Issue #52: Add a --dry-run option

cherry_picker/cherry_picker.py

@@ -5,16 +5,23 @@
 
 
 @click.command()
+@click.option('--dry-run', is_flag=True)
+@click.option('--push', 'pr_remote', metavar='REMOTE',
+              help='git remote to use for PR branches', default='origin')
 @click.argument('commit_sha1', 'The commit sha1 to be cherry-picked')
 @click.argument('branches', 'The branches to backport to', nargs=-1)
-def cherry_pick(commit_sha1, branches):
+def cherry_pick(dry_run, pr_remote, commit_sha1, branches):
     if not os.path.exists('./pyconfig.h.in'):
         os.chdir('./cpython/')
-    upstream = get_git_upstream_remote()
-    username = get_forked_repo_name()
+    upstream = get_git_fetch_remote()
+    username = get_forked_repo_name(pr_remote)
+
+    if dry_run:
+       click.echo("Dry run requested, listing expected command sequence")
+
 
     click.echo("fetching upstream ...")
-    run_cmd(f"git fetch {upstream}")
+    run_cmd(f"git fetch {upstream}", dry_run=dry_run)
 
     if not branches:
         raise ValueError("at least one branch is required")
@@ -23,65 +30,78 @@ def cherry_pick(commit_sha1, branches):
         click.echo(f"Now backporting '{commit_sha1}' into '{branch}'")
 
         # git checkout -b 61e2bc7-3.5 upstream/3.5
-        cherry_pick_branch = f"{commit_sha1[:7]}-{branch}"
+        cherry_pick_branch = f"backport-{commit_sha1[:7]}-{branch}"
         cmd = f"git checkout -b {cherry_pick_branch} {upstream}/{branch}"
-        run_cmd(cmd)
+        run_cmd(cmd, dry_run=dry_run)
 
         cmd = f"git cherry-pick -x {commit_sha1}"
-        if run_cmd(cmd):
-            cmd = f"git push origin {cherry_pick_branch}"
-            if not run_cmd(cmd):
-                click.echo(f"Failed to push to origin :(")
+        if run_cmd(cmd, dry_run=dry_run):
+            cmd = f"git push {pr_remote} {cherry_pick_branch}"
+            if not run_cmd(cmd, dry_run=dry_run):
+                click.echo(f"Failed to push to {pr_remote} :(")
             else:
-                open_pr(username, branch, cherry_pick_branch)
+                open_pr(username, branch, cherry_pick_branch, dry_run=dry_run)
         else:
             click.echo(f"Failed to cherry-pick {commit_sha1} into {branch} :(")
 
         cmd = "git checkout master"
-        run_cmd(cmd)
+        run_cmd(cmd, dry_run=dry_run)
 
         cmd = f"git branch -D {cherry_pick_branch}"
-        if run_cmd(cmd):
-            click.echo(f"branch {cherry_pick_branch} has been deleted.")
+        if run_cmd(cmd, dry_run=dry_run):
+            if not dry_run:
+                click.echo(f"branch {cherry_pick_branch} has been deleted.")
         else:
             click.echo(f"branch {cherry_pick_branch} NOT deleted.")
 
 
-def get_git_upstream_remote():
+def get_git_fetch_remote():
     """Get the remote name to use for upstream branches
     Uses "upstream" if it exists, "origin" otherwise
     """
     cmd = "git remote get-url upstream"
-    if run_cmd(cmd):
-        return "upstream"
-    else:
+    try:
+        subprocess.check_output(cmd.split(), stderr=subprocess.DEVNULL)
+    except subprocess.CalledProcessError:
         return "origin"
+    return "upstream"
 
 
-def get_forked_repo_name():
+def get_forked_repo_name(pr_remote):
     """
     Return 'myusername' out of https://github.com/myusername/cpython
     :return:
     """
-    cmd = "git config --get remote.origin.url"
-    result = subprocess.check_output(cmd.split(), stderr=subprocess.STDOUT).decode('utf-8')
-    username = result[len("https://github.com/"):result.index('/cpython.git')]
+    cmd = f"git config --get remote.{pr_remote}.url"
+    raw_result = subprocess.check_output(cmd.split(), stderr=subprocess.STDOUT)
+    result = raw_result.decode('utf-8')
+    username_end = result.index('/cpython.git')
+    if result.startswith("https"):
+        username = result[len("https://github.com/"):username_end]
+    else:
+        username = result[len("git@github.com:"):username_end]
     return username
 
 
-def run_cmd(cmd):
+def run_cmd(cmd, *, dry_run=False):
+    if dry_run:
+        click.echo(f"  dry-run: {cmd}")
+        return True
     try:
         subprocess.check_output(cmd.split())
     except subprocess.CalledProcessError:
         return False
     return True
 
 
-def open_pr(forked_repo, base_branch, cherry_pick_branch):
+def open_pr(forked_repo, base_branch, cherry_pick_branch, *, dry_run=False):
     """
     construct the url for pull request and open it in the web browser
     """
     url = f"https://github.com/python/cpython/compare/{base_branch}...{forked_repo}:{cherry_pick_branch}?expand=1"
+    if dry_run:
+        click.echo(f"  dry-run: Create new PR: {url}")
+        return
     webbrowser.open_new_tab(url)
 
 

cherry_picker/readme.rst

@@ -1,6 +1,6 @@
 Usage::
 
-   python -m cherry_picker <commit_sha1> <branches>
+   python -m cherry_picker [--push REMOTE] [--dry-run] <commit_sha1> <branches>
 
 
 
@@ -34,6 +34,14 @@ Requires Python 3.6.
     (venv) $ git remote add upstream https://github.com/python/cpython.git
     (venv) $ cd ../
 
+The cherry picking script assumes that if an `upstream` remote is defined, then
+it should be used as the source of upstream changes and as the base for
+cherry-pick branches. Otherwise, `origin` is used for that purpose.
+
+By default, the PR branches used to submit pull requests back to the main
+repository are pushed to `origin`. If this is incorrect, then the correct
+remote will need be specified using the ``--push`` option (e.g.
+``--push pr`` to use a remote named ``pr``).
 
 Cherry-picking :snake: :cherries: :pick:
 ==============
@@ -62,20 +70,41 @@ What this will do:
 
     (venv) $ git fetch upstream
 
-    (venv) $ git checkout -b 6de2b78-3.5 upstream/3.5
+    (venv) $ git checkout -b backport-6de2b78-3.5 upstream/3.5
     (venv) $ git cherry-pick -x 6de2b7817f-some-commit-sha1-d064 
-    (venv) $ git push origin 6de2b78-3.5
+    (venv) $ git push origin backport-6de2b78-3.5
     (venv) $ git checkout master
-    (venv) $ git branch -D 6de2b78-3.5
+    (venv) $ git branch -D backport-6de2b78-3.5
 
-    (venv) $ git checkout -b 6de2b78-3.6 upstream/3.6
+    (venv) $ git checkout -b backport-6de2b78-3.6 upstream/3.6
     (venv) $ git cherry-pick -x 6de2b7817f-some-commit-sha1-d064 
-    (venv) $ git push origin 6de2b78-3.6
+    (venv) $ git push origin backport-6de2b78-3.6
     (venv) $ git checkout master
-    (venv) $ git branch -D 6de2b78-3.6
+    (venv) $ git branch -D backport-6de2b78-3.6
 
 In case of merge conflicts or errors, then... the script will fail :stuck_out_tongue:
 
+Passing the `--dry-run` option will cause the script to print out all the
+steps it would execute without actually executing any of them. For example::
+
+    $ python -m cherry_picker --dry-run --push pr 1e32a1be4a1705e34011770026cb64ada2d340b5 3.6 3.5
+    Dry run requested, listing expected command sequence
+    fetching upstream ...
+    dry_run: git fetch origin
+    Now backporting '1e32a1be4a1705e34011770026cb64ada2d340b5' into '3.6'
+    dry_run: git checkout -b backport-1e32a1b-3.6 origin/3.6
+    dry_run: git cherry-pick -x 1e32a1be4a1705e34011770026cb64ada2d340b5
+    dry_run: git push pr backport-1e32a1b-3.6
+    dry_run: Create new PR: https://github.com/python/cpython/compare/3.6...ncoghlan:backport-1e32a1b-3.6?expand=1
+    dry_run: git checkout master
+    dry_run: git branch -D backport-1e32a1b-3.6
+    Now backporting '1e32a1be4a1705e34011770026cb64ada2d340b5' into '3.5'
+    dry_run: git checkout -b backport-1e32a1b-3.5 origin/3.5
+    dry_run: git cherry-pick -x 1e32a1be4a1705e34011770026cb64ada2d340b5
+    dry_run: git push pr backport-1e32a1b-3.5
+    dry_run: Create new PR: https://github.com/python/cpython/compare/3.5...ncoghlan:backport-1e32a1b-3.5?expand=1
+    dry_run: git checkout master
+    dry_run: git branch -D backport-1e32a1b-3.5
 
 Creating Pull Requests
 ======================
@@ -85,8 +114,7 @@ tab that points to the pull request creation page.
 
 The url of the pull request page looks similar to the following::
 
-   https://github.com/python/cpython/compare/3.5...<username>:6de2b78-3.5?expand=1
-
+   https://github.com/python/cpython/compare/3.5...<username>:backport-6de2b78-3.5?expand=1
 
 
 1. Prefix the pull request description with the branch ``[X.Y]``, e.g.::