Add support for renaming columns within a table

GRDB/QueryInterface/Schema/TableDefinition.swift

@@ -656,7 +656,13 @@ public final class TableDefinition {
 /// See https://www.sqlite.org/lang_altertable.html
 public final class TableAlteration {
     private let name: String
-    private var addedColumns: [ColumnDefinition] = []
+
+    private enum TableAlterationKind {
+        case add(ColumnDefinition)
+        case rename(old: String, new: String)
+    }
+
+    private var alterations: [TableAlterationKind] = []
 
     init(name: String) {
         self.name = name
@@ -677,27 +683,75 @@ public final class TableAlteration {
     @discardableResult
     public func add(column name: String, _ type: Database.ColumnType? = nil) -> ColumnDefinition {
         let column = ColumnDefinition(name: name, type: type)
-        addedColumns.append(column)
+        alterations.append(.add(column))
         return column
     }
+
+    #if GRDBCUSTOMSQLITE || GRDBCipher
+    /// Renames a column in a table.
+    ///
+    ///     try db.alter(table: "player") { t in
+    ///         t.rename(column: "url", to: "home_url")
+    ///     }
+    ///
+    /// See https://www.sqlite.org/lang_altertable.html
+    ///
+    /// - parameter name: the column name to rename.
+    /// - parameter newName: the new name of the column.
+    public func rename(column name: String, to newName: String) {
+        _rename(column: name, to: newName)
+    }
+    #else
+    /// Renames a column in a table.
+    ///
+    ///     try db.alter(table: "player") { t in
+    ///         t.rename(column: "url", to: "home_url")
+    ///     }
+    ///
+    /// See https://www.sqlite.org/lang_altertable.html
+    ///
+    /// - parameter name: the column name to rename.
+    /// - parameter newName: the new name of the column.
+    @available(iOS 13.0, tvOS 13.0, watchOS 6.0, *)
+    public func rename(column name: String, to newName: String) {
+        _rename(column: name, to: newName)
+    }
+    #endif
+
+    private func _rename(column name: String, to newName: String) {
+        alterations.append(.rename(old: name, new: newName))
+    }
 
     fileprivate func sql(_ db: Database) throws -> String {
         var statements: [String] = []
-
-        for column in addedColumns {
-            var chunks: [String] = []
-            chunks.append("ALTER TABLE")
-            chunks.append(name.quotedDatabaseIdentifier)
-            chunks.append("ADD COLUMN")
-            try chunks.append(column.sql(db, tableName: name, primaryKeyColumns: nil))
-            let statement = chunks.joined(separator: " ")
-            statements.append(statement)
-
-            if let indexDefinition = column.indexDefinition(in: name) {
-                statements.append(indexDefinition.sql())
+
+        for alteration in alterations {
+            switch alteration {
+            case let .add(column):
+                var chunks: [String] = []
+                chunks.append("ALTER TABLE")
+                chunks.append(name.quotedDatabaseIdentifier)
+                chunks.append("ADD COLUMN")
+                try chunks.append(column.sql(db, tableName: name, primaryKeyColumns: nil))
+                let statement = chunks.joined(separator: " ")
+                statements.append(statement)
+
+                if let indexDefinition = column.indexDefinition(in: name) {
+                    statements.append(indexDefinition.sql())
+                }
+            case let .rename(oldName, newName):
+                var chunks: [String] = []
+                chunks.append("ALTER TABLE")
+                chunks.append(name.quotedDatabaseIdentifier)
+                chunks.append("RENAME COLUMN")
+                chunks.append(oldName.quotedDatabaseIdentifier)
+                chunks.append("TO")
+                chunks.append(newName.quotedDatabaseIdentifier)
+                let statement = chunks.joined(separator: " ")
+                statements.append(statement)
             }
         }
-        
+
         return statements.joined(separator: "; ")
     }
 }

Tests/GRDBTests/TableDefinitionTests.swift

@@ -2,6 +2,13 @@ import XCTest
 #if GRDBCUSTOMSQLITE
     import GRDBCustomSQLite
 #else
+    #if GRDBCIPHER
+        import SQLCipher
+    #elseif SWIFT_PACKAGE
+        import CSQLite
+    #else
+        import SQLite3
+    #endif
     import GRDB
 #endif
 
@@ -495,6 +502,34 @@ class TableDefinitionTests: GRDBTestCase {
             assertEqualSQL(sqlQueries[sqlQueries.count - 1], "ALTER TABLE \"test\" ADD COLUMN \"e\"")
         }
     }
+
+    func testAlterTableRenameColumn() throws {
+        guard sqlite3_libversion_number() >= 3025000 else {
+            return
+        }
+        #if !GRDBCUSTOMSQLITE && !GRDBCIPHER
+            guard #available(iOS 13.0, tvOS 13.0, watchOS 6.0, *) else {
+                return
+            }
+        #endif
+        let dbQueue = try makeDatabaseQueue()
+        try dbQueue.inDatabase { db in
+            try db.create(table: "test") { t in
+                t.column("a", .text)
+            }
+
+            sqlQueries.removeAll()
+            try db.alter(table: "test") { t in
+                t.rename(column: "a", to: "b")
+                t.add(column: "c")
+                t.rename(column: "c", to: "d")
+            }
+
+            assertEqualSQL(sqlQueries[sqlQueries.count - 3], "ALTER TABLE \"test\" RENAME COLUMN \"a\" TO \"b\"")
+            assertEqualSQL(sqlQueries[sqlQueries.count - 2], "ALTER TABLE \"test\" ADD COLUMN \"c\"")
+            assertEqualSQL(sqlQueries[sqlQueries.count - 1], "ALTER TABLE \"test\" RENAME COLUMN \"c\" TO \"d\"")
+        }
+    }
 
     func testDropTable() throws {
         let dbQueue = try makeDatabaseQueue()