Final prototype comments and top level statements local adjustments (#…

…61551)

Clean up the last of the prototype comments and adjust the parsing of locals named required in top level statements.

docs/compilers/CSharp/Compiler Breaking Changes - DotNet 7.md

@@ -391,3 +391,16 @@ Console.WriteLine($"{{{12:X}}}");
 The workaround is to remove the extra braces in the format string.
 
 You can learn more about this change in the associated [roslyn issue](https://github.com/dotnet/roslyn/issues/57750).
+
+## Types cannot be named `required`
+
+***Introduced in Visual Studio 2022 version 17.3.*** Starting in C# 11, types cannot be named `required`. The compiler will report an error on all such type names. To work around this, the type name and all usages must be escaped with an `@`:
+
+```csharp
+class required {} // Error CS9029
+class @required {} // No error
+```
+
+This was done as `required` is now a member modifier for properties and fields.
+
+You can learn more about this change in the associated [csharplang issue](https://github.com/dotnet/csharplang/issues/3630).

docs/contributing/Compiler Test Plan.md

@@ -39,8 +39,8 @@ This document provides guidance for thinking about language interactions and tes
 - Access modifiers (public, protected, internal, protected internal, private protected, private), static, ref
 - type declarations (class, record class/struct with or without positional members, struct, interface, type parameter)
 - methods
-- fields
-- properties (including get/set/init accessors)
+- fields (required and not)
+- properties (including get/set/init accessors, required and not)
 - events (including add/remove accessors)
 - Parameter modifiers (ref, out, in, params)
 - Attributes (including generic attributes and security attributes)
@@ -110,6 +110,7 @@ This document provides guidance for thinking about language interactions and tes
 - pre-processing directives
 - COM interop
 - modopt and modreq
+- CompilerFeatureRequiredAttribute
 - ref assemblies
 - extern alias
 - UnmanagedCallersOnly

src/Compilers/CSharp/Portable/Errors/ErrorCode.cs

@@ -2070,26 +2070,24 @@ internal enum ErrorCode
         ERR_ExpressionTreeContainsUTF8StringLiterals = 9027,
         ERR_MisplacedUnchecked = 9028,
 
+        ERR_RequiredNameDisallowed = 9029,
+        ERR_OverrideMustHaveRequired = 9030,
+        ERR_RequiredMemberCannotBeHidden = 9031,
+        ERR_RequiredMemberCannotBeLessVisibleThanContainingType = 9032,
+        ERR_ExplicitRequiredMember = 9033,
+        ERR_RequiredMemberMustBeSettable = 9034,
+        ERR_RequiredMemberMustBeSet = 9035,
+        ERR_RequiredMembersMustBeAssignedValue = 9036,
+        ERR_RequiredMembersInvalid = 9037,
+        ERR_RequiredMembersBaseTypeInvalid = 9038,
+        ERR_ChainingToSetsRequiredMembersRequiresSetsRequiredMembers = 9039,
+        ERR_NewConstraintCannotHaveRequiredMembers = 9040,
+        ERR_UnsupportedCompilerFeature = 9041,
+        WRN_ObsoleteMembersShouldNotBeRequired = 9042,
+        ERR_RefReturningPropertiesCannotBeRequired = 9043,
+
         #endregion
 
         // Note: you will need to re-generate compiler code after adding warnings (eng\generate-compiler-code.cmd)
-
-        // PROTOTYPE(req): Move above the comment and condense before merge
-
-        ERR_RequiredNameDisallowed = 9500,
-        ERR_OverrideMustHaveRequired = 9501,
-        ERR_RequiredMemberCannotBeHidden = 9502,
-        ERR_RequiredMemberCannotBeLessVisibleThanContainingType = 9503,
-        ERR_ExplicitRequiredMember = 9504,
-        ERR_RequiredMemberMustBeSettable = 9505,
-        ERR_RequiredMemberMustBeSet = 9506,
-        ERR_RequiredMembersMustBeAssignedValue = 9507,
-        ERR_RequiredMembersInvalid = 9508,
-        ERR_RequiredMembersBaseTypeInvalid = 9509,
-        ERR_ChainingToSetsRequiredMembersRequiresSetsRequiredMembers = 9510,
-        ERR_NewConstraintCannotHaveRequiredMembers = 9511,
-        ERR_UnsupportedCompilerFeature = 9512,
-        WRN_ObsoleteMembersShouldNotBeRequired = 9513,
-        ERR_RefReturningPropertiesCannotBeRequired = 9514,
     }
 }

src/Compilers/CSharp/Portable/Errors/MessageID.cs

@@ -238,9 +238,6 @@ internal enum MessageID
 
         IDS_FeatureGenericAttributes = MessageBase + 12812,
 
-        // PROTOTYPE(req): here for avoiding merge conflicts. Move to the end and condense before merge.
-        IDS_FeatureRequiredMembers = MessageBase + 13000,
-
         IDS_FeatureNewLinesInInterpolations = MessageBase + 12813,
         IDS_FeatureListPattern = MessageBase + 12814,
         IDS_ParameterNullChecking = MessageBase + 12815,
@@ -257,6 +254,7 @@ internal enum MessageID
         IDS_FeatureUnsignedRightShift = MessageBase + 12823,
         IDS_FeatureExtendedNameofScope = MessageBase + 12824,
         IDS_FeatureRelaxedShiftOperator = MessageBase + 12825,
+        IDS_FeatureRequiredMembers = MessageBase + 12826,
     }
 
     // Message IDs may refer to strings that need to be localized.

src/Compilers/CSharp/Portable/Parser/LanguageParser.cs

@@ -1173,8 +1173,9 @@ internal static DeclarationModifiers GetModifier(SyntaxKind kind, SyntaxKind con
             }
         }
 
-        private void ParseModifiers(SyntaxListBuilder tokens, bool forAccessors)
+        private void ParseModifiers(SyntaxListBuilder tokens, bool forAccessors, bool forTopLevelStatements)
         {
+            Debug.Assert(!(forAccessors && forTopLevelStatements));
             while (true)
             {
                 var newMod = GetModifier(this.CurrentToken);
@@ -1258,8 +1259,9 @@ private void ParseModifiers(SyntaxListBuilder tokens, bool forAccessors)
                     case DeclarationModifiers.Required:
                         // In C# 11, required in a modifier position is always a keyword if not escaped. Otherwise, we reuse the async detection
                         // machinery to make a conservative guess as to whether the user meant required to be a keyword, so that they get a good langver
-                        // diagnostic and all the machinery to upgrade their project kicks in.
-                        if (!IsFeatureEnabled(MessageID.IDS_FeatureRequiredMembers) && !ShouldAsyncOrRequiredBeTreatedAsModifier(parsingStatementNotDeclaration: false))
+                        // diagnostic and all the machinery to upgrade their project kicks in. The only exception to this rule is top level statements,
+                        // where the user could conceivably have a local named required. For these locations, we need to disambiguate as well.
+                        if ((!IsFeatureEnabled(MessageID.IDS_FeatureRequiredMembers) || forTopLevelStatements) && !ShouldAsyncOrRequiredBeTreatedAsModifier(parsingStatementNotDeclaration: false))
                         {
                             return;
                         }
@@ -2373,7 +2375,7 @@ private MemberDeclarationSyntax ParseMemberDeclarationOrStatementCore(SyntaxKind
                 }
 
                 // All modifiers that might start an expression are processed above.
-                this.ParseModifiers(modifiers, forAccessors: false);
+                this.ParseModifiers(modifiers, forAccessors: false, forTopLevelStatements: true);
                 bool haveModifiers = (modifiers.Count > 0);
                 MemberDeclarationSyntax result;
 
@@ -2826,7 +2828,7 @@ private MemberDeclarationSyntax ParseMemberDeclarationCore(SyntaxKind parentKind
             {
                 var attributes = this.ParseAttributeDeclarations();
 
-                this.ParseModifiers(modifiers, forAccessors: false);
+                this.ParseModifiers(modifiers, forAccessors: false, forTopLevelStatements: false);
 
                 // Check for constructor form
                 if (this.CurrentToken.Kind == SyntaxKind.IdentifierToken && this.PeekToken(1).Kind == SyntaxKind.OpenParenToken)
@@ -4120,7 +4122,7 @@ private AccessorDeclarationSyntax ParseAccessorDeclaration(bool isEvent)
             try
             {
                 var accAttrs = this.ParseAttributeDeclarations();
-                this.ParseModifiers(accMods, forAccessors: true);
+                this.ParseModifiers(accMods, forAccessors: true, forTopLevelStatements: false);
 
                 // check availability of readonly members feature for accessors
                 CheckForVersionSpecificModifiers(accMods, SyntaxKind.ReadOnlyKeyword, MessageID.IDS_FeatureReadOnlyMembers);