Make lastError optional

Return it only when the result code is an error code.

Signed-off-by: Stephen Celis <stephen@stephencelis.com>

Author: stephencelis

SQLite Tests/DatabaseTests.swift

@@ -396,4 +396,27 @@ class DatabaseTests: SQLiteTestCase {
         XCTAssertEqual(1, db.scalar("SELECT ? = ? COLLATE \"NO DIACRITIC\"", "cafe", "café") as! Int64)
     }
 
+    func test_lastError_withOK_returnsNil() {
+        XCTAssertNil(db.lastError)
+    }
+
+    func test_lastError_withRow_returnsNil() {
+        insertUsers("alice", "betty")
+        db.prepare("SELECT * FROM users").step()
+
+        XCTAssertNil(db.lastError)
+    }
+
+    func test_lastError_withDone_returnsNil() {
+        db.prepare("SELECT * FROM users").step()
+
+        XCTAssertNil(db.lastError)
+    }
+
+    func test_lastError_withError_returnsError() {
+        insertUsers("alice", "alice")
+
+        XCTAssertNotNil(db.lastError)
+    }
+
 }

SQLite/Database.swift

@@ -604,12 +604,15 @@ public final class Database {
     // MARK: - Error Handling
 
     /// Returns the last error produced on this connection.
-    public var lastError: String {
+    public var lastError: String? {
+        if successCodes.contains(sqlite3_errcode(handle)) {
+            return nil
+        }
         return String.fromCString(sqlite3_errmsg(handle))!
     }
 
     internal func try(block: () -> Int32) {
-        perform { if block() != SQLITE_OK { assertionFailure("\(self.lastError)") } }
+        perform { if block() != SQLITE_OK { assertionFailure("\(self.lastError!)") } }
     }
 
     // MARK: - Threading
@@ -644,6 +647,8 @@ extension Database.Location: Printable {
 
 }
 
+internal let successCodes: Set<Int32> = [SQLITE_OK, SQLITE_ROW, SQLITE_DONE]
+
 internal func quote(#literal: String) -> String {
     return quote(literal, "'")
 }

SQLite/Statement.swift

@@ -180,7 +180,7 @@ public final class Statement {
 
     /// :returns: Whether or not a statement has produced an error.
     public var failed: Bool {
-        return !(status == SQLITE_OK || status == SQLITE_ROW || status == SQLITE_DONE)
+        return reason != nil
     }
 
     /// :returns: The reason for an error.
@@ -192,9 +192,9 @@ public final class Statement {
         if failed { return }
         database.perform {
             self.status = block()
-            if self.failed {
-                self.reason = String.fromCString(sqlite3_errmsg(self.database.handle))
-                assert(self.status == SQLITE_CONSTRAINT || self.status == SQLITE_INTERRUPT, "\(self.reason!)")
+            if let error = self.database.lastError {
+                self.reason = error
+                assert(self.status == SQLITE_CONSTRAINT || self.status == SQLITE_INTERRUPT, "\(error)")
             }
         }
     }