Fix #7931: Resolve opened namespaces for attributes in recursive scopes (#19502)

Author: Copilot

docs/release-notes/.FSharp.Compiler.Service/11.0.100.md

@@ -3,6 +3,7 @@
 * Fix attributes on return type of unparenthesized tuple methods being silently dropped from IL. ([Issue #462](https://github.com/dotnet/fsharp/issues/462), [PR #19714](https://github.com/dotnet/fsharp/pull/19714))
 * Fix internal error FS0073 "Undefined or unsolved type variable" in IlxGen when nested inline SRTP functions with multiple overloads leave unsolved typars in the non-witness codegen path. ([Issue #19709](https://github.com/dotnet/fsharp/issues/19709), [PR #19710](https://github.com/dotnet/fsharp/pull/19710))
 * Fix NRE when calling virtual Object methods on value types through inline SRTP functions. ([Issue #8098](https://github.com/dotnet/fsharp/issues/8098), [PR #19511](https://github.com/dotnet/fsharp/pull/19511))
+* Fix attributes not resolved from opened namespaces in `namespace rec` / `module rec` scopes. ([Issue #7931](https://github.com/dotnet/fsharp/issues/7931), [PR #19502](https://github.com/dotnet/fsharp/pull/19502))
 * Fix DU case names matching IWSAM member names no longer cause duplicate property entries. (Issue [#14321](https://github.com/dotnet/fsharp/issues/14321), [PR #19341](https://github.com/dotnet/fsharp/pull/19341))
 * Fix DefaultAugmentation(false) duplicate entry in method table. (Issue [#16565](https://github.com/dotnet/fsharp/issues/16565), [PR #19341](https://github.com/dotnet/fsharp/pull/19341))
 * Fix abstract event accessors now have SpecialName flag. (Issue [#5834](https://github.com/dotnet/fsharp/issues/5834), [PR #19341](https://github.com/dotnet/fsharp/pull/19341))

src/Compiler/Checking/CheckDeclarations.fs

@@ -2735,6 +2735,23 @@ module EstablishTypeDefinitionCores =
                | _ -> () ]
             |> set
 
+    /// Pre-process open declarations from a list of mutually recursive shapes so that
+    /// opened namespaces are available during Phase1A attribute checking.
+    /// In recursive scopes, opens are normally processed in Phase1AB (after Phase1A builds
+    /// module/type entities), but attributes on modules need the opened namespaces.
+    /// Errors are suppressed because some opens may refer to modules being defined in the
+    /// current recursive scope, which don't exist yet during Phase1A. Those opens will be
+    /// properly processed (with full error reporting) during Phase1AB.
+    let private preProcessOpensForPhase1A (cenv: cenv) (env: TcEnv) (shapes: MutRecShapes<_, _, _>) =
+        suppressErrorReporting (fun () ->
+            use _holder = TemporarilySuspendReportingTypecheckResultsToSink cenv.tcSink
+            (env, shapes) ||> List.fold (fun env shape ->
+                match shape with
+                | MutRecShape.Open(MutRecDataForOpen(SynOpenDeclTarget.ModuleOrNamespace _ as target, openm, moduleRange, _)) ->
+                    let env, _ = TcOpenDecl cenv openm moduleRange env target
+                    env
+                | _ -> env))
+
     let TcTyconDefnCore_Phase1A_BuildInitialModule (cenv: cenv) envInitial parent typeNames compInfo decls =
         let g = cenv.g
         let (SynComponentInfo(Attributes attribs, _, _, longPath, xml, _, vis, im)) = compInfo 
@@ -2750,7 +2767,11 @@ module EstablishTypeDefinitionCores =
         CheckForDuplicateConcreteType envInitial id.idText im
         CheckNamespaceModuleOrTypeName g id
 
-        let envForDecls, moduleTyAcc = MakeInnerEnv true envInitial id moduleKind    
+        let envForDecls, moduleTyAcc = MakeInnerEnv true envInitial id moduleKind
+
+        // Pre-process opens from children so nested modules can see opened namespaces during attribute checking
+        let envForDecls = preProcessOpensForPhase1A cenv envForDecls decls
+
         let moduleTy = Construct.NewEmptyModuleOrNamespaceType moduleKind
 
         let checkXmlDocs = cenv.diagnosticOptions.CheckXmlDocs
@@ -4039,12 +4060,18 @@ module EstablishTypeDefinitionCores =
 
 
     let TcMutRecDefns_Phase1 mkLetInfo (cenv: cenv) envInitial parent typeNames inSig tpenv m scopem mutRecNSInfo (mutRecDefns: MutRecShapes<MutRecDefnsPhase1DataForTycon * 'MemberInfo, 'LetInfo, SynComponentInfo>) =
+        // Pre-process top-level opens so they are available during attribute checking in Phase1A.
+        // In recursive scopes (namespace rec / module rec), opens are normally processed in Phase1AB
+        // after module entities are built, but module attributes need access to opened namespaces.
+        // See https://github.com/dotnet/fsharp/issues/7931
+        let envWithOpens = preProcessOpensForPhase1A cenv envInitial mutRecDefns
+
         // Phase1A - build Entity for type definitions, exception definitions and module definitions.
         // Also for abbreviations of any of these. Augmentations are skipped in this phase.
         let withEntities = 
             mutRecDefns 
             |> MutRecShapes.mapWithParent 
-                 (parent, typeNames, envInitial)
+                 (parent, typeNames, envWithOpens)
                  // Build the initial entity for each module definition
                  (fun (innerParent, typeNames, envForDecls) compInfo decls -> 
                      TcTyconDefnCore_Phase1A_BuildInitialModule cenv envForDecls innerParent typeNames compInfo decls) 

tests/FSharp.Compiler.ComponentTests/Conformance/BasicGrammarElements/CustomAttributes/AttributeUsage/AttributeResolutionInRecursiveScopes.fs

@@ -0,0 +1,224 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+namespace Conformance.BasicGrammarElements
+
+open Xunit
+open FSharp.Test.Compiler
+
+module AttributeResolutionInRecursiveScopes =
+
+    // https://github.com/dotnet/fsharp/issues/7931
+    [<Fact>]
+    let ``Extension attribute on module in namespace rec`` () =
+        FSharp """
+namespace rec Ns
+
+open System.Runtime.CompilerServices
+
+[<Extension>]
+module Module =
+    [<Extension>]
+    let ext1 (x: int) = x.ToString()
+        """
+        |> asLibrary
+        |> typecheck
+        |> shouldSucceed
+
+    // https://github.com/dotnet/fsharp/issues/7931
+    [<Fact>]
+    let ``Extension attribute on type in namespace rec`` () =
+        FSharp """
+namespace rec Ns
+
+open System.Runtime.CompilerServices
+
+[<Extension>]
+type T() =
+    class end
+        """
+        |> asLibrary
+        |> typecheck
+        |> shouldSucceed
+
+    // Custom attribute defined in same rec module used on type and let declarations
+    [<Fact>]
+    let ``Custom attribute on type and let in rec module`` () =
+        FSharp """
+module rec M
+
+type CustomAttribute() =
+    inherit System.Attribute()
+
+[<Custom>] type A = | A
+[<Custom>] let a = ()
+        """
+        |> typecheck
+        |> shouldSucceed
+
+    // https://github.com/dotnet/fsharp/issues/5795 - attribute on union case in rec module is not yet resolved
+    [<Fact>]
+    let ``Issue 5795 - attribute on union case in rec module`` () =
+        FSharp """
+module rec M
+
+type CustomAttribute() =
+    inherit System.Attribute()
+
+type A = | [<CustomAttribute>] A
+        """
+        |> typecheck
+        |> shouldFail
+        |> withDiagnostics
+            [ Error 1133, Line 7, Col 14, Line 7, Col 29, "No constructors are available for the type 'CustomAttribute'" ]
+
+    // https://github.com/dotnet/fsharp/issues/5795 - attribute on type parameter in rec module is not yet resolved
+    [<Fact>]
+    let ``Issue 5795 - attribute on type parameter in rec module`` () =
+        FSharp """
+module rec M
+
+type CustomAttribute() =
+    inherit System.Attribute()
+
+type B<[<CustomAttribute>]'a> = | B of 'a
+        """
+        |> typecheck
+        |> shouldFail
+        |> withErrorCode 39
+
+    // Nested module case: open inside outer module, attribute on inner module
+    [<Fact>]
+    let ``Open inside nested module resolves for attribute on inner module in namespace rec`` () =
+        FSharp """
+namespace rec Ns
+
+module Outer =
+    open System.Runtime.CompilerServices
+
+    [<Extension>]
+    module Inner =
+        [<Extension>]
+        let ext1 (x: int) = x.ToString()
+        """
+        |> asLibrary
+        |> typecheck
+        |> shouldSucceed
+
+    // Non-recursive baseline: should always work
+    [<Fact>]
+    let ``Extension attribute works without rec - baseline`` () =
+        FSharp """
+namespace Ns
+
+open System.Runtime.CompilerServices
+
+[<Extension>]
+module Module =
+    [<Extension>]
+    let ext1 (x: int) = x.ToString()
+        """
+        |> asLibrary
+        |> typecheck
+        |> shouldSucceed
+
+    // Multiple opens in namespace rec
+    [<Fact>]
+    let ``Multiple opens resolve for attributes in namespace rec`` () =
+        FSharp """
+namespace rec Ns
+
+open System
+open System.Runtime.CompilerServices
+
+[<Extension>]
+module Module =
+    [<Extension>]
+    [<Obsolete("test")>]
+    let ext1 (x: int) = x.ToString()
+        """
+        |> asLibrary
+        |> typecheck
+        |> shouldSucceed
+
+    // Open in module rec resolves for module attributes
+    [<Fact>]
+    let ``Open in module rec resolves for nested module attribute`` () =
+        FSharp """
+module rec M
+
+open System.Runtime.CompilerServices
+
+[<Extension>]
+module Inner =
+    [<Extension>]
+    let ext1 (x: int) = x.ToString()
+        """
+        |> typecheck
+        |> shouldSucceed
+
+    // Open with Obsolete attribute in namespace rec
+    [<Fact>]
+    let ``Obsolete attribute resolves via open in namespace rec`` () =
+        FSharp """
+namespace rec Ns
+
+open System
+
+[<Obsolete("deprecated")>]
+module DeprecatedModule =
+    let x = 42
+        """
+        |> asLibrary
+        |> typecheck
+        |> shouldSucceed
+
+    // Negative test: undefined attribute still errors in namespace rec
+    [<Fact>]
+    let ``Undefined attribute still errors in namespace rec`` () =
+        FSharp """
+namespace rec Ns
+
+[<DoesNotExist>]
+module M =
+    let x = 1
+        """
+        |> asLibrary
+        |> typecheck
+        |> shouldFail
+        |> withErrorCode 39
+
+    // Negative test: invalid open target still errors despite error suppression in pre-pass
+    [<Fact>]
+    let ``Invalid open target still errors in namespace rec`` () =
+        FSharp """
+namespace rec Ns
+
+open DoesNotExist.Namespace
+
+[<System.Obsolete>]
+module M =
+    let x = 1
+        """
+        |> asLibrary
+        |> typecheck
+        |> shouldFail
+        |> withErrorCode 39
+
+    // Forward-reference open to sibling module in the same recursive scope
+    [<Fact>]
+    let ``Forward reference open to sibling module in namespace rec`` () =
+        FSharp """
+namespace rec Ns
+
+open Ns.Later
+
+module Earlier =
+    let x = Later.y
+
+module Later =
+    let y = 42
+        """
+        |> asLibrary
+        |> withOptions [ "--nowarn:22"; "--nowarn:40" ]
+        |> typecheck
+        |> shouldSucceed

tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj

@@ -39,6 +39,7 @@
     <Compile Include="Conformance\BasicGrammarElements\AccessibilityAnnotations\PermittedLocations\PermittedLocations.fs" />
     <Compile Include="Conformance\BasicGrammarElements\CustomAttributes\AttributeInheritance\AttributeInheritance.fs" />
     <Compile Include="Conformance\BasicGrammarElements\CustomAttributes\AttributeUsage\AttributeUsage.fs" />
+    <Compile Include="Conformance\BasicGrammarElements\CustomAttributes\AttributeUsage\AttributeResolutionInRecursiveScopes.fs" />
     <Compile Include="Conformance\BasicGrammarElements\CustomAttributes\Basic\Basic.fs" />
     <Compile Include="Conformance\BasicGrammarElements\CustomAttributes\ImportedAttributes\ImportedAttributes.fs" />
     <Compile Include="Conformance\BasicGrammarElements\CustomAttributes\ArgumentsOfAllTypes\ArgumentsOfAllTypes.fs" />