class Column<T>(
     private val isLastColumnInPK: Boolean
         get() = this == table.primaryKey?.columns?.last()
 
-    internal val isPrimaryConstraintWillBeDefined: Boolean get() = when {
-        currentDialect is SQLiteDialect && columnType.isAutoInc -> false
-        table.isCustomPKNameDefined() -> isLastColumnInPK
-        isOneColumnPK() -> false
-        else -> isLastColumnInPK
-    }
+    internal val isPrimaryConstraintWillBeDefined: Boolean
+        get() = when {
+            currentDialect is SQLiteDialect && columnType.isAutoInc -> false
+            table.isCustomPKNameDefined() -> isLastColumnInPK
+            isOneColumnPK() -> false
+            else -> isLastColumnInPK
+        }
 
     override fun createStatement(): List<String> {
         val alterTablePrefix = "ALTER TABLE ${TransactionManager.current().identity(table)} ADD"
@@ -154,7 +155,7 @@ class Column<T>(
     /**
      * Returns a copy of this column, but with the given column type.
      */
-    fun withColumnType(columnType: IColumnType) = Column<T>(
+    fun withColumnType(columnType: IColumnType<T & Any>) = Column<T>(
         table = this.table,
         name = this.name,
         columnType = columnType