Skip accessibility checks for compiler-generated pattern inputs when used within the same module scope.

docs/release-notes/.FSharp.Compiler.Service/9.0.300.md

@@ -20,6 +20,7 @@
 * Fix duplicate parse error reporting for GetBackgroundCheckResultsForFileInProject ([Issue #18379](https://github.com/dotnet/fsharp/issues/18379) [PR #18380](https://github.com/dotnet/fsharp/pull/18380))
 * Fix MethodDefNotFound when compiling code invoking delegate with option parameter ([Issue #5171](https://github.com/dotnet/fsharp/issues/5171), [PR #18385](https://github.com/dotnet/fsharp/pull/18385))
 * Fix #r nuget ..." downloads unneeded packages ([Issue #18231](https://github.com/dotnet/fsharp/issues/18231), [PR #18393](https://github.com/dotnet/fsharp/pull/18393))
+* Skip accessibility checks for compiler-generated pattern inputs when used within the same module scope. ([Issue #4161](https://github.com/dotnet/fsharp/issues/4161), [PR #18426](https://github.com/dotnet/fsharp/pull/18426))
 * Reenable β-reduction and subsequent reoptimization of immediately-invoked F#-defined generic delegates. ([PR #18401](https://github.com/dotnet/fsharp/pull/18401))
 * Fixed [#18433](https://github.com/dotnet/fsharp/issues/18433), a rare case of an internal error in xml comment processing. ([PR #18436](https://github.com/dotnet/fsharp/pull/18436))
 

src/Compiler/Checking/PostInferenceChecks.fs

@@ -521,7 +521,7 @@ 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 accessedValIsCompilerGenerated m ty =
     if cenv.reportErrors then
 
         let visitType ty =
@@ -532,8 +532,9 @@ 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
-                    errorR(Error(FSComp.SR.chkTypeLessAccessibleThanType(tcref.DisplayName, (objName())), m))
+                // Skip accessibility checks for compiler-generated pattern inputs
+                if not accessedValIsCompilerGenerated && 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
 
@@ -2058,7 +2059,7 @@ 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
+        CheckTypeForAccess cenv env (fun () -> NicePrint.stringOfQualifiedValOrMember cenv.denv cenv.infoReader vref) access vref.IsCompilerGenerated v.Range v.Type
 
     if cenv.reportErrors  then
 
@@ -2283,7 +2284,7 @@ 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
@@ -2551,7 +2552,7 @@ 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)
 

tests/FSharp.Compiler.ComponentTests/Conformance/PatternMatching/Tuple/Tuple.fs

@@ -25,6 +25,38 @@ module Tuple =
         |> 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"|])>]
     let ``Tuple - W_IncompleteMatches01_fs - --test:ErrorRanges`` compilation =

tests/FSharp.Compiler.ComponentTests/Conformance/PatternMatching/Tuple/tuples02.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 }

tests/FSharp.Compiler.ComponentTests/Conformance/PatternMatching/Tuple/tuples03.fs

@@ -0,0 +1,6 @@
+namespace N
+
+type internal T = T
+
+module public M =
+    let t, t' = T, T

tests/FSharp.Compiler.ComponentTests/Conformance/PatternMatching/Tuple/tuples04.fs

@@ -0,0 +1,6 @@
+namespace N
+
+type private T = T
+
+module internal M =
+    let t, t' = T, T