Automatically retry creating a PR after 422 on `--push`

Since `--push` has just created a new branch, there could be a slight
delay before GitHub registers it, and there's a possibility that a 422
would be returned for the "head" field. If that happens, retry the POST
a couple of times until it either succeeds or times out.

commands/pull_request.go

@@ -5,6 +5,7 @@ import (
 	"regexp"
 	"strconv"
 	"strings"
+	"time"
 
 	"github.com/github/hub/git"
 	"github.com/github/hub/github"
@@ -264,7 +265,35 @@ func pullRequest(cmd *Command, args *Args) {
 			issueNum, _ := strconv.Atoi(flagPullRequestIssue)
 			params["issue"] = issueNum
 		}
-		pr, err := client.CreatePullRequest(baseProject, params)
+
+		startedAt := time.Now()
+		numRetries := 0
+		retryDelay := 2
+		retryAllowance := 0
+		if flagPullRequestPush {
+			retryAllowance = 9
+		}
+
+		var pr *github.PullRequest
+		for {
+			pr, err = client.CreatePullRequest(baseProject, params)
+			if err != nil && strings.Contains(err.Error(), `Invalid value for "head"`) {
+				if retryAllowance > 0 {
+					retryAllowance -= retryDelay
+					time.Sleep(time.Duration(retryDelay) * time.Second)
+					retryDelay += 1
+					numRetries += 1
+				} else {
+					if numRetries > 0 {
+						duration := time.Now().Sub(startedAt)
+						err = fmt.Errorf("%s\nGiven up after retrying for %.1f seconds.", err, duration.Seconds())
+					}
+					break
+				}
+			} else {
+				break
+			}
+		}
 
 		if err == nil && editor != nil {
 			defer editor.DeleteFile()

features/pull_request.feature

@@ -500,17 +500,29 @@ BODY
     Given I am on the "feature" branch with upstream "origin/feature"
     Given the GitHub API server:
       """
+      tries = 0
       post('/repos/mislav/coral/pulls') {
-        status 422
-        json(:message => "I haz fail!")
+        tries += 1
+        if tries == 1
+          status 422
+          json :message => 'Validation Failed',
+               :errors => [{
+                 :resource => 'PullRequest',
+                 :code => 'invalid',
+                 :field => 'head'
+               }]
+        else
+          status 400
+        end
       }
       """
     When I run `hub pull-request -m message`
     Then the stderr should contain exactly:
       """
       Error creating pull request: Unprocessable Entity (HTTP 422)
-      I haz fail!\n
+      Invalid value for "head"\n
       """
+    And the exit status should be 1
 
   Scenario: Convert issue to pull request
     Given I am on the "feature" branch with upstream "origin/feature"
@@ -842,3 +854,66 @@ BODY
     And the exit status should be 1
     And the file ".git/PULLREQ_EDITMSG" should not exist
     And "git push origin HEAD:topic" should not be run
+
+  Scenario: Automatically retry when --push resulted in 422
+    Given The default aruba timeout is 7 seconds
+    And the text editor adds:
+      """
+      hello!
+      """
+    Given the GitHub API server:
+      """
+      first_try_at = nil
+      tries = 0
+
+      post('/repos/mislav/coral/pulls') {
+        tries += 1
+        assert :title => 'hello!', :head => 'mislav:topic'
+
+        if !first_try_at || (Time.now - first_try_at) < 5
+          first_try_at ||= Time.now
+          status 422
+          json :message => 'Validation Failed',
+               :errors => [{
+                 :resource => 'PullRequest',
+                 :code => 'invalid',
+                 :field => 'head'
+               }]
+        else
+          status 201
+          json :html_url => "the://url?tries=#{tries}"
+        end
+      }
+      """
+    Given I am on the "topic" branch
+    When I successfully run `hub pull-request -p`
+    Then the output should contain exactly "the://url?tries=3\n"
+    And the file ".git/PULLREQ_EDITMSG" should not exist
+
+  Scenario: Eventually give up on retries for --push
+    Given The default aruba timeout is 12 seconds
+    And the text editor adds:
+      """
+      hello!
+      """
+    Given the GitHub API server:
+      """
+      post('/repos/mislav/coral/pulls') {
+        status 422
+        json :message => 'Validation Failed',
+             :errors => [{
+               :resource => 'PullRequest',
+               :code => 'invalid',
+               :field => 'head'
+             }]
+      }
+      """
+    Given I am on the "topic" branch
+    When I run `hub pull-request -p`
+    Then the stderr should contain:
+      """
+      Error creating pull request: Unprocessable Entity (HTTP 422)
+      Invalid value for "head"\n
+      """
+    And the output should match /Given up after retrying for 9\.\d seconds\./
+    And a file named ".git/PULLREQ_EDITMSG" should exist