Add missing space after literal token during normalization (#70202)

Fixes: #70135

Author: pyoub

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

@@ -904,7 +904,7 @@ private static bool NeedsSeparator(SyntaxToken token, SyntaxToken next)
                 }
             }
 
-            if (IsWord(token.Kind()) && IsWord(next.Kind()))
+            if (IsWordOrLiteral(token.Kind()) && IsWordOrLiteral(next.Kind()))
             {
                 return true;
             }
@@ -1259,6 +1259,14 @@ private static bool IsWord(SyntaxKind kind)
             return kind == SyntaxKind.IdentifierToken || IsKeyword(kind);
         }
 
+        private static bool IsWordOrLiteral(SyntaxKind kind)
+        {
+            return SyntaxFacts.IsLiteral(kind)
+                || IsKeyword(kind)
+                || kind == SyntaxKind.InterpolatedStringEndToken
+                || kind == SyntaxKind.InterpolatedRawStringEndToken;
+        }
+
         private static bool IsKeyword(SyntaxKind kind)
         {
             return SyntaxFacts.IsKeywordKind(kind) || SyntaxFacts.IsPreprocessorKeyword(kind);

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

@@ -5958,5 +5958,28 @@ class C
                 }
                 """);
         }
+
+        [Theory, WorkItem("https://github.com/dotnet/roslyn/issues/70135")]
+        [InlineData("if (\"\" is var I)")]
+        [InlineData("if ('' is var I)")]
+        [InlineData("if ('x' is var I)")]
+        public void TestNormalizeParseStatementLiteralCharacter(string expression)
+        {
+            var syntaxNode = SyntaxFactory.ParseStatement(expression).NormalizeWhitespace();
+            Assert.Equal(expression, syntaxNode.ToFullString());
+        }
+
+        [Theory, WorkItem("https://github.com/dotnet/roslyn/issues/70135")]
+        [InlineData("1 is var i")]
+        [InlineData("@\"\" is var s")]
+        [InlineData("\"\"\"a\"\"\" is var s")]
+        [InlineData("$@\"\" is var s")]
+        [InlineData("$\"\"\"a\"\"\" is var s")]
+        [InlineData("\"\"u8 is var s")]
+        public void TestNormalizeParseExpressionLiteralCharacter(string expression)
+        {
+            var syntaxNode = SyntaxFactory.ParseExpression(expression).NormalizeWhitespace();
+            Assert.Equal(expression, syntaxNode.ToFullString());
+        }
     }
 }