# This test demonstrates a simple case in which 'go mod tidy' may resolve a
# missing package, only to remove that package when resolving its dependencies.
#
# If we naively iterate 'go mod tidy' until the dependency graph converges, this
# scenario may fail to converge.

# The import graph used in this test looks like:
#
# m --- w
# |
# + --- x
# |
# + --- y
# |
# + --- z
#
# The module dependency graph of m initially contains w.1 (and, by extension,
# y.2-pre and z.2-pre). This is an arbitrary point in the cycle of possible
# configurations.
#
# w.1 requires y.2-pre and z.2-pre
# x.1 requires z.2-pre and w.2-pre
# y.1 requires w.2-pre and x.2-pre
# z.1 requires x.2-pre and y.2-pre
#
# At each point, exactly one missing package can be resolved by adding a
# dependency on the .1 release of the module that provides that package.
# However, adding that dependency causes the module providing another package to
# roll over from its .1 release to its .2-pre release, which removes the
# package. Once the package is removed, 'go mod tidy -e' no longer sees the
# module as relevant to the main module, and will happily remove the existing
# dependency on it.
#
# The cycle is of length 4 so that at every step only one package can be
# resolved. This is important because it prevents the iteration from ever
# reaching a state in which every package is simultaneously over-upgraded — such
# a state is stable and does not exhibit failure to converge.

cp go.mod go.mod.orig

# 'go mod tidy' without -e should fail without modifying go.mod,
# because it cannot resolve x, y, and z simultaneously.
! go mod tidy

cmp go.mod go.mod.orig

stderr '^go: finding module for package example\.net/w$'
stderr '^go: finding module for package example\.net/x$'
stderr -count=2 '^go: finding module for package example\.net/y$'
stderr -count=2 '^go: finding module for package example\.net/z$'
stderr '^go: found example\.net/x in example\.net/x v0.1.0$'

	# TODO: These error messages should be clearer — it doesn't indicate why v0.2.0-pre is required.
stderr '^go: example\.net/m imports\n\texample\.net/w: package example\.net/w provided by example\.net/w at latest version v0\.1\.0 but not at required version v0\.2\.0-pre$'
stderr '^go: example\.net/m imports\n\texample\.net/y: package example\.net/y provided by example\.net/y at latest version v0\.1\.0 but not at required version v0\.2\.0-pre$'
stderr '^go: example\.net/m imports\n\texample\.net/z: package example\.net/z provided by example\.net/z at latest version v0\.1\.0 but not at required version v0\.2\.0-pre$'


# 'go mod tidy -e' should preserve all of the upgrades to modules that could
# provide the missing packages but don't. That would at least explain why they
# are missing, and why no individual module can be upgraded in order to satisfy
# a missing import.
#
# TODO(bcmills): Today, it doesn't preserve those upgrades, and instead advances
# the state by one through the cycle of semi-tidy states.

go mod tidy -e

cmp go.mod go.mod.tidye1

stderr '^go: finding module for package example\.net/w$'
stderr '^go: finding module for package example\.net/x$'
stderr -count=2 '^go: finding module for package example\.net/y$'
stderr -count=2 '^go: finding module for package example\.net/z$'
stderr '^go: found example\.net/x in example\.net/x v0.1.0$'

stderr '^go: example\.net/m imports\n\texample\.net/w: package example\.net/w provided by example\.net/w at latest version v0\.1\.0 but not at required version v0\.2\.0-pre$'
stderr '^go: example\.net/m imports\n\texample\.net/y: package example\.net/y provided by example\.net/y at latest version v0\.1\.0 but not at required version v0\.2\.0-pre$'
stderr '^go: example\.net/m imports\n\texample\.net/z: package example\.net/z provided by example\.net/z at latest version v0\.1\.0 but not at required version v0\.2\.0-pre$'


go mod tidy -e
cmp go.mod go.mod.tidye2

go mod tidy -e
cmp go.mod go.mod.tidye3

go mod tidy -e
cmp go.mod go.mod.orig


# If we upgrade away all of the packages simultaneously, the resulting tidy
# state converges at "no dependencies", because simultaneously adding all of the
# packages simultaneously over-upgrades all of the dependencies, and 'go mod
# tidy' treats "no package can be added" as a terminal state.

go get example.net/w@v0.2.0-pre example.net/x@v0.2.0-pre example.net/y@v0.2.0-pre example.net/z@v0.2.0-pre
go mod tidy -e
cmp go.mod go.mod.postget
go mod tidy -e
cmp go.mod go.mod.postget


# The 'tidy' logic for a lazy main module requires more iterations to converge,
# because it is willing to drop dependencies on non-root modules that do not
# otherwise provide imported packages.
#
# On the first iteration, it adds x.1 as a root, which upgrades z and w,
# dropping w.1's requirement on y. w.1 was initially a root, so the upgraded
# w.2-pre is retained as a root.
#
# On the second iteration, it adds y.1 as a root, which upgrades w and x,
# dropping x.1's requirement on z. x.1 was added as a root in the previous step,
# so the upgraded x.2-pre is retained as a root.
#
# On the third iteration, it adds z.1 as a root, which upgrades x and y.
# x and y were already roots (from the previous steps), so their upgraded versions
# are retained (not dropped) and the iteration stops.
#
# At that point, we have z.1 as a root providing package z,
# and w, x, and y have all been upgraded to no longer provide any packages.
# So only z is retained as a new root.
#
# (From the above, we can see that in a lazy module we still cycle through the
# same possible root states, but in a different order from the eager case.)
#
# TODO(bcmills): if we retained the upgrades on w, x, and y (since they are
# lexical prefixes for unresolved packages w, x, and y, respectively), then 'go
# mod tidy -e' itself would become stable and no longer cycle through states.

cp go.mod.orig go.mod
go mod edit -go=1.17 go.mod
cp go.mod go.mod.117
go mod edit -go=1.17 go.mod.tidye1
go mod edit -go=1.17 go.mod.tidye2
go mod edit -go=1.17 go.mod.tidye3
go mod edit -go=1.17 go.mod.postget

go list -m all

go mod tidy -e
cmp go.mod go.mod.tidye3

go mod tidy -e
cmp go.mod go.mod.tidye2

go mod tidy -e
cmp go.mod go.mod.tidye1

go mod tidy -e
cmp go.mod go.mod.117


# As in the eager case, for the lazy module the fully-upgraded dependency graph
# becomes empty, and the empty graph is stable.

go get example.net/w@v0.2.0-pre example.net/x@v0.2.0-pre example.net/y@v0.2.0-pre example.net/z@v0.2.0-pre
go mod tidy -e
cmp go.mod go.mod.postget
go mod tidy -e
cmp go.mod go.mod.postget


-- m.go --
package m

import (
	_ "example.net/w"
	_ "example.net/x"
	_ "example.net/y"
	_ "example.net/z"
)

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

go 1.16

replace (
	example.net/w v0.1.0 => ./w1
	example.net/w v0.2.0-pre => ./w2-pre
	example.net/x v0.1.0 => ./x1
	example.net/x v0.2.0-pre => ./x2-pre
	example.net/y v0.1.0 => ./y1
	example.net/y v0.2.0-pre => ./y2-pre
	example.net/z v0.1.0 => ./z1
	example.net/z v0.2.0-pre => ./z2-pre
)

require example.net/w v0.1.0
-- go.mod.tidye1 --
module example.net/m

go 1.16

replace (
	example.net/w v0.1.0 => ./w1
	example.net/w v0.2.0-pre => ./w2-pre
	example.net/x v0.1.0 => ./x1
	example.net/x v0.2.0-pre => ./x2-pre
	example.net/y v0.1.0 => ./y1
	example.net/y v0.2.0-pre => ./y2-pre
	example.net/z v0.1.0 => ./z1
	example.net/z v0.2.0-pre => ./z2-pre
)

require example.net/x v0.1.0
-- go.mod.tidye2 --
module example.net/m

go 1.16

replace (
	example.net/w v0.1.0 => ./w1
	example.net/w v0.2.0-pre => ./w2-pre
	example.net/x v0.1.0 => ./x1
	example.net/x v0.2.0-pre => ./x2-pre
	example.net/y v0.1.0 => ./y1
	example.net/y v0.2.0-pre => ./y2-pre
	example.net/z v0.1.0 => ./z1
	example.net/z v0.2.0-pre => ./z2-pre
)

require example.net/y v0.1.0
-- go.mod.tidye3 --
module example.net/m

go 1.16

replace (
	example.net/w v0.1.0 => ./w1
	example.net/w v0.2.0-pre => ./w2-pre
	example.net/x v0.1.0 => ./x1
	example.net/x v0.2.0-pre => ./x2-pre
	example.net/y v0.1.0 => ./y1
	example.net/y v0.2.0-pre => ./y2-pre
	example.net/z v0.1.0 => ./z1
	example.net/z v0.2.0-pre => ./z2-pre
)

require example.net/z v0.1.0
-- go.mod.postget --
module example.net/m

go 1.16

replace (
	example.net/w v0.1.0 => ./w1
	example.net/w v0.2.0-pre => ./w2-pre
	example.net/x v0.1.0 => ./x1
	example.net/x v0.2.0-pre => ./x2-pre
	example.net/y v0.1.0 => ./y1
	example.net/y v0.2.0-pre => ./y2-pre
	example.net/z v0.1.0 => ./z1
	example.net/z v0.2.0-pre => ./z2-pre
)
-- w1/go.mod --
module example.net/w

go 1.16

require (
	example.net/y v0.2.0-pre
	example.net/z v0.2.0-pre
)
-- w1/w.go --
package w
-- w2-pre/go.mod --
module example.net/w

go 1.16
-- w2-pre/README.txt --
Package w has been removed.

-- x1/go.mod --
module example.net/x

go 1.16

require (
	example.net/z v0.2.0-pre
	example.net/w v0.2.0-pre
)
-- x1/x.go --
package x
-- x2-pre/go.mod --
module example.net/x

go 1.16
-- x2-pre/README.txt --
Package x has been removed.

-- y1/go.mod --
module example.net/y

go 1.16

require (
	example.net/w v0.2.0-pre
	example.net/x v0.2.0-pre
)
-- y1/y.go --
package y

-- y2-pre/go.mod --
module example.net/y

go 1.16
-- y2-pre/README.txt --
Package y has been removed.

-- z1/go.mod --
module example.net/z

go 1.16

require (
	example.net/x v0.2.0-pre
	example.net/y v0.2.0-pre
)
-- z1/z.go --
package z

-- z2-pre/go.mod --
module example.net/z

go 1.16
-- z2-pre/README.txt --
Package z has been removed.