cmd/gomvpkg: Only process paths that are children

When determining children of a parent directory, look for the expected /
to avoid processing directories that look similar but are not direct
descendants.

Fixes golang/go#21991

Change-Id: I5c7d18076540e5588a856845f04645231856196f
Reviewed-on: https://go-review.googlesource.com/65672
Reviewed-by: Michael Matloob <matloob@golang.org>

refactor/rename/mvpkg.go

@@ -145,7 +145,9 @@ func subpackages(ctxt *build.Context, srcDir string, dir string) map[string]bool
 			log.Fatalf("unexpected error in ForEachPackage: %v", err)
 		}
 
-		if !strings.HasPrefix(pkg, path.Join(dir, "")) {
+		// Only process the package or a sub-package
+		if !(strings.HasPrefix(pkg, dir) &&
+			(len(pkg) == len(dir) || pkg[len(dir)] == '/')) {
 			return
 		}
 

refactor/rename/mvpkg_test.go

@@ -214,6 +214,23 @@ var _ a.T
 			},
 		},
 
+		// References into subpackages where directories have overlapped names
+		{
+			ctxt: fakeContext(map[string][]string{
+				"foo":    {},
+				"foo/a":  {`package a`},
+				"foo/aa": {`package bar`},
+				"foo/c":  {`package c; import _ "foo/bar";`},
+			}),
+			from: "foo/a", to: "foo/spam",
+			want: map[string]string{
+				"/go/src/foo/spam/0.go": `package spam
+`,
+				"/go/src/foo/aa/0.go": `package bar`,
+				"/go/src/foo/c/0.go":  `package c; import _ "foo/bar";`,
+			},
+		},
+
 		// External test packages
 		{
 			ctxt: buildutil.FakeContext(map[string]map[string]string{
@@ -398,11 +415,13 @@ var _ foo.T
 		}
 		moveDirectory = func(from, to string) error {
 			for path, contents := range got {
-				if strings.HasPrefix(path, from) {
-					newPath := strings.Replace(path, from, to, 1)
-					delete(got, path)
-					got[newPath] = contents
+				if !(strings.HasPrefix(path, from) &&
+					(len(path) == len(from) || path[len(from)] == filepath.Separator)) {
+					continue
 				}
+				newPath := strings.Replace(path, from, to, 1)
+				delete(got, path)
+				got[newPath] = contents
 			}
 			return nil
 		}