"Information Loss" caused by use of default in SyntaxNode-Update methods

[bernd5]

Version Used: 16.10.0 Preview 1.0

Steps to Reproduce:

1. call of LocalDeclarationStatementSyntax.Update-Method

Expected Behavior:
No loose of "UsingKeyword".

Actual Behavior:
UsingKeyword is set to null

See the following discussion:
#51986

[RikkiGibson]

The issue is specifically that default is passed as an argument in Update methods:

roslyn/src/Compilers/CSharp/Portable/Syntax/LocalDeclarationStatementSyntax.cs

Lines 11 to 12 in dafd1b8

	public LocalDeclarationStatementSyntax Update(SyntaxTokenList modifiers, VariableDeclarationSyntax declaration, SyntaxToken semicolonToken)
	=> Update(awaitKeyword: default, usingKeyword: default, modifiers, declaration, semicolonToken);

[bernd5]

Thanks for point that out.
Most Update methods are generated but there are some nodes which have additional custom Update methods.
In my eyes the usage of default should be avoided even if the node does not really support the property (e.g. attributes which are introduced because of the inheritance hierarchy).

One additional sample is: CheckedStatementSyntax (there it is not so critical because it does not support attributes)
But for example at: ForEachStatementSyntax it is a bug.

[bernd5]

see: PR