Remove unnecessary parentheses from spread elements (#76348)

Author: CyrusNajmabadi

src/Analyzers/CSharp/Tests/RemoveUnnecessaryParentheses/RemoveUnnecessaryExpressionParenthesesTests.cs

@@ -3530,4 +3530,26 @@ public void M(object o, object?[] c)
             }
             """);
     }
+
+    [Fact]
+    public async Task TestCollectionExpressionSpread()
+    {
+        await TestInRegularAndScript1Async("""
+            class C
+            {
+                public void M()
+                {
+                    var v = [.. $$(a ? b : c)];
+                }
+            }
+            """, """
+            class C
+            {
+                public void M()
+                {
+                    var v = [.. a ? b : c];
+                }
+            }
+            """);
+    }
 }

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/CSharp/Extensions/ParenthesizedExpressionSyntaxExtensions.cs

@@ -280,6 +280,13 @@ nodeParent is BinaryExpressionSyntax(SyntaxKind.CoalesceExpression) binary &&
         if (nodeParent is SwitchExpressionArmSyntax arm && arm.Expression == node)
             return true;
 
+        // [.. (expr)]    ->    [.. expr]
+        //
+        // Note: There is no precedence with `..` it's always just part of the collection expr, with the expr being
+        // parsed independently of it.  That's why no parens are ever needed here.
+        if (nodeParent is SpreadElementSyntax)
+            return true;
+
         // If we have: (X)(++x) or (X)(--x), we don't want to remove the parens. doing so can
         // make the ++/-- now associate with the previous part of the cast expression.
         if (parentExpression.IsKind(SyntaxKind.CastExpression) &&