! go build
stderr 'case-insensitive import collision'

! go mod vendor
stderr 'case-insensitive import collision'

-- foo.go --
package main

import (
	_ "example.com/Foo"
	_ "example.com/foo"
)

func main() {}
-- go.mod --
module play.ground

go 1.14

require (
	example.com/foo v0.1.0
	example.com/Foo v0.1.0
)

replace (
	example.com/foo => ./foo
	example.com/Foo => ./foo_alt
)
-- foo/go.mod --
module example.com/foo
-- foo/foo.go --
package foo

-- foo_alt/go.mod --
module example.com/Foo
-- foo_alt/foo.go --
package Foo