dotnet · T-Gro · Jun 9, 2026 · Jun 9, 2026 · Jun 9, 2026 · Jun 9, 2026
@@ -75,6 +75,7 @@
 ([PR #19724](https://github.com/dotnet/fsharp/pull/19724))
 * Emit debug points at a stack-empty position ([PR #19877](https://github.com/dotnet/fsharp/pull/19877))
 * Fix spurious XmlDoc warnings (unknown parameter / no documentation for parameter) under `--warnon:3390` when a get/set property documents the full parameter set across both accessors. ([Issue #13684](https://github.com/dotnet/fsharp/issues/13684), [PR #19884](https://github.com/dotnet/fsharp/pull/19884))
+* Fix FSI pretty printing to distinguish anonymous records (`{| ... |}`) from nominal records (`{ ... }`). ([Issue #6116](https://github.com/dotnet/fsharp/issues/6116), [PR #19919](https://github.com/dotnet/fsharp/pull/19919))
 
 ### Added
 

@@ -149,6 +149,8 @@ module TaggedText =
     let rightBracket = tagPunctuation "]"
     let leftBrace = tagPunctuation "{"
     let rightBrace = tagPunctuation "}"
+    let leftBraceBar = tagPunctuation "{|"
+    let rightBraceBar = tagPunctuation "|}"
     let equals = tagOperator "="
 
 #if COMPILER
@@ -216,8 +218,6 @@ module TaggedText =
     // common tagged literals
     let lineBreak = tagLineBreak "\n"
     let space = tagSpace " "
-    let leftBraceBar = tagPunctuation "{|"
-    let rightBraceBar = tagPunctuation "|}"
     let arrow = tagPunctuation "->"
     let dot = tagPunctuation "."
     let leftAngle = tagPunctuation "<"
@@ -487,11 +487,17 @@ module ReflectUtils =
         | Value
         | Reference
 
+    [<RequireQualifiedAccess; StructuralComparison; StructuralEquality>]
+    type RecordKind =
+        | Nominal
+        | AnonReference
+        | AnonStruct
+
     [<NoEquality; NoComparison>]
     type ValueInfo =
         | TupleValue of TupleType * (obj * Type)[]
         | FunctionClosureValue of Type
-        | RecordValue of (string * obj * Type)[]
+        | RecordValue of kind: RecordKind * (string * obj * Type)[]
         | UnionCaseValue of string * (string * (obj * Type))[]
         | ExceptionValue of Type * (string * (obj * Type))[]
         | NullValue
@@ -555,7 +561,17 @@ module ReflectUtils =
                 elif FSharpType.IsRecord(reprty, bindingFlags) then
                     let props = FSharpType.GetRecordFields(reprty, bindingFlags)
 
+                    let kind =
+                        if reprty.Name.StartsWith("<>f__AnonymousType", StringComparison.Ordinal) then
+                            if reprty.IsValueType then
+                                RecordKind.AnonStruct
+                            else
+                                RecordKind.AnonReference
+                        else
+                            RecordKind.Nominal
+
                     RecordValue(
+                        kind,
                         props
                         |> Array.map (fun prop -> prop.Name, prop.GetValue(obj, null), prop.PropertyType)
                     )
@@ -861,13 +877,18 @@ module Display =
 
     let unitL = wordL (tagPunctuation "()")
 
-    let makeRecordL nameXs =
+    let makeRecordL kind nameXs =
         let itemL (name, xL) = (wordL name ^^ wordL equals) -- xL
 
         let braceL xs =
-            (wordL leftBrace) ^^ xs ^^ (wordL rightBrace)
+            match kind with
+            | RecordKind.AnonReference
+            | RecordKind.AnonStruct -> (wordL leftBraceBar) ^^ xs ^^ (wordL rightBraceBar)
+            | RecordKind.Nominal -> (wordL leftBrace) ^^ xs ^^ (wordL rightBrace)
 
-        nameXs |> List.map itemL |> aboveListL |> braceL
+        let itemLayouts = nameXs |> List.map itemL
+
+        braceL (aboveListL itemLayouts)
 
     let makePropertiesL nameXs =
         let itemL (name, v) =
@@ -1200,12 +1221,17 @@ module Display =
             | TupleType.Value -> structL ^^ fields
             | TupleType.Reference -> fields
 
-        and recordValueL depthLim items =
+        and recordValueL depthLim kind items =
             let itemL (name, x, ty) =
                 countNodes 1
                 tagRecordField name, nestedObjL depthLim Precedence.BracketIfTuple (x, ty)
 
-            makeRecordL (List.map itemL items)
+            let body = makeRecordL kind (List.map itemL items)
+
+            match kind with
+            | RecordKind.AnonStruct -> structL -- body
+            | RecordKind.AnonReference
+            | RecordKind.Nominal -> body
 
         and listValueL depthLim constr recd =
             match constr with
@@ -1471,7 +1497,7 @@ module Display =
             match repr with
             | TupleValue(tupleType, vals) -> tupleValueL depthLim prec vals tupleType
 
-            | RecordValue items -> recordValueL depthLim (Array.toList items)
+            | RecordValue(kind, items) -> recordValueL depthLim kind (Array.toList items)
 
             | UnionCaseValue(constr, recd) when // x is List<T>. Note: "null" is never a valid list value.
                 (not (isNull x)) && isListType (x.GetType())

@@ -9093,7 +9093,7 @@ module PercentAPublicTests =
 
     let testPercentAMyAnonymousRecord () =
         let data = {| A = "Hello, World!"; B = 1.027m; C = 1028; D = 1.029 |}
-        test "test8901" (lazy (sprintf "%A" data).Replace("\n", ";"))  """{ A = "Hello, World!";  B = 1.027M;  C = 1028;  D = 1.029 }"""
+        test "test8901" (lazy (sprintf "%A" data).Replace("\n", ";"))  """{| A = "Hello, World!";   B = 1.027M;   C = 1028;   D = 1.029 |}"""
 
     let testDiscriminatedUnion () =
         test "test8902" (lazy (sprintf "%A" (IntNumber 10 )).Replace("\n", ";"))  """IntNumber 10"""

@@ -63,10 +63,10 @@ function CheckTrim($root, $tfm, $outputfile, $expected_len, $callerLineNumber) {
 $allErrors = @()
 
 # Check net9.0 trimmed assemblies
-$allErrors += CheckTrim -root "SelfContained_Trimming_Test" -tfm "net9.0" -outputfile "FSharp.Core.dll" -expected_len 311808 -callerLineNumber 66
+$allErrors += CheckTrim -root "SelfContained_Trimming_Test" -tfm "net9.0" -outputfile "FSharp.Core.dll" -expected_len 314880 -callerLineNumber 66
 
 # Check net9.0 trimmed assemblies with static linked FSharpCore
-$allErrors += CheckTrim -root "StaticLinkedFSharpCore_Trimming_Test" -tfm "net9.0" -outputfile "StaticLinkedFSharpCore_Trimming_Test.dll" -expected_len 9169408 -callerLineNumber 69
+$allErrors += CheckTrim -root "StaticLinkedFSharpCore_Trimming_Test" -tfm "net9.0" -outputfile "StaticLinkedFSharpCore_Trimming_Test.dll" -expected_len 9172992 -callerLineNumber 69
 
 # Check net9.0 trimmed assemblies with F# metadata resources removed
 $allErrors += CheckTrim -root "FSharpMetadataResource_Trimming_Test" -tfm "net9.0" -outputfile "FSharpMetadataResource_Trimming_Test.dll" -expected_len 7609344 -callerLineNumber 72

@@ -388,6 +388,7 @@
     <Compile Include="Scripting\TypeCheckOnlyTests.fs" />
     <Compile Include="Scripting\PreferredUiLangTests.fs" />
     <Compile Include="InteractiveSession\Misc.fs" />
+    <Compile Include="InteractiveSession\AnonRecordPrinting.fs" />
     <Compile Include="TypeChecks\TypeRelations.fs" />
     <Compile Include="TypeChecks\SeqTypeCheckTests.fs" />
     <Compile Include="TypeChecks\CheckDeclarationsTests.fs" />

@@ -0,0 +1,127 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+/// Tests for FSI pretty-printing of anonymous records (regression for dotnet/fsharp#6116).
+/// Anonymous records must be printed with `{| |}` braces, distinct from nominal records which use `{ }`.
+namespace InteractiveSession
+
+open Xunit
+open FSharp.Test.Compiler
+
+module AnonRecordPrinting =
+
+    // --- Anonymous records: must use {| |} ---
+
+    // NOTE: Assertions target the VALUE portion (after `=`) only, because the
+    // `val it: ...` type-annotation already contains `{| ... |}` for anon
+    // record types regardless of the value-printing bug being fixed here.
+
+    [<Fact>]
+    let ``Anonymous record prints with bar braces``() =
+        // The layout engine may break multi-field records across lines, so the
+        // opening and closing bar-braces are checked separately (mirrors the
+        // approach used by the nominal-record test below).
+        Fsx """
+let r = {| Name = "Phillip"; Age = 28 |};;
+()
+"""
+        |> withOptions ["--nologo"]
+        |> runFsi
+        |> shouldSucceed
+        |> withStdOutContains "= {| Age = 28"
+        |> withStdOutContains "Name = \"Phillip\" |}"
+        |> ignore
+
+    [<Fact>]
+    let ``Anonymous record with single field prints with bar braces``() =
+        Fsx """
+{| X = 1 |};;
+()
+"""
+        |> withOptions ["--nologo"]
+        |> runFsi
+        |> shouldSucceed
+        |> withStdOutContains "= {| X = 1 |}"
+        |> ignore
+
+    [<Fact>]
+    let ``Nested anonymous record prints with bar braces at both levels``() =
+        Fsx """
+{| Inner = {| X = 1 |} |};;
+()
+"""
+        |> withOptions ["--nologo"]
+        |> runFsi
+        |> shouldSucceed
+        // Both outer and inner record values must use bar-braces.
+        |> withStdOutContains "= {| Inner = {| X = 1 |} |}"
+        |> ignore
+
+    [<Fact>]
+    let ``Struct anonymous record prints with struct keyword and bar braces``() =
+        // The layout engine may break multi-field records across lines, so the
+        // `struct {|` opener and the `|}` closer are checked separately.
+        Fsx """
+struct {| X = 1; Y = 2 |};;
+()
+"""
+        |> withOptions ["--nologo"]
+        |> runFsi
+        |> shouldSucceed
+        |> withStdOutContains "= struct {| X = 1"
+        |> withStdOutContains "Y = 2 |}"
+        |> ignore
+
+    // --- Nominal records: must KEEP printing with { } (regression guard) ---
+
+    [<Fact>]
+    let ``Nominal record still prints with plain braces and not bar braces``() =
+        Fsx """
+type R = { Name: string; Age: int }
+let r = { Name = "Phillip"; Age = 28 };;
+()
+"""
+        |> withOptions ["--nologo"]
+        |> runFsi
+        |> shouldSucceed
+        |> withStdOutContains "{ Name = \"Phillip\""
+        |> withStdOutContains "Age = 28 }"
+        |> ignore
+
+    // --- Other shapes must be unchanged (regression guard) ---
+
+    [<Fact>]
+    let ``Tuple printing unchanged``() =
+        Fsx """
+(1, "x");;
+()
+"""
+        |> withOptions ["--nologo"]
+        |> runFsi
+        |> shouldSucceed
+        |> withStdOutContains "(1, \"x\")"
+        |> ignore
+
+    [<Fact>]
+    let ``Discriminated union printing unchanged``() =
+        Fsx """
+type DU = A of int | B of string
+A 42;;
+()
+"""
+        |> withOptions ["--nologo"]
+        |> runFsi
+        |> shouldSucceed
+        |> withStdOutContains "A 42"
+        |> ignore
+
+    [<Fact>]
+    let ``List printing unchanged``() =
+        Fsx """
+[1; 2; 3];;
+()
+"""
+        |> withOptions ["--nologo"]
+        |> runFsi
+        |> shouldSucceed
+        |> withStdOutContains "[1; 2; 3]"
+        |> ignore
@@ -52,8 +52,8 @@ module KindB1 =
     check "coijoiwcnkwle1"  {| a = 1 |} {| a = 1 |}
     check "coijoiwcnkwle2"  {| a = 2 |}  {| a = 2 |}
 
-    check "coijoiwcnkwle3"  (sprintf "%A"  {| X = 10 |}) "{ X = 10 }"
-    check "coijoiwcnkwle4"  (sprintf "%A"  {| X = 10; Y = 1 |}) "{ X = 10\n  Y = 1 }"
+    check "coijoiwcnkwle3"  (sprintf "%A"  {| X = 10 |}) "{| X = 10 |}"
+    check "coijoiwcnkwle4"  (sprintf "%A"  {| X = 10; Y = 1 |}) "{| X = 10\n   Y = 1 |}"
     check "clekoiew09" (f2 {| X = {| X = 10 |} |}) 10
     check "cewkew0oijew" (f2 {| X = {| X = 20 |} |})  20
 

@@ -25,13 +25,13 @@ module Test =
 
     let testAccess = (KindB1.data1.X, KindB1.data3.X)
 
-    check "coijoiwcnkwle2"  (sprintf "%A"  KindB1.data1) "{ X = 1 }"
+    check "coijoiwcnkwle2"  (sprintf "%A"  KindB1.data1) "{| X = 1 |}"
 
 module Tests2 = 
 
     let testAccess = (KindB2.data1.X, KindB2.data3.X, KindB2.data3.Y)
 
-    check "coijoiwcnkwle3"  (sprintf "%A"  KindB2.data1) "{ X = 1 }"
+    check "coijoiwcnkwle3"  (sprintf "%A"  KindB2.data1) "{| X = 1 |}"
 
     let _ = (KindB2.data1 = KindB2.data1)
 
@@ -49,7 +49,7 @@ module CrossAssemblyTest =
         check "vrknvio1" (SampleAPI.SampleFunction {| A=1; B = "abc" |}) 4 // note, this is creating an instance of an anonymous record from another assembly.
         check "vrknvio2" (SampleAPI.SampleFunctionAcceptingList [ {| A=1; B = "abc" |}; {| A=2; B = "def" |} ]) [4; 5] // note, this is creating an instance of an anonymous record from another assembly.
         check "vrknvio3" (let d = SampleAPI.SampleFunctionReturningAnonRecd() in d.A + d.B.Length) 4 
-        check "vrknvio4" (let d = SampleAPIStruct.SampleFunctionReturningAnonRecd() in d.ToString()) ("{ A = 1\n  " + """B = "abc" }""")
+        check "vrknvio4" (let d = SampleAPIStruct.SampleFunctionReturningAnonRecd() in d.ToString()) ("struct {| A = 1\n          " + """B = "abc" |}""")
     tests()
 
 module CrossAssemblyTestStruct = 

@@ -2810,7 +2810,7 @@ val it: unit = ()
 > {"AnonRecordField2":10}
 val it: unit = ()
 
-> val it: {| AnonRecordField2: int |} = { AnonRecordField2 = 11 }
+> val it: {| AnonRecordField2: int |} = {| AnonRecordField2 = 11 |}
 
 module FSI_0326.Project.fsproj
 
@@ -2837,10 +2837,10 @@ val test4a: string = "{"MutableField4":15}"
 > type R5 = {| AnonRecordField5: int |}
 val test5a: string = "{"AnonRecordField5":17}"
 
-> val test5b: R5 = { AnonRecordField5 = 17 }
+> val test5b: R5 = {| AnonRecordField5 = 17 |}
 
 > val test5c: string = "{"AnonRecordField5":18}"
 
-> val test5d: R5 = { AnonRecordField5 = 18 }
+> val test5d: R5 = {| AnonRecordField5 = 18 |}
 
 > > > 
@@ -2055,7 +2055,7 @@ val it: unit = ()
 > {"AnonRecordField2":10}
 val it: unit = ()
 
-> val it: {| AnonRecordField2: int |} = { AnonRecordField2 = 11 }
+> val it: {| AnonRecordField2: int |} = {| AnonRecordField2 = 11 |}
 
 module FSI_0326.Project.fsproj
 
@@ -2082,10 +2082,10 @@ val test4a: string = "{"MutableField4":15}"
 > type R5 = {| AnonRecordField5: int |}
 val test5a: string = "{"AnonRecordField5":17}"
 
-> val test5b: R5 = { AnonRecordField5 = 17 }
+> val test5b: R5 = {| AnonRecordField5 = 17 |}
 
 > val test5c: string = "{"AnonRecordField5":18}"
 
-> val test5d: R5 = { AnonRecordField5 = 18 }
+> val test5d: R5 = {| AnonRecordField5 = 18 |}
 
 > > > 
@@ -6357,7 +6357,7 @@ val it: unit = ()
 > {"AnonRecordField2":10}
 val it: unit = ()
 
-> val it: {| AnonRecordField2: int |} = { AnonRecordField2 = 11 }
+> val it: {| AnonRecordField2: int |} = {| AnonRecordField2 = 11 |}
 
 module FSI_0325.Project.fsproj
 
@@ -6384,10 +6384,10 @@ val test4a: string = "{"MutableField4":15}"
 > type R5 = {| AnonRecordField5: int |}
 val test5a: string = "{"AnonRecordField5":17}"
 
-> val test5b: R5 = { AnonRecordField5 = 17 }
+> val test5b: R5 = {| AnonRecordField5 = 17 |}
 
 > val test5c: string = "{"AnonRecordField5":18}"
 
-> val test5d: R5 = { AnonRecordField5 = 18 }
+> val test5d: R5 = {| AnonRecordField5 = 18 |}
 
 > > > 
@@ -1824,7 +1824,7 @@ val it: unit
 > {"AnonRecordField2":10}
 val it: unit = ()
 
-> val it: {| AnonRecordField2: int |} = { AnonRecordField2 = 11 }
+> val it: {| AnonRecordField2: int |} = {| AnonRecordField2 = 11 |}
 
 module FSI_0326.Project.fsproj