Avoid duplicate misplaced 'partial' diagnostics

src/Compilers/CSharp/Portable/Declarations/DeclarationTreeBuilder.cs

@@ -785,6 +785,13 @@ ClassDeclarationSyntax or
             }
 
             var modifiers = node.Modifiers.ToDeclarationModifiers(isForTypeDeclaration: true, diagnostics: diagnostics);
+            // Extensions never allow 'partial', so there is no need to report an ordering error.
+            // The invalid modifier is reported later.
+            if (kind != DeclarationKind.Extension)
+            {
+                node.Modifiers.CheckPartialModifierOrder(diagnostics, isOrdinaryMethod: false);
+            }
+
             var quickAttributes = GetQuickAttributes(node.AttributeLists);
 
             foreach (var modifier in node.Modifiers)

src/Compilers/CSharp/Portable/Symbols/Source/ModifierUtils.cs

@@ -23,7 +23,15 @@ internal static DeclarationModifiers MakeAndCheckNonTypeMemberModifiers(
             out bool modifierErrors,
             out bool hasExplicitAccessModifier)
         {
-            var result = modifiers.ToDeclarationModifiers(isForTypeDeclaration: false, diagnostics.DiagnosticBag ?? new DiagnosticBag(), isOrdinaryMethod: isOrdinaryMethod);
+            var diagnosticBag = diagnostics.DiagnosticBag ?? new DiagnosticBag();
+            var result = modifiers.ToDeclarationModifiers(isForTypeDeclaration: false, diagnosticBag);
+            // There is no need to report an ordering error when 'partial' is not allowed.
+            // The invalid modifier is reported below.
+            if ((allowedModifiers & DeclarationModifiers.Partial) != 0)
+            {
+                modifiers.CheckPartialModifierOrder(diagnosticBag, isOrdinaryMethod);
+            }
+
             result = CheckModifiers(isForTypeDeclaration: false, isForInterfaceMember, result, allowedModifiers, errorLocation, diagnostics, modifiers, out modifierErrors);
 
             var readonlyToken = modifiers.FirstOrDefault(SyntaxKind.ReadOnlyKeyword);
@@ -463,7 +471,9 @@ private static DeclarationModifiers GetDeclarationModifiersAndCheckForDuplicateM
         }
 
         public static DeclarationModifiers ToDeclarationModifiers(
-            this SyntaxTokenList modifiers, bool isForTypeDeclaration, DiagnosticBag diagnostics, bool isOrdinaryMethod = false)
+            this SyntaxTokenList modifiers,
+            bool isForTypeDeclaration,
+            DiagnosticBag diagnostics)
         {
             var result = GetDeclarationModifiersAndCheckForDuplicateModifiers(modifiers, diagnostics);
             if ((result & DeclarationModifiers.Partial) == DeclarationModifiers.Partial)
@@ -473,18 +483,6 @@ public static DeclarationModifiers ToDeclarationModifiers(
 
                 var messageId = isForTypeDeclaration ? MessageID.IDS_FeaturePartialTypes : MessageID.IDS_FeaturePartialMethod;
                 messageId.CheckFeatureAvailability(diagnostics, modifier);
-
-                // `partial` must always be the last modifier according to the language.  However, there was a bug
-                // where we allowed `partial async` at the end of modifiers on methods. We keep this behavior for
-                // backcompat.
-                var isLast = i == modifiers.Count - 1;
-                var isPartialAsyncMethod = isOrdinaryMethod && i == modifiers.Count - 2 && modifiers[i + 1].ContextualKind() is SyntaxKind.AsyncKeyword;
-                if (!isLast && !isPartialAsyncMethod)
-                {
-                    diagnostics.Add(
-                        ErrorCode.ERR_PartialMisplaced,
-                        modifier.GetLocation());
-                }
             }
 
             switch (result & DeclarationModifiers.AccessibilityMask)
@@ -505,6 +503,27 @@ public static DeclarationModifiers ToDeclarationModifiers(
             return result;
         }
 
+        internal static void CheckPartialModifierOrder(this SyntaxTokenList modifiers, DiagnosticBag diagnostics, bool isOrdinaryMethod)
+        {
+            var i = modifiers.IndexOf(SyntaxKind.PartialKeyword);
+            if (i < 0)
+            {
+                return;
+            }
+
+            // `partial` must always be the last modifier according to the language.  However, there was a bug
+            // where we allowed `partial async` at the end of modifiers on methods. We keep this behavior for
+            // backcompat.
+            var isLast = i == modifiers.Count - 1;
+            var isPartialAsyncMethod = isOrdinaryMethod && i == modifiers.Count - 2 && modifiers[i + 1].ContextualKind() is SyntaxKind.AsyncKeyword;
+            if (!isLast && !isPartialAsyncMethod)
+            {
+                diagnostics.Add(
+                    ErrorCode.ERR_PartialMisplaced,
+                    modifiers[i].GetLocation());
+            }
+        }
+
         private static void ReportDuplicateModifiers(
             SyntaxToken modifierToken,
             DeclarationModifiers modifierKind,

src/Compilers/CSharp/Test/Symbol/Symbols/DefaultInterfaceImplementationTests.cs

@@ -45105,18 +45105,12 @@ interface I19
                 // (66,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                 //     partial static I14();
                 Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(66, 5),
-                // (66,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
-                //     partial static I14();
-                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(66, 5),
                 // (70,12): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                 //     static partial I15();
                 Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(70, 12),
                 // (74,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                 //     partial static I16() {}
                 Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(74, 5),
-                // (74,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
-                //     partial static I16() {}
-                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(74, 5),
                 // (78,12): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                 //     static partial I17() => throw null;
                 Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(78, 12),

src/Compilers/CSharp/Test/Symbol/Symbols/EnumTests.cs

@@ -404,9 +404,6 @@ static void Main()
         public void PartialPublicEnum()
         {
             CreateCompilation("partial public enum E { }").VerifyDiagnostics(
-                // (1,1): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', or a method return type.
-                // partial public enum E { }
-                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(1, 1),
                 // (1,21): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', or a method return type.
                 // partial public enum E { }
                 Diagnostic(ErrorCode.ERR_PartialMisplaced, "E").WithLocation(1, 21));

src/Compilers/CSharp/Test/Symbol/Symbols/Source/DelegateTests.cs

@@ -841,9 +841,6 @@ public static void Main()
         public void PartialPublicDelegate()
         {
             CreateCompilation("partial public delegate void M();").VerifyDiagnostics(
-                // (1,1): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', or a method return type.
-                // partial public delegate void M();
-                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(1, 1),
                 // (1,30): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', or a method return type.
                 // partial public delegate void M();
                 Diagnostic(ErrorCode.ERR_PartialMisplaced, "M").WithLocation(1, 30));

src/Compilers/CSharp/Test/Symbol/Symbols/StaticAbstractMembersInInterfacesTests.cs

@@ -822,30 +822,18 @@ partial sealed static I3() {}
                 // (9,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                 //     partial sealed static I2();
                 Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(9, 5),
-                // (9,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
-                //     partial sealed static I2();
-                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(9, 5),
                 // (9,27): error CS0106: The modifier 'sealed' is not valid for this item
                 //     partial sealed static I2();
                 Diagnostic(ErrorCode.ERR_BadMemberFlag, "I2").WithArguments("sealed").WithLocation(9, 27),
                 // (14,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                 //     partial static I2() {}
                 Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(14, 5),
-                // (14,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
-                //     partial static I2() {}
-                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(14, 5),
                 // (14,20): error CS0111: Type 'I2' already defines a member called 'I2' with the same parameter types
                 //     partial static I2() {}
                 Diagnostic(ErrorCode.ERR_MemberAlreadyExists, "I2").WithArguments("I2", "I2").WithLocation(14, 20),
                 // (19,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                 //     partial static I3();
                 Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(19, 5),
-                // (19,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
-                //     partial static I3();
-                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(19, 5),
-                // (24,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
-                //     partial sealed static I3() {}
-                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(24, 5),
                 // (24,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                 //     partial sealed static I3() {}
                 Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(24, 5),

src/Compilers/CSharp/Test/Symbol/Symbols/SymbolErrorTests.cs

@@ -22309,24 +22309,12 @@ partial public static PartialPublicStaticCtor() { }
                 // 6.cs(3,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                 //     partial static public PartialStaticPublicCtor() { }
                 Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(3, 5),
-                // 6.cs(3,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
-                //     partial static public PartialStaticPublicCtor() { }
-                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(3, 5),
-                // 0.cs(3,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
-                //     partial static PartialStaticCtor() { }
-                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(3, 5),
                 // 0.cs(3,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                 //     partial static PartialStaticCtor() { }
                 Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(3, 5),
                 // 7.cs(3,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                 //     partial public static PartialPublicStaticCtor() { }
                 Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(3, 5),
-                // 7.cs(3,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
-                //     partial public static PartialPublicStaticCtor() { }
-                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(3, 5),
-                // 3.cs(3,12): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
-                //     public partial static PublicPartialStaticCtor() { }
-                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(3, 12),
                 // 3.cs(3,12): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                 //     public partial static PublicPartialStaticCtor() { }
                 Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(3, 12),
@@ -22336,9 +22324,6 @@ partial public static PartialPublicStaticCtor() { }
                 // 5.cs(3,12): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                 //     static partial public StaticPartialPublicCtor() { }
                 Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(3, 12),
-                // 5.cs(3,12): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
-                //     static partial public StaticPartialPublicCtor() { }
-                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(3, 12),
                 // 2.cs(3,19): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                 //     public static partial PublicStaticPartialCtor() { }
                 Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(3, 19),

src/Compilers/CSharp/Test/Symbol/Symbols/UserDefinedOperatorErrorTests.cs

@@ -195,9 +195,6 @@ partial class C
 
             var comp = CreateCompilation(text);
             comp.VerifyDiagnostics(
-                // (4,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', or a method return type.
-                //     partial public static int operator + (C c1, C c2) { return 0; }
-                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(4, 5),
                 // (4,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', or a method return type.
                 //     partial public static int operator + (C c1, C c2) { return 0; }
                 Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(4, 5),

src/Compilers/CSharp/Test/Syntax/Parsing/AccessorDeclarationParsingTests.cs

@@ -99,9 +99,6 @@ class C
         EOF();
 
         CreateCompilation(source).VerifyDiagnostics(
-            // (3,13): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
-            //     int P { partial ref get; }
-            Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(3, 13),
             // (3,13): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
             //     int P { partial ref get; }
             Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(3, 13),