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go/token: articulate what "base offset" is in FileSet.AddFile docs #36648

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jeanbza opened this issue Jan 20, 2020 · 5 comments
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go/token: articulate what "base offset" is in FileSet.AddFile docs #36648

jeanbza opened this issue Jan 20, 2020 · 5 comments
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Go1.15

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@jeanbza
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jeanbza commented Jan 20, 2020

https://golang.org/pkg/go/token/#FileSet.AddFile

AddFile adds a new file with a given filename, base offset, [...]

What is "base offset"? How does one calculate it? There are only self-references in this godoc, and Google search doesn't return anything obviously useful.
@josharian josharian added Documentation NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels Jan 20, 2020
@ianlancetaylor ianlancetaylor added this to the Backlog milestone Jan 21, 2020
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Assigning to @griesemer for a doc update.

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@jadekler A token.Pos is simply a byte offset from a file's base offset, which is the offset corresponding to the file's first byte. The next file's base offset is usually the current file's base offset plus the file size + 1 (for padding). This maps a set (list) of files' positions to contiguous integer values. Usually you don't need to worry about this, just provide a negative value (-1) and AddFile will take care of it.

I'll add a bit more documentation.

@griesemer griesemer modified the milestones: Backlog, Go1.15 Jan 21, 2020
@griesemer griesemer removed the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Jan 21, 2020
@odeke-em odeke-em changed the title go/token: what is base offset? go/token: articulate what "base offset" is in FileSet.AddFile docs Jan 22, 2020
@jeanbza
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jeanbza commented Jan 29, 2020

Thank you! This helps a lot.

@ianlancetaylor
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@griesemer Still want to do this doc fix for 1.15?

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Change https://golang.org/cl/238117 mentions this issue: go/token: explain file base offset better in documentation

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