File types IDE changes

src/Compilers/CSharp/Portable/Symbols/PublicModel/NamedTypeSymbol.cs

@@ -194,6 +194,8 @@ INamedTypeSymbol INamedTypeSymbol.TupleUnderlyingType
 
         bool INamedTypeSymbol.IsSerializable => UnderlyingNamedTypeSymbol.IsSerializable;
 
+        bool INamedTypeSymbol.IsFile => UnderlyingNamedTypeSymbol.AssociatedSyntaxTree is not null;
+
         INamedTypeSymbol INamedTypeSymbol.NativeIntegerUnderlyingType => UnderlyingNamedTypeSymbol.NativeIntegerUnderlyingType.GetPublicSymbol();
 
         #region ISymbol Members

src/Compilers/Core/Portable/Symbols/INamedTypeSymbol.cs

@@ -56,6 +56,11 @@ public interface INamedTypeSymbol : ITypeSymbol
         /// </summary>
         bool IsComImport { get; }
 
+        /// <summary>
+        /// Indicates the type is declared in source and is only visible in the file it is declared in.
+        /// </summary>
+        bool IsFile { get; }
+
         /// <summary>
         /// Returns collection of names of members declared within this type.
         /// </summary>

src/Compilers/VisualBasic/Portable/Symbols/NamedTypeSymbol.vb

@@ -1216,6 +1216,12 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols
             End Get
         End Property
 
+        Private ReadOnly Property INamedTypeSymbol_IsFile As Boolean Implements INamedTypeSymbol.IsFile
+            Get
+                Return False
+            End Get
+        End Property
+
         Private ReadOnly Property INamedTypeSymbol_NativeIntegerUnderlyingType As INamedTypeSymbol Implements INamedTypeSymbol.NativeIntegerUnderlyingType
             Get
                 Return Nothing

src/EditorFeatures/CSharpTest/Completion/CompletionProviders/KeywordCompletionProviderTests.cs

@@ -684,5 +684,130 @@ class C
 
             await VerifyItemIsAbsentAsync(markup, "required");
         }
+
+        [Fact]
+        public async Task SuggestFileOnTypes()
+        {
+            var markup = $$"""
+                $$ class C { }
+                """;
+
+            await VerifyItemExistsAsync(markup, "file");
+        }
+
+        [Fact]
+        public async Task DoNotSuggestFileAfterFile()
+        {
+            var markup = $$"""
+                file $$
+                """;
+
+            await VerifyItemIsAbsentAsync(markup, "file");
+        }
+
+        [Fact]
+        public async Task SuggestFileBeforeFileType()
+        {
+            var markup = $$"""
+                $$
+
+                file class C { }
+                """;
+
+            // it might seem like we want to prevent 'file file class',
+            // but it's likely the user is declaring a file type above an existing file type here.
+            await VerifyItemExistsAsync(markup, "file");
+        }
+
+        [Fact]
+        public async Task DoNotSuggestFileOnNestedTypes()
+        {
+            var markup = $$"""
+                class Outer
+                {
+                    $$ class C { }
+                }
+                """;
+
+            await VerifyItemIsAbsentAsync(markup, "file");
+        }
+
+        [Fact]
+        public async Task DoNotSuggestFileOnNonTypeMembers()
+        {
+            var markup = $$"""
+                class C
+                {
+                    $$
+                }
+                """;
+
+            await VerifyItemIsAbsentAsync(markup, "file");
+        }
+
+        [Theory]
+        [InlineData("public")]
+        [InlineData("internal")]
+        [InlineData("protected")]
+        [InlineData("private")]
+        public async Task DoNotSuggestFileAfterFilteredKeywords(string keyword)
+        {
+            var markup = $$"""
+                {{keyword}} $$
+                """;
+
+            await VerifyItemIsAbsentAsync(markup, "file");
+        }
+
+        [Theory]
+        [InlineData("public")]
+        [InlineData("internal")]
+        [InlineData("protected")]
+        [InlineData("private")]
+        public async Task DoNotSuggestFilteredKeywordsAfterFile(string keyword)
+        {
+            var markup = $$"""
+                file $$
+                """;
+
+            await VerifyItemIsAbsentAsync(markup, keyword);
+        }
+
+        [Fact]
+        public async Task SuggestFileInFileScopedNamespace()
+        {
+            var markup = $$"""
+                namespace NS;
+
+                $$
+                """;
+
+            await VerifyItemExistsAsync(markup, "file");
+        }
+
+        [Fact]
+        public async Task SuggestFileInNamespace()
+        {
+            var markup = $$"""
+                namespace NS
+                {
+                    $$
+                }
+                """;
+
+            await VerifyItemExistsAsync(markup, "file");
+        }
+
+        [Fact]
+        public async Task SuggestFileAfterClass()
+        {
+            var markup = $$"""
+                file class C { }
+
+                $$
+                """;
+
+            await VerifyItemExistsAsync(markup, "file");
+        }
     }
 }

src/EditorFeatures/CSharpTest/SymbolKey/SymbolKeyCompilationsTests.cs

@@ -239,6 +239,98 @@ public void M<Z>(List<Z> list)
             ResolveAndVerifySymbolList(members1, members2, comp1);
         }
 
+        [Fact]
+        public void FileType1()
+        {
+            var src1 = @"using System;
+
+namespace N1.N2
+{
+    file class C { }
+}
+";
+            var originalComp = CreateCompilation(src1, assemblyName: "Test");
+            var newComp = CreateCompilation(src1, assemblyName: "Test");
+
+            var originalSymbols = GetSourceSymbols(originalComp, SymbolCategory.DeclaredType | SymbolCategory.DeclaredNamespace).OrderBy(s => s.Name).ToArray();
+            var newSymbols = GetSourceSymbols(newComp, SymbolCategory.DeclaredType | SymbolCategory.DeclaredNamespace).OrderBy(s => s.Name).ToArray();
+
+            Assert.Equal(3, originalSymbols.Length);
+            ResolveAndVerifySymbolList(newSymbols, originalSymbols, originalComp);
+        }
+
+        [Fact]
+        public void FileType2()
+        {
+            var src1 = @"using System;
+
+namespace N1.N2
+{
+    file class C<T> { }
+}
+";
+            var originalComp = CreateCompilation(src1, assemblyName: "Test");
+            var newComp = CreateCompilation(src1, assemblyName: "Test");
+
+            var originalSymbols = GetSourceSymbols(originalComp, SymbolCategory.DeclaredType | SymbolCategory.DeclaredNamespace).OrderBy(s => s.Name).ToArray();
+            var newSymbols = GetSourceSymbols(newComp, SymbolCategory.DeclaredType | SymbolCategory.DeclaredNamespace).OrderBy(s => s.Name).ToArray();
+
+            Assert.Equal(3, originalSymbols.Length);
+            ResolveAndVerifySymbolList(newSymbols, originalSymbols, originalComp);
+        }
+
+        [Fact]
+        public void FileType3()
+        {
+            var src1 = @"using System;
+
+namespace N1.N2
+{
+    file class C { }
+}
+";
+            // this should result in two entirely separate file symbols.
+            // note that the IDE can only distinguish file type symbols with the same name when they have distinct file paths.
+            // We are OK with this as we will require file types with identical names to have distinct file paths later in the preview.
+            // See https://github.com/dotnet/roslyn/issues/61999
+            var originalComp = CreateCompilation(new[] { SyntaxFactory.ParseSyntaxTree(src1, path: "file1.cs"), SyntaxFactory.ParseSyntaxTree(src1, path: "file2.cs") }, assemblyName: "Test");
+            var newComp = CreateCompilation(new[] { SyntaxFactory.ParseSyntaxTree(src1, path: "file1.cs"), SyntaxFactory.ParseSyntaxTree(src1, path: "file2.cs") }, assemblyName: "Test");
+
+            var originalSymbols = GetSourceSymbols(originalComp, SymbolCategory.DeclaredType | SymbolCategory.DeclaredNamespace).OrderBy(s => s.Name).ToArray();
+            var newSymbols = GetSourceSymbols(newComp, SymbolCategory.DeclaredType | SymbolCategory.DeclaredNamespace).OrderBy(s => s.Name).ToArray();
+
+            Assert.Equal(4, originalSymbols.Length);
+            ResolveAndVerifySymbolList(newSymbols, originalSymbols, originalComp);
+        }
+
+        [Fact]
+        public void FileType4()
+        {
+            // we should be able to distinguish a file type and non-file type when they have the same source name.
+            var src1 = SyntaxFactory.ParseSyntaxTree(@"using System;
+
+namespace N1.N2
+{
+    file class C { }
+}
+", path: "File1.cs");
+
+            var src2 = SyntaxFactory.ParseSyntaxTree(@"
+namespace N1.N2
+{
+    class C { }
+}
+", path: "File2.cs");
+            var originalComp = CreateCompilation(new[] { src1, src2 }, assemblyName: "Test");
+            var newComp = CreateCompilation(new[] { src1, src2 }, assemblyName: "Test");
+
+            var originalSymbols = GetSourceSymbols(originalComp, SymbolCategory.DeclaredType | SymbolCategory.DeclaredNamespace).OrderBy(s => s.Name).ToArray();
+            var newSymbols = GetSourceSymbols(newComp, SymbolCategory.DeclaredType | SymbolCategory.DeclaredNamespace).OrderBy(s => s.Name).ToArray();
+
+            Assert.Equal(4, originalSymbols.Length);
+            ResolveAndVerifySymbolList(newSymbols, originalSymbols, originalComp);
+        }
+
         #endregion
 
         #region "Change to symbol"

src/EditorFeatures/CSharpTest/SymbolKey/SymbolKeyTests.cs

@@ -19,6 +19,111 @@ namespace Microsoft.CodeAnalysis.Editor.CSharp.UnitTests.SymbolId
     [UseExportProvider]
     public class SymbolKeyTests
     {
+        [Fact]
+        public async Task FileType_01()
+        {
+            var typeSource = @"
+file class C1
+{
+    public static void M() { }
+}
+";
+
+            var workspaceXml = @$"
+<Workspace>
+    <Project Language=""C#"">
+        <CompilationOptions Nullable=""Enable""/>
+        <Document FilePath=""C.cs"">
+{typeSource}
+        </Document>
+    </Project>
+</Workspace>
+";
+            using var workspace = TestWorkspace.Create(workspaceXml);
+
+            var solution = workspace.CurrentSolution;
+            var project = solution.Projects.Single();
+
+            var compilation = await project.GetCompilationAsync();
+            var type = compilation.GetTypeByMetadataName("<C>F0__C1");
+            Assert.NotNull(type);
+            var symbolKey = SymbolKey.Create(type);
+            var resolved = symbolKey.Resolve(compilation).Symbol;
+            Assert.Same(type, resolved);
+        }
+
+        [Fact]
+        public async Task FileType_02()
+        {
+            var workspaceXml = $$"""
+<Workspace>
+    <Project Language="C#">
+        <CompilationOptions Nullable="Enable"/>
+        <Document FilePath="File0.cs">
+file class C
+{
+    public static void M() { }
+}
+        </Document>
+        <Document FilePath="File1.cs">
+file class C
+{
+    public static void M() { }
+}
+        </Document>
+    </Project>
+</Workspace>
+""";
+            using var workspace = TestWorkspace.Create(workspaceXml);
+
+            var solution = workspace.CurrentSolution;
+            var project = solution.Projects.Single();
+
+            var compilation = await project.GetCompilationAsync();
+
+            var type = compilation.GetTypeByMetadataName("<File1>F1__C");
+            Assert.NotNull(type);
+            var symbolKey = SymbolKey.Create(type);
+            var resolved = symbolKey.Resolve(compilation).Symbol;
+            Assert.Same(type, resolved);
+
+            type = compilation.GetTypeByMetadataName("<File0>F0__C");
+            Assert.NotNull(type);
+            symbolKey = SymbolKey.Create(type);
+            resolved = symbolKey.Resolve(compilation).Symbol;
+            Assert.Same(type, resolved);
+        }
+
+        [Fact]
+        public async Task FileType_03()
+        {
+            var workspaceXml = $$"""
+<Workspace>
+    <Project Language="C#">
+        <CompilationOptions Nullable="Enable"/>
+        <Document FilePath="File0.cs">
+file class C
+{
+    public class Inner { }
+}
+        </Document>
+    </Project>
+</Workspace>
+""";
+            using var workspace = TestWorkspace.Create(workspaceXml);
+
+            var solution = workspace.CurrentSolution;
+            var project = solution.Projects.Single();
+
+            var compilation = await project.GetCompilationAsync();
+
+            var type = compilation.GetTypeByMetadataName("<File0>F0__C+Inner");
+            Assert.NotNull(type);
+            var symbolKey = SymbolKey.Create(type);
+            var resolved = symbolKey.Resolve(compilation).Symbol;
+            Assert.Same(type, resolved);
+        }
+
         [Fact, WorkItem(45437, "https://github.com/dotnet/roslyn/issues/45437")]
         public async Task TestGenericsAndNullability()
         {

src/Features/CSharp/Portable/Completion/CompletionProviders/KeywordCompletionProvider.cs

@@ -68,6 +68,7 @@ public KeywordCompletionProvider()
                 new ExternKeywordRecommender(),
                 new FalseKeywordRecommender(),
                 new FieldKeywordRecommender(),
+                new FileKeywordRecommender(),
                 new FinallyKeywordRecommender(),
                 new FixedKeywordRecommender(),
                 new FloatKeywordRecommender(),