# 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}}'

# For this module, the dependency providing package
# example.net/ambiguous/nested/pkg is unambiguous in Go 1.17 (because only one
# root of the module graph contains the package), whereas it is ambiguous in
# Go 1.16 (because two different modules contain plausible packages and Go 1.16
# does not privilege roots above other dependencies).
#
# However, the overall build list is identical for both versions.

cp go.mod go.mod.orig

! go mod tidy

stderr '^example\.com/m imports\n\texample\.net/indirect imports\n\texample\.net/ambiguous/nested/pkg loaded from example\.net/ambiguous/nested@v0\.1\.0,\n\tbut go 1.16 would fail to locate it:\n\tambiguous import: found package example\.net/ambiguous/nested/pkg in multiple modules:\n\texample\.net/ambiguous v0.1.0 \(.*\)\n\texample\.net/ambiguous/nested v0.1.0 \(.*\)\n\n'

stderr '\n\nTo proceed despite packages unresolved in go 1\.16:\n\tgo mod tidy -e\nIf reproducibility with go 1.16 is not needed:\n\tgo mod tidy -compat=1\.17\nFor other options, see:\n\thttps://golang\.org/doc/modules/pruning\n'

cmp go.mod go.mod.orig


# If we run 'go mod tidy -e', we should still save enough checksums to run
# 'go list -m all' reproducibly with go 1.16, even though we can't list
# the specific package.

go mod tidy -e
! stderr '\n\tgo mod tidy'
cmp go.mod go.mod.orig

go list -m all
cmp stdout all-m.txt

go list -f $MODFMT example.net/ambiguous/nested/pkg
stdout '^example.net/ambiguous/nested v0\.1\.0$'
! stderr .

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

! go list -f $MODFMT example.net/ambiguous/nested/pkg
stderr '^ambiguous import: found package example\.net/ambiguous/nested/pkg in multiple modules:\n\texample\.net/ambiguous v0\.1\.0 \(.*\)\n\texample\.net/ambiguous/nested v0\.1\.0 \(.*\)\n'


# On the other hand, if we use -compat=1.17, 1.16 can't even load
# the build list (due to missing checksums).

cp go.mod.orig go.mod
go mod tidy -compat=1.17
! stderr .
go list -m all
cmp stdout all-m.txt

go mod edit -go=1.16
! go list -m all
stderr '^go: example\.net/indirect@v0\.1\.0 requires\n\texample\.net/ambiguous@v0\.1\.0: missing go\.sum entry; to add it:\n\tgo mod download example\.net/ambiguous\n'


-- go.mod --
module example.com/m

go 1.17

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

require example.net/indirect v0.1.0

require example.net/ambiguous/nested v0.1.0 // indirect
-- all-m.txt --
example.com/m
example.net/ambiguous v0.1.0
example.net/ambiguous/nested v0.1.0
example.net/indirect v0.1.0 => ./indirect
-- m.go --
package m

import _ "example.net/indirect"

-- indirect/go.mod --
module example.net/indirect

go 1.17

require example.net/ambiguous v0.1.0
-- indirect/indirect.go --
package indirect

import _ "example.net/ambiguous/nested/pkg"