cmd/go: add tests for convergence in 'go mod tidy'

For #36460

Change-Id: I40194bb1ebab77459e5c9d43bdac4d9c1b826ac2
Reviewed-on: https://go-review.googlesource.com/c/go/+/312449
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>

diff --git a/src/cmd/go/testdata/script/mod_tidy_convergence.txt b/src/cmd/go/testdata/script/mod_tidy_convergence.txt
new file mode 100644 (file)
index 0000000..de85d23
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_tidy_convergence.txt
@@ -0,0 +1,174 @@
+# 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
+
+
+
+# TODO(#36460): Repeat this test with a lazy main module.
+
+
+-- 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
+)
+-- 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"

diff --git a/src/cmd/go/testdata/script/mod_tidy_convergence_loop.txt b/src/cmd/go/testdata/script/mod_tidy_convergence_loop.txt
new file mode 100644 (file)
index 0000000..efcd8f2
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_tidy_convergence_loop.txt
@@ -0,0 +1,272 @@
+# 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$'
+
+       # TODO: These error messages should be clearer — it doesn't indicate why v0.2.0-pre is required.
+stderr '^example\.net/m imports\n\texample\.net/w: package example\.net/w provided by example\.net/w at latest version v0\.1\.0 but not at required version v0\.2\.0-pre$'
+stderr '^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$'
+stderr '^example\.net/m imports\n\texample\.net/z: package example\.net/z provided by example\.net/z at latest version v0\.1\.0 but not at required version v0\.2\.0-pre$'
+
+
+# '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$'
+
+stderr '^example\.net/m imports\n\texample\.net/w: package example\.net/w provided by example\.net/w at latest version v0\.1\.0 but not at required version v0\.2\.0-pre$'
+stderr '^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$'
+stderr '^example\.net/m imports\n\texample\.net/z: package example\.net/z provided by example\.net/z at latest version v0\.1\.0 but not at required version v0\.2\.0-pre$'
+
+
+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 -d 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
+
+
+# TODO(#36460): Repeat this test with a lazy main module.
+
+
+-- 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.