# 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 --- x
#       |
#       x_test --- y
#
# The module dependency graph of m is initially empty.
# Modules x and y look like:
#
# x.1 (provides package x that imports y, but does not depend on module y)
#
# x.2-pre (no dependencies, but does not provide package x)
#
# y.1 (no dependencies, but provides package y)
#
# y.2 --- x.2-pre (provides package y)
#
#
# When we resolve the missing import of y in x_test, we add y@latest — which is
# y.2, not y.1 — as a new dependency. That upgrades to x to x.2-pre, which
# removes package x (and also the need for module y). We can then safely remove
# the dependency on module y, because nothing imports package y any more!
#
# We might be tempted to remove the dependency on module x for the same reason:
# it no longer provides any imported package. However, that would cause 'go mod
# tidy -e' to become unstable: with x.2-pre out of the way, we could once again
# resolve the missing import of package x by re-adding x.1.

cp go.mod go.mod.orig

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

cmp go.mod go.mod.orig

stderr '^go: found example\.net/y in example\.net/y v0.2.0$'
stderr '^go: finding module for package example\.net/x$'

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


# 'go mod tidy -e' should follow upgrades to try to resolve the modules that it
# can, and then stop. When we resolve example.net/y, we upgrade to example.net/x
# to v0.2.0-pre. At that version, package x no longer exists and no longer
# imports package y, so the import of x should be left unsatisfied and the
# existing dependency on example.net/x removed.
#
# TODO(bcmills): It would be ever better if we could keep the original
# dependency on example.net/x v0.1.0, but I don't see a way to do that without
# making the algorithm way too complicated. (We would have to detect that the
# new dependency on example.net/y interferes with the package that caused us to
# to add that dependency in the first place, and back out that part of the change
# without also backing out any other needed changes.)

go mod tidy -e
cmp go.mod go.mod.tidye
stderr '^go: found example\.net/y in example\.net/y v0.2.0$'

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


# Since we attempt to resolve the dependencies of package x whenever we add x itself,
# this end state is stable.

go mod tidy -e
cmp go.mod go.mod.tidye


# An explicit 'go get' with the correct versions should allow 'go mod tidy' to
# succeed and remain stable. y.1 does not upgrade x, and can therefore be used
# with it.

go get -d example.net/x@v0.1.0 example.net/y@v0.1.0
go mod tidy
cmp go.mod go.mod.postget


# The 'tidy' logic for a lazy main module is somewhat different from that for an
# eager main module, but the overall behavior is the same.

cp go.mod.orig go.mod
go mod edit -go=1.17 go.mod
go mod edit -go=1.17 go.mod.tidye

go mod tidy -e
cmp go.mod go.mod.tidye
stderr '^go: found example\.net/y in example\.net/y v0.2.0$'
stderr '^example\.net/m imports\n\texample\.net/x: package example\.net/x provided by example\.net/x at latest version v0\.1\.0 but not at required version v0\.2\.0-pre$'

go get -d example.net/x@v0.1.0 example.net/y@v0.1.0
go mod tidy
cmp go.mod go.mod.postget-117


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

go 1.16

replace (
	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 => ./y2
)

require (
	example.net/x v0.1.0
)
-- go.mod.tidye --
module example.net/m

go 1.16

replace (
	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 => ./y2
)
-- go.mod.postget --
module example.net/m

go 1.16

replace (
	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 => ./y2
)

require (
	example.net/x v0.1.0
	example.net/y v0.1.0 // indirect
)
-- go.mod.postget-117 --
module example.net/m

go 1.17

replace (
	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 => ./y2
)

require example.net/x v0.1.0

require example.net/y v0.1.0 // indirect
-- m.go --
package m

import _ "example.net/x"

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

go 1.16
-- x1/x.go --
package x
-- x1/x_test.go --
package x

import _ "example.net/y"

-- x2-pre/go.mod --
module example.net/x

go 1.16
-- x2-pre/README.txt --
There is no package x here. Use example.com/x/subpkg instead.
-- x2-pre/subpkg/subpkg.go --
package subpkg  // import "example.net/x/subpkg"

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

go 1.16
-- y1/y.go --
package y

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

go 1.16

require example.net/x v0.2.0-pre
-- y2/y.go --
package y

import _ "example.net/x/subpkg"