Type check: recover in Set expressions when left side value is not mutable (#7682)

* Recover ValNoMutable and PropertyCannotBeSet errors

* Recover FieldNotMutable error

* Refactor tests

* Refactor tests

* Update baseline

src/fsharp/MethodCalls.fs

@@ -1638,5 +1638,6 @@ let MethInfoChecks g amap isInstance tyargsOpt objArgs ad m (minfo: MethInfo)  =
 exception FieldNotMutable of DisplayEnv * Tast.RecdFieldRef * range
 
 let CheckRecdFieldMutation m denv (rfinfo: RecdFieldInfo) = 
-    if not rfinfo.RecdField.IsMutable then error (FieldNotMutable(denv, rfinfo.RecdFieldRef, m))
+    if not rfinfo.RecdField.IsMutable then
+        errorR (FieldNotMutable (denv, rfinfo.RecdFieldRef, m))
 

src/fsharp/TypeChecker.fs

@@ -9362,7 +9362,8 @@ and TcItemThen cenv overallTy env tpenv (item, mItem, rest, afterResolution) del
                 if isByrefTy g vty then 
                     destByrefTy g vty 
                 else 
-                    if not vref.IsMutable then error (ValNotMutable(env.DisplayEnv, vref, mStmt))
+                    if not vref.IsMutable then
+                        errorR (ValNotMutable (env.DisplayEnv, vref, mStmt))
                     vty 
             // Always allow subsumption on assignment to fields
             let e2', tpenv = TcExprFlex cenv true false vty2 env tpenv e2
@@ -9415,15 +9416,15 @@ and TcItemThen cenv overallTy env tpenv (item, mItem, rest, afterResolution) del
             if meths.IsEmpty then 
                 let meths = pinfos |> GettersOfPropInfos
                 let isByrefMethReturnSetter = meths |> List.exists (function (_,Some pinfo) -> isByrefTy g (pinfo.GetPropertyType(cenv.amap,mItem)) | _ -> false)
-                if isByrefMethReturnSetter then
-                    // x.P <- ... byref setter
-                    if isNil meths then error (Error (FSComp.SR.tcPropertyIsNotReadable nm, mItem))
-                    TcMethodApplicationThen cenv env overallTy None tpenv tyargsOpt [] mItem mItem nm ad NeverMutates true meths afterResolution NormalValUse args ExprAtomicFlag.Atomic delayed
-                else
-                    error (Error (FSComp.SR.tcPropertyCannotBeSet1 nm, mItem))
+                if not isByrefMethReturnSetter then
+                    errorR (Error (FSComp.SR.tcPropertyCannotBeSet1 nm, mItem))
+                // x.P <- ... byref setter
+                if isNil meths then error (Error (FSComp.SR.tcPropertyIsNotReadable nm, mItem))
+                TcMethodApplicationThen cenv env overallTy None tpenv tyargsOpt [] mItem mItem nm ad NeverMutates true meths afterResolution NormalValUse args ExprAtomicFlag.Atomic delayed
             else
                 let args = if pinfo.IsIndexer then args else []
-                if isNil meths then error (Error (FSComp.SR.tcPropertyCannotBeSet1 nm, mItem))
+                if isNil meths then
+                    errorR (Error (FSComp.SR.tcPropertyCannotBeSet1 nm, mItem))
                 // Note: static calls never mutate a struct object argument
                 TcMethodApplicationThen cenv env overallTy None tpenv tyargsOpt [] mStmt mItem nm ad NeverMutates true meths afterResolution NormalValUse (args@[e2]) ExprAtomicFlag.NonAtomic otherDelayed
         | _ -> 
@@ -9600,12 +9601,11 @@ and TcLookupThen cenv overallTy env tpenv mObjExpr objExpr objExprTy longId dela
             if meths.IsEmpty then 
                 let meths = pinfos |> GettersOfPropInfos
                 let isByrefMethReturnSetter = meths |> List.exists (function (_,Some pinfo) -> isByrefTy cenv.g (pinfo.GetPropertyType(cenv.amap,mItem)) | _ -> false)
-                if isByrefMethReturnSetter then
-                    // x.P <- ... byref setter
-                    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
-                    error (Error (FSComp.SR.tcPropertyCannotBeSet1 nm, mItem))
+                if not isByrefMethReturnSetter then
+                    errorR (Error (FSComp.SR.tcPropertyCannotBeSet1 nm, mItem))
+                // x.P <- ... byref setter
+                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
                 let args = if pinfo.IsIndexer then args else []
                 let mut = (if isStructTy cenv.g (tyOfExpr cenv.g objExpr) then DefinitelyMutates else PossiblyMutates)

tests/fsharp/core/span/test3.bsl

@@ -10,5 +10,5 @@ test3.fsx(47,21,47,27): typecheck error FS0027: This value is not mutable. Consi
 test3.fsx(46,26,46,27): typecheck error FS0193: Type constraint mismatch. The type 
     'Span<int>'    
 is not compatible with type
-    'seq<'a>'    
+    'seq<int>'    
 

tests/service/Common.fs

@@ -5,6 +5,7 @@ open System.IO
 open System.Collections.Generic
 open FSharp.Compiler
 open FSharp.Compiler.SourceCodeServices
+open FsUnit
 
 #if NETCOREAPP2_0
 let readRefs (folder : string) (projectFile: string) =
@@ -304,6 +305,34 @@ let rec allSymbolsInEntities compGen (entities: IList<FSharpEntity>) =
           yield! allSymbolsInEntities compGen e.NestedEntities ]
 
 
+let getSymbolUses (source: string) =
+    let _, typeCheckResults = parseAndCheckScript("/home/user/Test.fsx", source) 
+    typeCheckResults.GetAllUsesOfAllSymbolsInFile() |> Async.RunSynchronously
+
+let getSymbols (source: string) =
+    getSymbolUses source
+    |> Array.map (fun symbolUse -> symbolUse.Symbol)
+
+
+let getSymbolName (symbol: FSharpSymbol) =
+    match symbol with
+    | :? FSharpMemberOrFunctionOrValue as mfv -> Some mfv.LogicalName
+    | :? FSharpEntity as entity -> Some entity.LogicalName
+    | :? FSharpGenericParameter as parameter -> Some parameter.Name
+    | :? FSharpParameter as parameter -> parameter.Name
+    | :? FSharpStaticParameter as parameter -> Some parameter.Name
+    | :? FSharpActivePatternCase as case -> Some case.Name
+    | :? FSharpUnionCase as case -> Some case.Name
+    | _ -> None
+
+
+let assertContainsSymbolWithName name source =
+    getSymbols source
+    |> Array.choose getSymbolName
+    |> Array.contains name
+    |> shouldEqual true
+
+
 let coreLibAssemblyName =
 #if NETCOREAPP2_0
     "System.Runtime"

tests/service/EditorTests.fs

@@ -1319,3 +1319,40 @@ let ``FSharpField.IsNameGenerated`` () =
      "type U = Case of string * Item2: string * string * Name: string",
         ["Item1", true; "Item2", false; "Item3", true; "Name", false]]
     |> List.iter (fun (source, expected) -> checkFields source |> shouldEqual expected)
+
+
+[<Test>]
+let ``ValNoMutable recovery`` () =
+    let source = """
+let x = 1
+x <-
+    let y = 1
+    y
+"""
+    assertContainsSymbolWithName "y" source
+
+
+[<Test>]
+let ``PropertyCannotBeSet recovery`` () =
+    let source = """
+type T =
+    static member P = 1
+
+T.P <-
+    let y = 1
+    y
+"""
+    assertContainsSymbolWithName "y" source
+
+
+[<Test>]
+let ``FieldNotMutable recovery`` () =
+    let source = """
+type R =
+    { F: int }
+
+{ F = 1 }.F <-
+    let y = 1
+    y
+"""
+    assertContainsSymbolWithName "y" source