preferredimports: support regular expressions for the import path

Having to list all packages isn't very manageable and requires constant
maintenance that is easy to miss. For example, test/e2e/framework/daemonset was
created without adding an entry for it. Promptly one file doesn't use the
intended e2edaemonset alias.

A simpler solution is to support matching the import path against a regular
expression and deriving the intended alias by expanding placeholders (${name},
$1, etc.) with the corresponding submatches from the import path. Example:

   k8s.io/kubernetes/test/e2e/framework/([^/]*) -> e2e$1

This support is backwards compatible because normal import paths don't contain
characters that are special in a regular expression and normal aliases don't
contain placeholders.

A regular expression must match the entire import path, otherwise it is
skipped.

cmd/preferredimports/preferredimports.go

@@ -43,7 +43,7 @@ var (
 	regex         = flag.String("include-path", "(test/e2e/|test/e2e_node)", "only files with paths matching this regex is touched")
 	isTerminal    = term.IsTerminal(int(os.Stdout.Fd()))
 	logPrefix     = ""
-	aliases       map[string]string
+	aliases       = map[*regexp.Regexp]string{}
 )
 
 type analyzer struct {
@@ -95,7 +95,17 @@ func (a *analyzer) collect(dir string) {
 				if imp.Name != nil {
 					importName = imp.Name.Name
 				}
-				if alias, ok := aliases[importPath]; ok {
+				for re, template := range aliases {
+					match := re.FindStringSubmatchIndex(importPath)
+					if match == nil {
+						// No match.
+						continue
+					}
+					if match[0] > 0 || match[1] < len(importPath) {
+						// Not a full match.
+						continue
+					}
+					alias := string(re.ExpandString(nil, template, importPath, match))
 					if alias != importName {
 						if !*confirm {
 							fmt.Fprintf(os.Stderr, "%sERROR wrong alias for import \"%s\" should be %s in file %s\n", logPrefix, importPath, alias, pathToFile)
@@ -108,6 +118,7 @@ func (a *analyzer) collect(dir string) {
 							imp.Name = ast.NewIdent(alias)
 						}
 					}
+					break
 				}
 			}
 
@@ -238,10 +249,18 @@ func main() {
 		if err != nil {
 			log.Fatalf("Error reading import aliases: %v", err)
 		}
-		err = json.Unmarshal(bytes, &aliases)
+		var stringAliases map[string]string
+		err = json.Unmarshal(bytes, &stringAliases)
 		if err != nil {
 			log.Fatalf("Error loading aliases: %v", err)
 		}
+		for pattern, name := range stringAliases {
+			re, err := regexp.Compile(pattern)
+			if err != nil {
+				log.Fatalf("Error parsing import path pattern %q as regular expression: %v", pattern, err)
+			}
+			aliases[re] = name
+		}
 	}
 	if isTerminal {
 		logPrefix = "\r" // clear status bar when printing