Merge pull request #1606 from fsprojects/repo-assist/fix-json-float-serialization-1356-923b690f238a89a3

[Repo Assist] Fix JsonValue.Float serialization: append '.0' for whole-number floats

Author: dsyme

src/FSharp.Data.Json.Core/JsonValue.fs

@@ -86,7 +86,13 @@ type JsonValue =
             | Boolean b -> w.Write(if b then "true" else "false")
             | Number number -> w.Write number
             | Float v when Double.IsInfinity v || Double.IsNaN v -> w.Write "null"
-            | Float number -> w.Write number
+            | Float number ->
+                let s = number.ToString("R", CultureInfo.InvariantCulture)
+                w.Write s
+                // Ensure the output looks like a float (has a decimal point or exponent),
+                // so that round-tripping through JSON preserves the Float type.
+                if s.IndexOfAny([| '.'; 'E'; 'e' |]) = -1 then
+                    w.Write ".0"
             | String s ->
                 w.Write "\""
                 JsonValue.JsonStringEncodeTo w s

tests/FSharp.Data.Core.Tests/JsonValue.fs

@@ -293,6 +293,20 @@ let ``Serializes special float value as null`` v =
     let json = JsonValue.Float v
     json.ToString(JsonSaveOptions.DisableFormatting) |> should equal "null"
 
+[<Test>]
+let ``Float value 100.0 serializes with decimal point`` () =
+    // Regression test for https://github.com/fsprojects/FSharp.Data/issues/1356
+    // JsonValue.Float(100.0) should serialize as "100.0", not "100"
+    JsonValue.Float(100.0).ToString(JsonSaveOptions.DisableFormatting) |> should equal "100.0"
+
+[<Test>]
+let ``Float value with fractional part serializes correctly`` () =
+    JsonValue.Float(100.5).ToString(JsonSaveOptions.DisableFormatting) |> should equal "100.5"
+
+[<Test>]
+let ``Float value in scientific notation serializes correctly`` () =
+    JsonValue.Float(1e20).ToString(JsonSaveOptions.DisableFormatting) |> should equal "1E+20"
+
 let normalize (str:string) =
   str.Replace("\r\n", "\n")
      .Replace("\r", "\n")