Add FS3889 diagnostic for namespace/type collision

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

@@ -92,6 +92,7 @@
 * Symbols: add ObsoleteDiagnosticInfo ([PR #19359](https://github.com/dotnet/fsharp/pull/19359))
 * FCS: add FSharpCheckFileResults.HasErrors ([PR #19892](https://github.com/dotnet/fsharp/pull/19892))
 * Add `#version;;` directive to F# Interactive to display version and environment information. ([Issue #13307](https://github.com/dotnet/fsharp/issues/13307), [PR #19332](https://github.com/dotnet/fsharp/pull/19332))
+* Add diagnostic FS3889 when a namespace and a type have the same fully-qualified name in the same assembly, replacing the misleading FS0247 "namespace and a module" error. ([Issue #17827](https://github.com/dotnet/fsharp/issues/17827), [PR #19802](https://github.com/dotnet/fsharp/pull/19802))
 * Debug: rework for expressions stepping ([PR #19894](https://github.com/dotnet/fsharp/pull/19894))
 * Debug: rework conditional erasure, fix stepping over literals ([PR #19897](https://github.com/dotnet/fsharp/pull/19897))
 * Debug: fix if and match condition sequence points ([PR #19932](https://github.com/dotnet/fsharp/pull/19932))

src/Compiler/FSComp.txt

@@ -1819,5 +1819,6 @@ featurePreprocessorElif,"#elif preprocessor directive"
 3886,tcListLiteralWithSingleTupleElement,"This list expression contains a single tuple element. Did you mean to use ';' instead of ',' to separate list elements?"
 3887,ilCustomAttrInvalidArrayElemType,"The type '%s' is not a valid custom attribute argument type. Custom attribute arrays must have elements of primitive types, enums, string, System.Type, or System.Object."
 3888,implAttributeMissingFromSignature,"The attribute '%s' is present on '%s' in the implementation but not in the signature, which takes precedence for tooling and consumers. Add the attribute to the signature, to ensure the attribute is not ignored by the compiler."
+3889,tastNamespaceAndTypeWithSameNameInAssembly,"The namespace '%s' clashes with the type '%s'."
 featureExceptionFieldSerializationSupport,"emit GetObjectData and field-restoring deserialization constructor for exception types"
 featureErrorOnMissingSignatureAttribute,"error (rather than warning) when an enforced compiler-semantic attribute is present in the .fs but missing from the .fsi"

src/Compiler/TypedTree/TypedTreeOps.Remapping.fs

@@ -622,8 +622,11 @@ module internal SignatureOps =
 
             match entity1.IsNamespace, entity2.IsNamespace, entity1.IsModule, entity2.IsModule with
             | true, true, _, _ -> ()
+            | true, _, _, true
+            | _, true, true, _ -> errorR (Error(FSComp.SR.tastNamespaceAndModuleWithSameNameInAssembly (textOfPath path2), entity2.Range))
             | true, _, _, _
-            | _, true, _, _ -> errorR (Error(FSComp.SR.tastNamespaceAndModuleWithSameNameInAssembly (textOfPath path2), entity2.Range))
+            | _, true, _, _ ->
+                errorR (Error(FSComp.SR.tastNamespaceAndTypeWithSameNameInAssembly (textOfPath path2, entity2.LogicalName), entity2.Range))
             | false, false, false, false ->
                 errorR (Error(FSComp.SR.tastDuplicateTypeDefinitionInAssembly (entity2.LogicalName, textOfPath path), entity2.Range))
             | false, false, true, true -> errorR (Error(FSComp.SR.tastTwoModulesWithSameNameInAssembly (textOfPath path2), entity2.Range))

tests/FSharp.Compiler.ComponentTests/ErrorMessages/NamespaceTests.fs

@@ -80,4 +80,33 @@ do printfn "test"
         |> shouldFail
         |> withDiagnostics [
             (Error 201, Line 4, Col 1, Line 4, Col 18, "Namespaces cannot contain values. Consider using a module to hold your value declarations.")
-        ]
+        ]
+
+[<Fact>]
+let ``Namespace-type collision says type not module (FS3889)`` () =
+    let source1 = """namespace Ns
+type T = { Field: int }
+"""
+    let source2 = "namespace Ns.T"
+    FSharp source1
+    |> withAdditionalSourceFile (FsSourceWithFileName "second.fs" source2)
+    |> compile
+    |> shouldFail
+    |> withErrorCode 3889
+    |> withDiagnosticMessageMatches "type"
+    |> ignore
+
+[<Fact>]
+let ``Namespace-module collision still says module (FS0247)`` () =
+    let source1 = """namespace Ns
+module M =
+    let x = 1
+"""
+    let source2 = "namespace Ns.M"
+    FSharp source1
+    |> withAdditionalSourceFile (FsSourceWithFileName "second.fs" source2)
+    |> compile
+    |> shouldFail
+    |> withErrorCode 0247
+    |> withDiagnosticMessageMatches "namespace and a module"
+    |> ignore