[elastic] Move the deps downloading into 'intialize' request handle

[movie-travel-code]

The original implementation relies on 'go list' to download the deps.
'go list' is called by other request handler indirectly. This approach
is unpredictable and 'go list' is black box to us. So it's better
download the deps manually in 'ManageDeps', i.e. inside 'initialize'
request handler.

[AppVeyorBot]

✅ Build go-langserver 1.0.189 completed (commit 9901839715 by @movie-travel-code)

[zfy0701]

should this guarded by the downloading deps flag?

[movie-travel-code]

Yea, will do

[AppVeyorBot]

✅ Build go-langserver 1.0.191 completed (commit 50c2e7a386 by @movie-travel-code)

[movie-travel-code]

Move the deps download into 'initialize' handler. And in order to disable the deps download by go list ... automatically, put the GO111MODULE=off to every view, i.e. workspace folder. So for now, there is a strong guarantee that only enables installGoDependency=true can enable the deps download.

Result of index github.com/etcd-io/etcd.

| | symbol count | time |
|:--|:--|:--|
| GO111MODULE=off | 12617 | 148.828s |
| installGoDependency=true | 15074 | 87.092s |

GO111MODULE=off is not the perfect approach to control deps download. There are symbols missing and don't support different packages jump in the same repo.

The official option to disable network access is GOPROXY=off, related issue golang/go#32337.

[AppVeyorBot]

✅ Build go-langserver 1.0.192 completed (commit 5d849046de by @movie-travel-code)

[movie-travel-code]

summary

Under module mode, any standard go command, include go list ..., will automatically download the dependencies, see https://github.com/golang/go/wiki/Modules#daily-workflow. Since we convert the repos into modules, when langserver try to call go list ... it will download the deps automatically.

Code has an option installGoDependency to enable the deps download.

• If installGoDependency set to false or not set, we will append GOPROXY=off and ENABLEVENDOR=on to the os environment, GOPROXY=off is a strong guarantee that disables the network access. ENABLEVENDOR=on is a flag created manually to tell go list ... use mod=vendor to find deps from vendor folder.
• If installGoDependency set to true, langserver will download the deps to data/code/gopath/pkg/mod in the initialize request handler. And go list ... will find the deps from data/code/gopath/pkg/mod.

---

Test results

repos	symbols	total time	time per go file
mongo-go-driver module mode contain vendor folder, 949-583 .go	5981	53.213s	145.4ms
mongo-go-driver vendor mode _contain vendor folder, 949 .go	5460	33.662s	92.0ms
etcd module mode contain vendor folder, 1888-962 .go	15074	66.766s	72.1ms
etcd vendor mode contain vendor folder, 1888 .go	15074	84.813s	91.6ms
Gin module mode just vendor.json, 73 .go	1339	9.639s	132ms
Gin vendor mode just vendor.json, 73 .go	756	5.592s	76.6ms
logrus module mode no vendor folder, 38 .go	477	7.96s	209.5ms
logrus vendor mode no vendor folder, 38 .go	320	6.8s	179ms
tidb module mode no vendor, 824 .go	23795	92.896s	112.7ms
tidb vendor mode no vendor, 824 .go	18728	58.333ms	71.4ms
docker-engine module mode contain vendor folder, 4921-3272 .go	13158	224.459s	136.1ms
docker-engine vendor mode contain vendor folder, 4921-3272 .go	11637	158.486s	96.1ms

Test result of Kubernetes:

	Symbol	Time	Time per go file	go list ... time
12685-5016 .go file	116707	1005.466s	131.107ms	637.859s( 63.44% )

The test for https://github.com/prometheus/prometheus got stuck in the end.

[AppVeyorBot]

✅ Build go-langserver 1.0.193 completed (commit ecb8026b48 by @movie-travel-code)

[AppVeyorBot]

✅ Build go-langserver 1.0.194 completed (commit 9675f29d17 by @movie-travel-code)

[AppVeyorBot]

✅ Build go-langserver 1.0.195 completed (commit 682392673b by @movie-travel-code)

[movie-travel-code]

@zfy0701 this PR has come to the final stage, for now, the option installGoDependency is the only approach to control the deps download.

Related PR: elastic/kibana#43940

[AppVeyorBot]

✅ Build go-langserver 1.0.197 completed (commit d9e43c927a by @movie-travel-code)