[Repo Assist] Add DateOnly/TimeOnly inference support (closes #1461) (#1609)

* Add DateOnly/TimeOnly inference support (closes #1461)

- Multi-target library projects to netstandard2.0;net8.0 to enable
  NET6_0_OR_GREATER conditional compilation
- Add AsDateOnly/AsTimeOnly to TextConversions with guards against
  datetime strings being accepted by DateOnly/TimeOnly parsers
- Add DateOnly to automatic type inference (matchValue); TimeOnly is
  NOT auto-inferred (ambiguous with TimeSpan) but available via explicit
  schema annotation (dateonly?/timeonly? in CSV headers)
- Add DateOnly as subtype of DateTime in conversionTable; columns with
  mixed DateOnly+DateTime values unify to DateTime
- Add ConvertDateOnly/ConvertTimeOnly to TextRuntime and JsonRuntime
- Add DateOnly/TimeOnly cases to StructuralTypes, ConversionsGenerator,
  JsonConversionsGenerator, JsonConversions, JsonRuntime, CsvInference
- Update tests for new DateOnly inference behaviour

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Initial plan

* Update documentation and samples for DateOnly/TimeOnly inference

Co-authored-by: dsyme <7204669+dsyme@users.noreply.github.com>

* Initial plan

* Fix DateOnly design-time type resolution error for netstandard2.0 targets

Co-authored-by: dsyme <7204669+dsyme@users.noreply.github.com>

* apply fantomas formatting

* make optional

* fix tests

* fix tests

* fix tests

---------

Co-authored-by: Repo Assist <repo-assist@github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: dsyme <7204669+dsyme@users.noreply.github.com>
Co-authored-by: Don Syme <dsyme@users.noreply.github.com>
Co-authored-by: Don Syme <dsyme@github.com>

Author: 5 people

docs/library/CsvProvider.fsx

@@ -89,7 +89,9 @@ The following sample calls the `Load` method with an URL that points to a live C
 let msft = Stocks.Load(__SOURCE_DIRECTORY__ + "/../data/MSFT.csv").Cache()
 
 // Look at the most recent row. Note the 'Date' property
-// is of type 'DateTime' and 'Open' has a type 'decimal'
+// is of type 'DateTime' by default. Set PreferDateOnly = true
+// to use 'DateOnly' on .NET 6+
+// and 'Open' has a type 'decimal'
 let firstRow = msft.Rows |> Seq.head
 let lastDate = firstRow.Date
 let lastOpen = firstRow.Open
@@ -107,8 +109,9 @@ collection of rows. We iterate over the rows using a `for` loop. As you can see
 to the columns in the CSV file.
 
 As you can see, the type provider also infers types of individual rows. The `Date`
-property is inferred to be a `DateTime` (because the values in the sample file can all
-be parsed as dates) while HLOC prices are inferred as `decimal`.
+property is inferred as `DateTime` by default. When you set `PreferDateOnly = true`
+on .NET 6 and later, date-only strings (without a time component) are inferred as `DateOnly`.
+HLOC prices are inferred as `decimal`.
 
 ## Using units of measure
 
@@ -269,8 +272,12 @@ it by specifying the `InferRows` static parameter of `CsvProvider`. If you speci
 Columns with only `0`, `1`, `Yes`, `No`, `True`, or `False` will be set to `bool`. Columns with numerical values
 will be set to either `int`, `int64`, `decimal`, or `float`, in that order of preference.
 
-If a value is missing in any row, by default the CSV type provider will infer a nullable (for `int` and `int64`) or an optional
-(for `bool`, `DateTime` and `Guid`). When a `decimal` would be inferred but there are missing values, we will infer a
+On .NET 6 and later, when you set `PreferDateOnly = true`, columns whose values are all date-only strings (without a time component, e.g. `2023-01-15`)
+are inferred as `DateOnly`. Time-only strings are inferred as `TimeOnly`. If a column mixes `DateOnly` and `DateTime` values, it is unified to `DateTime`.
+By default (`PreferDateOnly = false`), all date values are inferred as `DateTime` for backward compatibility.
+
+If a value is missing in any row, by default the CSV type provider will infer a nullable (for `int`, `int64`, and `DateOnly`) or an optional
+(for `bool`, `DateTime`, `DateTimeOffset`, and `Guid`). When a `decimal` would be inferred but there are missing values, we will infer a
 `float` instead, and use `Double.NaN` to represent those missing values. The `string` type is already inherently nullable,
 so by default, we won't generate a `string option`. If you prefer to use optionals in all cases, you can set the static parameter
 `PreferOptionals` to `true`. In that case, you'll never get an empty string or a `Double.NaN` and will always get a `None` instead.
@@ -303,6 +310,12 @@ specify the units of measure. This will override both `AssumeMissingValues` and
 * `guid`
 * `guid?`
 * `guid option`
+* `dateonly` (.NET 6+ only)
+* `dateonly?` (.NET 6+ only)
+* `dateonly option` (.NET 6+ only)
+* `timeonly` (.NET 6+ only)
+* `timeonly?` (.NET 6+ only)
+* `timeonly option` (.NET 6+ only)
 * `string`
 * `string option`.
 
@@ -373,6 +386,23 @@ for row in titanic2.Rows |> Seq.truncate 10 do
 
 You can even mix and match the two syntaxes like this `Schema="int64,DidSurvive,PClass->Passenger Class=string"`
 
+### DateOnly and TimeOnly (on .NET 6+)
+
+On .NET 6 and later, when you set `PreferDateOnly = true`, date-only strings are inferred as `DateOnly`
+and time-only strings as `TimeOnly`. For example, a column like `EventDate` containing values such as
+`2023-06-01` will be given the type `DateOnly`. By default (`PreferDateOnly = false`), dates are
+inferred as `DateTime` for backward compatibility.
+
+You can also explicitly request a `DateOnly` or `TimeOnly` column using schema annotations:
+
+    [lang=text]
+    EventDate (dateonly),Duration (timeonly?)
+    2023-06-01,08:30:00
+    2023-06-02,
+
+In the example above, `EventDate` is explicitly annotated as `dateonly` and `Duration` is explicitly
+annotated as `timeonly?` (a nullable `TimeOnly`).
+
 ## Transforming CSV files
 
 In addition to reading, `CsvProvider` also has support for transforming the row collection of CSV files. The operations

docs/library/JsonProvider.fsx

@@ -119,6 +119,13 @@ type-safe access to the values, but not in the original order (if order matters,
 you can use the `mixed.JsonValue` property to get the underlying `JsonValue` and
 process it dynamically as described in [the documentation for `JsonValue`](JsonValue.html).
 
+### Inferring date types
+
+String values in JSON that look like dates are inferred as `DateTime` or `DateTimeOffset`.
+On .NET 6 and later, when you set `PreferDateOnly = true`, strings that represent a date without a time component (e.g. `"2023-01-15"`)
+are inferred as `DateOnly`, and time-only strings are inferred as `TimeOnly`. By default (`PreferDateOnly = false`),
+all dates are inferred as `DateTime` for backward compatibility.
+
 ### Inferring record types
 
 Now let's look at a sample JSON document that contains a list of records. The

src/FSharp.Data.Csv.Core/CsvInference.fs

@@ -32,7 +32,14 @@ let private nameToTypeForCsv =
         "datetimeoffset option", (typeof<DateTimeOffset>, TypeWrapper.Option)
         "timespan option", (typeof<TimeSpan>, TypeWrapper.Option)
         "guid option", (typeof<Guid>, TypeWrapper.Option)
-        "string option", (typeof<string>, TypeWrapper.Option) ]
+        "string option", (typeof<string>, TypeWrapper.Option)
+#if NET6_0_OR_GREATER
+        "dateonly?", (typeof<DateOnly>, TypeWrapper.Nullable)
+        "timeonly?", (typeof<TimeOnly>, TypeWrapper.Nullable)
+        "dateonly option", (typeof<DateOnly>, TypeWrapper.Option)
+        "timeonly option", (typeof<TimeOnly>, TypeWrapper.Option)
+#endif
+        ]
     |> dict
 
 let private nameAndTypeRegex =

src/FSharp.Data.Csv.Core/FSharp.Data.Csv.Core.fsproj

@@ -2,7 +2,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Library</OutputType>
-    <TargetFramework>netstandard2.0</TargetFramework>
+    <TargetFrameworks>netstandard2.0;net8.0</TargetFrameworks>
     <OtherFlags>$(OtherFlags) --warnon:1182 --nowarn:10001 --nowarn:44</OtherFlags>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
     <GenerateAssemblyInfo>false</GenerateAssemblyInfo>

src/FSharp.Data.DesignTime/CommonProviderImplementation/ConversionsGenerator.fs

@@ -32,6 +32,12 @@ let getConversionQuotation missingValuesStr cultureStr typ (value: Expr<string o
         <@@ TextRuntime.ConvertDateTimeOffset(cultureStr, %value) @@>
     elif typ = typeof<TimeSpan> then
         <@@ TextRuntime.ConvertTimeSpan(cultureStr, %value) @@>
+#if NET6_0_OR_GREATER
+    elif typ = typeof<DateOnly> then
+        <@@ TextRuntime.ConvertDateOnly(cultureStr, %value) @@>
+    elif typ = typeof<TimeOnly> then
+        <@@ TextRuntime.ConvertTimeOnly(cultureStr, %value) @@>
+#endif
     elif typ = typeof<Guid> then
         <@@ TextRuntime.ConvertGuid(%value) @@>
     else
@@ -58,6 +64,12 @@ let getBackConversionQuotation missingValuesStr cultureStr typ value : Expr<stri
         <@ TextRuntime.ConvertDateTimeOffsetBack(cultureStr, %%value) @>
     elif typ = typeof<TimeSpan> then
         <@ TextRuntime.ConvertTimeSpanBack(cultureStr, %%value) @>
+#if NET6_0_OR_GREATER
+    elif typ = typeof<DateOnly> then
+        <@ TextRuntime.ConvertDateOnlyBack(cultureStr, %%value) @>
+    elif typ = typeof<TimeOnly> then
+        <@ TextRuntime.ConvertTimeOnlyBack(cultureStr, %%value) @>
+#endif
     else
         failwith "getBackConversionQuotation: Unsupported primitive type"
 

src/FSharp.Data.DesignTime/CommonProviderImplementation/Helpers.fs

@@ -150,6 +150,17 @@ module internal ProviderHelpers =
             member x.Inverse(denominator) : Type =
                 ProvidedMeasureBuilder.Inverse(denominator) }
 
+#if NET6_0_OR_GREATER
+    /// Returns true when the target runtime assembly is a .NET 6+ build and therefore
+    /// supports System.DateOnly / System.TimeOnly in generated types.
+    let runtimeSupportsNet6Types (runtimeAssemblyPath: string) =
+        // The assembly path contains the TFM, e.g. "…/net8.0/FSharp.Data.dll".
+        // Anything matching "/net<N>." where N ≥ 6 is a net6+ target.
+        let path = runtimeAssemblyPath.Replace('\\', '/').ToLowerInvariant()
+        let m = System.Text.RegularExpressions.Regex.Match(path, @"/net(\d+)\.")
+        m.Success && (int m.Groups.[1].Value) >= 6
+#endif
+
     let asyncMap (resultType: Type) (valueAsync: Expr<Async<'T>>) (body: Expr<'T> -> Expr) =
         let (?) = QuotationBuilder.(?)
         let convFunc = ReflectionHelpers.makeDelegate (Expr.Cast >> body) typeof<'T>

src/FSharp.Data.DesignTime/Csv/CsvProvider.fs

@@ -55,6 +55,7 @@ type public CsvProvider(cfg: TypeProviderConfig) as this =
         let encodingStr = args.[13] :?> string
         let resolutionFolder = args.[14] :?> string
         let resource = args.[15] :?> string
+        let preferDateOnly = args.[16] :?> bool
 
         // This provider already has a schema mechanism, so let's disable inline schemas.
         let inferenceMode = InferenceMode'.ValuesOnly
@@ -103,16 +104,25 @@ type public CsvProvider(cfg: TypeProviderConfig) as this =
             let inferredFields =
                 use _holder = IO.logTime "Inference" sample
 
-                sampleCsv.InferColumnTypes(
-                    inferRows,
-                    TextRuntime.GetMissingValues missingValuesStr,
-                    inferenceMode,
-                    TextRuntime.GetCulture cultureStr,
-                    schema,
-                    assumeMissingValues,
-                    preferOptionals,
-                    unitsOfMeasureProvider
-                )
+                let fields =
+                    sampleCsv.InferColumnTypes(
+                        inferRows,
+                        TextRuntime.GetMissingValues missingValuesStr,
+                        inferenceMode,
+                        TextRuntime.GetCulture cultureStr,
+                        schema,
+                        assumeMissingValues,
+                        preferOptionals,
+                        unitsOfMeasureProvider
+                    )
+#if NET6_0_OR_GREATER
+                if preferDateOnly && ProviderHelpers.runtimeSupportsNet6Types cfg.RuntimeAssembly then
+                    fields
+                else
+                    fields |> List.map StructuralInference.downgradeNet6PrimitiveProperty
+#else
+                fields
+#endif
 
             use _holder = IO.logTime "TypeGeneration" sample
 
@@ -223,7 +233,8 @@ type public CsvProvider(cfg: TypeProviderConfig) as this =
           ProvidedStaticParameter("Culture", typeof<string>, parameterDefaultValue = "")
           ProvidedStaticParameter("Encoding", typeof<string>, parameterDefaultValue = "")
           ProvidedStaticParameter("ResolutionFolder", typeof<string>, parameterDefaultValue = "")
-          ProvidedStaticParameter("EmbeddedResource", typeof<string>, parameterDefaultValue = "") ]
+          ProvidedStaticParameter("EmbeddedResource", typeof<string>, parameterDefaultValue = "")
+          ProvidedStaticParameter("PreferDateOnly", typeof<bool>, parameterDefaultValue = false) ]
 
     let helpText =
         """<summary>Typed representation of a CSV file.</summary>
@@ -246,7 +257,8 @@ type public CsvProvider(cfg: TypeProviderConfig) as this =
            <param name='Encoding'>The encoding used to read the sample. You can specify either the character set name or the codepage number. Defaults to UTF8 for files, and to ISO-8859-1 the for HTTP requests, unless <c>charset</c> is specified in the <c>Content-Type</c> response header.</param>
            <param name='ResolutionFolder'>A directory that is used when resolving relative file references (at design time and in hosted execution).</param>
            <param name='EmbeddedResource'>When specified, the type provider first attempts to load the sample from the specified resource 
-              (e.g. 'MyCompany.MyAssembly, resource_name.csv'). This is useful when exposing types generated by the type provider.</param>"""
+              (e.g. 'MyCompany.MyAssembly, resource_name.csv'). This is useful when exposing types generated by the type provider.</param>
+           <param name='PreferDateOnly'>When true on .NET 6+, date-only strings are inferred as DateOnly and time-only strings as TimeOnly. Defaults to false for backward compatibility.</param>"""
 
     do csvProvTy.AddXmlDoc helpText
     do csvProvTy.DefineStaticParameters(parameters, buildTypes)

src/FSharp.Data.DesignTime/FSharp.Data.DesignTime.fsproj

@@ -2,7 +2,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <IsPackable>false</IsPackable>
-    <TargetFramework>netstandard2.0</TargetFramework>
+    <TargetFrameworks>netstandard2.0;net8.0</TargetFrameworks>
     <DefineConstants>IS_DESIGNTIME;NO_GENERATIVE;$(DefineConstants)</DefineConstants>
     <OtherFlags>$(OtherFlags) --warnon:1182 --nowarn:44</OtherFlags>
     <GenerateDocumentationFile>false</GenerateDocumentationFile>

src/FSharp.Data.DesignTime/Html/HtmlGenerator.fs

@@ -37,10 +37,11 @@ module internal HtmlGenerator =
     let private createTableType
         getTableTypeName
         (inferenceParameters, missingValuesStr, cultureStr)
+        supportsNet6Types
         (table: HtmlTable)
         =
 
-        let columns =
+        let rawColumns =
             match table.InferedProperties with
             | Some inferedProperties -> inferedProperties
             | None ->
@@ -52,6 +53,16 @@ module internal HtmlGenerator =
                      else
                          table.Rows)
 
+        let columns =
+#if NET6_0_OR_GREATER
+            if supportsNet6Types then
+                rawColumns
+            else
+                rawColumns |> List.map StructuralInference.downgradeNet6PrimitiveProperty
+#else
+            rawColumns
+#endif
+
         let fields =
             columns
             |> List.mapi (fun index field ->
@@ -128,9 +139,24 @@ module internal HtmlGenerator =
 
         create, tableType
 
-    let private createListType getListTypeName (inferenceParameters, missingValuesStr, cultureStr) (list: HtmlList) =
+    let private createListType
+        getListTypeName
+        (inferenceParameters, missingValuesStr, cultureStr)
+        supportsNet6Types
+        (list: HtmlList)
+        =
+
+        let rawColumns = HtmlInference.inferListType inferenceParameters list.Values
 
-        let columns = HtmlInference.inferListType inferenceParameters list.Values
+        let columns =
+#if NET6_0_OR_GREATER
+            if supportsNet6Types then
+                rawColumns
+            else
+                StructuralInference.downgradeNet6Types rawColumns
+#else
+            rawColumns
+#endif
 
         let listItemType, conv =
             match columns with
@@ -185,14 +211,25 @@ module internal HtmlGenerator =
     let private createDefinitionListType
         getDefinitionListTypeName
         (inferenceParameters, missingValuesStr, cultureStr)
+        supportsNet6Types
         (definitionList: HtmlDefinitionList)
         =
 
         let getListTypeName = typeNameGenerator ()
 
         let createListType index (list: HtmlList) =
 
-            let columns = HtmlInference.inferListType inferenceParameters list.Values
+            let rawColumns = HtmlInference.inferListType inferenceParameters list.Values
+
+            let columns =
+#if NET6_0_OR_GREATER
+                if supportsNet6Types then
+                    rawColumns
+                else
+                    StructuralInference.downgradeNet6Types rawColumns
+#else
+                rawColumns
+#endif
 
             let listItemType, conv =
                 match columns with
@@ -264,7 +301,7 @@ module internal HtmlGenerator =
 
         definitionListType
 
-    let generateTypes asm ns typeName parameters htmlObjects =
+    let generateTypes asm ns typeName parameters supportsNet6Types htmlObjects =
 
         let htmlType =
             ProvidedTypeDefinition(
@@ -303,7 +340,10 @@ module internal HtmlGenerator =
             match htmlObj with
             | Table table ->
                 let containerType = getOrCreateContainer "Tables"
-                let create, tableType = createTableType getTypeName parameters table
+
+                let create, tableType =
+                    createTableType getTypeName parameters supportsNet6Types table
+
                 htmlType.AddMember tableType
 
                 containerType.AddMember
@@ -315,7 +355,7 @@ module internal HtmlGenerator =
 
             | List list ->
                 let containerType = getOrCreateContainer "Lists"
-                let create, tableType = createListType getTypeName parameters list
+                let create, tableType = createListType getTypeName parameters supportsNet6Types list
                 htmlType.AddMember tableType
 
                 containerType.AddMember
@@ -326,7 +366,10 @@ module internal HtmlGenerator =
                 )
             | DefinitionList definitionList ->
                 let containerType = getOrCreateContainer "DefinitionLists"
-                let tableType = createDefinitionListType getTypeName parameters definitionList
+
+                let tableType =
+                    createDefinitionListType getTypeName parameters supportsNet6Types definitionList
+
                 htmlType.AddMember tableType
 
                 containerType.AddMember