Fix checking nested fields for records (#18964)

Author: evgTSV

docs/release-notes/.FSharp.Compiler.Service/11.0.0.md

@@ -2,8 +2,9 @@
 
 * Scripts: Fix resolving the dotnet host path when an SDK directory is specified. ([PR #18960](https://github.com/dotnet/fsharp/pull/18960))
 * Fix excessive StackGuard thread jumping ([PR #18971](https://github.com/dotnet/fsharp/pull/18971))
+* Checking: Fix checking nested fields for records and anonymous ([PR #18964](https://github.com/dotnet/fsharp/pull/18964))
 * Fix name is bound multiple times is not reported in 'as' pattern ([PR #18984](https://github.com/dotnet/fsharp/pull/18984))
-* Type relations cache: handle potentially "infinite" types ([PR #19010](https://github.com/dotnet/fsharp/pull/19010))  
+* Type relations cache: handle potentially "infinite" types ([PR #19010](https://github.com/dotnet/fsharp/pull/19010))
 
 ### Added
 

src/Compiler/Checking/CheckRecordSyntaxHelpers.fs

@@ -156,12 +156,26 @@ let TransformAstForNestedUpdates (cenv: TcFileState) (env: TcEnv) overallTy (lid
         (accessIds, outerFieldId),
         Some(synExprRecd (recdExprCopyInfo (fields |> List.map fst) withExpr) outerFieldId rest exprBeingAssigned)
 
+/// This name is used when a complex expression is bound for use as a binding in a copy-and-update expression.
+/// For example, in `{ f () with ... }`, `f ()` is replaced by `let bind@ = f ()`
+let BindIdText = "bind@"
+
+/// Finding the 'bind@' identifier is the only way to detect that an expression has already been bound.
+let inline (|IsSimpleOrBoundExpr|_|) (withExprOpt: (SynExpr * BlockSeparator) option) =
+    match withExprOpt with
+    | None -> true
+    | Some(expr, _) ->
+        match expr with
+        | SynExpr.LongIdent(_, lIds, _, _) -> lIds.LongIdent |> List.exists (fun id -> id.idText = BindIdText)
+        | SynExpr.Ident _ -> true
+        | _ -> false
+
 /// When the original expression in copy-and-update is more complex than `{ x with ... }`, like `{ f () with ... }`,
 /// we bind it first, so that it's not evaluated multiple times during a nested update
 let BindOriginalRecdExpr (withExpr: SynExpr * BlockSeparator) mkRecdExpr =
     let originalExpr, blockSep = withExpr
     let mOrigExprSynth = originalExpr.Range.MakeSynthetic()
-    let id = mkSynId mOrigExprSynth "bind@"
+    let id = mkSynId mOrigExprSynth BindIdText
     let withExpr = SynExpr.Ident id, blockSep
 
     let binding =

src/Compiler/Checking/CheckRecordSyntaxHelpers.fsi

@@ -19,5 +19,9 @@ val TransformAstForNestedUpdates<'a> :
     withExpr: SynExpr * (range * 'a) ->
         (Ident list * Ident) * SynExpr option
 
+val BindIdText: string
+
+val inline (|IsSimpleOrBoundExpr|_|): withExprOpt: (SynExpr * BlockSeparator) option -> bool
+
 val BindOriginalRecdExpr:
     withExpr: SynExpr * BlockSeparator -> mkRecdExpr: ((SynExpr * BlockSeparator) option -> SynExpr) -> SynExpr

src/Compiler/Checking/Expressions/CheckExpressions.fs

@@ -5895,9 +5895,8 @@ and TcExprUndelayed (cenv: cenv) (overallTy: OverallTy) env tpenv (synExpr: SynE
         TcExprTuple cenv overallTy env tpenv (isExplicitStruct, args, m)
 
     | SynExpr.AnonRecd (isStruct, withExprOpt, unsortedFieldExprs, mWholeExpr, trivia) ->
-        match withExprOpt with
-        | None
-        | Some(SynExpr.Ident _, _) ->
+        match withExprOpt with 
+        | None | IsSimpleOrBoundExpr ->
             TcNonControlFlowExpr env <| fun env ->
             TcPossiblyPropagatingExprLeafThenConvert (fun ty -> isAnonRecdTy g ty || isTyparTy g ty) cenv overallTy env mWholeExpr (fun overallTy ->
                 TcAnonRecdExpr cenv overallTy env tpenv (isStruct, withExprOpt, unsortedFieldExprs, mWholeExpr)
@@ -5929,10 +5928,9 @@ and TcExprUndelayed (cenv: cenv) (overallTy: OverallTy) env tpenv (synExpr: SynE
         let binds = unionBindingAndMembers binds members
         TcExprObjectExpr cenv overallTy env tpenv (synObjTy, argopt, binds, extraImpls, mNewExpr, m)
 
-    | SynExpr.Record (inherits, withExprOpt, synRecdFields, mWholeExpr) ->
+    | SynExpr.Record (inherits, withExprOpt, synRecdFields, mWholeExpr) ->        
         match withExprOpt with
-        | None
-        | Some(SynExpr.Ident _, _) ->
+        | None | IsSimpleOrBoundExpr ->
             TcNonControlFlowExpr env <| fun env ->
             TcExprRecord cenv overallTy env tpenv (inherits, withExprOpt, synRecdFields, mWholeExpr)
         | Some withExpr ->

tests/FSharp.Compiler.ComponentTests/Language/CopyAndUpdateTests.fs

@@ -480,3 +480,56 @@ if actual <> expected then
     |> withLangVersion80
     |> compileExeAndRun
     |> verifyOutput "once"
+
+[<Fact>]
+let ``N-Nested copy-and-update works when the starting expression is not a simple identifier``() =
+    FSharp """
+module CopyAndUpdateTests
+type SubSubTest = {
+    Z: int
+}
+
+type SubTest = {
+    Y: SubSubTest
+}
+
+type Test = {
+    X: SubTest
+}
+
+let getTest () =
+    { X = { Y = { Z = 0 } } }
+
+[<EntryPoint>]
+let main argv =
+    let a = {
+         getTest () with
+            X.Y.Z = 1 
+    }
+    printfn "%i" a.X.Y.Z |> ignore
+    0
+    """
+    |> typecheck
+    |> shouldSucceed
+    |> verifyOutput "1"
+
+[<Fact>]
+let ``N-Nested, anonymous copy-and-update works when the starting expression is not a simple identifier``() =
+    FSharp """
+module CopyAndUpdateTests
+
+let getTest () =
+    {| X = {| Y = {| Z = 0 |} |} |}
+
+[<EntryPoint>]
+let main argv =
+    let a = {|
+         getTest () with
+            X.Y.Z = 1 
+    |}
+    printfn "%i" a.X.Y.Z |> ignore
+    0
+    """
+    |> typecheck
+    |> shouldSucceed
+    |> verifyOutput "1"