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

$ go version
go version go1.12.5 darwin/amd64

$ gopls version
golang.org/x/tools/gopls v0.1.1

also reproduces at master:
$ gopls version
golang.org/x/tools/gopls v0.1.1
    golang.org/x/tools/gopls@v0.1.2-0.20190708200955-c93f28baaae0

Does this issue reproduce with the latest release?

Yes. Reproduces at master as well.

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

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/suzmue/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/suzmue/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/suzmue/go/src/golang.org/x/tools/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/q0/0bxb5hrs08l_vhzptkl5gd2400fkl_/T/go-build594969232=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Call rename on "int"

package hello

var x int

What did you expect to see?

An error.

What did you see instead?

gopls crashed with:

[Error - 2:09:07 PM] Request textDocument/rename failed.
Message: method "textDocument/rename" did not reply
Code: -32603
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x14d2cc8]

goroutine 162 [running]:
go/types.(*Package).Name(...)
/usr/local/go/src/go/types/package.go:33
golang.org/x/tools/internal/lsp/source.(*IdentifierInfo).Rename(0xc000420a90, 0x1785220, 0xc0003f1170, 0xc0003e8d7a, 0x3, 0xc000304640, 0x2c34, 0xc000420a90)
/Users/suzmue/go/pkg/mod/golang.org/x/tools@v0.0.0-20190628153133-6cdbf07be9d0/internal/lsp/source/rename.go:49 +0x798
golang.org/x/tools/internal/lsp.(*Server).rename(0xc0001b4900, 0x1785220, 0xc0003f1170, 0xc0003f11a0, 0x0, 0x0, 0xc0003e6460)
/Users/suzmue/go/pkg/mod/golang.org/x/tools@v0.0.0-20190628153133-6cdbf07be9d0/internal/lsp/rename.go:34 +0x292
golang.org/x/tools/internal/lsp.(*Server).Rename(0xc0001b4900, 0x1785220, 0xc0003f1170, 0xc0003f11a0, 0xc0003f11a0, 0x0, 0x0)
/Users/suzmue/go/pkg/mod/golang.org/x/tools@v0.0.0-20190628153133-6cdbf07be9d0/internal/lsp/server.go:241 +0x49
golang.org/x/tools/internal/lsp/protocol.serverHandler.func1(0x1785220, 0xc0003f1170, 0xc0003e4240)
/Users/suzmue/go/pkg/mod/golang.org/x/tools@v0.0.0-20190628153133-6cdbf07be9d0/internal/lsp/protocol/tsserver.go:415 +0x1291
golang.org/x/tools/internal/jsonrpc2.(*Conn).Run.func1(0xc00044a060, 0xc0003e4240, 0xc00020a000, 0x1785220, 0xc0003f1170, 0xc00041e460, 0xc000406750)
/Users/suzmue/go/pkg/mod/golang.org/x/tools@v0.0.0-20190628153133-6cdbf07be9d0/internal/jsonrpc2/jsonrpc2.go:441 +0x117
created by golang.org/x/tools/internal/jsonrpc2.(*Conn).Run
/Users/suzmue/go/pkg/mod/golang.org/x/tools@v0.0.0-20190628153133-6cdbf07be9d0/internal/jsonrpc2/jsonrpc2.go:428 +0x6fc