[Repo Assist] Fix #1221 — JsonValue.Float always infers as float, not int/int64

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

@@ -16,9 +16,7 @@ open FSharp.Data.Runtime.StructuralInference
 /// here we just need to infer types of primitive JSON values.
 let rec internal inferType unitsOfMeasureProvider inferenceMode cultureInfo parentName json =
     let inline inRangeDecimal lo hi (v: decimal) : bool = (v >= decimal lo) && (v <= decimal hi)
-    let inline inRangeFloat lo hi (v: float) : bool = (v >= float lo) && (v <= float hi)
     let inline isIntegerDecimal (v: decimal) : bool = Math.Round v = v
-    let inline isIntegerFloat (v: float) : bool = Math.Round v = v
 
     let shouldInferNonStringFromValue =
         match inferenceMode with
@@ -49,18 +47,10 @@ let rec internal inferType unitsOfMeasureProvider inferenceMode cultureInfo pare
         ->
         InferedType.Primitive(typeof<int64>, None, false, false)
     | JsonValue.Number _ -> InferedType.Primitive(typeof<decimal>, None, false, false)
-    | JsonValue.Float f when
-        shouldInferNonStringFromValue
-        && inRangeFloat Int32.MinValue Int32.MaxValue f
-        && isIntegerFloat f
-        ->
-        InferedType.Primitive(typeof<int>, None, false, false)
-    | JsonValue.Float f when
-        shouldInferNonStringFromValue
-        && inRangeFloat Int64.MinValue Int64.MaxValue f
-        && isIntegerFloat f
-        ->
-        InferedType.Primitive(typeof<int64>, None, false, false)
+    // JsonValue.Float is produced when the JSON number uses exponential notation (e.g. 0.1e1, 2.34E5)
+    // because TextConversions.AsDecimal uses NumberStyles.Currency which excludes AllowExponent.
+    // Such values are always inferred as float regardless of whether the value happens to be a whole
+    // number, so that e.g. [0.1e1, 0.2e1] is inferred as float[] not int[]. See issue #1221.
     | JsonValue.Float _ -> InferedType.Primitive(typeof<float>, None, false, false)
     // More interesting types
     | JsonValue.Array ar ->

tests/FSharp.Data.DesignTime.Tests/InferenceTests.fs

@@ -89,6 +89,18 @@ let ``Finds common subtype of numeric types (float)``() =
   let actual = JsonInference.inferType unitsOfMeasureProvider inferenceMode culture "" source
   actual |> should equal expected
 
+// Regression test for https://github.com/fsprojects/FSharp.Data/issues/1221
+// Exponential-notation JSON numbers (parsed as JsonValue.Float) should always infer as float,
+// not be promoted to int/int64 when the value happens to be a whole number.
+[<Test>]
+let ``Exponential-notation numbers infer as float not int (issue 1221)``() =
+  // 0.1e1 = 1.0, 0.2e1 = 2.0 — these are stored as JsonValue.Float because
+  // TextConversions.AsDecimal (NumberStyles.Currency) does not allow exponent notation
+  let source = JsonValue.Parse """[ 0.1e1, 0.2e1, 1e3 ]"""
+  let expected = SimpleCollection(InferedType.Primitive(typeof<float>, None, false, false))
+  let actual = JsonInference.inferType unitsOfMeasureProvider inferenceMode culture "" source
+  actual |> should equal expected
+
 [<Test>]
 let ``Infers heterogeneous type of InferedType.Primitives and records``() =
   let source = JsonValue.Parse """[ {"a":0}, 1,2 ]"""

tests/FSharp.Data.Tests/JsonProvider.fs

@@ -816,17 +816,18 @@ let ``ParseList return result list`` () =
   let prov = NumericFields.ParseList(""" [{"a":123}, {"a":987}] """)
   prov |> Array.map (fun v -> v.A) |> Array.sort |> should equal [|123M; 987M|]
 
-// Regression test for https://github.com/fsprojects/FSharp.Data/issues/1230
+// Regression test for https://github.com/fsprojects/FSharp.Data/issues/1230 / #1221
 // When a JSON array sample mixes decimal and exponential-notation numbers, the inferred
-// type is decimal (because the exponential value is stored as JsonValue.Float and inferred
-// as integer, which is then unified with decimal).  At runtime, any exponential-notation
-// number in the actual JSON must also be convertible to decimal.
+// type is float. Exponential-notation numbers (e.g. 2.34567E5) are stored as JsonValue.Float
+// (because TextConversions.AsDecimal uses NumberStyles.Currency which excludes AllowExponent)
+// and are always inferred as float, not promoted to int/int64 as in earlier versions.
+// This means [1, 2.34567E5, 3.14] is inferred as float[].
 type ExponentialDecimalProvider = JsonProvider<"""{"mydata": [1, 2.34567E5, 3.14]}""">
 
 [<Test>]
-let ``Decimal inferred from mixed-notation array can parse exponential notation at runtime`` () =
+let ``Mixed-notation array with exponential numbers is inferred as float`` () =
     let result = ExponentialDecimalProvider.Parse("""{"mydata": [2, 3.45678E5, 9.01]}""")
-    result.Mydata |> should equal [| 2M; 345678M; 9.01M |]
+    result.Mydata |> should equal [| 2.0; 345678.0; 9.01 |]
 
 
 type ServiceResponse = JsonProvider<"""[