x/tools/gopls: ignore line directives

[findleyr]

From a discussion with @pjweinb and @adonovan:

The existence of line directives causes gopls all sorts of problems, because it means that there are two potentially valid source positions for a token.Pos, and it's not always clear which is correct in context. It also means that we need to access multiple files from operations that would otherwise be local to a single file. This has been a source of historical (and in all likelihood ongoing) bugs.

This issue records an outcome from that discussion: we should ignore line directives internally to gopls (in particular, being careful to call token.File.PositionFor instead of token.File.Position). If this causes usability issues in e.g. CGo programs, we should address those issues individually. For example, we could perform a post-processing pass on diagnostics that duplicates them to their mapped positions.

CC @golang/tools-team

[adonovan]

We could even offer an operation that jumps the cursor to the image of the current position through any applicable //line mapping.

[gopherbot]

Change https://go.dev/cl/457656 mentions this issue: gopls/internal/lsp: drop support for line directives

[kortschak]

https://go.dev/cl/439115 is marked as having addressed this (with a digit transpose). Should this be closed?

[pjweinb]

not quite yet. 457656 is still open

…

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[adonovan]

It's fine to close this issue since @pjweinb your CL addressed it. My CL 457656 is now just the some follow-up simplifications to location processing (with more to follow).