[errors] Greatly simplify common/errors package.

logdog/common/types/streamaddr.go

 // Copyright 2017 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package types
 
 import (
         "flag"
         "net/url"
         "strings"
@@ skipping 60 matching lines @@
 }
 
 // ParseURL parses a LogDog URL into a Stream. If the URL is malformed, or
 // if the host, project, or path is invalid, an error will be returned.
 //
 // A LogDog URL has the form:
 // logdog://<host>/<project>/<prefix>/+/<name>
 func ParseURL(v string) (*StreamAddr, error) {
         u, err := url.Parse(v)
         if err != nil {
-                return nil, errors.Annotate(err).Reason("failed to parse URL").Err()
+                return nil, errors.Annotate(err, "failed to parse URL").Err()
         }
 
         // Validate Scheme.
         if u.Scheme != logDogURLScheme {
-                return nil, errors.Reason("URL scheme %(scheme)q is not "+logDogURLScheme).
-                        D("scheme", u.Scheme).
-                        Err()
+                return nil, errors.Reason("URL scheme %q is not %s", u.Scheme, logDogURLScheme).Err()
         }
         addr := StreamAddr{
                 Host: u.Host,
         }
 
         parts := strings.SplitN(u.Path, "/", 3)
         if len(parts) != 3 || len(parts[0]) != 0 {
-                return nil, errors.Reason("URL path does not include both project and path components: %(path)s").
-                        D("path", u.Path).
-                        Err()
+                return nil, errors.Reason("URL path does not include both project and path components: %s", u.Path).Err()
         }
 
         addr.Project, addr.Path = cfgtypes.ProjectName(parts[1]), StreamPath(parts[2])
         if err := addr.Project.Validate(); err != nil {
-                return nil, errors.Annotate(err).Reason("invalid project name: %(project)q").
-                        D("project", addr.Project).
-                        Err()
+                return nil, errors.Annotate(err, "invalid project name: %q", addr.Project).Err()
         }
 
         if err := addr.Path.Validate(); err != nil {
-                return nil, errors.Annotate(err).Reason("invalid stream path: %(path)q").
-                        D("path", addr.Path).
-                        Err()
+                return nil, errors.Annotate(err, "invalid stream path: %q", addr.Path).Err()
         }
 
         return &addr, nil
 }