cmd/go: go mod vendor does not produce a consistent modules.txt #28102
Description
What did you do?
Ran go mod vendor and committed the results to source control. Then ran it in continuous integration by copying the folder, running go mod vendor, and diffing the folders with diff -qr vendor.orig/ vendor/ to find differences.
What did you expect to see?
I expected to see no differences.
What did you see instead?
There were many differences. Running diff -qr <(sort vendor.orig/modules.txt) <(sort vendor/modules.txt) caused it to report no differences between the files, so it appears the ordering was different.
System details
go version go1.11.1 darwin/amd64
GOARCH="amd64"
GOBIN="/Users/jsternberg/go/pkg/bin/github.com/influxdata/idpe"
GOCACHE="/Users/jsternberg/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/jsternberg/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/Cellar/go/1.11.1/libexec"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.11.1/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/jsternberg/go/src/github.com/influxdata/idpe/go.mod"
GOROOT/bin/go version: go version go1.11.1 darwin/amd64
GOROOT/bin/go tool compile -V: compile version go1.11.1
uname -v: Darwin Kernel Version 18.0.0: Wed Aug 22 20:13:40 PDT 2018; root:xnu-4903.201.2~1/RELEASE_X86_64
ProductName: Mac OS X
ProductVersion: 10.14
BuildVersion: 18A391
lldb --version: lldb-1000.11.37.1
Swift-4.2