dotnet · KirtiRamchandani · Jun 14, 2026
@@ -1,5 +1,6 @@
 ### Fixed
 
+* Fix spurious FS0410 accessibility error when tuple-deconstructing bindings use private types in the same module scope. ([Issue #4161](https://github.com/dotnet/fsharp/issues/4161), [PR #19947](https://github.com/dotnet/fsharp/pull/19947))
 * Fix internal error (FS0193) when calling an indexed property setter with a named argument that matches an indexer parameter. ([Issue #16034](https://github.com/dotnet/fsharp/issues/16034), [PR #19851](https://github.com/dotnet/fsharp/pull/19851))
 * Fix missing FS1182 ("unused binding") warning for unused `let` function bindings inside class types. ([Issue #13849](https://github.com/dotnet/fsharp/issues/13849), [PR #19805](https://github.com/dotnet/fsharp/pull/19805))
 * Fix inner mutually-recursive `let rec ... and ...` functions under `--realsig+` not being lifted to top-level static methods (TLR), causing `FSharpFunc` closure allocations and loss of `tail.` opcodes — the large struct-mutual-recursion perf regression reported in [Issue #17607](https://github.com/dotnet/fsharp/issues/17607). ([PR #19882](https://github.com/dotnet/fsharp/pull/19882))

@@ -520,7 +520,7 @@ let AccessInternalsVisibleToAsInternal thisCompPath internalsVisibleToPaths acce
         accessSubstPaths (thisCompPath, internalsVisibleToPath) access)
 
 
-let CheckTypeForAccess (cenv: cenv) env objName valAcc m ty =
+let CheckTypeForAccess (cenv: cenv) env objName valAcc skipAccessibilityCheckForCompilerGeneratedVal m ty =
     if cenv.reportErrors then
 
         let visitType ty =
@@ -531,7 +531,7 @@ let CheckTypeForAccess (cenv: cenv) env objName valAcc m ty =
             | ValueSome tcref ->
                 let thisCompPath = compPathOfCcu cenv.viewCcu
                 let tyconAcc = tcref.Accessibility |> AccessInternalsVisibleToAsInternal thisCompPath cenv.internalsVisibleToPaths
-                if isLessAccessible tyconAcc valAcc then
+                if not skipAccessibilityCheckForCompilerGeneratedVal && isLessAccessible tyconAcc valAcc then
                     errorR(Error(FSComp.SR.chkTypeLessAccessibleThanType(tcref.DisplayName, objName()), m))
 
         CheckTypeDeep cenv (visitType, None, None, None, None) cenv.g env NoInfo ty
@@ -2111,7 +2111,10 @@ and CheckBinding cenv env alwaysCheckNoReraise ctxt (TBind(v, bindRhs, _) as bin
     // Check accessibility
     if (v.IsMemberOrModuleBinding || v.IsMember) && not v.IsIncrClassGeneratedMember then
         let access =  AdjustAccess (IsHiddenVal env.sigToImplRemapInfo v) (fun () -> v.DeclaringEntity.CompilationPath) v.Accessibility
-        CheckTypeForAccess cenv env (fun () -> NicePrint.stringOfQualifiedValOrMember cenv.denv cenv.infoReader vref) access v.Range v.Type
+        // Compiler-generated patternInput temps are module-init scaffolding; their promoted
+        // accessibility does not reflect the enclosing binding scope (dotnet/fsharp#4161).
+        let skipAccessibilityCheck = v.IsCompilerGenerated && v.LogicalName.StartsWith("patternInput")
+        CheckTypeForAccess cenv env (fun () -> NicePrint.stringOfQualifiedValOrMember cenv.denv cenv.infoReader vref) access skipAccessibilityCheck v.Range v.Type
 
     if cenv.reportErrors  then
 
@@ -2336,7 +2339,7 @@ let CheckRecdField isUnion cenv env (tycon: Tycon) (rfield: RecdField) =
         IsHiddenTyconRepr env.sigToImplRemapInfo tycon ||
         (not isUnion && IsHiddenRecdField env.sigToImplRemapInfo (tcref.MakeNestedRecdFieldRef rfield))
     let access = AdjustAccess isHidden (fun () -> tycon.CompilationPath) rfield.Accessibility
-    CheckTypeForAccess cenv env (fun () -> rfield.LogicalName) access m fieldTy
+    CheckTypeForAccess cenv env (fun () -> rfield.LogicalName) access false m fieldTy
 
     if isByrefLikeTyconRef g m tcref then
         // Permit Span fields in IsByRefLike types
@@ -2616,7 +2619,7 @@ let CheckEntityDefn cenv env (tycon: Entity) =
 
     // Access checks
     let access = AdjustAccess (IsHiddenTycon env.sigToImplRemapInfo tycon) (fun () -> tycon.CompilationPath) tycon.Accessibility
-    let visitType ty = CheckTypeForAccess cenv env (fun () -> tycon.DisplayNameWithStaticParametersAndUnderscoreTypars) access tycon.Range ty
+    let visitType ty = CheckTypeForAccess cenv env (fun () -> tycon.DisplayNameWithStaticParametersAndUnderscoreTypars) access false tycon.Range ty
 
     abstractSlotValsOfTycons [tycon] |> List.iter (typeOfVal >> visitType)
 

@@ -24,6 +24,38 @@ module Tuple =
         |> withOptions ["--test:ErrorRanges"]
         |> typecheck
         |> shouldSucceed
+
+    [<Theory; Directory(__SOURCE_DIRECTORY__, Includes = [|"tuples02.fs"|])>]
+    let ``Tuple - tuples02_fs - --test:ErrorRanges`` compilation =
+        compilation
+        |> asFs
+        |> withOptions ["--test:ErrorRanges"]
+        |> compileExeAndRun
+        |> shouldSucceed
+
+    [<Theory; Directory(__SOURCE_DIRECTORY__, Includes = [|"tuples03.fs"|])>]
+    let ``Tuple - tuples03_fs - --test:ErrorRanges`` compilation =
+        compilation
+        |> asFs
+        |> withOptions ["--test:ErrorRanges"]
+        |> typecheck
+        |> shouldFail
+        |> withDiagnostics [
+            Error 410, Line 6, Col 12, Line 6, Col 14, "The type 'T' is less accessible than the value, member or type 'val t': T' it is used in."
+            Error 410, Line 6, Col 9, Line 6, Col 10, "The type 'T' is less accessible than the value, member or type 'val t: T' it is used in."
+        ]
+
+    [<Theory; Directory(__SOURCE_DIRECTORY__, Includes = [|"tuples04.fs"|])>]
+    let ``Tuple - tuples04_fs - --test:ErrorRanges`` compilation =
+        compilation
+        |> asFs
+        |> withOptions ["--test:ErrorRanges"]
+        |> typecheck
+        |> shouldFail
+        |> withDiagnostics [
+            Error 410, Line 6, Col 12, Line 6, Col 14, "The type 'T' is less accessible than the value, member or type 'val internal t': T' it is used in."
+            Error 410, Line 6, Col 9, Line 6, Col 10, "The type 'T' is less accessible than the value, member or type 'val internal t: T' it is used in."
+        ]
 
     // This test was automatically generated (moved from FSharpQA suite - Conformance/PatternMatching/Tuple)
     [<Theory; Directory(__SOURCE_DIRECTORY__, Includes = [|"W_IncompleteMatches01.fs"|])>]

@@ -0,0 +1,15 @@
+module PM =
+    type PT =
+        abstract A : int
+    let a = { new PT with member __.A = 1 }
+    let b, c =
+        { new PT with member __.A = 1 }
+        , { new PT with member __.A = 1 }
+
+module private PM2 =
+    type PT =
+        abstract A : int
+    let a = { new PT with member __.A = 1 }
+    let b, c =
+        { new PT with member __.A = 1 }
+        , { new PT with member __.A = 1 }
@@ -0,0 +1,6 @@
+namespace N
+
+type internal T = T
+
+module public M =
+    let t, t' = T, T
@@ -0,0 +1,6 @@
+namespace N
+
+type private T = T
+
+module internal M =
+    let t, t' = T, T