How to print an AST without formatting?

[ju...@sqreen.io]

Hello,

I am looking for a way to keep to original token positioning but I cannot find how to avoid it when using `go/printer` or `go/format`.

Basically, how to make this example print the same string that was parsed: https://play.golang.org/p/dI7WcevQJAZ

Thanks for your help!

Julio

[Julio Guerra]

I saw `go tool cover` does it, but I don't see anything else but a simple call to printer.Fprint(w, f.fset, f.astFile) at https://github.com/golang/tools/blob/master/cmd/cover/cover.go#L384

[David Finkel]

In the general case, this is not possible because the `go/ast` package types drop the positions of some tokens. (e.g. the `range` token in a `for := range` loop)

I'm reasonably certain code is only likely to round-trip (via `go/format.Node`) if it was previously formatted with the same version's `gofmt` (or `go/format.Source`).

Based on the documentation on `go/printer`'s `Fprint` function, it doesn't seem to make any guarantees about matching the parsed format. From that doc:

Fprint "pretty-prints" an AST node to output. It calls Config.Fprint with default settings. Note that gofmt uses tabs for indentation but spaces for alignment; use format.Node (package go/format) for output that matches gofmt.

I wish I had more helpful advice.

Thanks for your help!

Julio

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