x/tools/gopls: crash - index out of range

[bmhatfield]

Hey there,

I manually keep gopls at current master to track upcoming changes.

This morning, VSCode warned me that it had stopped restarting gopls due to it crashing too many times (installed commit: f7ea15e6, go version go1.13.4 darwin/amd64):

2019/11/08 08:55:07 : go/packages.Load: no packages found for ./...
[Info  - 8:55:07 AM] 2019/11/08 08:55:07 go/packages.Load
	packages = 0
[Error - 8:55:07 AM] 2019/11/08 08:55:07 : go/packages.Load: no packages found for ./...
panic: runtime error: index out of range [0] with length 0

goroutine 14 [running]:
golang.org/x/tools/internal/lsp/cache.(*session).bestView(0xc0000bd8c0, 0xc00038c000, 0x66, 0x0, 0x0)
	/Users/bhatfield/go/src/github.com/golang/tools/internal/lsp/cache/session.go:217 +0x18f
golang.org/x/tools/internal/lsp/cache.(*session).DidOpen(0xc0000bd8c0, 0x18337c0, 0xc0001fa5a0, 0xc00038c000, 0x66, 0x0, 0xc000394c00, 0xbb6, 0xc00, 0x1601d60, ...)
	/Users/bhatfield/go/src/github.com/golang/tools/internal/lsp/cache/session.go:254 +0x2b8
golang.org/x/tools/internal/lsp.(*Server).didOpen(0xc0001ced20, 0x18337c0, 0xc0001fa5a0, 0xc000288700, 0x0, 0xc000388000)
	/Users/bhatfield/go/src/github.com/golang/tools/internal/lsp/text_synchronization.go:29 +0x15e
golang.org/x/tools/internal/lsp.(*Server).DidOpen(0xc0001ced20, 0x18337c0, 0xc0001fa5a0, 0xc000288700, 0xc000288700, 0x0)
	/Users/bhatfield/go/src/github.com/golang/tools/internal/lsp/server.go:135 +0x49
golang.org/x/tools/internal/lsp/protocol.serverHandler.Deliver(0x18484c0, 0xc0001ced20, 0x18337c0, 0xc0001fa5a0, 0xc0001cd8c0, 0xc0001fa500, 0xc00027a000)
	/Users/bhatfield/go/src/github.com/golang/tools/internal/lsp/protocol/tsserver.go:111 +0x1b66
golang.org/x/tools/internal/jsonrpc2.(*Conn).Run.func1(0xc00002e660, 0xc0001cd8c0, 0xc0001ced80, 0x18337c0, 0xc0001fa5a0, 0x0, 0x0, 0xc0002000b0)
	/Users/bhatfield/go/src/github.com/golang/tools/internal/jsonrpc2/jsonrpc2.go:370 +0x170
created by golang.org/x/tools/internal/jsonrpc2.(*Conn).Run
	/Users/bhatfield/go/src/github.com/golang/tools/internal/jsonrpc2/jsonrpc2.go:354 +0x877
[Error - 8:55:07 AM] Connection to server got closed. Server will not be restarted.
[Error - 8:55:07 AM] Request textDocument/documentSymbol failed.
Error: Connection got disposed.
	at Object.dispose (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-jsonrpc/lib/main.js:876:25)
	at Object.dispose (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-languageclient/lib/client.js:71:35)
	at LanguageClient.handleConnectionClosed (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-languageclient/lib/client.js:2153:42)
	at LanguageClient.handleConnectionClosed (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-languageclient/lib/main.js:151:15)
	at closeHandler (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-languageclient/lib/client.js:2140:18)
	at CallbackList.invoke (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-jsonrpc/lib/events.js:62:39)
	at Emitter.fire (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-jsonrpc/lib/events.js:120:36)
	at closeHandler (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-jsonrpc/lib/main.js:226:26)
	at CallbackList.invoke (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-jsonrpc/lib/events.js:62:39)
	at Emitter.fire (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-jsonrpc/lib/events.js:120:36)
	at StreamMessageReader.fireClose (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-jsonrpc/lib/messageReader.js:111:27)
	at Socket.<anonymous> (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-jsonrpc/lib/messageReader.js:151:46)
	at Socket.emit (events.js:205:15)
	at Pipe.<anonymous> (net.js:586:12)
[Error - 8:55:07 AM] Request textDocument/documentLink failed.
Error: Connection got disposed.
	at Object.dispose (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-jsonrpc/lib/main.js:876:25)
	at Object.dispose (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-languageclient/lib/client.js:71:35)
	at LanguageClient.handleConnectionClosed (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-languageclient/lib/client.js:2153:42)
	at LanguageClient.handleConnectionClosed (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-languageclient/lib/main.js:151:15)
	at closeHandler (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-languageclient/lib/client.js:2140:18)
	at CallbackList.invoke (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-jsonrpc/lib/events.js:62:39)
	at Emitter.fire (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-jsonrpc/lib/events.js:120:36)
	at closeHandler (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-jsonrpc/lib/main.js:226:26)
	at CallbackList.invoke (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-jsonrpc/lib/events.js:62:39)
	at Emitter.fire (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-jsonrpc/lib/events.js:120:36)
	at StreamMessageReader.fireClose (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-jsonrpc/lib/messageReader.js:111:27)
	at Socket.<anonymous> (/Users/bhatfield/.vscode/extensions/ms-vscode.go-0.11.9/node_modules/vscode-jsonrpc/lib/messageReader.js:151:46)
	at Socket.emit (events.js:205:15)
	at Pipe.<anonymous> (net.js:586:12)

[gopherbot]

Thank you for filing a gopls issue! Please take a look at the Troubleshooting guide, and make sure that you have provided all of the relevant information here.

[matloob]

Hi, I think I have an idea where this is happening: I'm wondering if you could provide some information about the workspace you opened VSCode in: Specifically

• Is your workspace in a module?
• Is your workspace empty or are there packages inside of it?

[bmhatfield]

Sure!

The VSCode workspace features multiple directories mapped together (ie, our go monorepo, our frontend code, etc).

The go directory is in a module.

The root of the go directory contains a module, but all of the packages within it start at least two levels deep. As an example:

./go.mod
./shared/<packagename>
./services/<servicename>

I believe there are 0 packages closer than 2 directories away from the root, due to code organization reasons. All of the go tools (go build, go mod, etc) seem to work totally fine with this organization structure.

[matloob]

Just to make sure I understand, each of the directories in your VSCode workspace are root directories of a module (that is, each of them contain go.mod files) right?

[bmhatfield]

No - only one does. The rest are not go related:

In that image, frontend-webapp and development are separate repositories, in separate folders, mapped into the workspace via VSCode's "Add Folder to Workspace..." feature. These mapped workspace directories do not exist in a common location on the underlying filesystem.

In the image, go-services is a go monorepo (subdirectories redacted) containing many different packages (200+) but everything shares just one common go.mod at the root. go-services is the only mapped workspace folder containing go-related code.

Edit: I noticed that VSCode sometimes only loads plugins/etc when working on related files. For the avoidance of doubt, I was working on .go files somewhere deep within the structure of go-services when I observed the initial vscode warning about gopls crashing.

[gopherbot]

Change https://golang.org/cl/206140 mentions this issue: go/packages: ignore no packages error from (*snapshot).load in (*session).NewView

[matloob]

@bmhatfield, Could you patch in https://golang.org/cl/206140 and let us know if it works?

[bmhatfield]

Confirmed that it's working for me locally:

[Info  - 12:40:33 PM] 2019/11/08 12:40:33 go/packages.Load
	packages = 0
[Info  - 12:40:33 PM] 2019/11/08 12:40:33 go/packages.Load
	packages = 0
[Info  - 12:40:33 PM] 2019/11/08 12:40:33 go/packages.Load
	packages = 0
[Info  - 12:40:47 PM] 2019/11/08 12:40:47 go/packages.Load
	packages = 0
[Info  - 12:40:47 PM] 2019/11/08 12:40:47 go/packages.Load
	packages = 0
[Info  - 12:40:50 PM] 2019/11/08 12:40:50 go/packages.Load
	packages = 374

(the first 5 packages = 0 line up with the 5 non-go mapped folders in my workspace, I believe)

[bmhatfield]

Thanks for the fast turnaround!