Allow dot-prefixed packages as valid import paths

Fixes golang#564

internal/gps/_testdata/src/disallow/.m1p/a.go

@@ -7,7 +7,7 @@ package m1p
 import (
 	"sort"
 
-	"github.com/golang/dep/gps"
+	"github.com/golang/dep/internal/gps"
 )
 
 var (

internal/gps/_testdata/src/dotgodir/.go/dot.go

@@ -0,0 +1,3 @@
+package dot
+
+// nothing to see here

internal/gps/pkgtree/pkgtree.go

@@ -28,6 +28,15 @@ type Package struct {
 	TestImports []string // Imports from all go test files (in go/build parlance: both TestImports and XTestImports)
 }
 
+// svnRoots is a set of directories we should not descend into in ListPackages when
+// searching for Go packages
+var svnRoots = map[string]struct{}{
+	".git": struct{}{},
+	".bzr": struct{}{},
+	".svn": struct{}{},
+	".hg":  struct{}{},
+}
+
 // ListPackages reports Go package information about all directories in the tree
 // at or below the provided fileRoot.
 //
@@ -78,10 +87,13 @@ func ListPackages(fileRoot, importRoot string) (PackageTree, error) {
 		case "vendor", "Godeps":
 			return filepath.SkipDir
 		}
-		// We do skip dot-dirs, though, because it's such a ubiquitous standard
-		// that they not be visited by normal commands, and because things get
-		// really weird if we don't.
-		if strings.HasPrefix(fi.Name(), ".") {
+
+		// Skip dirs that are known to be VCS roots.
+		//
+		// Note that there are some pathological edge cases this doesn't cover,
+		// such as a user using Git for version control, but having a package
+		// named "svn" in a directory named ".svn".
+		if _, ok := svnRoots[fi.Name()]; ok {
 			return filepath.SkipDir
 		}
 

internal/gps/pkgtree/pkgtree_test.go

@@ -1073,20 +1073,18 @@ func TestListPackages(t *testing.T) {
 							},
 						},
 					},
-					// disallow/.m1p is ignored by listPackages...for now. Kept
-					// here commented because this might change again...
-					//"disallow/.m1p": {
-					//P: Package{
-					//ImportPath:  "disallow/.m1p",
-					//CommentPath: "",
-					//Name:        "m1p",
-					//Imports: []string{
-					//"github.com/golang/dep/internal/gps",
-					//"os",
-					//"sort",
-					//},
-					//},
-					//},
+					"disallow/.m1p": {
+						P: Package{
+							ImportPath:  "disallow/.m1p",
+							CommentPath: "",
+							Name:        "m1p",
+							Imports: []string{
+								"github.com/golang/dep/internal/gps",
+								"os",
+								"sort",
+							},
+						},
+					},
 					"disallow/testdata": {
 						P: Package{
 							ImportPath:  "disallow/testdata",
@@ -1292,6 +1290,13 @@ func TestListPackages(t *testing.T) {
 							Imports:    []string{},
 						},
 					},
+					"dotgodir/.go": {
+						P: Package{
+							ImportPath: "dotgodir/.go",
+							Name:       "dot",
+							Imports:    []string{},
+						},
+					},
 					"dotgodir/foo.go": {
 						P: Package{
 							ImportPath: "dotgodir/foo.go",