cmd/go: re-resolve and check vcs roots during go get -u

If you do 'go get -u rsc.io/pdf' and then rsc.io/pdf's redirect
changes to point somewhere else, after this CL a later
'go get -u rsc.io/pdf' will tell you that.

Fixes #8548.

LGTM=iant
R=golang-codereviews, iant
CC=adg, golang-codereviews, n13m3y3r, r
https://golang.org/cl/147170043

src/cmd/go/get.go

@@ -266,6 +266,18 @@ func downloadPackage(p *Package) error {
 			return err
 		}
 		repo = "<local>" // should be unused; make distinctive
+
+		// Double-check where it came from.
+		if *getU && vcs.remoteRepo != nil {
+			dir := filepath.Join(p.build.SrcRoot, rootPath)
+			if remote, err := vcs.remoteRepo(vcs, dir); err == nil {
+				if rr, err := repoRootForImportPath(p.ImportPath); err == nil {
+					if remote != rr.repo {
+						return fmt.Errorf("%s is from %s, should be from %s", dir, remote, rr.repo)
+					}
+				}
+			}
+		}
 	} else {
 		// Analyze the import path to determine the version control system,
 		// repository, and the import path for the root of the repository.

src/cmd/go/test.bash

@@ -126,6 +126,56 @@ if ! ./testgo build -v ./testdata/testinternal2; then
 	ok=false
 fi
 
+# Test that 'go get -u' reports moved packages.
+testmove() {
+	vcs=$1
+	url=$2
+	base=$3
+	config=$4
+
+	TEST go get -u notices $vcs package that moved
+	d=$(mktemp -d -t testgoXXX)
+	mkdir -p $d/src
+	if ! GOPATH=$d ./testgo get -d $url; then
+		echo 'go get -d $url failed'
+		ok=false
+	elif ! GOPATH=$d ./testgo get -d -u $url; then
+		echo 'go get -d -u $url failed'
+		ok=false
+	else
+		set +e
+		case "$vcs" in
+		svn)
+			# SVN doesn't believe in text files so we can't just edit the config.
+			# Check out a different repo into the wrong place.
+			rm -rf $d/src/code.google.com/p/rsc-svn
+			GOPATH=$d ./testgo get -d -u code.google.com/p/rsc-svn2/trunk
+			mv $d/src/code.google.com/p/rsc-svn2 $d/src/code.google.com/p/rsc-svn
+			;;
+		*)
+			echo '1,$s;'"$base"';'"$base"'XXX;
+w
+q' | ed $d/src/$config >/dev/null 2>&1
+		esac
+		set -e
+
+		if GOPATH=$d ./testgo get -d -u $url 2>$d/err; then
+			echo "go get -d -u $url succeeded with wrong remote repo"
+			cat $d/err
+			ok=false
+		elif ! grep 'should be from' $d/err >/dev/null; then
+			echo "go get -d -u $url failed for wrong reason"
+			cat $d/err
+			ok=false
+		fi
+	fi
+	rm -rf $d
+}
+
+testmove hg rsc.io/x86/x86asm x86 rsc.io/x86/.hg/hgrc
+testmove git rsc.io/pdf pdf rsc.io/pdf/.git/config
+testmove svn code.google.com/p/rsc-svn/trunk - -
+
 export GOPATH=$(pwd)/testdata/importcom
 TEST 'import comment - match'
 if ! ./testgo build ./testdata/importcom/works.go; then

src/cmd/go/vcs.go

@@ -33,6 +33,8 @@ type vcsCmd struct {
 
 	scheme  []string
 	pingCmd string
+
+	remoteRepo func(v *vcsCmd, rootDir string) (remoteRepo string, err error)
 }
 
 // A tagCmd describes a command to list available tags
@@ -81,8 +83,17 @@ var vcsHg = &vcsCmd{
 	tagSyncCmd:     "update -r {tag}",
 	tagSyncDefault: "update default",
 
-	scheme:  []string{"https", "http", "ssh"},
-	pingCmd: "identify {scheme}://{repo}",
+	scheme:     []string{"https", "http", "ssh"},
+	pingCmd:    "identify {scheme}://{repo}",
+	remoteRepo: hgRemoteRepo,
+}
+
+func hgRemoteRepo(vcsHg *vcsCmd, rootDir string) (remoteRepo string, err error) {
+	out, err := vcsHg.runOutput(rootDir, "paths default")
+	if err != nil {
+		return "", err
+	}
+	return strings.TrimSpace(string(out)), nil
 }
 
 // vcsGit describes how to use Git.
@@ -104,8 +115,38 @@ var vcsGit = &vcsCmd{
 	tagSyncCmd:     "checkout {tag}",
 	tagSyncDefault: "checkout master",
 
-	scheme:  []string{"git", "https", "http", "git+ssh"},
-	pingCmd: "ls-remote {scheme}://{repo}",
+	scheme:     []string{"git", "https", "http", "git+ssh"},
+	pingCmd:    "ls-remote {scheme}://{repo}",
+	remoteRepo: gitRemoteRepo,
+}
+
+func gitRemoteRepo(vcsGit *vcsCmd, rootDir string) (remoteRepo string, err error) {
+	outb, err := vcsGit.runOutput(rootDir, "remote -v")
+	if err != nil {
+		return "", err
+	}
+	out := string(outb)
+
+	// Expect:
+	// origin	https://github.com/rsc/pdf (fetch)
+	// origin	https://github.com/rsc/pdf (push)
+	// use first line only.
+
+	if !strings.HasPrefix(out, "origin\t") {
+		return "", fmt.Errorf("unable to parse output of git remote -v")
+	}
+	out = strings.TrimPrefix(out, "origin\t")
+	i := strings.Index(out, "\n")
+	if i < 0 {
+		return "", fmt.Errorf("unable to parse output of git remote -v")
+	}
+	out = out[:i]
+	i = strings.LastIndex(out, " ")
+	if i < 0 {
+		return "", fmt.Errorf("unable to parse output of git remote -v")
+	}
+	out = out[:i]
+	return strings.TrimSpace(string(out)), nil
 }
 
 // vcsBzr describes how to use Bazaar.
@@ -138,8 +179,34 @@ var vcsSvn = &vcsCmd{
 	// There is no tag command in subversion.
 	// The branch information is all in the path names.
 
-	scheme:  []string{"https", "http", "svn", "svn+ssh"},
-	pingCmd: "info {scheme}://{repo}",
+	scheme:     []string{"https", "http", "svn", "svn+ssh"},
+	pingCmd:    "info {scheme}://{repo}",
+	remoteRepo: svnRemoteRepo,
+}
+
+func svnRemoteRepo(vcsSvn *vcsCmd, rootDir string) (remoteRepo string, err error) {
+	outb, err := vcsSvn.runOutput(rootDir, "info")
+	if err != nil {
+		return "", err
+	}
+	out := string(outb)
+
+	// Expect:
+	// ...
+	// Repository Root: <URL>
+	// ...
+
+	i := strings.Index(out, "\nRepository Root: ")
+	if i < 0 {
+		return "", fmt.Errorf("unable to parse output of svn info")
+	}
+	out = out[i+len("\nRepository Root: "):]
+	i = strings.Index(out, "\n")
+	if i < 0 {
+		return "", fmt.Errorf("unable to parse output of svn info")
+	}
+	out = out[:i]
+	return strings.TrimSpace(string(out)), nil
 }
 
 func (v *vcsCmd) String() string {