Add support for Goto Declaration

[dbaeumer]

VS Code currently only supports Goto Defintition inside the editor. However there are languages like C++ that distinguish between declarations and definitions. We should add official support to have Goto Declaration in the UI and a corresponding provider in the API.

This should also include a corresponding complex command to invoke the request.

[jrieken]

All pretty straight forward: https://github.com/Microsoft/vscode/blob/f6bf792deab85e59e971096dc58a502d24cedaf9/src/vs/vscode.proposed.d.ts#L25-L50

The only weird thing is that the return type is Definition | DefinitionLink[]... We could alias the type, esp DefinitionLink as SymbolLink or leave it as it. @mjbvz @dbaeumer ideas?

[dbaeumer]

What about aliasing it to Declaration and DeclarationLink. From all the discussions I had in LSP so far I try to avoid talking about a Symbol since users tend to associate it with symbols in compilers / type checkers. And for us it is simply a range(s) in a document.

[jrieken]

Yeah, DefinitionLink wasn't a good choice maybe. I have the following ideas, feedback welcome

• We rename DefinitionLink to LocationLink
• Since step 1 was breaking, we create an alias type DefinitionLink for LocationLink
• We declare yet another alias Declaration as type Declaration = Location | Location[] | LocationLink[]

[jrieken]

This is now in latest insiders

[joaomoreno]

@jrieken Fixed the smoketest.

[dbaeumer]

@jrieken thanks