SWIFT-154: Int should encode as Int32 or Int64 as needed

Sources/MongoSwift/BSON/BsonValue.swift

@@ -377,19 +377,18 @@ extension Double: BsonValue {
     }
 }
 
-/// An extension of `Int` to represent the BSON Int32 type.
-/// While the bitwidth of Int is machine-dependent, we assume for simplicity
-/// that it is always 32 bits. Use `Int64` if 64 bits are needed.
+/// An extension of `Int` to represent the BSON Int32 or Int64 type.
+/// The `Int` will be encoded as an Int32 if possible, or an Int64 if necessary.
 extension Int: BsonValue {
     public var bsonType: BsonType { return .int32 }
     public func encode(to data: UnsafeMutablePointer<bson_t>, forKey key: String) throws {
-        guard let int32 = Int32(exactly: self) else {
-            throw MongoError.bsonEncodeError(message:
-                "`Int` value \(self) does not fit in an `Int32`. Use an `Int64` instead")
+        if let int32 = Int32(exactly: self) {
+            return try int32.encode(to: data, forKey: key)
         }
-        if !bson_append_int32(data, key, Int32(key.count), int32) {
-            throw bsonEncodeError(value: self, forKey: key)
+        if let int64 = Int64(exactly: self) {
+            return try int64.encode(to: data, forKey: key)
         }
+        throw MongoError.bsonEncodeError(message: "`Int` value \(self) could not be encoded as `Int32` or `Int64`")
     }
 
     public static func from(iter: inout bson_iter_t) -> BsonValue {

Tests/MongoSwiftTests/DocumentTests.swift

@@ -36,7 +36,7 @@ final class DocumentTests: XCTestCase {
             ("testEquatable", testEquatable),
             ("testRawBSON", testRawBSON),
             ("testValueBehavior", testValueBehavior),
-            ("testInvalidInt", testInvalidInt),
+            ("testIntEncodesAsInt32OrInt64", testIntEncodesAsInt32OrInt64),
             ("testBSONCorpus", testBSONCorpus),
             ("testMerge", testMerge)
         ]
@@ -198,11 +198,32 @@ final class DocumentTests: XCTestCase {
         XCTAssertNotEqual(doc1, doc2)
     }
 
-    func testInvalidInt() {
-        let doc1 = Document()
-        let v = Int(Int32.max) + 1
-        expect(try v.encode(to: doc1.data, forKey: "x")).to(throwError())
+    func testIntEncodesAsInt32OrInt64() {
+        /* Skip this test on 32-bit platforms. Use MemoryLayout instead of
+         * Int.bitWidth to avoid a compiler warning.
+         * See: https://forums.swift.org/t/how-can-i-condition-on-the-size-of-int/9080/4 */
+        if MemoryLayout<Int>.size == 4 {
+            return
+        }
+
+        let int32min_sub1 = Int64(Int32.min) - Int64(1)
+        let int32max_add1 = Int64(Int32.max) + Int64(1)
+
+        var doc: Document = [
+            "int32min": Int(Int32.min),
+            "int32max": Int(Int32.max),
+            "int32min-1": Int(int32min_sub1),
+            "int32max+1": Int(int32max_add1),
+            "int64min": Int(Int64.min),
+            "int64max": Int(Int64.max)
+        ]
 
+        expect(doc["int32min"] as? Int).to(equal(Int(Int32.min)))
+        expect(doc["int32max"] as? Int).to(equal(Int(Int32.max)))
+        expect(doc["int32min-1"] as? Int64).to(equal(int32min_sub1))
+        expect(doc["int32max+1"] as? Int64).to(equal(int32max_add1))
+        expect(doc["int64min"] as? Int64).to(equal(Int64.min))
+        expect(doc["int64max"] as? Int64).to(equal(Int64.max))
     }
 
     // swiftlint:disable:next cyclomatic_complexity