Global, package-level queries can be done without typechecking.
This makes it significantly cheaper.
Instead of typechecking, consider all packages that directly
import the query package. In each of those packages, filter out:
* files that don't contain the query name
* files that don't import the query package
Fully parse the remaining files and look for selector expressions
matching the query package and name.
There are a few twists (dot imports, the query package, xtests).
They are described, along with how they are handled,
in the large comment at the beginning of globalReferrersPkgLevel.
On my machine and GOPATH, this reduces typical time
needed to find referrers to encoding/json.MarshalIndent
from (roughly)
real 0m39.946s
user 2m27.844s
sys 0m54.774s
to (roughly)
real 0m5.687s
user 0m15.793s
sys 0m16.001s
The processing of packages could be parallelized;
that is left for a future change, to ease reviewing.
Benefits from that will be limited;
building the reverse import graph accounts for 73%
of the runtime, and that is dominated by syscalls.
Optimization idea from Alan Donovan.
This work supported by Sourcegraph.
Change-Id: Ib19e25fcdcb27673fb03d7300dba2a53198901ad
Reviewed-on: https://go-review.googlesource.com/97800
Reviewed-by: Alan Donovan <adonovan@google.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
1e1ec013b9