Add support for C# Experimental attribute

docs/release-notes/.FSharp.Compiler.Service/9.0.300.md

@@ -12,6 +12,7 @@
 ### Added
 * Added missing type constraints in FCS. ([PR #18241](https://github.com/dotnet/fsharp/pull/18241))
 * The 'use' keyword can be used on IDisposable|null without nullness warnings ([PR #18262](https://github.com/dotnet/fsharp/pull/18262))
+* Add support for C# `Experimental` attribute. ([PR #18253](https://github.com/dotnet/fsharp/pull/18253))
 * Nullness warnings are issued for signature<>implementation conformance ([PR #18186](https://github.com/dotnet/fsharp/pull/18186))
 * Symbols: Add FSharpAssembly.IsFSharp ([PR #18290](https://github.com/dotnet/fsharp/pull/18290))
 

src/Compiler/Checking/AttributeChecking.fs

@@ -24,13 +24,6 @@ open FSharp.Compiler.TypeProviders
 open FSharp.Core.CompilerServices
 #endif
 
-exception ObsoleteDiagnostic of
-    isError: bool *
-    diagnosticId: string *
-    message: string *
-    urlFormat: string *
-    range: range
-
 let fail() = failwith "This custom attribute has an argument that cannot yet be converted using this API"
 
 let rec private evalILAttribElem elem = 
@@ -247,44 +240,68 @@ let private CheckCompilerFeatureRequiredAttribute (g: TcGlobals) cattrs msg m =
     | Some([ILAttribElem.String (Some featureName) ], _) when featureName = "RequiredMembers" ->
         CompleteD
     | _ ->
-        ErrorD (ObsoleteDiagnostic(true, "", msg, "", m))
+        ErrorD (ObsoleteDiagnostic(true, None, msg, None, m))
+
+let private extractILAttribValueFrom name namedArgs   =
+    match namedArgs with 
+    | ExtractILAttributeNamedArg name (AttribElemStringArg v) -> Some v 
+    | _ -> None
 
-let private extractILObsoleteAttributeInfo namedArgs =
-    let extractILAttribValueFrom name namedArgs   =
-        match namedArgs with 
-        | ExtractILAttributeNamedArg name (AttribElemStringArg v) -> v 
-        | _ -> ""
+let private extractILAttributeInfo namedArgs =
     let diagnosticId = extractILAttribValueFrom "DiagnosticId" namedArgs
     let urlFormat = extractILAttribValueFrom "UrlFormat" namedArgs
     (diagnosticId, urlFormat)
 
+let private CheckILExperimentalAttributes (g: TcGlobals) cattrs m =
+    let (AttribInfo(tref,_)) = g.attrib_IlExperimentalAttribute
+    match TryDecodeILAttribute tref cattrs with
+    // [Experimental("DiagnosticId")]
+    // [Experimental(diagnosticId: "DiagnosticId")]
+    // [Experimental("DiagnosticId", UrlFormat = "UrlFormat")]
+    // [Experimental(diagnosticId = "DiagnosticId", UrlFormat = "UrlFormat")]
+    // Constructors deciding on DiagnosticId and UrlFormat properties.
+    | Some ([ attribElement ], namedArgs) ->
+        let diagnosticId = 
+            match attribElement with 
+            | ILAttribElem.String (Some msg) -> Some msg
+            | ILAttribElem.String None
+            | _ -> None
+
+        let message = extractILAttribValueFrom "Message" namedArgs
+        let urlFormat = extractILAttribValueFrom "UrlFormat" namedArgs
+
+        WarnD(Experimental(message, diagnosticId, urlFormat, m))
+    // Empty constructor or only UrlFormat property are not allowed.
+    | Some _
+    | None -> CompleteD
+
 let private CheckILObsoleteAttributes (g: TcGlobals) isByrefLikeTyconRef cattrs m =
     if isByrefLikeTyconRef then
         CompleteD
     else
         let (AttribInfo(tref,_)) = g.attrib_SystemObsolete
         match TryDecodeILAttribute tref cattrs with
-        // [<Obsolete>]
-        // [<Obsolete("Message")>]
-        // [<Obsolete("Message", true)>]
-        // [<Obsolete("Message", DiagnosticId = "DiagnosticId")>]
-        // [<Obsolete("Message", DiagnosticId = "DiagnosticId", UrlFormat = "UrlFormat")>]
-        // [<Obsolete(DiagnosticId = "DiagnosticId")>]
-        // [<Obsolete(DiagnosticId = "DiagnosticId", UrlFormat = "UrlFormat")>]
-        // [<Obsolete("Message", true, DiagnosticId = "DiagnosticId")>]
-        // [<Obsolete("Message", true, DiagnosticId = "DiagnosticId", UrlFormat = "UrlFormat")>]
+        // [Obsolete]
+        // [Obsolete("Message")]
+        // [Obsolete("Message", true)]
+        // [Obsolete("Message", DiagnosticId = "DiagnosticId")]
+        // [Obsolete("Message", DiagnosticId = "DiagnosticId", UrlFormat = "UrlFormat")]
+        // [Obsolete(DiagnosticId = "DiagnosticId")]
+        // [Obsolete(DiagnosticId = "DiagnosticId", UrlFormat = "UrlFormat")]
+        // [Obsolete("Message", true, DiagnosticId = "DiagnosticId")]
+        // [Obsolete("Message", true, DiagnosticId = "DiagnosticId", UrlFormat = "UrlFormat")]
         // Constructors deciding on IsError and Message properties.
         | Some ([ attribElement ], namedArgs) ->
-            let diagnosticId, urlFormat = extractILObsoleteAttributeInfo namedArgs
+            let diagnosticId, urlFormat = extractILAttributeInfo namedArgs
             let msg = 
                 match attribElement with 
-                | ILAttribElem.String (Some msg) -> msg
+                | ILAttribElem.String (Some msg) -> Some msg
                 | ILAttribElem.String None
-                | _ -> ""
+                | _ -> None
 
             WarnD (ObsoleteDiagnostic(false, diagnosticId, msg, urlFormat, m))
-        | Some ([ILAttribElem.String (Some msg); ILAttribElem.Bool isError ], namedArgs) ->
-            let diagnosticId, urlFormat = extractILObsoleteAttributeInfo namedArgs
+        | Some ([ILAttribElem.String msg; ILAttribElem.Bool isError ], namedArgs) ->
+            let diagnosticId, urlFormat = extractILAttributeInfo namedArgs
             if isError then
                 if g.langVersion.SupportsFeature(LanguageFeature.RequiredPropertiesSupport) then
                     CheckCompilerFeatureRequiredAttribute g cattrs msg m
@@ -294,24 +311,23 @@ let private CheckILObsoleteAttributes (g: TcGlobals) isByrefLikeTyconRef cattrs
                 WarnD (ObsoleteDiagnostic(false, diagnosticId, msg, urlFormat, m))
         // Only DiagnosticId, UrlFormat
         | Some (_, namedArgs) ->
-            let diagnosticId, urlFormat = extractILObsoleteAttributeInfo namedArgs
-            WarnD(ObsoleteDiagnostic(false, diagnosticId, "", urlFormat, m))
+            let diagnosticId, urlFormat = extractILAttributeInfo namedArgs
+            WarnD(ObsoleteDiagnostic(false, diagnosticId, None, urlFormat, m))
         // No arguments
         | None -> CompleteD
 
-/// Check IL attributes for 'ObsoleteAttribute', returning errors and warnings as data
+/// Check IL attributes for Experimental, warnings as data
 let private CheckILAttributes (g: TcGlobals) isByrefLikeTyconRef cattrs m =
     trackErrors {
         do! CheckILObsoleteAttributes g isByrefLikeTyconRef cattrs m
+        do! CheckILExperimentalAttributes g cattrs m
     }
 
-let langVersionPrefix = "--langversion:preview"
-
 let private extractObsoleteAttributeInfo namedArgs =
     let extractILAttribValueFrom name namedArgs   =
         match namedArgs with 
-        | ExtractAttribNamedArg name (AttribStringArg v) -> v 
-        | _ -> ""
+        | ExtractAttribNamedArg name (AttribStringArg v) -> Some v 
+        | _ -> None
     let diagnosticId = extractILAttribValueFrom "DiagnosticId" namedArgs
     let urlFormat = extractILAttribValueFrom "UrlFormat" namedArgs
     (diagnosticId, urlFormat)
@@ -331,17 +347,17 @@ let private CheckObsoleteAttributes g attribs m =
         // Constructors deciding on IsError and Message properties.
         | Some(Attrib(unnamedArgs= [ AttribStringArg s ]; propVal= namedArgs)) ->
             let diagnosticId, urlFormat = extractObsoleteAttributeInfo namedArgs
-            do! WarnD(ObsoleteDiagnostic(false, diagnosticId, s, urlFormat, m))
+            do! WarnD(ObsoleteDiagnostic(false, diagnosticId, Some s, urlFormat, m))
         | Some(Attrib(unnamedArgs= [ AttribStringArg s; AttribBoolArg(isError) ]; propVal= namedArgs)) -> 
             let diagnosticId, urlFormat = extractObsoleteAttributeInfo namedArgs
             if isError then
-                do! ErrorD (ObsoleteDiagnostic(true, diagnosticId, s, urlFormat, m))
+                do! ErrorD (ObsoleteDiagnostic(true, diagnosticId, Some s, urlFormat, m))
             else
-                do! WarnD (ObsoleteDiagnostic(false, diagnosticId, s, urlFormat, m))
+                do! WarnD (ObsoleteDiagnostic(false, diagnosticId, Some s, urlFormat, m))
         // Only DiagnosticId, UrlFormat
         | Some(Attrib(propVal= namedArgs)) ->
             let diagnosticId, urlFormat = extractObsoleteAttributeInfo namedArgs
-            do! WarnD(ObsoleteDiagnostic(false, diagnosticId, "", urlFormat, m))
+            do! WarnD(ObsoleteDiagnostic(false, diagnosticId, None, urlFormat, m))
         | None ->  ()
     }
 
@@ -366,21 +382,21 @@ let private CheckCompilerMessageAttribute g attribs m =
             ()
     }
 
-let private CheckExperimentalAttribute g attribs m =
+let private CheckFSharpExperimentalAttribute g attribs m =
     trackErrors {
         match TryFindFSharpAttribute g g.attrib_ExperimentalAttribute attribs with
+        // [<Experimental("Message")>]
         | Some(Attrib(unnamedArgs= [ AttribStringArg(s) ])) ->
             let isExperimentalAttributeDisabled (s:string) =
                 if g.compilingFSharpCore then
                     true
                 else
-                    g.langVersion.IsPreviewEnabled && (s.IndexOf(langVersionPrefix, StringComparison.OrdinalIgnoreCase) >= 0)
+                    g.langVersion.IsPreviewEnabled && (s.IndexOf("--langversion:preview", StringComparison.OrdinalIgnoreCase) >= 0)
             if not (isExperimentalAttributeDisabled s) then
-                do! WarnD(Experimental(s, m))
-        | Some _ ->
-            do! WarnD(Experimental(FSComp.SR.experimentalConstruct (), m))
-        | _ ->
-            ()
+                do! WarnD(Experimental(Some s, None, None, m))
+        // Empty constructor is not allowed.
+        | Some _
+        | _ -> ()
     }
 
 let private CheckUnverifiableAttribute g attribs m  =
@@ -399,7 +415,7 @@ let CheckFSharpAttributes (g:TcGlobals) attribs m =
         trackErrors {
             do! CheckObsoleteAttributes g attribs m
             do! CheckCompilerMessageAttribute g attribs m
-            do! CheckExperimentalAttribute g attribs m
+            do! CheckFSharpExperimentalAttribute g attribs m
             do! CheckUnverifiableAttribute g attribs m
         }
 
@@ -408,16 +424,16 @@ let CheckFSharpAttributes (g:TcGlobals) attribs m =
 let private CheckProvidedAttributes (g: TcGlobals) m (provAttribs: Tainted<IProvidedCustomAttributeProvider>)  = 
     let (AttribInfo(tref, _)) = g.attrib_SystemObsolete
     match provAttribs.PUntaint((fun a -> a.GetAttributeConstructorArgs(provAttribs.TypeProvider.PUntaintNoFailure(id), tref.FullName)), m) with
-    | Some ([ Some (:? string as msg) ], _) -> WarnD(ObsoleteDiagnostic(false, "", msg, "", m))
+    | Some ([ Some (:? string as msg) ], _) -> WarnD(ObsoleteDiagnostic(false, None, Some msg, None, m))
     | Some ([ Some (:? string as msg); Some (:?bool as isError) ], _) ->
         if isError then 
-            ErrorD (ObsoleteDiagnostic(true, "", msg, "", m))
+            ErrorD (ObsoleteDiagnostic(true, None, Some msg, None, m))
         else 
-            WarnD (ObsoleteDiagnostic(false, "", msg, "", m))
+            WarnD (ObsoleteDiagnostic(false, None, Some msg, None, m))
     | Some ([ None ], _) -> 
-        WarnD(ObsoleteDiagnostic(false, "", "", "", m))
+        WarnD(ObsoleteDiagnostic(false, None, None, None, m))
     | Some _ -> 
-        WarnD(ObsoleteDiagnostic(false, "", "", "", m))
+        WarnD(ObsoleteDiagnostic(false, None, None, None, m))
     | None -> 
         CompleteD
 #endif

src/Compiler/Checking/AttributeChecking.fsi

@@ -13,13 +13,6 @@ open FSharp.Compiler.TcGlobals
 open FSharp.Compiler.Text
 open FSharp.Compiler.TypedTree
 
-exception ObsoleteDiagnostic of
-    isError: bool *
-    diagnosticId: string *
-    message: string *
-    urlFormat: string *
-    range: range
-
 type AttribInfo =
     | FSAttribInfo of TcGlobals * Attrib
     | ILAttribInfo of TcGlobals * Import.ImportMap * ILScopeRef * ILAttribute * range

src/Compiler/Checking/PostInferenceChecks.fs

@@ -551,7 +551,7 @@ let WarnOnWrongTypeForAccess (cenv: cenv) env objName valAcc m ty =
                 if isLessAccessible tyconAcc valAcc then
                     let errorText = FSComp.SR.chkTypeLessAccessibleThanType(tcref.DisplayName, (objName())) |> snd
                     let warningText = errorText + Environment.NewLine + FSComp.SR.tcTypeAbbreviationsCheckedAtCompileTime()
-                    warning(AttributeChecking.ObsoleteDiagnostic(false, "", warningText, "", m))
+                    warning(ObsoleteDiagnostic(false, None, Some warningText, None, m))
 
         CheckTypeDeep cenv (visitType, None, None, None, None) cenv.g env NoInfo ty
 

src/Compiler/Driver/CompilerDiagnostics.fs

@@ -14,7 +14,6 @@ open Internal.Utilities.Library
 open Internal.Utilities.Text
 
 open FSharp.Compiler
-open FSharp.Compiler.AttributeChecking
 open FSharp.Compiler.CheckExpressions
 open FSharp.Compiler.CheckDeclarations
 open FSharp.Compiler.CheckIncrementalClasses
@@ -149,7 +148,7 @@ type Exception with
         | ValueRestriction(_, _, _, _, m)
         | LetRecUnsound(_, _, m)
         | ObsoleteDiagnostic(_, _, _, _, m)
-        | Experimental(_, m)
+        | Experimental(range = m)
         | PossibleUnverifiableCode m
         | UserCompilerMessage(_, _, m)
         | Deprecated(_, m)
@@ -568,7 +567,9 @@ module OldStyleMessages =
     let ValNotLocalE () = Message("ValNotLocal", "")
     let Obsolete1E () = Message("Obsolete1", "")
     let Obsolete2E () = Message("Obsolete2", "%s")
-    let ExperimentalE () = Message("Experimental", "%s")
+    let Experimental1E () = Message("Experimental1", "")
+    let Experimental2E () = Message("Experimental2", "%s")
+    let Experimental3E () = Message("Experimental3", "")
     let PossibleUnverifiableCodeE () = Message("PossibleUnverifiableCode", "")
     let DeprecatedE () = Message("Deprecated", "%s")
     let LibraryUseOnlyE () = Message("LibraryUseOnly", "")
@@ -1791,13 +1792,21 @@ type Exception with
 
         | ValNotLocal _ -> os.AppendString(ValNotLocalE().Format)
 
-        | ObsoleteDiagnostic(message = s) ->
+        | ObsoleteDiagnostic(message = message) ->
             os.AppendString(Obsolete1E().Format)
 
-            if s <> "" then
-                os.AppendString(Obsolete2E().Format s)
+            match message with
+            | Some message when message <> "" -> os.AppendString(Obsolete2E().Format message)
+            | _ -> ()
+
+        | Experimental(message = message) ->
+            os.AppendString(Experimental1E().Format)
+
+            match message with
+            | Some message when message <> "" -> os.AppendString(Experimental2E().Format message)
+            | _ -> ()
 
-        | Experimental(s, _) -> os.AppendString(ExperimentalE().Format s)
+            os.AppendString(Experimental3E().Format)
 
         | PossibleUnverifiableCode _ -> os.AppendString(PossibleUnverifiableCodeE().Format)
 

src/Compiler/FSStrings.resx

@@ -1029,8 +1029,14 @@
   <data name="Obsolete2" xml:space="preserve">
     <value>. {0}</value>
   </data>
-  <data name="Experimental" xml:space="preserve">
-    <value>{0}. This warning can be disabled using '--nowarn:57' or '#nowarn "57"'.</value>
+  <data name="Experimental1" xml:space="preserve">
+    <value>This construct is experimental</value>
+  </data>
+  <data name="Experimental2" xml:space="preserve">
+    <value>. {0}</value>
+  </data>
+  <data name="Experimental3" xml:space="preserve">
+    <value>. This warning can be disabled using '--nowarn:57' or '#nowarn "57"'.</value>
   </data>
   <data name="PossibleUnverifiableCode" xml:space="preserve">
     <value>Uses of this construct may result in the generation of unverifiable .NET IL code. This warning can be disabled using '--nowarn:9' or '#nowarn "9"'.</value>

src/Compiler/Facilities/DiagnosticsLogger.fs

@@ -108,7 +108,7 @@ exception LibraryUseOnly of range: range
 
 exception Deprecated of message: string * range: range
 
-exception Experimental of message: string * range: range
+exception Experimental of message: string option * diagnosticId: string option * urlFormat: string option * range: range
 
 exception PossibleUnverifiableCode of range: range
 
@@ -133,6 +133,14 @@ exception DiagnosticWithSuggestions of number: int * message: string * range: ra
 /// A diagnostic that is raised when enabled manually, or by default with a language feature
 exception DiagnosticEnabledWithLanguageFeature of number: int * message: string * range: range * enabledByLangFeature: bool
 
+/// A diagnostic that is raised when a diagnostic is obsolete
+exception ObsoleteDiagnostic of
+    isError: bool *
+    diagnosticId: string option *
+    message: string option *
+    urlFormat: string option *
+    range: range
+
 /// The F# compiler code currently uses 'Error(...)' in many places to create
 /// an DiagnosticWithText as an exception even if it's a warning.
 ///

src/Compiler/Facilities/DiagnosticsLogger.fsi

@@ -68,7 +68,7 @@ exception LibraryUseOnly of range: range
 
 exception Deprecated of message: string * range: range
 
-exception Experimental of message: string * range: range
+exception Experimental of message: string option * diagnosticId: string option * urlFormat: string option * range: range
 
 exception PossibleUnverifiableCode of range: range
 
@@ -87,6 +87,13 @@ exception DiagnosticWithSuggestions of
     identifier: string *
     suggestions: Suggestions
 
+exception ObsoleteDiagnostic of
+    isError: bool *
+    diagnosticId: string option *
+    message: string option *
+    urlFormat: string option *
+    range: range
+
 /// Creates a DiagnosticWithSuggestions whose text comes via SR.*
 val ErrorWithSuggestions: (int * string) * range * string * Suggestions -> exn