B3: D2
C1: B2.hidden
C2: D2
D1:
D2:
build A1: A1 B3 D2
downgrade A1 D1: A1 B1 D1 E1
build A: A B3 C2 D2
downgrade A D1: A B2.hidden C1 D1

# Both B3 and C3 require D2.
# If we downgrade D to D1, then in isolation B3 would downgrade to B1,
# and C3 would downgrade to C1.
# But C1 requires B2.hidden, and B1 requires C2.hidden, so we can't
# downgrade to either of those without pulling the other back up a little.
#

go list -m -u all
stdout '^example.com/pseudoupgrade v0.1.1-0.20190429073117-b5426c86b553$'

# 'get -u' should not downgrade to the (lower) tagged version.
go get -u
go list -m -u all
stdout '^example.com/pseudoupgrade v0.1.1-0.20190429073117-b5426c86b553$'

# 'get example.com/pseudoupgrade@upgrade' should not downgrade.
go get example.com/pseudoupgrade@upgrade
go list -m all

env GO111MODULE=on
[short] skip

# downgrade sampler should downgrade quote
cp go.mod.orig go.mod
go get rsc.io/sampler@v1.0.0
go list -m all
stdout 'rsc.io/quote v1.4.0'
stdout 'rsc.io/sampler v1.0.0'

# downgrade sampler away should downgrade quote further
go get rsc.io/sampler@none
go list -m all
stdout 'rsc.io/quote v1.3.0'

# downgrade should report inconsistencies and not change go.mod
go get rsc.io/quote@v1.5.1
go list -m all

example.com/downgrade/v2 v2.0.1
written by hand

-- .mod --
module example.com/downgrade/v2

require rsc.io/quote v1.5.2
-- .info --
{"Version":"v2.0.1"}
-- go.mod --
module example.com/downgrade/v2

example.com/downgrade v2.0.0
written by hand

-- .mod --
module example.com/downgrade

require rsc.io/quote v1.5.2
-- .info --

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

go list -m all
stdout '^example.com/a v0.1.0 '
stdout '^example.com/b v0.3.0 '
stdout '^example.com/c v0.2.0 '

# Downgrading c should also downgrade the b that requires it.

go get example.com/c@v0.1.0
go list -m all
stdout '^example.com/a v0.1.0 '
stdout '^example.com/b v0.2.0 '
stdout '^example.com/c v0.1.0 '

		target: target,
		list:   downgraded,
		Reqs:   reqs,
	})
	if err != nil {
		return nil, err
	}
	actualVersion := make(map[string]string, len(actual))
	for _, m := range actual {
		actualVersion[m.Path] = m.Version
	}

	downgraded = downgraded[:0]
	for _, m := range list {
		if v, ok := actualVersion[m.Path]; ok {
			downgraded = append(downgraded, module.Version{Path: m.Path, Version: v})
		}

#
# a ---- b ---- d
#
# The module dependency graph originally looks like:
#
# a ---- b.2 ---- d.2
#
# b.1 ---- c.1
#
# If we downgrade module d to version 1, we must downgrade b as well.
# If that downgrade selects b version 1, we will add a new dependency on module c.

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

go get example.com/d@v0.1.0
go list -m all

#   \      \
#    \      \
#     ----- c.1 ---- d.2
#
# b.1 ---- c.2
#
# If we downgrade module d to version 1, we must downgrade b as well.
# If that downgrade selects b version 1, we will upgrade module c to version 2.

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

# Downgrading d to version 1 downgrades b, which upgrades c.
go get example.com/d@v0.1.0
go list -m all
stdout '^example.com/b v0.1.0 '

go mod edit -require example.com/retract/self/prev@v1.1.0
go get example.com/retract/self/prev
go list -m example.com/retract/self/prev
stdout '^example.com/retract/self/prev v1.1.0$'

# 'go get pkg' should not downgrade from a retracted version when no higher
# version is available.
cp go.mod.orig go.mod
go mod edit -require example.com/retract/self/prev@v1.9.0
go get example.com/retract/self/prev