EBNF error with declaration_statement or embedded_statement (draft-v8).

[kaby76]

Describe the bug
Consider this example:

using System.IO;
class Program
{
    static void Main()
    {
            using var r = new StringReader("hello");
    }
}

This code compiles and runs perfectly fine with version 8 of the Roslyn compiler. (It does not for version 7.)

This input does not parse using the scraped grammar, using the latest on "draft-v8" branch. This is because there is an error with the statement rules.

csharpstandard/standard/statements.md

Lines 10 to 31 in 089fae9

	statement
	: labeled_statement
	| declaration_statement
	| embedded_statement
	;
	embedded_statement
	: block
	| empty_statement
	| expression_statement
	| selection_statement
	| iteration_statement
	| jump_statement
	| try_statement
	| checked_statement
	| unchecked_statement
	| lock_statement
	| using_statement
	| yield_statement
	| unsafe_statement // unsafe code support
	| fixed_statement // unsafe code support
	;

And, more critically,

csharpstandard/standard/statements.md

Lines 284 to 288 in 089fae9

	declaration_statement
	: local_variable_declaration ';'
	| local_constant_declaration ';'
	| local_function_declaration
	;

The Roslyn compiler parser performs the test in ParseStatementStartingWithUsing():

https://github.com/dotnet/roslyn/blob/f881263cdd42dc2526afe797d678c644414f7b3f/src/Compilers/CSharp/Portable/Parser/LanguageParser.cs#L8475-L8476

The most natural location for "| using_declaration" would be in "declaration_statement".

 declaration_statement
      : local_variable_declaration ';'
      | local_constant_declaration ';'
      | local_function_declaration
      | using_declaration
      ;

You'll need to decide what may be more natural point in the EBNF to make a change, perhaps local_variable_declaration but that would require a bit more refactoring.

In any case, the grammar as is does not work.

Example

v8test-embedded-statement.zip

[Nigel-Ecma]

@kaby76 – Well spotted, thank you. While using_declaration has so far been added to the draft v8 it is not actually referenced anywhere! Oops.

We’ll get it fixed.

[jskeet]

We think this may just be a matter of adding using_declaration as an alternative in using_statement or in local_variable_declaration, or declaration_statement as suggested above. Assigning to @BillWagner to check and create a PR.