Merge changes from #10004

Merges changes from @williammartin including acceptance tests and word changes.

Co-authored-by: William Martin <williammartin@github.com>

acceptance/testdata/pr/pr-create-from-issue-develop-base.txtar

@@ -0,0 +1,37 @@
+# Set up env vars
+env REPO=${SCRIPT_NAME}-${RANDOM_STRING}
+
+# Use gh as a credential helper
+exec gh auth setup-git
+
+# Create a repository with a file so it has a default branch
+exec gh repo create ${ORG}/${REPO} --add-readme --private
+
+# Defer repo cleanup
+defer gh repo delete --yes ${ORG}/${REPO}
+
+# Clone the repo
+exec gh repo clone ${ORG}/${REPO}
+
+# Create a branch to act as the merge base branch
+cd ${REPO}
+exec git checkout -b long-lived-feature-branch
+exec git push -u origin long-lived-feature-branch
+
+# Create an issue to develop against
+exec gh issue create --title 'Feature Request' --body 'Request Body'
+stdout2env ISSUE_URL
+
+# Create a new branch using issue develop with the long lived branch as the base
+exec gh issue develop --name 'feature-branch' --base 'long-lived-feature-branch' --checkout ${ISSUE_URL}
+
+# Prepare a PR on the develop branch
+exec git commit --allow-empty -m 'Empty Commit'
+exec git push -u origin feature-branch
+
+# Create the PR
+exec gh pr create --title 'Feature Title' --body 'Feature Body'
+
+# Check the PR is created against the base branch we specified
+exec gh pr view --json 'baseRefName' --jq '.baseRefName'
+stdout 'long-lived-feature-branch'

acceptance/testdata/pr/pr-create-from-manual-merge-base.txtar

@@ -0,0 +1,34 @@
+# Set up env vars
+env REPO=${SCRIPT_NAME}-${RANDOM_STRING}
+
+# Use gh as a credential helper
+exec gh auth setup-git
+
+# Create a repository with a file so it has a default branch
+exec gh repo create ${ORG}/${REPO} --add-readme --private
+
+# Defer repo cleanup
+defer gh repo delete --yes ${ORG}/${REPO}
+
+# Clone the repo
+exec gh repo clone ${ORG}/${REPO}
+
+# Create a branch to act as the merge base branch
+cd ${REPO}
+exec git checkout -b long-lived-feature-branch
+exec git push -u origin long-lived-feature-branch
+
+# Prepare a branch from the merge base to PR
+exec git checkout -b feature-branch
+exec git commit --allow-empty -m 'Empty Commit'
+exec git push -u origin feature-branch
+
+# Set the merge-base branch config
+exec git config 'branch.feature-branch.gh-merge-base' 'long-lived-feature-branch'
+
+# Create the PR
+exec gh pr create --title 'Feature Title' --body 'Feature Body'
+
+# Check the PR is created against the merge base branch
+exec gh pr view --json 'baseRefName' --jq '.baseRefName'
+stdout 'long-lived-feature-branch'

git/client.go

@@ -376,7 +376,7 @@ func (c *Client) lookupCommit(ctx context.Context, sha, format string) ([]byte,
 	return out, nil
 }
 
-// ReadBranchConfig parses the `branch.BRANCH.(remote|merge)` part of git config.
+// ReadBranchConfig parses the `branch.BRANCH.(remote|merge|gh-merge-base)` part of git config.
 func (c *Client) ReadBranchConfig(ctx context.Context, branch string) (cfg BranchConfig) {
 	prefix := regexp.QuoteMeta(fmt.Sprintf("branch.%s.", branch))
 	args := []string{"config", "--get-regexp", fmt.Sprintf("^%s(remote|merge|%s)$", prefix, MergeBaseConfig)}

pkg/cmd/issue/develop/develop.go

@@ -44,6 +44,13 @@ func NewCmdDevelop(f *cmdutil.Factory, runF func(*DevelopOptions) error) *cobra.
 	cmd := &cobra.Command{
 		Use:   "develop {<number> | <url>}",
 		Short: "Manage linked branches for an issue",
+		Long: heredoc.Docf(`
+			Manage linked branches for an issue.
+
+			When using the %[1]s--base%[1]s flag, the new development branch will be created from the specified
+			remote branch. The new branch will be configured as the base branch for pull requests created using
+			%[1]sgh pr create%[1]s.
+		`, "`"),
 		Example: heredoc.Doc(`
 			# List branches for issue 123
 			$ gh issue develop --list 123

pkg/cmd/pr/create/create.go

@@ -119,6 +119,10 @@ func NewCmdCreate(f *cmdutil.Factory, runF func(*CreateOptions) error) *cobra.Co
 			alongside %[1]s--fill%[1]s, the values specified by %[1]s--title%[1]s and/or %[1]s--body%[1]s will
 			take precedence and overwrite any autofilled content.
 
+			The base branch for the created PR can be specified using the %[1]s--base%[1]s flag. If not provided,
+			the value of %[1]sgh-merge-base%[1]s git branch config will be used. If not configured, the repository's
+			default branch will be used.
+
 			Link an issue to the pull request by referencing the issue in the body of the pull
 			request. If the body text mentions %[1]sFixes #123%[1]s or %[1]sCloses #123%[1]s, the referenced issue
 			will automatically get closed when the pull request gets merged.