Compiler error when declaring multiple parameters with the same name in abstract methods

src/Compiler/Checking/CheckDeclarations.fs

@@ -385,7 +385,7 @@ let CheckNamespaceModuleOrTypeName (g: TcGlobals) (id: Ident) =
     // type names '[]' etc. are used in fslib
     if not g.compilingFSharpCore && id.idText.IndexOfAny IllegalCharactersInTypeAndNamespaceNames <> -1 then 
         errorR(Error(FSComp.SR.tcInvalidNamespaceModuleTypeUnionName(), id.idRange))
-
+        
 let CheckDuplicates (idf: _ -> Ident) k elems = 
     elems |> List.iteri (fun i uc1 -> 
         elems |> List.iteri (fun j uc2 -> 
@@ -394,7 +394,22 @@ let CheckDuplicates (idf: _ -> Ident) k elems =
             if j > i && id1.idText = id2.idText then 
                 errorR (Duplicate(k, id1.idText, id1.idRange))))
     elems
-
+
+let private CheckDuplicatesArgNames (synVal: SynValSig) m =
+    let argNames = synVal.SynInfo.ArgNames |> List.duplicates
+    for name in argNames do
+        errorR(Error((FSComp.SR.chkDuplicatedMethodParameter(name), m)))
+
+let private CheckDuplicatesAbstractMethodParmsSig (typeSpecs:  SynTypeDefnSig list) =
+    for SynTypeDefnSig(typeRepr= trepr) in typeSpecs do 
+        match trepr with 
+        | SynTypeDefnSigRepr.ObjectModel(_, synMemberSigs, _) ->
+         for sms in synMemberSigs do
+             match sms with
+             | SynMemberSig.Member(synValSig, _, m) ->
+                CheckDuplicatesArgNames synValSig m
+             | _ -> ()
+        | _ -> ()
 
 module TcRecdUnionAndEnumDeclarations =
 
@@ -3946,7 +3961,16 @@ module TcDeclarations =
              | SynMemberDefn.NestedType (range=m) :: _ -> errorR(Error(FSComp.SR.tcTypesCannotContainNestedTypes(), m))
              | _ -> ()
         | ds ->
-            // Classic class construction 
+
+            // Check for duplicated parameters in abstract methods
+            for slot in ds do
+                if isAbstractSlot slot then
+                    match slot with
+                    | SynMemberDefn.AbstractSlot (synVal, _, m) ->
+                        CheckDuplicatesArgNames synVal m
+                    | _ -> ()
+
+            // Classic class construction    
             let _, ds = List.takeUntil (allFalse [isMember;isAbstractSlot;isInterface;isInherit;isField;isTycon]) ds
             match ds with
              | SynMemberDefn.Member (range=m) :: _ -> errorR(InternalError("CheckMembersForm: List.takeUntil is wrong", m))
@@ -3960,7 +3984,6 @@ module TcDeclarations =
              | SynMemberDefn.ValField (range=m) :: _ 
              | SynMemberDefn.NestedType (range=m) :: _ -> errorR(InternalError("CheckMembersForm: List.takeUntil is wrong", m))
              | _ -> ()
-
 
     /// Separates the definition into core (shape) and body.
     ///
@@ -4351,7 +4374,8 @@ let rec TcSignatureElementNonMutRec (cenv: cenv) parent typeNames endm (env: TcE
             let _, _, _, env = TcExceptionDeclarations.TcExnSignature cenv env parent emptyUnscopedTyparEnv (edef, scopem)
             return env
 
-        | SynModuleSigDecl.Types (typeSpecs, m) -> 
+        | SynModuleSigDecl.Types (typeSpecs, m) ->
+            CheckDuplicatesAbstractMethodParmsSig typeSpecs
             let scopem = unionRanges m endm
             let mutRecDefns = typeSpecs |> List.map MutRecShape.Tycon
             let env = TcDeclarations.TcMutRecSignatureDecls cenv env parent typeNames emptyUnscopedTyparEnv m scopem None mutRecDefns
@@ -4521,7 +4545,8 @@ and TcSignatureElementsMutRec cenv parent typeNames m mutRecNSInfo envInitial (d
           let rec loop isNamespace moduleRange defs: MutRecSigsInitialData = 
             ((true, true), defs) ||> List.collectFold (fun (openOk, moduleAbbrevOk) def -> 
                 match def with 
-                | SynModuleSigDecl.Types (typeSpecs, _) -> 
+                | SynModuleSigDecl.Types (typeSpecs, _) ->
+                    CheckDuplicatesAbstractMethodParmsSig typeSpecs
                     let decls = typeSpecs |> List.map MutRecShape.Tycon
                     decls, (false, false)
 

src/Compiler/FSComp.txt

@@ -1656,3 +1656,5 @@ reprStateMachineInvalidForm,"The state machine has an unexpected form"
 3546,parsExpectingPatternInTuple,"Expecting pattern"
 3547,parsExpectedPatternAfterToken,"Expected a pattern after this point"
 3548,matchNotAllowedForUnionCaseWithNoData,"Pattern discard is not allowed for union case that takes no data."
+3549,chkDuplicatedMethodParameter,"Duplicate parameter. The parameter '%s' has been used more that once in this method."
+

src/Compiler/xlf/FSComp.txt.cs.xlf

@@ -12,6 +12,11 @@
         <target state="translated">Soubor {0} má nerozpoznanou příponu. Zdrojové soubory musí mít příponu .fs, .fsi, .fsx nebo .fsscript.</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkDuplicatedMethodParameter">
+        <source>Duplicate parameter. The parameter '{0}' has been used more that once in this method.</source>
+        <target state="new">Duplicate parameter. The parameter '{0}' has been used more that once in this method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkFeatureNotLanguageSupported">
         <source>Feature '{0}' is not available in F# {1}. Please use language version {2} or greater.</source>
         <target state="translated">Funkce {0} není v jazyce F# {1} dostupná. Použijte prosím jazyk verze {2} nebo vyšší.</target>

src/Compiler/xlf/FSComp.txt.de.xlf

@@ -12,6 +12,11 @@
         <target state="translated">Die Dateierweiterung von „{0}“ wurde nicht erkannt. Quelldateien müssen die Erweiterung .fs, .fsi, .fsx oder .fsscript haben</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkDuplicatedMethodParameter">
+        <source>Duplicate parameter. The parameter '{0}' has been used more that once in this method.</source>
+        <target state="new">Duplicate parameter. The parameter '{0}' has been used more that once in this method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkFeatureNotLanguageSupported">
         <source>Feature '{0}' is not available in F# {1}. Please use language version {2} or greater.</source>
         <target state="translated">Das Feature "{0}" ist in F# {1} nicht verfügbar. Verwenden Sie Sprachversion {2} oder höher.</target>

src/Compiler/xlf/FSComp.txt.es.xlf

@@ -12,6 +12,11 @@
         <target state="translated">No se reconoce la extensión de archivo de '{0}'. Los archivos de código fuente deben tener las extensiones .fs, .fsi, .fsx o .fsscript</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkDuplicatedMethodParameter">
+        <source>Duplicate parameter. The parameter '{0}' has been used more that once in this method.</source>
+        <target state="new">Duplicate parameter. The parameter '{0}' has been used more that once in this method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkFeatureNotLanguageSupported">
         <source>Feature '{0}' is not available in F# {1}. Please use language version {2} or greater.</source>
         <target state="translated">La característica "{0}" no está disponible en F# {1}. Use la versión {2} del lenguaje o una posterior.</target>

src/Compiler/xlf/FSComp.txt.fr.xlf

@@ -12,6 +12,11 @@
         <target state="translated">L'extension de fichier de '{0}' n'est pas reconnue. Les fichiers sources doivent avoir l'extension .fs, .fsi, .fsx, ou .fsscript.</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkDuplicatedMethodParameter">
+        <source>Duplicate parameter. The parameter '{0}' has been used more that once in this method.</source>
+        <target state="new">Duplicate parameter. The parameter '{0}' has been used more that once in this method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkFeatureNotLanguageSupported">
         <source>Feature '{0}' is not available in F# {1}. Please use language version {2} or greater.</source>
         <target state="translated">La fonctionnalité '{0}' n'est pas disponible en F# {1}. Utilisez la version de langage {2} ou une version ultérieure.</target>

src/Compiler/xlf/FSComp.txt.it.xlf

@@ -12,6 +12,11 @@
         <target state="translated">Estensione di file di '{0}' non riconosciuta. I file di origine devono avere estensione .fs, .fsi, .fsx or .fsscript</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkDuplicatedMethodParameter">
+        <source>Duplicate parameter. The parameter '{0}' has been used more that once in this method.</source>
+        <target state="new">Duplicate parameter. The parameter '{0}' has been used more that once in this method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkFeatureNotLanguageSupported">
         <source>Feature '{0}' is not available in F# {1}. Please use language version {2} or greater.</source>
         <target state="translated">La funzionalità '{0}' non è disponibile in F# {1}. Usare la versione {2} o versioni successive del linguaggio.</target>

src/Compiler/xlf/FSComp.txt.ja.xlf

@@ -12,6 +12,11 @@
         <target state="translated">'{0}' のファイル拡張子は認識されません。ソース ファイルの拡張子は .fs、.fsi、.fsx、または .fsscript にする必要があります。</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkDuplicatedMethodParameter">
+        <source>Duplicate parameter. The parameter '{0}' has been used more that once in this method.</source>
+        <target state="new">Duplicate parameter. The parameter '{0}' has been used more that once in this method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkFeatureNotLanguageSupported">
         <source>Feature '{0}' is not available in F# {1}. Please use language version {2} or greater.</source>
         <target state="translated">機能 '{0}' は F# {1} では使用できません。{2} 以上の言語バージョンをお使いください。</target>

src/Compiler/xlf/FSComp.txt.ko.xlf

@@ -12,6 +12,11 @@
         <target state="translated">'{0}'의 파일 확장명을 인식할 수 없습니다. 원본 파일의 확장명은 .fs, .fsi, .fsx 또는 .fsscript여야 합니다.</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkDuplicatedMethodParameter">
+        <source>Duplicate parameter. The parameter '{0}' has been used more that once in this method.</source>
+        <target state="new">Duplicate parameter. The parameter '{0}' has been used more that once in this method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkFeatureNotLanguageSupported">
         <source>Feature '{0}' is not available in F# {1}. Please use language version {2} or greater.</source>
         <target state="translated">'{0}' 기능은 F# {1}에서 사용할 수 없습니다. {2} 이상의 언어 버전을 사용하세요.</target>

src/Compiler/xlf/FSComp.txt.pl.xlf

@@ -12,6 +12,11 @@
         <target state="translated">Rozszerzenie pliku "{0}" nie zostało rozpoznane. Pliki źródłowe muszą mieć rozszerzenie .fs, .fsi, .fsx lub .fsscript</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkDuplicatedMethodParameter">
+        <source>Duplicate parameter. The parameter '{0}' has been used more that once in this method.</source>
+        <target state="new">Duplicate parameter. The parameter '{0}' has been used more that once in this method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkFeatureNotLanguageSupported">
         <source>Feature '{0}' is not available in F# {1}. Please use language version {2} or greater.</source>
         <target state="translated">Funkcja „{0}” nie jest dostępna w języku F# {1}. Użyj języka w wersji {2} lub nowszej.</target>

src/Compiler/xlf/FSComp.txt.pt-BR.xlf

@@ -12,6 +12,11 @@
         <target state="translated">A extensão do arquivo de '{0}' não foi reconhecida. Os arquivos de origem devem ter a extensão .fs, .fsi, .fsx or .fsscript</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkDuplicatedMethodParameter">
+        <source>Duplicate parameter. The parameter '{0}' has been used more that once in this method.</source>
+        <target state="new">Duplicate parameter. The parameter '{0}' has been used more that once in this method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkFeatureNotLanguageSupported">
         <source>Feature '{0}' is not available in F# {1}. Please use language version {2} or greater.</source>
         <target state="translated">O recurso '{0}' não está disponível no F# {1}. Use a versão da linguagem {2} ou superior.</target>

src/Compiler/xlf/FSComp.txt.ru.xlf

@@ -12,6 +12,11 @@
         <target state="translated">Расширение файла "{0}" не распознано. Исходные файлы должны иметь расширения FS, FSI, FSX или FSSCRIPT</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkDuplicatedMethodParameter">
+        <source>Duplicate parameter. The parameter '{0}' has been used more that once in this method.</source>
+        <target state="new">Duplicate parameter. The parameter '{0}' has been used more that once in this method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkFeatureNotLanguageSupported">
         <source>Feature '{0}' is not available in F# {1}. Please use language version {2} or greater.</source>
         <target state="translated">Компонент "{0}" недоступен в F# {1}. Используйте версию языка {2} или выше.</target>

src/Compiler/xlf/FSComp.txt.tr.xlf

@@ -12,6 +12,11 @@
         <target state="translated">'{0}' kaynak dosyasının dosya uzantısı tanınmadı. Kaynak dosyaların uzantısı .fs, .fsi, .fsx veya .fsscript olmalıdır.</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkDuplicatedMethodParameter">
+        <source>Duplicate parameter. The parameter '{0}' has been used more that once in this method.</source>
+        <target state="new">Duplicate parameter. The parameter '{0}' has been used more that once in this method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkFeatureNotLanguageSupported">
         <source>Feature '{0}' is not available in F# {1}. Please use language version {2} or greater.</source>
         <target state="translated">'{0}' özelliği F# {1} sürümünde kullanılamıyor. Lütfen {2} veya daha yüksek bir dil sürümünü kullanın.</target>

src/Compiler/xlf/FSComp.txt.zh-Hans.xlf

@@ -12,6 +12,11 @@
         <target state="translated">无法识别“{0}”的文件扩展名。源文件必须具有扩展名 .fs、.fsi、.fsx 或 .fsscript</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkDuplicatedMethodParameter">
+        <source>Duplicate parameter. The parameter '{0}' has been used more that once in this method.</source>
+        <target state="new">Duplicate parameter. The parameter '{0}' has been used more that once in this method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkFeatureNotLanguageSupported">
         <source>Feature '{0}' is not available in F# {1}. Please use language version {2} or greater.</source>
         <target state="translated">功能“{0}”在 F# {1} 中不可用。请使用 {2} 或更高的语言版本。</target>

src/Compiler/xlf/FSComp.txt.zh-Hant.xlf

@@ -12,6 +12,11 @@
         <target state="translated">無法辨識 '{0}' 的副檔名。來源檔案的副檔名必須是 .fs、.fsi、.fsx 或 .fsscript。</target>
         <note />
       </trans-unit>
+      <trans-unit id="chkDuplicatedMethodParameter">
+        <source>Duplicate parameter. The parameter '{0}' has been used more that once in this method.</source>
+        <target state="new">Duplicate parameter. The parameter '{0}' has been used more that once in this method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="chkFeatureNotLanguageSupported">
         <source>Feature '{0}' is not available in F# {1}. Please use language version {2} or greater.</source>
         <target state="translated">F# {1} 中無法使用 '{0}' 功能。請使用語言版本 {2} 或更新的版本。</target>

tests/FSharp.Compiler.ComponentTests/Conformance/DeclarationElements/MemberDefinitions/MethodsAndProperties/E_Abstract_ReusedParam.fs

@@ -0,0 +1,11 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+type I =
+    // Tupled.
+    abstract M : i:int * i:int -> int
+    // Curried.
+    abstract N : i:int -> i:int -> int
+    // More than two.
+    abstract O : i:int * i: int * i:int -> int
+    // Multiple distinct names repeated.
+    abstract P : i:int * j:int * i:int * j:int -> int