# https://golang.org/issue/46141: 'go mod tidy' for a Go 1.17 module should by
# default preserve enough checksums for the module to be used by Go 1.16.
#
# We don't have a copy of Go 1.16 handy, but we can simulate it by editing the
# 'go' version in the go.mod file to 1.16, without actually updating the
# requirements to match.

[short] skip

env MODFMT='{{with .Module}}{{.Path}} {{.Version}}{{end}}'


# This module has the same module dependency graph in Go 1.16 as in Go 1.17,
# but in 1.16 requires (checksums for) additional (irrelevant) go.mod files.
#
# The module graph under both versions looks like:
#
# m ---- example.com/version v1.1.0
# |
# + ---- example.net/lazy v0.1.0 ---- example.com/version v1.0.1
#
# Go 1.17 avoids loading the go.mod file for example.com/version v1.0.1
# (because it is lower than the verison explicitly required by m,
# and the module that requires it — m — specifies 'go 1.17').
#
# That go.mod file happens not to affect the final 1.16 module graph anyway,
# so the pruned graph is equivalent to the unpruned one.

cp go.mod go.mod.orig
go mod tidy
cmp go.mod go.mod.orig

go list -m all
cmp stdout m_all.txt

go mod edit -go=1.16
go list -m all
cmp stdout m_all.txt


# If we explicitly drop compatibility with 1.16, we retain fewer checksums,
# which gives a cleaner go.sum file but causes 1.16 to fail in readonly mode.

cp go.mod.orig go.mod
go mod tidy -compat=1.17
cmp go.mod go.mod.orig

go list -m all
cmp stdout m_all.txt

go mod edit -go=1.16
! go list -m all
stderr '^go list -m: example.net/lazy@v0.1.0 requires\n\texample.com/version@v1.0.1: missing go.sum entry; to add it:\n\tgo mod download example.com/version$'


-- go.mod --
// Module m happens to have the exact same build list as what would be
// selected under Go 1.16, but computes that build list without looking at
// as many go.mod files.
module example.com/m

go 1.17

replace example.net/lazy v0.1.0 => ./lazy

require (
	example.com/version v1.1.0
	example.net/lazy v0.1.0
)
-- m_all.txt --
example.com/m
example.com/version v1.1.0
example.net/lazy v0.1.0 => ./lazy
-- compatible.go --
package compatible

import (
	_ "example.com/version"
	_ "example.net/lazy"
)
-- lazy/go.mod --
// Module lazy requires example.com/version v1.0.1.
//
// However, since this module is lazy, its dependents
// should not need checksums for that version of the module
// unless they actually import packages from it.
module example.net/lazy

go 1.17

require example.com/version v1.0.1
-- lazy/lazy.go --
package lazy

import _ "example.com/version"