(experimental) forbid setter call on init properties

eng/Build.ps1

@@ -497,7 +497,7 @@ try {
         Create-Directory $resultsRoot
         UpdatePath
         $env:HOSTED_COMPILER = 1
-        $env:CSC_PIPE = "$nugetPackages\Microsoft.Net.Compilers\2.7.0\tools\csc.exe"
+        $env:CSC_PIPE = "$nugetPackages\Microsoft.Net.Compilers\3.9.0\tools\csc.exe"
         $env:FSCOREDLLPATH = "$ArtifactsDir\bin\fsc\$configuration\net472\FSharp.Core.dll"
         $env:LINK_EXE = "$RepoRoot\tests\fsharpqa\testenv\bin\link\link.exe"
         $env:OSARCH = $env:PROCESSOR_ARCHITECTURE

eng/Versions.props

@@ -188,7 +188,7 @@
     <FSharpDataTypeProvidersVersion>4.3.0.0</FSharpDataTypeProvidersVersion>
     <MicrosoftCompositionVersion>1.0.30</MicrosoftCompositionVersion>
     <MicrosoftMSXMLVersion>8.0.0</MicrosoftMSXMLVersion>
-    <MicrosoftNetCompilersVersion>2.7.0</MicrosoftNetCompilersVersion>
+    <MicrosoftNetCompilersVersion>3.9.0</MicrosoftNetCompilersVersion>
     <MicrosoftNETCoreAppRefVersion>3.1.0</MicrosoftNETCoreAppRefVersion>
     <MicrosoftNETCoreILDAsmVersion>5.0.0-preview.7.20364.11</MicrosoftNETCoreILDAsmVersion>
     <MicrosoftNETCoreILAsmVersion>5.0.0-preview.7.20364.11</MicrosoftNETCoreILAsmVersion>

src/fsharp/CheckExpressions.fs

@@ -8243,6 +8243,8 @@ and TcLookupThen cenv overallTy env tpenv mObjExpr objExpr objExprTy longId dela
                 if isNil meths then error (Error (FSComp.SR.tcPropertyIsNotReadable nm, mItem))
                 TcMethodApplicationThen cenv env overallTy None tpenv tyargsOpt objArgs mExprAndItem mItem nm ad PossiblyMutates true meths afterResolution NormalValUse args atomicFlag delayed
             else
+                if pinfo.SetterIsInitOnly then
+                    errorR (Error (FSComp.SR.tcPropertyCannotBeSet1 nm, mItem))
                 let args = if pinfo.IsIndexer then args else []
                 let mut = (if isStructTy cenv.g (tyOfExpr cenv.g objExpr) then DefinitelyMutates else PossiblyMutates)
                 TcMethodApplicationThen cenv env overallTy None tpenv tyargsOpt objArgs mStmt mItem nm ad mut true meths afterResolution NormalValUse (args @ [e2]) atomicFlag []

src/fsharp/MethodCalls.fs

@@ -107,7 +107,7 @@ type AssignedItemSetterTarget =
     | AssignedRecdFieldSetter of RecdFieldInfo 
 
 /// Represents the resolution of a caller argument as a named-setter argument
-type AssignedItemSetter<'T> = AssignedItemSetter of Ident * AssignedItemSetterTarget * CallerArg<'T> 
+type AssignedItemSetter<'T> = AssignedItemSetter of name: Ident * setterTarget: AssignedItemSetterTarget * callerArg: CallerArg<'T> 
 
 type CallerNamedArg<'T> = 
     | CallerNamedArg of Ident * CallerArg<'T>  
@@ -435,7 +435,7 @@ type CalledMeth<'T>
                     let pinfos = GetIntrinsicPropInfoSetsOfType infoReader (Some nm) ad AllowMultiIntfInstantiations.Yes IgnoreOverrides id.idRange returnedObjTy
                     let pinfos = pinfos |> ExcludeHiddenOfPropInfos g infoReader.amap m 
                     match pinfos with 
-                    | [pinfo] when pinfo.HasSetter && not pinfo.IsIndexer -> 
+                    | [pinfo] when pinfo.HasSetter && not pinfo.IsIndexer && not pinfo.SetterIsInitOnly -> 
                         let pminfo = pinfo.SetterMethod
                         let pminst = freshenMethInfo m pminfo
                         Choice1Of2(AssignedItemSetter(id, AssignedPropSetter(pinfo, pminfo, pminst), e))

src/fsharp/MethodCalls.fsi

@@ -77,7 +77,12 @@ type AssignedItemSetterTarget =
 /// Represents the resolution of a caller argument as a named-setter argument
 type AssignedItemSetter<'T> =
     | AssignedItemSetter of
-      Ident * AssignedItemSetterTarget * CallerArg<'T>
+      /// named-setter identifier
+      name: Ident * 
+      /// named-setter target
+      setterTarget: AssignedItemSetterTarget * 
+      /// caller argument that resolved into AssignedItemSetter
+      callerArg: CallerArg<'T>
 
 type CallerNamedArg<'T> =
     | CallerNamedArg of Ident * CallerArg<'T>

src/fsharp/NameResolution.fs

@@ -185,7 +185,7 @@ type Item =
     | Event of EventInfo
 
     /// Represents the resolution of a name to a property
-    | Property of string * PropInfo list
+    | Property of propertyName: string * propertyInfos: PropInfo list
 
     /// Represents the resolution of a name to a group of methods.
     | MethodGroup of displayName: string * methods: MethInfo list * uninstantiatedMethodOpt: MethInfo option

src/fsharp/NameResolution.fsi

@@ -80,7 +80,7 @@ type Item =
     | Event of EventInfo
 
     /// Represents the resolution of a name to a property
-    | Property of string * PropInfo list
+    | Property of propertyName: string * propertyInfos: PropInfo list
 
     /// Represents the resolution of a name to a group of methods. 
     | MethodGroup of displayName: string * methods: MethInfo list * uninstantiatedMethodOpt: MethInfo option

src/fsharp/absil/il.fs

@@ -719,7 +719,7 @@ and [<RequireQualifiedAccess; StructuralEquality; StructuralComparison; Structur
     | Byref of ILType
     | FunctionPointer of ILCallingSignature
     | TypeVar of uint16
-    | Modified of bool * ILTypeRef * ILType
+    | Modified of isRequired: bool * modifierClass: ILTypeRef * modifiedType: ILType
 
     member x.BasicQualifiedName =
         match x with

src/fsharp/absil/il.fsi

@@ -276,11 +276,11 @@ type ILType =
     /// Custom modifiers.
     | Modified of
           /// True if modifier is "required".
-          bool *
+          isRequired: bool *
           /// The class of the custom modifier.
-          ILTypeRef *
+          modifierClass: ILTypeRef *
           /// The type being modified.
-          ILType
+          modifiedType: ILType
 
     member TypeSpec: ILTypeSpec
 

src/fsharp/infos.fs

@@ -1890,6 +1890,12 @@ type ILPropInfo =
     /// Indicates if the IL property has a 'set' method
     member x.HasSetter = Option.isSome x.RawMetadata.SetMethod
 
+    member x.SetterIsInitOnly =
+        match x.SetterMethod.ILMethodRef.ReturnType with
+        | ILType.Modified(modifierClass=modifierClass) -> 
+            modifierClass.BasicQualifiedName = "System.Runtime.CompilerServices.IsExternalInit"
+        | _ -> false
+
     /// Indicates if the IL property is static
     member x.IsStatic = (x.RawMetadata.CallingConv = ILThisConvention.Static)
 
@@ -2016,6 +2022,14 @@ type PropInfo =
         | ProvidedProp(_, pi, m) -> pi.PUntaint((fun pi -> pi.CanWrite), m)
 #endif
 
+    member x.SetterIsInitOnly =
+        match x with
+        | ILProp ilpinfo -> ilpinfo.SetterIsInitOnly
+        | FSProp _ -> false // F# doesn't support this
+#if !NO_EXTENSIONTYPING
+        | ProvidedProp _ -> false
+#endif
+
     /// Indicates if this is an extension member
     member x.IsExtensionMember =
         match x.ArbitraryValRef with

src/fsharp/infos.fsi

@@ -723,6 +723,9 @@ type ILPropInfo =
     /// Indicates if the IL property has a 'set' method
     member HasSetter: bool
 
+    /// Indicates if the IL property setter is marked as 'init'
+    member SetterIsInitOnly: bool
+
     /// Get the declaring IL type of the IL property, including any generic instantiation
     member ILTypeInfo: ILTypeInfo
 
@@ -818,6 +821,9 @@ type PropInfo =
     /// Indicates if this property has an associated setter method.
     member HasSetter: bool
 
+    /// Indicates ...
+    member SetterIsInitOnly: bool
+
     member ImplementedSlotSignatures: SlotSig list
 
     /// Indicates if this property is marked 'override' and thus definitely overrides another property.

tests/FSharp.Test.Utilities/TestFramework.fs

@@ -285,8 +285,8 @@ let config configurationName envVars =
     let packagesDir = getPackagesDir ()
     let requirePackage = requireFile packagesDir
     let requireArtifact = requireFile artifactsBinPath
-    let CSC = requirePackage ("Microsoft.Net.Compilers" ++ "2.7.0" ++ "tools" ++ "csc.exe")
-    let VBC = requirePackage ("Microsoft.Net.Compilers" ++ "2.7.0" ++ "tools" ++ "vbc.exe")
+    let CSC = requirePackage ("Microsoft.Net.Compilers" ++ "3.9.0" ++ "tools" ++ "csc.exe")
+    let VBC = requirePackage ("Microsoft.Net.Compilers" ++ "3.9.0" ++ "tools" ++ "vbc.exe")
     let ILDASM_EXE = if operatingSystem = "win" then "ildasm.exe" else "ildasm"
     let ILDASM = requirePackage (("runtime." + operatingSystem + "-" + architectureMoniker + ".Microsoft.NETCore.ILDAsm") ++ coreClrRuntimePackageVersion ++ "runtimes" ++ (operatingSystem + "-" + architectureMoniker) ++ "native" ++ ILDASM_EXE)
     let ILASM_EXE = if operatingSystem = "win" then "ilasm.exe" else "ilasm"

tests/fsharp/tests.fs

@@ -1851,6 +1851,12 @@ module CoreTests =
         fsc cfg @"%s /target:library /out:fs.dll" cfg.fsc_flags ["fs.fs"]
         singleNegTest cfg "calls"
 
+    [<Test>]
+    let ``play nice with init properties and assignment syntax``() =
+        let cfg = testConfig "typecheck/init-property"
+        csc cfg "%s /target:library /out:niceinit.dll" cfg.csc_flags ["niceinit.cs"]
+        singleNegTest cfg "niceinit"
+
 #endif
 
 module VersionTests =

tests/fsharp/typecheck/init-property/niceinit.bsl

@@ -0,0 +1,12 @@
+
+niceinit.fsx(3,25,3,28): typecheck error FS0495: The object constructor 'NiceInit' has no argument or settable return property 'Val'. The required signature is NiceInit() : NiceInit.
+
+niceinit.fsx(6,1,6,14): typecheck error FS0810: Property 'Val' cannot be set
+
+niceinit.fsx(13,47,13,50): typecheck error FS0495: The member or object constructor 'mkInlineNiceInit' has no argument or settable return property 'Val'. The required signature is static member StraightNewFactory.mkInlineNiceInit : unit -> NiceInit.
+
+niceinit.fsx(14,41,14,44): typecheck error FS0495: The member or object constructor 'mkNiceInit' has no argument or settable return property 'Val'. The required signature is static member StraightNewFactory.mkNiceInit : unit -> NiceInit.
+
+niceinit.fsx(26,73,26,76): typecheck error FS0495: The member or object constructor 'mkInlineNiceInit' has no argument or settable return property 'Val'. The required signature is static member IntermediateVariableWithInterleavedOpFactory.mkInlineNiceInit : unit -> NiceInit.
+
+niceinit.fsx(27,67,27,70): typecheck error FS0495: The member or object constructor 'mkNiceInit' has no argument or settable return property 'Val'. The required signature is static member IntermediateVariableWithInterleavedOpFactory.mkNiceInit : unit -> NiceInit.

tests/fsharp/typecheck/init-property/niceinit.cs

@@ -0,0 +1,10 @@
+namespace System.Runtime.CompilerServices{
+
+  internal class IsExternalInit {}
+}
+
+public class NiceInit {
+  public NiceInit() {}
+  public int Val {get; init;}
+  public int OkVal {get; set;}
+}

tests/fsharp/typecheck/init-property/niceinit.fsx

@@ -0,0 +1,27 @@
+#r @"niceinit.dll"
+
+let niceinit = NiceInit(Val = 1);;
+
+let niceinit2 = NiceInit();;
+niceinit2.Val <- 5;;
+niceinit2.set_Val 5;;
+
+type StraightNewFactory =
+  static member inline mkInlineNiceInit () = NiceInit()
+  static member mkNiceInit () = NiceInit()
+;;
+let ni1 = StraightNewFactory.mkInlineNiceInit(Val=1);;
+let ni2 = StraightNewFactory.mkNiceInit(Val=1);;
+
+type IntermediateVariableWithInterleavedOpFactory =
+  static member inline mkInlineNiceInit () = 
+    let n = NiceInit()
+    printfn "inline nice init"
+    n
+  static member mkNiceInit () =
+    let n = NiceInit()
+    printfn "nice init"
+    n
+;;
+let ni3 = IntermediateVariableWithInterleavedOpFactory.mkInlineNiceInit(Val=1);;
+let ni4 = IntermediateVariableWithInterleavedOpFactory.mkNiceInit(Val=1);;