Do not store union case compiled name

src/fsharp/TastPickle.fs

@@ -2018,15 +2018,16 @@ and u_attribs_ext extraf st = u_list_ext extraf u_attrib st
 and u_unioncase_spec st = 
     let a = u_rfield_table  st
     let b = u_ty st
-    let c = u_string st
+
+    // The union case compiled name is now computed from Id field when needed and is not stored in UnionCase record.
+    let _c = u_string st
     let d = u_ident  st
     // The XmlDoc is only present in the extended in-memory format. We detect its presence using a marker bit here
     let xmldoc, e = u_attribs_ext u_xmldoc st
     let f = u_string st
     let i = u_access st
     { FieldTable=a 
       ReturnType=b 
-      CompiledName=c 
       Id=d 
       Attribs=e
       XmlDoc= defaultArg xmldoc XmlDoc.Empty

src/fsharp/TypeChecker.fs

@@ -12254,11 +12254,15 @@ module TcRecdUnionAndEnumDeclarations = begin
     // Bind other elements of type definitions (constructors etc.)
     //------------------------------------------------------------------------- 
 
-    let CheckUnionCaseName cenv realUnionCaseName m =    
-        CheckNamespaceModuleOrTypeName cenv.g (mkSynId m realUnionCaseName)
-        if not (String.isUpper realUnionCaseName) && realUnionCaseName <> opNameCons && realUnionCaseName <> opNameNil then 
-            errorR(NotUpperCaseConstructor(m))
-
+    let CheckUnionCaseName cenv (id: Ident) =
+        let name = id.idText
+        if name = "Tags" then
+            errorR(Error(FSComp.SR.tcUnionCaseNameConflictsWithGeneratedType(name, "Tags"), id.idRange))
+
+        CheckNamespaceModuleOrTypeName cenv.g id
+        if not (String.isUpper name) && name <> opNameCons && name <> opNameNil then
+            errorR(NotUpperCaseConstructor(id.idRange))
+
     let ValidateFieldNames (synFields : SynField list, tastFields : RecdField list) = 
         let seen = Dictionary()
         for (sf, f) in List.zip synFields tastFields do
@@ -12278,16 +12282,9 @@ module TcRecdUnionAndEnumDeclarations = begin
         let attrs = TcAttributes cenv env AttributeTargets.UnionCaseDecl synAttrs // the attributes of a union case decl get attached to the generated "static factory" method
         let vis, _ = ComputeAccessAndCompPath env None m vis None parent
         let vis = CombineReprAccess parent vis
-        let realUnionCaseName =  
-            if id.idText = opNameCons then "Cons" 
-            elif id.idText = opNameNil then "Empty"
-            else id.idText
-
-        if realUnionCaseName = "Tags" then
-            errorR(Error(FSComp.SR.tcUnionCaseNameConflictsWithGeneratedType(realUnionCaseName, "Tags"), m))
-
-        CheckUnionCaseName cenv realUnionCaseName id.idRange 
-
+
+        CheckUnionCaseName cenv id
+
         let mkName nFields i = if nFields <= 1 then "Item" else "Item"+string (i+1)
         let rfields, recordTy = 
             match args with
@@ -12311,7 +12308,7 @@ module TcRecdUnionAndEnumDeclarations = begin
                 if not (typeEquiv cenv.g recordTy thisTy) then 
                     error(Error(FSComp.SR.tcReturnTypesForUnionMustBeSameAsType(), m))
                 rfields, recordTy
-        NewUnionCase id realUnionCaseName rfields recordTy attrs (xmldoc.ToXmlDoc()) vis
+        NewUnionCase id rfields recordTy attrs (xmldoc.ToXmlDoc()) vis
 
 
     let TcUnionCaseDecls cenv env parent (thisTy : TType) tpenv unionCases =
@@ -15538,8 +15535,8 @@ module EstablishTypeDefinitionCores =
 
                     structLayoutAttributeCheck(false)
                     noAllowNullLiteralAttributeCheck()
-                    TcRecdUnionAndEnumDeclarations.CheckUnionCaseName  cenv unionCaseName.idText unionCaseName.idRange
-                    let unionCase = NewUnionCase unionCaseName unionCaseName.idText [] thisTy [] XmlDoc.Empty tycon.Accessibility
+                    TcRecdUnionAndEnumDeclarations.CheckUnionCaseName cenv unionCaseName
+                    let unionCase = NewUnionCase unionCaseName [] thisTy [] XmlDoc.Empty tycon.Accessibility
                     writeFakeUnionCtorsToSink [ unionCase ]
                     MakeUnionRepr [ unionCase ], None, NoSafeInitInfo
 

src/fsharp/tast.fs

@@ -1580,9 +1580,6 @@ and
       /// Return type constructed by the case. Normally exactly the type of the enclosing type, sometimes an abbreviation of it 
       ReturnType: TType
 
-      /// Name of the case in generated IL code 
-      CompiledName: string
-
       /// Documentation for the case 
       XmlDoc : XmlDoc
 
@@ -1618,6 +1615,13 @@ and
 
     member uc.DisplayName = uc.Id.idText
 
+    /// Name of the case in generated IL code.
+    member uc.CompiledName =
+        let idText = uc.Id.idText
+        if idText = opNameCons then "Cons" 
+        elif idText = opNameNil then "Empty"
+        else idText
+
     member uc.RecdFieldsArray = uc.FieldTable.FieldsByIndex 
 
     member uc.RecdFields = uc.FieldTable.FieldsByIndex |> Array.toList
@@ -5618,9 +5622,8 @@ let NewTypar (kind,rigid,Typar(id,staticReq,isCompGen),isFromError,dynamicReq,at
 
 let NewRigidTypar nm m = NewTypar (TyparKind.Type,TyparRigidity.Rigid,Typar(mkSynId m nm,NoStaticReq,true),false,TyparDynamicReq.Yes,[],false,false)
 
-let NewUnionCase id nm tys rty attribs docOption access : UnionCase = 
+let NewUnionCase id tys rty attribs docOption access : UnionCase = 
     { Id=id
-      CompiledName=nm
       XmlDoc=docOption
       XmlDocSig=""
       Accessibility=access

tests/fsharpqa/Source/Conformance/BasicTypeAndModuleDefinitions/UnionTypes/E_UnionFieldNamedTagNoDefault.fs

@@ -1,6 +1,6 @@
 // #Conformance #TypesAndModules #Unions 
 // RegressionTest for bug 6308 
-//<Expects status="error" id="FS1219" span="(7,7-7,19)">The union case named 'Tags' conflicts with the generated type 'Tags'</Expects>
+//<Expects status="error" id="FS1219" span="(7,7-7,11)">The union case named 'Tags' conflicts with the generated type 'Tags'</Expects>
 [<DefaultAugmentation(false)>]
 type BigUnion2 = 
     | Case0

tests/fsharpqa/Source/Conformance/BasicTypeAndModuleDefinitions/UnionTypes/E_UnionMemberNamedTag.fs

@@ -1,6 +1,6 @@
 // #Conformance #TypesAndModules #Unions 
 // RegressionTest for bug 6308 
-//<Expects status="error" id="FS1219" span="(9,7-9,19)">The union case named 'Tags' conflicts with the generated type 'Tags'</Expects>
+//<Expects status="error" id="FS1219" span="(9,7-9,11)">The union case named 'Tags' conflicts with the generated type 'Tags'</Expects>
 //<Expects status="notin" id="FS0023" span="(21,14-21,17)">The member 'Tag' can not be defined because the name 'Tag' clashes with the generated property 'Tag' in this type or module</Expects>
 
 [<DefaultAugmentation(true)>]