# 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, Go 1.17 prunes out a (transitive and otherwise-irrelevant)
# requirement on a retracted higher version of a dependency.
# However, when Go 1.16 reads the same requirements from the go.mod file,
# it does not prune out that requirement, and selects the retracted version.
#
# The Go 1.16 module graph looks like:
#
# m ---- lazy v0.1.0 ---- requireincompatible v0.1.0 ---- incompatible v2.0.0+incompatible
# |        |
# + -------+------------- incompatible v1.0.0
#
# The Go 1.17 module graph is the same except that the dependencies of
# requireincompatible are pruned out (because the module that requires
# it — lazy v0.1.0 — specifies 'go 1.17', and it is not otherwise relevant to
# the main module).


# 'go mod tidy' should by default diagnose the difference in dependencies as an
# error, with useful suggestions about how to resolve it.

cp go.mod go.mod.orig
! go mod tidy
stderr '^go: example\.com/m imports\n\texample\.net/lazy imports\n\texample\.com/retract/incompatible loaded from example\.com/retract/incompatible@v1\.0\.0,\n\tbut go 1\.16 would select v2\.0\.0\+incompatible\n\n'
stderr '\n\nTo upgrade to the versions selected by go 1\.16:\n\tgo mod tidy -go=1\.16 && go mod tidy -go=1\.17\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


# The suggested '-compat' flag to ignore differences should silence the error
# and leave go.mod unchanged, resulting in checksum errors when Go 1.16 tries
# to load a module pruned out by Go 1.17.

go mod tidy -compat=1.17
! stderr .
cmp go.mod go.mod.orig

go mod edit -go=1.16
! go list -f $MODFMT -deps ./...
stderr -count=1 '^go: example\.net/lazy@v0\.1\.0 requires\n\texample\.net/requireincompatible@v0\.1\.0 requires\n\texample\.com/retract/incompatible@v2\.0\.0\+incompatible: missing go.sum entry for go.mod file; to add it:\n\tgo mod download example.com/retract/incompatible$'


# There are two ways for the module author to bring the two into alignment.
# One is to *explicitly* 'exclude' the version that is already *implicitly*
# pruned out under 1.17.

go mod edit -exclude=example.com/retract/incompatible@v2.0.0+incompatible
go list -f $MODFMT -deps ./...
stdout '^example.com/retract/incompatible v1\.0\.0$'
! stdout 'v2\.0\.0'


# The other is to explicitly upgrade the version required under Go 1.17
# to match the version selected by Go 1.16. The commands suggested by
# 'go mod tidy' should do exactly that.

cp go.mod.orig go.mod

go mod tidy -go=1.16
go list -f $MODFMT -deps ./...
stdout '^example.com/retract/incompatible v2\.0\.0\+incompatible$'
! stdout 'v1\.0\.0'

go mod tidy -go=1.17
go list -f $MODFMT -deps ./...
stdout '^example.com/retract/incompatible v2\.0\.0\+incompatible$'
! stdout 'v1\.0\.0'

go mod edit -go=1.16
go list -f $MODFMT -deps ./...
stdout '^example.com/retract/incompatible v2\.0\.0\+incompatible$'
! stdout 'v1\.0\.0'


-- go.mod --
// Module m indirectly imports a package from
// example.com/retract/incompatible. Its selected version of
// that module is lower under Go 1.17 semantics than under Go 1.16.
module example.com/m

go 1.17

replace (
	example.net/lazy v0.1.0 => ./lazy
	example.net/requireincompatible v0.1.0 => ./requireincompatible
)

require example.net/lazy v0.1.0

require example.com/retract/incompatible v1.0.0 // indirect
-- incompatible.go --
package incompatible

import _ "example.net/lazy"

-- lazy/go.mod --
// Module lazy requires example.com/retract/incompatible v1.0.0.
//
// When viewed from the outside it also has a transitive dependency
// on v2.0.0+incompatible, but in lazy mode that transitive dependency
// is pruned out.
module example.net/lazy

go 1.17

exclude example.com/retract/incompatible v2.0.0+incompatible

require (
	example.com/retract/incompatible v1.0.0
	example.net/requireincompatible v0.1.0
)
-- lazy/lazy.go --
package lazy

import _ "example.com/retract/incompatible"

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

go 1.15

require example.com/retract/incompatible v2.0.0+incompatible