This change implements an AST walker, Apply, with the capability
to perform various actions (including rewrites) during the AST
walk, in pre- and post-iteration order.
Ideally we would like to have this functionality in the std lib
(go/ast), but as this change contains significant new API, it
is better to first gain some experience with it in x/tools.
Credits: This is joint work of Josh Bleecher Snyder, Roger
Peppe, and myself (author of this CL). The code is based on
proposal golang/go#17108 which I had started, together with an
initial implementation. It was then reworked significantly by
Josh in golang.org/cl/55790, further refined by suggestions
from Roger (allocation reduction), and finally cleaned up a bit
by me (AST simplifications).
Fixesgolang/go#17108.
Change-Id: I56d56b7f2bc5be2acfeb927f76aea7f264bb7b94
Reviewed-on: https://go-review.googlesource.com/77811
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>
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