List patterns: main IDE scenarios and AddRequiredParens

src/Compilers/CSharp/Portable/Syntax/SyntaxNormalizer.cs

@@ -520,6 +520,29 @@ private static bool NeedsSeparatorForPositionalPattern(SyntaxToken token, Syntax
             return false;
         }
 
+        private static bool NeedsSeparatorForListPattern(SyntaxToken token, SyntaxToken next)
+        {
+            var listPattern = token.Parent as ListPatternSyntax ?? next.Parent as ListPatternSyntax;
+            if (listPattern == null)
+            {
+                return false;
+            }
+
+            // is$$[1, 2]
+            if (next.IsKind(SyntaxKind.OpenBracketToken))
+            {
+                return true;
+            }
+
+            // is [1, 2]$$list
+            if (token.IsKind(SyntaxKind.OpenBracketToken))
+            {
+                return listPattern.Designation is not null;
+            }
+
+            return false;
+        }
+
         private static bool NeedsSeparator(SyntaxToken token, SyntaxToken next)
         {
             if (token.Parent == null || next.Parent == null)
@@ -806,15 +829,22 @@ private static bool NeedsSeparator(SyntaxToken token, SyntaxToken next)
                 case SyntaxKind.NotKeyword:
                     return true;
             }
+
             if (NeedsSeparatorForPropertyPattern(token, next))
             {
                 return true;
             }
+
             if (NeedsSeparatorForPositionalPattern(token, next))
             {
                 return true;
             }
 
+            if (NeedsSeparatorForListPattern(token, next))
+            {
+                return true;
+            }
+
             return false;
         }
 

src/Compilers/CSharp/Test/Syntax/Syntax/SyntaxNormalizerTests.cs

@@ -152,6 +152,30 @@ DeliveryTruck t when (t.GrossWeightClass < 3000) => 10.00m - 2.00m,
             TestNormalizeStatement(a, b);
         }
 
+        [Fact]
+        public void TestNormalizeListPattern()
+        {
+            var text = "_ = this is[ 1,2,.. var rest ];";
+            var expected = @"_ = this is [1, 2, ..var rest];";
+            TestNormalizeStatement(text, expected);
+        }
+
+        [Fact]
+        public void TestNormalizeListPattern_TrailingComma()
+        {
+            var text = "_ = this is[ 1,2, 3,];";
+            var expected = @"_ = this is [1, 2, 3, ];";
+            TestNormalizeStatement(text, expected);
+        }
+
+        [Fact]
+        public void TestNormalizeListPattern_EmptyList()
+        {
+            var text = "_ = this is[];";
+            var expected = @"_ = this is [];";
+            TestNormalizeStatement(text, expected);
+        }
+
         [Fact, WorkItem(50742, "https://github.com/dotnet/roslyn/issues/50742")]
         public void TestLineBreakInterpolations()
         {

src/EditorFeatures/CSharpTest/AutomaticCompletion/AutomaticBracketCompletionTests.cs

@@ -250,6 +250,36 @@ public void Array_Nested()
             CheckStart(session.Session);
         }
 
+        [WpfFact, Trait(Traits.Feature, Traits.Features.AutomaticCompletion)]
+        public void ListPattern()
+        {
+            var code = @"
+class C
+{
+    void M(object o)
+    {
+        _ = o is $$
+    }
+}
+";
+            var expected = @"
+class C
+{
+    void M(object o)
+    {
+        _ = o is [
+]
+    }
+}
+";
+            using var session = CreateSession(code);
+            CheckStart(session.Session);
+            // Open bracket probably should be moved to new line
+            // Close bracket probably should be aligned with open bracket
+            // Tracked by https://github.com/dotnet/roslyn/issues/57244
+            CheckReturn(session.Session, 0, expected);
+        }
+
         internal static Holder CreateSession(string code)
         {
             return CreateSession(

src/EditorFeatures/CSharpTest/Classification/SyntacticClassifierTests.cs

@@ -4889,6 +4889,51 @@ await TestInMethodAsync(@"
                 Punctuation.Semicolon);
         }
 
+        [Theory]
+        [CombinatorialData]
+        public async Task TestListPattern(TestHost testHost)
+        {
+            await TestInMethodAsync(@"
+_ = new int[0] switch
+{
+    case [1, 2]:
+        break;
+    case [1, .. var end]:
+        break;
+}",
+testHost,
+            Identifier("_"),
+            Operators.Equals,
+            Keyword("new"),
+            Keyword("int"),
+            Punctuation.OpenBracket,
+            Number("0"),
+            Punctuation.CloseBracket,
+            ControlKeyword("switch"),
+            Punctuation.OpenCurly,
+            Keyword("case"),
+            Punctuation.OpenBracket,
+            Number("1"),
+            Punctuation.Comma,
+            Number("2"),
+            Punctuation.CloseBracket,
+            Punctuation.Colon,
+            ControlKeyword("break"),
+            Punctuation.Semicolon,
+            Keyword("case"),
+            Punctuation.OpenBracket,
+            Number("1"),
+            Punctuation.Comma,
+            Punctuation.DotDot,
+            Identifier("var"),
+            Identifier("end"),
+            Punctuation.CloseBracket,
+            Punctuation.Colon,
+            ControlKeyword("break"),
+            Punctuation.Semicolon,
+            Punctuation.CloseCurly);
+        }
+
         [Theory]
         [CombinatorialData]
         public async Task TestTupleTypeSyntax(TestHost testHost)

src/EditorFeatures/CSharpTest/Formatting/Indentation/SmartIndenterEnterOnTokenTests.cs

@@ -1352,6 +1352,29 @@ await AssertIndentNotUsingSmartTokenFormatterButUsingIndenterAsync(
                 expectedIndentation: 12);
         }
 
+        [WpfFact]
+        [Trait(Traits.Feature, Traits.Features.SmartIndent)]
+        public async Task IndentListPattern()
+        {
+            var code = @"
+class C
+{
+    void Main(object o)
+    {
+        var y = o is
+        [
+
+        ]
+    }
+}";
+            // Expected indentation probably should be 12 instead
+            // Tracked by https://github.com/dotnet/roslyn/issues/57244
+            await AssertIndentNotUsingSmartTokenFormatterButUsingIndenterAsync(
+                code,
+                indentationLine: 7,
+                expectedIndentation: 8);
+        }
+
         [Trait(Traits.Feature, Traits.Features.SmartIndent)]
         [WpfTheory]
         [InlineData("x", "is < 7 and (>= 3 or > 50) or not <= 0;", 12)]

src/EditorFeatures/CSharpTest/QuickInfo/SemanticQuickInfoSourceTests.cs

@@ -7492,6 +7492,70 @@ void M2()
                 MainDescription($"({FeaturesResources.local_variable}) string? x"));
         }
 
+        [Fact, Trait(Traits.Feature, Traits.Features.QuickInfo)]
+        public async Task TestVarPatternOnVarKeyword_InListPattern()
+        {
+            await TestAsync(
+@"class C
+{
+    void M(char[] array)
+    {
+      if (array is [ va$$r one ])
+      {
+      }
+    }
+}",
+                MainDescription("struct System.Char"));
+        }
+
+        [Fact, Trait(Traits.Feature, Traits.Features.QuickInfo)]
+        public async Task TestVarPatternOnVariableItself_InListPattern()
+        {
+            await TestAsync(
+@"class C
+{
+    void M(char[] array)
+    {
+      if (array is [ var o$$ne ])
+      {
+      }
+    }
+}",
+                MainDescription($"({FeaturesResources.local_variable}) char one"));
+        }
+
+        [Fact, Trait(Traits.Feature, Traits.Features.QuickInfo)]
+        public async Task TestVarPatternOnVarKeyword_InSlicePattern()
+        {
+            await TestAsync(
+@"class C
+{
+    void M(char[] array)
+    {
+      if (array is [..va$$r one ])
+      {
+      }
+    }
+}",
+                MainDescription("char[]"));
+        }
+
+        [Fact, Trait(Traits.Feature, Traits.Features.QuickInfo)]
+        public async Task TestVarPatternOnVariableItself_InSlicePattern()
+        {
+            await TestAsync(
+@"class C
+{
+    void M(char[] array)
+    {
+      if (array is [ ..var o$$ne ])
+      {
+      }
+    }
+}",
+                MainDescription($"({FeaturesResources.local_variable}) char[]? one"));
+        }
+
         [WorkItem(53135, "https://github.com/dotnet/roslyn/issues/53135")]
         [Fact, Trait(Traits.Feature, Traits.Features.QuickInfo)]
         public async Task TestDocumentationCData()