diff --git a/src/cmd/go/testdata/script/reuse_hg.txt b/src/cmd/go/testdata/script/reuse_hg.txt
new file mode 100644
index 00000000000..ebc7643733d
--- /dev/null
+++ b/src/cmd/go/testdata/script/reuse_hg.txt
@@ -0,0 +1,483 @@
+skip
+
+[short] skip
+[!hg] skip
+
+env GO111MODULE=on
+env GOPROXY=direct
+env GOSUMDB=off
+
+# go mod download with the pseudo-version should invoke hg but not have a TagSum or Ref.
+go mod download -x -json vcs-test.golang.org/hg/hello.hg@v0.0.0-20170922010558-fc3a09f3dc5c
+stderr 'hg( .*)* pull'
+cp stdout hellopseudo.json
+! stdout '"(Query|TagPrefix|TagSum|Ref)"'
+stdout '"Version": "v0.0.0-20170922010558-fc3a09f3dc5c"'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/hello"'
+stdout '"Hash": "fc3a09f3dc5cfe0d7a743ea18f1f5226e68b3777"'
+! stdout '"RepoSum"'
+go clean -modcache
+
+# go mod download vcstest/hello should invoke hg, print origin info
+go mod download -x -json vcs-test.golang.org/hg/hello.hg@latest
+stderr 'hg( .*)* pull'
+cp stdout hello.json
+stdout '"Version": "v0.0.0-20170922010558-fc3a09f3dc5c"'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/hello"'
+stdout '"Query": "latest"'
+! stdout '"TagPrefix"'
+stdout '"TagSum": "t1:47DEQpj8HBSa[+]/TImW[+]5JCeuQeRkm5NMpJWZG3hSuFU="'
+stdout '"Ref": "HEAD"'
+stdout '"Hash": "fc3a09f3dc5cfe0d7a743ea18f1f5226e68b3777"'
+! stdout '"RepoSum"'
+
+# pseudo-version again should not invoke hg pull (it has the version from the @latest query)
+# but still be careful not to include a TagSum or a Ref, especially not Ref set to HEAD,
+# which is easy to do when reusing the cached version from the @latest query.
+go mod download -x -json vcs-test.golang.org/hg/hello.hg@v0.0.0-20170922010558-fc3a09f3dc5c
+! stderr 'hg( .*)* pull'
+cp stdout hellopseudo2.json
+cmpenv hellopseudo.json hellopseudo2.json
+
+# go mod download vcstest/hello@hash needs to check TagSum to find pseudoversion base.
+go mod download -x -json vcs-test.golang.org/hg/hello.hg@fc3a09f3dc5c
+! stderr 'hg( .*)* pull'
+cp stdout hellohash.json
+stdout '"Version": "v0.0.0-20170922010558-fc3a09f3dc5c"'
+stdout '"Query": "fc3a09f3dc5c"'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/hello"'
+stdout '"TagSum": "t1:47DEQpj8HBSa[+]/TImW[+]5JCeuQeRkm5NMpJWZG3hSuFU="'
+stdout '"Hash": "fc3a09f3dc5cfe0d7a743ea18f1f5226e68b3777"'
+! stdout '"RepoSum"'
+
+# go mod download vcstest/hello/v9 should fail, still print origin info
+! go mod download -x -json vcs-test.golang.org/hg/hello.hg/v9@latest
+cp stdout hellov9.json
+stdout '"Version": "latest"'
+stdout '"Error":.*no matching versions'
+! stdout '"TagPrefix"'
+stdout '"TagSum": "t1:47DEQpj8HBSa[+]/TImW[+]5JCeuQeRkm5NMpJWZG3hSuFU="'
+stdout '"Ref": "HEAD"'
+stdout '"Hash": "fc3a09f3dc5cfe0d7a743ea18f1f5226e68b3777"'
+! stdout 'RepoSum'
+
+# go mod download vcstest/hello/sub/v9 should also fail, print origin info with TagPrefix
+! go mod download -x -json vcs-test.golang.org/hg/hello.hg/sub/v9@latest
+cp stdout hellosubv9.json
+stdout '"Version": "latest"'
+stdout '"Error":.*no matching versions'
+stdout '"TagPrefix": "sub/"'
+stdout '"TagSum": "t1:47DEQpj8HBSa[+]/TImW[+]5JCeuQeRkm5NMpJWZG3hSuFU="'
+stdout '"Ref": "HEAD"'
+stdout '"Hash": "fc3a09f3dc5cfe0d7a743ea18f1f5226e68b3777"'
+! stdout 'RepoSum'
+
+# go mod download vcstest/hello@nonexist should fail, still print origin info
+! go mod download -x -json vcs-test.golang.org/hg/hello.hg@nonexist
+cp stdout hellononexist.json
+stdout '"Version": "nonexist"'
+stdout '"Error":.*unknown revision nonexist'
+stdout '"RepoSum": "r1:c0/9JCZ25lxoBiK3[+]3BhACU4giH49flcJmBynJ[+]Jvmc="'
+! stdout '"(TagPrefix|TagSum|Ref|Hash)"'
+
+# go mod download vcstest/hello@1234567890123456789012345678901234567890 should fail, still print origin info
+# (40 hex digits is assumed to be a full hash and is a slightly different code path from @nonexist)
+! go mod download -x -json vcs-test.golang.org/hg/hello.hg@1234567890123456789012345678901234567890
+cp stdout hellononhash.json
+stdout '"Version": "1234567890123456789012345678901234567890"'
+stdout '"Error":.*unknown revision 1234567890123456789012345678901234567890'
+stdout '"RepoSum": "r1:c0/9JCZ25lxoBiK3[+]3BhACU4giH49flcJmBynJ[+]Jvmc="'
+! stdout '"(TagPrefix|TagSum|Ref|Hash)"'
+
+# go mod download vcstest/hello@v0.0.0-20220101120101-123456789abc should fail, still print origin info
+# (non-existent pseudoversion)
+! go mod download -x -json vcs-test.golang.org/hg/hello.hg@v0.0.0-20220101120101-123456789abc
+cp stdout hellononpseudo.json
+stdout '"Version": "v0.0.0-20220101120101-123456789abc"'
+stdout '"Error":.*unknown revision 123456789abc'
+stdout '"RepoSum": "r1:c0/9JCZ25lxoBiK3[+]3BhACU4giH49flcJmBynJ[+]Jvmc="'
+! stdout '"(TagPrefix|TagSum|Ref|Hash)"'
+
+# go mod download vcstest/tagtests should invoke hg, print origin info
+go mod download -x -json vcs-test.golang.org/hg/tagtests.hg@latest
+stderr 'hg( .*)* pull'
+cp stdout tagtests.json
+stdout '"Version": "v0.2.2"'
+stdout '"Query": "latest"'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/tagtests"'
+! stdout '"TagPrefix"'
+stdout '"TagSum": "t1:Dp7yRKDuE8WjG0429PN9hYWjqhy2te7P9Oki/sMEOGo="'
+stdout '"Ref": "refs/tags/v0.2.2"'
+stdout '"Hash": "59356c8cd18c5fe9a598167d98a6843e52d57952"'
+! stdout '"RepoSum"'
+
+# go mod download vcstest/tagtests@v0.2.2 should print origin info, no TagSum needed
+go mod download -x -json vcs-test.golang.org/hg/tagtests.hg@v0.2.2
+cp stdout tagtestsv022.json
+stdout '"Version": "v0.2.2"'
+! stdout '"Query":'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/tagtests"'
+! stdout '"TagPrefix"'
+! stdout '"TagSum"'
+stdout '"Ref": "refs/tags/v0.2.2"'
+stdout '"Hash": "59356c8cd18c5fe9a598167d98a6843e52d57952"'
+! stdout '"RepoSum"'
+
+# go mod download vcstest/tagtests@master needs a TagSum again
+go mod download -x -json vcs-test.golang.org/hg/tagtests.hg@master
+cp stdout tagtestsmaster.json
+stdout '"Version": "v0.2.3-0.20190509225625-c7818c24fa2f"'
+stdout '"Query": "master"'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/tagtests"'
+! stdout '"TagPrefix"'
+stdout '"TagSum": "t1:Dp7yRKDuE8WjG0429PN9hYWjqhy2te7P9Oki/sMEOGo="'
+stdout '"Ref": "refs/heads/master"'
+stdout '"Hash": "c7818c24fa2f3f714c67d0a6d3e411c85a518d1f"'
+! stdout '"RepoSum"'
+
+# go mod download vcstest/prefixtagtests should invoke hg, print origin info
+go mod download -x -json vcs-test.golang.org/hg/prefixtagtests.hg/sub@latest
+stderr 'hg( .*)* pull'
+cp stdout prefixtagtests.json
+stdout '"Version": "v0.0.10"'
+stdout '"Query": "latest"'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/prefixtagtests"'
+stdout '"Subdir": "sub"'
+stdout '"TagPrefix": "sub/"'
+stdout '"TagSum": "t1:YGSbWkJ8dn9ORAr[+]BlKHFK/2ZhXLb9hVuYfTZ9D8C7g="'
+stdout '"Ref": "refs/tags/sub/v0.0.10"'
+stdout '"Hash": "2b7c4692e12c109263cab51b416fcc835ddd7eae"'
+! stdout '"RepoSum"'
+
+# go mod download of a bunch of these should fail (some are invalid) but write good JSON for later
+! go mod download -json vcs-test.golang.org/hg/hello.hg@latest vcs-test.golang.org/hg/hello.hg/v9@latest vcs-test.golang.org/hg/hello.hg/sub/v9@latest vcs-test.golang.org/hg/tagtests.hg@latest vcs-test.golang.org/hg/tagtests.hg@v0.2.2 vcs-test.golang.org/hg/tagtests.hg@master
+cp stdout all.json
+
+# clean the module cache, make sure that makes go mod download re-run hg pull, clean again
+go clean -modcache
+go mod download -x -json vcs-test.golang.org/hg/hello.hg@latest
+stderr 'hg( .*)* pull'
+go clean -modcache
+
+# reuse go mod download vcstest/hello result
+go clean -modcache
+go mod download -reuse=hello.json -x -json vcs-test.golang.org/hg/hello.hg@latest
+! stderr 'hg( .*)* pull'
+stdout '"Reuse": true'
+stdout '"Version": "v0.0.0-20170922010558-fc3a09f3dc5c"'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/hello"'
+! stdout '"TagPrefix"'
+stdout '"TagSum": "t1:47DEQpj8HBSa[+]/TImW[+]5JCeuQeRkm5NMpJWZG3hSuFU="'
+stdout '"Ref": "HEAD"'
+stdout '"Hash": "fc3a09f3dc5cfe0d7a743ea18f1f5226e68b3777"'
+! stdout '"(Dir|Info|GoMod|Zip|RepoSum)"'
+
+# reuse go mod download vcstest/hello pseudoversion result
+go clean -modcache
+go mod download -reuse=hellopseudo.json -x -json vcs-test.golang.org/hg/hello.hg@v0.0.0-20170922010558-fc3a09f3dc5c
+! stderr 'hg( .*)* pull'
+stdout '"Reuse": true'
+stdout '"Version": "v0.0.0-20170922010558-fc3a09f3dc5c"'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/hello"'
+! stdout '"(Query|TagPrefix|TagSum|Ref)"'
+stdout '"Hash": "fc3a09f3dc5cfe0d7a743ea18f1f5226e68b3777"'
+! stdout '"(Dir|Info|GoMod|Zip|RepoSum)"'
+
+# reuse go mod download vcstest/hello@hash
+go clean -modcache
+go mod download -reuse=hellohash.json -x -json vcs-test.golang.org/hg/hello.hg@fc3a09f3dc5c
+! stderr 'hg( .*)* pull'
+stdout '"Reuse": true'
+stdout '"Query": "fc3a09f3dc5c"'
+stdout '"Version": "v0.0.0-20170922010558-fc3a09f3dc5c"'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/hello"'
+! stdout '"(TagPrefix|Ref)"'
+stdout '"TagSum": "t1:47DEQpj8HBSa[+]/TImW[+]5JCeuQeRkm5NMpJWZG3hSuFU="'
+stdout '"Hash": "fc3a09f3dc5cfe0d7a743ea18f1f5226e68b3777"'
+! stdout '"(Dir|Info|GoMod|Zip|RepoSum)"'
+
+# reuse go mod download vcstest/hello/v9 error result
+go clean -modcache
+! go mod download -reuse=hellov9.json -x -json vcs-test.golang.org/hg/hello.hg/v9@latest
+! stderr 'hg( .*)* pull'
+stdout '"Reuse": true'
+stdout '"Error":.*no matching versions'
+! stdout '"TagPrefix"'
+stdout '"TagSum": "t1:47DEQpj8HBSa[+]/TImW[+]5JCeuQeRkm5NMpJWZG3hSuFU="'
+stdout '"Ref": "HEAD"'
+stdout '"Hash": "fc3a09f3dc5cfe0d7a743ea18f1f5226e68b3777"'
+! stdout '"(Dir|Info|GoMod|Zip|RepoSum)"'
+
+# reuse go mod download vcstest/hello/sub/v9 error result
+go clean -modcache
+! go mod download -reuse=hellosubv9.json -x -json vcs-test.golang.org/hg/hello.hg/sub/v9@latest
+! stderr 'hg( .*)* pull'
+stdout '"Reuse": true'
+stdout '"Error":.*no matching versions'
+stdout '"TagPrefix": "sub/"'
+stdout '"TagSum": "t1:47DEQpj8HBSa[+]/TImW[+]5JCeuQeRkm5NMpJWZG3hSuFU="'
+stdout '"Ref": "HEAD"'
+stdout '"Hash": "fc3a09f3dc5cfe0d7a743ea18f1f5226e68b3777"'
+! stdout '"(Dir|Info|GoMod|Zip|RepoSum)"'
+
+# reuse go mod download vcstest/hello@nonexist
+go clean -modcache
+! go mod download -reuse=hellononexist.json -x -json vcs-test.golang.org/hg/hello.hg@nonexist
+! stderr 'hg( .*)* pull'
+stdout '"Reuse": true'
+stdout '"Version": "nonexist"'
+stdout '"Error":.*unknown revision nonexist'
+stdout '"RepoSum": "r1:c0/9JCZ25lxoBiK3[+]3BhACU4giH49flcJmBynJ[+]Jvmc="'
+! stdout '"(TagPrefix|TagSum|Ref|Hash)"'
+! stdout '"(Dir|Info|GoMod|Zip)"'
+
+# reuse go mod download vcstest/hello@1234567890123456789012345678901234567890
+go clean -modcache
+! go mod download -reuse=hellononhash.json -x -json vcs-test.golang.org/hg/hello.hg@1234567890123456789012345678901234567890
+! stderr 'hg( .*)* pull'
+stdout '"Reuse": true'
+stdout '"Version": "1234567890123456789012345678901234567890"'
+stdout '"Error":.*unknown revision 1234567890123456789012345678901234567890'
+stdout '"RepoSum": "r1:c0/9JCZ25lxoBiK3[+]3BhACU4giH49flcJmBynJ[+]Jvmc="'
+! stdout '"(TagPrefix|TagSum|Ref|Hash)"'
+! stdout '"(Dir|Info|GoMod|Zip)"'
+
+# reuse go mod download vcstest/hello@v0.0.0-20220101120101-123456789abc
+go clean -modcache
+! go mod download -reuse=hellononpseudo.json -x -json vcs-test.golang.org/hg/hello.hg@v0.0.0-20220101120101-123456789abc
+! stderr 'hg( .*)* pull'
+stdout '"Reuse": true'
+stdout '"Version": "v0.0.0-20220101120101-123456789abc"'
+stdout '"Error":.*unknown revision 123456789abc'
+stdout '"RepoSum": "r1:c0/9JCZ25lxoBiK3[+]3BhACU4giH49flcJmBynJ[+]Jvmc="'
+! stdout '"(TagPrefix|TagSum|Ref|Hash)"'
+! stdout '"(Dir|Info|GoMod|Zip)"'
+
+# reuse go mod download vcstest/tagtests result
+go clean -modcache
+go mod download -reuse=tagtests.json -x -json vcs-test.golang.org/hg/tagtests.hg@latest
+! stderr 'hg( .*)* pull'
+stdout '"Reuse": true'
+stdout '"Version": "v0.2.2"'
+stdout '"Query": "latest"'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/tagtests"'
+! stdout '"TagPrefix"'
+stdout '"TagSum": "t1:Dp7yRKDuE8WjG0429PN9hYWjqhy2te7P9Oki/sMEOGo="'
+stdout '"Ref": "refs/tags/v0.2.2"'
+stdout '"Hash": "59356c8cd18c5fe9a598167d98a6843e52d57952"'
+! stdout '"(Dir|Info|GoMod|Zip|RepoSum)"'
+
+# reuse go mod download vcstest/tagtests@v0.2.2 result
+go clean -modcache
+go mod download -reuse=tagtestsv022.json -x -json vcs-test.golang.org/hg/tagtests.hg@v0.2.2
+! stderr 'hg( .*)* pull'
+stdout '"Reuse": true'
+stdout '"Version": "v0.2.2"'
+! stdout '"Query":'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/tagtests"'
+! stdout '"TagPrefix"'
+! stdout '"TagSum"'
+stdout '"Ref": "refs/tags/v0.2.2"'
+stdout '"Hash": "59356c8cd18c5fe9a598167d98a6843e52d57952"'
+! stdout '"(Dir|Info|GoMod|Zip|RepoSum)"'
+
+# reuse go mod download vcstest/tagtests@master result
+go clean -modcache
+go mod download -reuse=tagtestsmaster.json -x -json vcs-test.golang.org/hg/tagtests.hg@master
+! stderr 'hg( .*)* pull'
+stdout '"Reuse": true'
+stdout '"Version": "v0.2.3-0.20190509225625-c7818c24fa2f"'
+stdout '"Query": "master"'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/tagtests"'
+! stdout '"TagPrefix"'
+stdout '"TagSum": "t1:Dp7yRKDuE8WjG0429PN9hYWjqhy2te7P9Oki/sMEOGo="'
+stdout '"Ref": "refs/heads/master"'
+stdout '"Hash": "c7818c24fa2f3f714c67d0a6d3e411c85a518d1f"'
+! stdout '"(Dir|Info|GoMod|Zip|RepoSum)"'
+
+# reuse go mod download vcstest/tagtests@master result again with all.json
+go clean -modcache
+go mod download -reuse=all.json -x -json vcs-test.golang.org/hg/tagtests.hg@master
+! stderr 'hg( .*)* pull'
+stdout '"Reuse": true'
+stdout '"Version": "v0.2.3-0.20190509225625-c7818c24fa2f"'
+stdout '"Query": "master"'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/tagtests"'
+! stdout '"TagPrefix"'
+stdout '"TagSum": "t1:Dp7yRKDuE8WjG0429PN9hYWjqhy2te7P9Oki/sMEOGo="'
+stdout '"Ref": "refs/heads/master"'
+stdout '"Hash": "c7818c24fa2f3f714c67d0a6d3e411c85a518d1f"'
+! stdout '"(Dir|Info|GoMod|Zip|RepoSum)"'
+
+# go mod download vcstest/prefixtagtests result with json
+go clean -modcache
+go mod download -reuse=prefixtagtests.json -x -json vcs-test.golang.org/hg/prefixtagtests.hg/sub@latest
+! stderr 'hg( .*)* pull'
+stdout '"Version": "v0.0.10"'
+stdout '"Query": "latest"'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/prefixtagtests"'
+stdout '"Subdir": "sub"'
+stdout '"TagPrefix": "sub/"'
+stdout '"TagSum": "t1:YGSbWkJ8dn9ORAr[+]BlKHFK/2ZhXLb9hVuYfTZ9D8C7g="'
+stdout '"Ref": "refs/tags/sub/v0.0.10"'
+stdout '"Hash": "2b7c4692e12c109263cab51b416fcc835ddd7eae"'
+! stdout '"(Dir|Info|GoMod|Zip)"'
+
+# reuse the bulk results with all.json
+go clean -modcache
+! go mod download -reuse=all.json -json vcs-test.golang.org/hg/hello.hg@latest vcs-test.golang.org/hg/hello.hg/v9@latest vcs-test.golang.org/hg/hello.hg/sub/v9@latest vcs-test.golang.org/hg/tagtests.hg@latest vcs-test.golang.org/hg/tagtests.hg@v0.2.2 vcs-test.golang.org/hg/tagtests.hg@master
+! stderr 'hg( .*)* pull'
+stdout '"Reuse": true'
+! stdout '"(Dir|Info|GoMod|Zip)"'
+
+# reuse attempt with stale hash should reinvoke hg, not report reuse
+go clean -modcache
+cp tagtestsv022.json tagtestsv022badhash.json
+replace '57952' '56952XXX' tagtestsv022badhash.json
+go mod download -reuse=tagtestsv022badhash.json -x -json vcs-test.golang.org/hg/tagtests.hg@v0.2.2
+stderr 'hg( .*)* pull'
+! stdout '"Reuse": true'
+stdout '"Version": "v0.2.2"'
+! stdout '"Query"'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/tagtests"'
+! stdout '"(TagPrefix|TagSum|RepoSum)"'
+stdout '"Ref": "refs/tags/v0.2.2"'
+stdout '"Hash": "59356c8cd18c5fe9a598167d98a6843e52d57952"'
+stdout '"Dir"'
+stdout '"Info"'
+stdout '"GoMod"'
+stdout '"Zip"'
+
+# reuse with stale repo URL
+go clean -modcache
+cp tagtestsv022.json tagtestsv022badurl.json
+replace 'hg/tagtests\"' 'hg/tagtestsXXX\"' tagtestsv022badurl.json
+go mod download -reuse=tagtestsv022badurl.json -x -json vcs-test.golang.org/hg/tagtests.hg@v0.2.2
+! stdout '"Reuse": true'
+stdout '"URL": ".*/hg/tagtests"'
+stdout '"Dir"'
+stdout '"Info"'
+stdout '"GoMod"'
+stdout '"Zip"'
+
+# reuse with stale VCS
+go clean -modcache
+cp tagtestsv022.json tagtestsv022badvcs.json
+replace '\"hg\"' '\"hgXXX\"' tagtestsv022badvcs.json
+go mod download -reuse=tagtestsv022badvcs.json -x -json vcs-test.golang.org/hg/tagtests.hg@v0.2.2
+! stdout '"Reuse": true'
+stdout '"URL": ".*/hg/tagtests"'
+! stdout '"RepoSum"'
+
+# reuse with stale Dir
+go clean -modcache
+cp tagtestsv022.json tagtestsv022baddir.json
+replace '\t\t\"Ref\":' '\t\t\"Subdir\": \"subdir\",\n\t\t\"Ref\":' tagtestsv022baddir.json
+go mod download -reuse=tagtestsv022baddir.json -x -json vcs-test.golang.org/hg/tagtests.hg@v0.2.2
+! stdout '"Reuse": true'
+stdout '"URL": ".*/hg/tagtests"'
+! stdout '"RepoSum"'
+
+# reuse with stale TagSum
+go clean -modcache
+cp tagtests.json tagtestsbadtagsum.json
+replace 'sMEOGo=' 'sMEoGo=XXX' tagtestsbadtagsum.json
+go mod download -reuse=tagtestsbadtagsum.json -x -json vcs-test.golang.org/hg/tagtests.hg@latest
+! stdout '"Reuse": true'
+stdout '"TagSum": "t1:Dp7yRKDuE8WjG0429PN9hYWjqhy2te7P9Oki/sMEOGo="'
+! stdout '"RepoSum"'
+
+# go list on repo with no tags
+go clean -modcache
+go list -x -json -m -retracted -versions vcs-test.golang.org/hg/hello.hg@latest
+stderr 'hg( .*)* pull'
+cp stdout hellolist.json
+! stdout '"Versions"'
+stdout '"Version": "v0.0.0-20170922010558-fc3a09f3dc5c"'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/hello"'
+stdout '"Query": "latest"'
+! stdout '"TagPrefix"'
+stdout '"TagSum": "t1:47DEQpj8HBSa[+]/TImW[+]5JCeuQeRkm5NMpJWZG3hSuFU="'
+stdout '"Hash": "fc3a09f3dc5cfe0d7a743ea18f1f5226e68b3777"'
+! stdout '"RepoSum"'
+
+# reuse go list on repo with no tags
+go clean -modcache
+go list -x -reuse=hellolist.json -json -m -retracted -versions vcs-test.golang.org/hg/hello.hg@latest
+! stderr 'hg( .*)* pull'
+stdout '"Reuse": true'
+! stdout '"Versions"'
+stdout '"Version": "v0.0.0-20170922010558-fc3a09f3dc5c"'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/hello"'
+stdout '"Query": "latest"'
+! stdout '"TagPrefix"'
+stdout '"TagSum": "t1:47DEQpj8HBSa[+]/TImW[+]5JCeuQeRkm5NMpJWZG3hSuFU="'
+stdout '"Hash": "fc3a09f3dc5cfe0d7a743ea18f1f5226e68b3777"'
+! stdout '"RepoSum"'
+
+# reuse with stale list
+go clean -modcache
+cp hellolist.json hellolistbad.json
+replace '47DEQ' 'ZZZ' hellolistbad.json
+go clean -modcache
+go list -x -reuse=hellolistbad.json -json -m -retracted -versions vcs-test.golang.org/hg/hello.hg@latest
+stderr 'hg( .*)* pull'
+! stdout '"Reuse": true'
+stdout '"TagSum": "t1:47DEQpj8HBSa[+]/TImW[+]5JCeuQeRkm5NMpJWZG3hSuFU="'
+
+# go list on repo with tags
+go clean -modcache
+go list -x -json -m -retracted -versions vcs-test.golang.org/hg/tagtests.hg@latest
+cp stdout taglist.json
+stderr 'hg( .*)* pull'
+stdout '"Versions":'
+stdout '"v0.2.1"'
+stdout '"v0.2.2"'
+stdout '"Version": "v0.2.2"'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/tagtests"'
+stdout '"Hash": "59356c8cd18c5fe9a598167d98a6843e52d57952"'
+stdout '"TagSum": "t1:Dp7yRKDuE8WjG0429PN9hYWjqhy2te7P9Oki/sMEOGo="'
+stdout '"Ref": "refs/tags/v0.2.2"'
+
+# reuse go list on repo with tags
+go clean -modcache
+go list -reuse=taglist.json -x -json -m -retracted -versions vcs-test.golang.org/hg/tagtests.hg@latest
+! stderr 'hg( .*)* pull'
+stdout '"Reuse": true'
+stdout '"Versions":'
+stdout '"v0.2.1"'
+stdout '"v0.2.2"'
+stdout '"Version": "v0.2.2"'
+stdout '"VCS": "hg"'
+stdout '"URL": ".*/hg/tagtests"'
+stdout '"Hash": "59356c8cd18c5fe9a598167d98a6843e52d57952"'
+stdout '"TagSum": "t1:Dp7yRKDuE8WjG0429PN9hYWjqhy2te7P9Oki/sMEOGo="'
+stdout '"Ref": "refs/tags/v0.2.2"'
+
+# reuse with stale list
+go clean -modcache
+cp taglist.json taglistbad.json
+replace 'Dp7yRKDu' 'ZZZ' taglistbad.json
+go list -reuse=taglistbad.json -x -json -m -retracted -versions vcs-test.golang.org/hg/tagtests.hg@latest
+stderr 'hg( .*)* pull'
+! stdout '"Reuse": true'
+stdout '"TagSum": "t1:Dp7yRKDuE8WjG0429PN9hYWjqhy2te7P9Oki/sMEOGo="'
diff --git a/src/cmd/go/testdata/vcstest/hg/prefixtagtests.txt b/src/cmd/go/testdata/vcstest/hg/prefixtagtests.txt
new file mode 100644
index 00000000000..6c89c857f49
--- /dev/null
+++ b/src/cmd/go/testdata/vcstest/hg/prefixtagtests.txt
@@ -0,0 +1,53 @@
+handle git
+
+env GIT_AUTHOR_NAME='Jay Conrod'
+env GIT_AUTHOR_EMAIL='jayconrod@google.com'
+env GIT_COMMITTER_NAME=$GIT_AUTHOR_NAME
+env GIT_COMMITTER_EMAIL=$GIT_AUTHOR_EMAIL
+
+at 2019-05-09T18:35:00-04:00
+
+git init
+
+git add sub
+git commit -m 'create module sub'
+git branch -m master
+
+echo 'v0.1.0'
+cp stdout status
+git add status
+git commit -a -m 'v0.1.0'
+git tag 'v0.1.0'
+
+echo 'sub/v0.0.9'
+cp stdout status
+git commit -a -m 'sub/v0.0.9'
+git tag 'sub/v0.0.9'
+
+echo 'sub/v0.0.10'
+cp stdout status
+git commit -a -m 'sub/v0.0.10'
+git tag 'sub/v0.0.10'
+
+echo 'v0.2.0'
+cp stdout status
+git commit -a -m 'v0.2.0'
+git tag 'v0.2.0'
+
+echo 'after last tag'
+cp stdout status
+git commit -a -m 'after last tag'
+
+git show-ref --tags --heads
+cmp stdout .git-refs
+
+-- .git-refs --
+c3ee5d0dfbb9bf3c4d8bb2bce24cd8d14d2d4238 refs/heads/master
+2b7c4692e12c109263cab51b416fcc835ddd7eae refs/tags/sub/v0.0.10
+883885166298d79a0561d571a3044ec5db2e7c28 refs/tags/sub/v0.0.9
+db89fc573cfb939faf0aa0660671eb4cf8b8b673 refs/tags/v0.1.0
+1abe41965749e50828dd41de8d12c6ebc8e4e131 refs/tags/v0.2.0
+-- sub/go.mod --
+module vcs-test.golang.org/git/prefixtagtests.git/sub
+-- sub/sub.go --
+package sub
diff --git a/src/cmd/go/testdata/vcstest/hg/tagtests.txt b/src/cmd/go/testdata/vcstest/hg/tagtests.txt
new file mode 100644
index 00000000000..92e79cda877
--- /dev/null
+++ b/src/cmd/go/testdata/vcstest/hg/tagtests.txt
@@ -0,0 +1,44 @@
+handle git
+
+env GIT_AUTHOR_NAME='Jay Conrod'
+env GIT_AUTHOR_EMAIL='jayconrod@google.com'
+env GIT_COMMITTER_NAME=$GIT_AUTHOR_NAME
+env GIT_COMMITTER_EMAIL=$GIT_AUTHOR_EMAIL
+
+at 2019-05-09T18:56:25-04:00
+
+git init
+
+git add go.mod tagtests.go
+git commit -m 'create module tagtests'
+git branch -m master
+git branch b
+
+git add v0.2.1
+git commit -m 'v0.2.1'
+git tag 'v0.2.1'
+
+git checkout b
+git add 'v0.2.2'
+git commit -m 'v0.2.2'
+git tag 'v0.2.2'
+
+git checkout master
+git merge b -m 'merge'
+
+git show-ref --tags --heads
+cmp stdout .git-refs
+
+-- .git-refs --
+59356c8cd18c5fe9a598167d98a6843e52d57952 refs/heads/b
+c7818c24fa2f3f714c67d0a6d3e411c85a518d1f refs/heads/master
+101c49f5af1b2466332158058cf5f03c8cca6429 refs/tags/v0.2.1
+59356c8cd18c5fe9a598167d98a6843e52d57952 refs/tags/v0.2.2
+-- go.mod --
+module vcs-test.golang.org/git/tagtests.git
+-- tagtests.go --
+package tagtests
+-- v0.2.1 --
+v0.2.1
+-- v0.2.2 --
+v0.2.2