Indentation on colon not working for switches with patterns.

[CyrusNajmabadi]

In a normal switch, when you type colon in a case clause, the case clause is properly dedented and aligned. This does not work for case clauses with complex patterns in them.

[gafter]

@CyrusNajmabadi Can you please give me a hint where to start working on this?

[CyrusNajmabadi]

I did a search for SyntaxKind.ColonToken and found these interesting locations:

        private static bool TokenShouldNotFormatOnTypeChar(SyntaxToken token)
        {
            return (token.IsKind(SyntaxKind.CloseParenToken) && !token.Parent.IsKind(SyntaxKind.UsingStatement)) ||
                (token.IsKind(SyntaxKind.ColonToken) && !(token.Parent.IsKind(SyntaxKind.LabeledStatement) || token.Parent.IsKind(SyntaxKind.CaseSwitchLabel) || token.Parent.IsKind(SyntaxKind.DefaultSwitchLabel)));
        }
...
                    case SyntaxKind.ColonToken:
                        {
                            var nonTerminalNode = token.Parent;
                            Contract.ThrowIfNull(nonTerminalNode, @"Malformed code or bug in parser???");

                            if (nonTerminalNode is SwitchLabelSyntax)
                            {
                                return GetIndentationOfLine(snapshot.GetLineFromPosition(nonTerminalNode.GetFirstToken(includeZeroWidth: true).SpanStart), OptionSet.GetOption(FormattingOptions.IndentationSize, token.Language));
                            }

                            // default case
                            return GetDefaultIndentationFromToken(token);
                        }
...
                case SyntaxKind.ColonToken:
                    if (previousToken.Parent is LabeledStatementSyntax || previousToken.Parent is SwitchLabelSyntax)
                    {
                        return 1;
                    }
...
            // case * :
            // default:
            // <label> :
            if (currentToken.IsKind(SyntaxKind.ColonToken))
            {
                if (currentToken.Parent.IsKind(SyntaxKind.CaseSwitchLabel,
                                               SyntaxKind.DefaultSwitchLabel,
                                               SyntaxKind.LabeledStatement,
                                               SyntaxKind.AttributeTargetSpecifier,
                                               SyntaxKind.NameColon))
                {
                    return CreateAdjustSpacesOperation(0, AdjustSpacesOption.ForceSpacesIfOnSingleLine);
                }
            }
...
                case SyntaxKind.ColonToken:
                    {
                        return FindAppropriateRangeForColon(endToken);
                    }
...
        public static bool IsColonInSwitchLabel(SyntaxToken token)
        {
            var switchLabel = token.Parent as SwitchLabelSyntax;
            return token.Kind() == SyntaxKind.ColonToken &&
                switchLabel != null &&
                switchLabel.ColonToken == token;
        }

I would personally start with some of these :)

[gafter]

Fixed in dotnet:features/patterns via #9443.