x/tools/cmd/gopls: crashes with "slice bounds out of range"

[zippoxer]

What version of Go are you using (go version)?

$ go version
go version go1.12.4 windows/amd64

Does this issue reproduce with the latest release?

Yes. VSCode is up to date, and I updated gopls moments before.

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\User\AppData\Local\go-build
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOOS=windows
set GOPATH=C:\Users\User\go
set GOPROXY=
set GORACE=
set GOROOT=C:\Go
set GOTMPDIR=
set GOTOOLDIR=C:\Go\pkg\tool\windows_amd64
set GCCGO=gccgo
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=C:\Users\User\projects\devout\go.mod
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\User\AppData\Local\Temp\go-build351004186=/tmp/go-build -gno-record-gcc-switches

What did you do?

Edit the file below (in a sub-package of a project which has go.mod), place my caret at the position marked with [[*]], and press CTRL + Space to get suggestions.

package httpserver

import (
	"net/http"

	"github.com/go-chi/chi"
)

func (s *Server) apiRouter() chi.Router {
	r := chi.NewRouter()

	r.Post("/search", s.handleSearch)

	return r
}

func (s *Server) handleSearch(r http.[[*]])

What did you expect to see?

Suggestions.

What did you see instead?

This error, repeatedly, until VSCode tires and stops restarting gopls:

cacheAndDiagnose: file:///c:/Users/User/projects/devout/httpserver/api.go
cacheAndDiagnose: set content for file:///c:/Users/User/projects/devout/httpserver/api.go
cacheAndDiagnose: returned from diagnostics for file:///c:/Users/User/projects/devout/httpserver/api.go
cacheAndDiagnose: going to get diagnostics for file:///c:/Users/User/projects/devout/httpserver/api.go
found parse or type-checking errors for file:///c:/Users/User/projects/devout/httpserver/api.go, returning
panic: runtime error: slice bounds out of range

goroutine 19 [running]:
golang.org/x/tools/internal/span.ToUTF16Column(0x11, 0x29, 0xe0, 0xc0001c2380, 0xe0, 0xe0, 0x1, 0x0, 0x0)
	C:/Users/User/go/src/golang.org/x/tools/internal/span/utf16.go:43 +0x581
golang.org/x/tools/internal/lsp/protocol.(*ColumnMapper).Position(0xc00d2c00f0, 0x11, 0x29, 0xe0, 0x4030000000000000, 0x0, 0x0, 0x0)
	C:/Users/User/go/src/golang.org/x/tools/internal/lsp/protocol/span.go:62 +0x6a
golang.org/x/tools/internal/lsp/protocol.(*ColumnMapper).Range(0xc00d2c00f0, 0xc002b98fc0, 0x38, 0x11, 0x1, 0xb8, 0x11, 0x29, 0xe0, 0x4020000000000000, ...)
	C:/Users/User/go/src/golang.org/x/tools/internal/lsp/protocol/span.go:54 +0x4b7
golang.org/x/tools/internal/lsp.toProtocolDocumentSymbols(0xc00d2c00f0, 0xc005376900, 0x2, 0x2, 0xc005376900, 0x2, 0x2)
	C:/Users/User/go/src/golang.org/x/tools/internal/lsp/symbols.go:35 +0x267
golang.org/x/tools/internal/lsp.(*Server).documentSymbol(0xc0000aa7e0, 0x8d06c0, 0xc000068e80, 0xc00004c010, 0xc00004c010, 0x0, 0x0, 0x0, 0xc00020e000)
	C:/Users/User/go/src/golang.org/x/tools/internal/lsp/symbols.go:23 +0x17e
golang.org/x/tools/internal/lsp.(*Server).DocumentSymbol(0xc0000aa7e0, 0x8d06c0, 0xc000068e80, 0xc00004c010, 0xc00004c010, 0x0, 0x0, 0x0, 0x0)
	C:/Users/User/go/src/golang.org/x/tools/internal/lsp/server.go:198 +0x54
golang.org/x/tools/internal/lsp/protocol.serverHandler.func1(0x8d06c0, 0xc000068e80, 0xc0001443f0, 0xc000063320)
	C:/Users/User/go/src/golang.org/x/tools/internal/lsp/protocol/server.go:325 +0x42b1
golang.org/x/tools/internal/jsonrpc2.(*Conn).Run.func1(0xc00009e840, 0xc0001443f0)
	C:/Users/User/go/src/golang.org/x/tools/internal/jsonrpc2/jsonrpc2.go:276 +0xe1
created by golang.org/x/tools/internal/jsonrpc2.(*Conn).Run
	C:/Users/User/go/src/golang.org/x/tools/internal/jsonrpc2/jsonrpc2.go:270 +0xc1
[Info  - 2:41:22 AM] Connection to server got closed. Server will restart.

Hint

This bug doesn't happen when the handleSearch function has a body:

func (s *Server) handleSearch(r http.[[*]]) {}

[stamblerre]

/cc @ianthehat

[stamblerre]

https://golang.org/cl/174357 will likely have fixed this error. Please re-open if you see it again.