Detect open type use correctly for enums (#17628)

* Detect `open type` use correctly for enums

* Consider `open type` used when the type is an enum and any of
  the enum cases is used unqualified.

* Update release notes

Author: brianrourkeboll

docs/release-notes/.FSharp.Compiler.Service/9.0.100.md

@@ -14,6 +14,7 @@
 * Fixed checking failure when `global` namespace is involved with enabled GraphBasedChecking ([PR #17553](https://github.com/dotnet/fsharp/pull/17553))
 * Add missing byte chars notations, enforce limits in decimal notation in byte char & string (Issues [#15867](https://github.com/dotnet/fsharp/issues/15867), [#15868](https://github.com/dotnet/fsharp/issues/15868), [#15869](https://github.com/dotnet/fsharp/issues/15869), [PR #15898](https://github.com/dotnet/fsharp/pull/15898))
 * Parentheses analysis: keep extra parentheses around unit & tuples in method definitions. ([PR #17618](https://github.com/dotnet/fsharp/pull/17618))
+* Consider `open type` used when the type is an enum and any of the enum cases is used unqualified. ([PR #17628](https://github.com/dotnet/fsharp/pull/17628))
 
 ### Added
 

src/Compiler/Service/ServiceAnalysis.fs

@@ -51,6 +51,11 @@ module UnusedOpens =
                         if not entity.IsNamespace && not entity.IsFSharpModule then
                             for fv in entity.MembersFunctionsAndValues do
                                 fv
+
+                            if entity.IsEnum then
+                                for field in entity.FSharpFields do
+                                    if field.IsStatic && field.IsLiteral then
+                                        field
                     |]
 
                 HashSet<_>(symbols, symbolHash)

tests/FSharp.Compiler.Service.Tests/ProjectAnalysisTests.fs

@@ -5603,13 +5603,25 @@ open SomeUsedModuleContainingFunction
 open SomeUsedModuleContainingExtensionMember
 open SomeUsedModuleContainingActivePattern
 open SomeUsedModuleContainingUnion
+open type System.DayOfWeek // Used, should not appear.
+open type System.DateTimeKind // Unused, should appear.
+
+type FSharpEnum1 = X = 1 | Y = (1 <<< 1) | Z = (1 <<< 2)
+type FSharpEnum2 = H = 1 | I = (1 <<< 1) | J = (1 <<< 2)
+
+open type FSharpEnum1 // Used, should not appear.
+open type FSharpEnum2 // Unused, should appear.
 
 type UseTheThings(i:int) =
     member x.Value = Dictionary<int,int>() // use something from System.Collections.Generic, as a constructor
     member x.UseSomeUsedModuleContainingFunction() = g 3
     member x.UseSomeUsedModuleContainingActivePattern(ActivePattern g) = g
     member x.UseSomeUsedModuleContainingExtensionMember() = (3).Q
     member x.UseSomeUsedModuleContainingUnion() = A
+    member x.UseEnumCase = Monday // Use an enum case from System.DayOfWeek.
+    member x.UseEnumCaseQualified = System.DateTimeKind.Utc // Use a qualified enum case.
+    member x.UseFSharpEnumCase = Y // Use an enum case from FSharpEnum1.
+    member x.UseFSharpEnumCaseQualified = FSharpEnum2.J // Use a qualified enum case.
 """
     let fileSource1 = SourceText.ofString fileSource1Text
     FileSystem.OpenFileForWriteShim(fileName1).Write(fileSource1Text)
@@ -5637,7 +5649,9 @@ type UseTheThings(i:int) =
            (((6, 5), (6, 19)), "open FSharp.Control // unused");
            (((7, 5), (7, 16)), "open FSharp.Data // unused");
            (((8, 5), (8, 25)), "open System.Globalization // unused");
-           (((25, 5), (25, 21)), "open SomeUnusedModule")]
+           (((25, 5), (25, 21)), "open SomeUnusedModule");
+           (((31, 10), (31, 29)), "open type System.DateTimeKind // Unused, should appear.")
+           (((37, 10), (37, 21)), "open type FSharpEnum2 // Unused, should appear.")]
     unusedOpensData |> shouldEqual expected
 
 [<Theory>]