PropertyListEncoder should encode whole-value reals in XML without the .0 suffix for backward compatibility (#718)

Author: iCharlesHu

Sources/FoundationEssentials/PropertyList/XMLPlistEncodingFormat.swift

@@ -1001,7 +1001,14 @@ struct _XMLPlistEncodingFormat : PlistEncodingFormat {
                     return "-infinity"
                 }
             }
-            return val.description
+            // Historically whole-value reals (2.0, -5.0, etc) are
+            // encoded without the `.0` suffix.
+            // JSONEncoder also has the same behavior. See `JSONWriter.swift`
+            var string = val.description
+            if string.hasSuffix(".0") {
+                string.removeLast(2)
+            }
+            return string
         }
 
         mutating func appendDate(_ date: Date) {

Tests/FoundationEssentialsTests/PropertyListEncoderTests.swift

@@ -1055,6 +1055,36 @@ data1 = <7465
         XCTAssertEqual(d.timeIntervalSinceReferenceDate, -63145612800)
     }
 
+    func test_realEncodeRemoveZeroSuffix() throws {
+        // Tests that we encode "whole-value reals" (such as `2.0`, `-5.0`, etc)
+        // **without** the `.0` for backwards compactability
+        let encoder = PropertyListEncoder()
+        encoder.outputFormat = .xml
+        let template = "\(_XMLPlistEncodingFormat.Writer.header)<array>\n\t<real><%EXPECTED%></real>\n</array>\n</plist>\n"
+
+        let wholeFloat: Float = 2.0
+        var data = try encoder.encode([wholeFloat])
+        var str = try XCTUnwrap(String(data: data, encoding: String.Encoding.utf8))
+        var expected = template.replacingOccurrences(
+            of: "<%EXPECTED%>", with: "2")
+        XCTAssertEqual(str, expected)
+
+        let wholeDouble: Double = -5.0
+        data = try encoder.encode([wholeDouble])
+        str = try XCTUnwrap(String(data: data, encoding: String.Encoding.utf8))
+        expected = template.replacingOccurrences(
+            of: "<%EXPECTED%>", with: "-5")
+        XCTAssertEqual(str, expected)
+
+        // Make sure other reals are not affacted
+        let notWholeDouble = 0.5
+        data = try encoder.encode([notWholeDouble])
+        str = try XCTUnwrap(String(data: data, encoding: String.Encoding.utf8))
+        expected = template.replacingOccurrences(
+            of: "<%EXPECTED%>", with: "0.5")
+        XCTAssertEqual(str, expected)
+    }
+
     func test_farFutureDates() throws {
         let date = Date(timeIntervalSince1970: 999999999999.0)