Improve editor lookup algorithm

Author: PawelLipski

CONTRIBUTING.md

@@ -60,7 +60,7 @@ Output format of any non-plumbing command can change in non-backward-compatible
 1. Verify that a build started for [Snap](https://build.snapcraft.io/user/VirtusLab/git-machete).
    If not, check build.snapcraft.io webhook on Github (under Settings > Webhooks) -
    sometimes the build system responds with 500 status for no clear reason, in such case `Redeliver` the call.
-   Once ready, install the `latest/edge` revision locally (`sudo snap install --edge git-machete`)
+   Once ready, install the `latest/edge` revision locally (`sudo snap install --edge --classic git-machete`)
    and verify that it works correctly, esp. wrt. push/pull via ssh/https and editor (`git machete edit` and interactive rebases).
 
 1. Run `./tag-release.sh` script to create an annotated tag for the release.
@@ -90,7 +90,7 @@ Output format of any non-plumbing command can change in non-backward-compatible
 1. Verify that a build started on [git-machete PPA](https://launchpad.net/~virtuslab/+archive/ubuntu/git-machete/+packages).
 
    Once the new version package is published and the old one is removed (typically takes around 20-30 min),
-   follow the instructions from ci/deb-ppa-test-install/README.md.
+   follow the instructions from [ci/deb-ppa-test-install/README.md](https://github.com/VirtusLab/git-machete/tree/master/ci/deb-ppa-test-install).
    Inspect the output of `docker-compose` and verify that the latest version gets correctly installed on Ubuntu (esp. see the output of `git machete --version`).
 
 1. Perform a release from `latest/edge` to `latest/stable` for each architecture from [Snapcraft web dashboard](https://snapcraft.io/git-machete/releases) or via CLI.

RELEASE_NOTES.md

@@ -6,6 +6,7 @@
 - changed: confinement of snaps from `strict` to `classic`
 - changed: Docker images moved from under `virtuslab` organization to `gitmachete`
 - changed: `apt-ppa` in all contexts to `deb-ppa`
+- improved: determining the default editor (also including `git config core.editor`, `$GIT_EDITOR`, `editor` and `$VISUAL`)
 
 ## New in git-machete 2.13.5
 

git_machete/cmd.py

@@ -451,43 +451,52 @@ def is_executable(path):
     return os.access(path, os.X_OK)
 
 
-# Copied from distutils.spawn to avoid dependency on distutils
-def find_executable(executable, path=None):
-    """Tries to find 'executable' in the directories listed in 'path'.
-
-    A string listing directories separated by 'os.pathsep'; defaults to
-    os.environ['PATH'].  Returns the complete filename or None if not found.
-    """
-    if path is None:
-        path = os.environ.get('PATH', os.defpath)
-
-    paths = path.split(os.pathsep)
+def find_executable(executable):
     base, ext = os.path.splitext(executable)
 
     if (sys.platform == 'win32' or os.name == 'os2') and (ext != '.exe'):
         executable = executable + '.exe'
 
-    if not os.path.isfile(executable):
-        for p in paths:
-            f = os.path.join(p, executable)
-            if os.path.isfile(f):
-                # the file exists, we have a shot at spawn working
-                return f
-        return None
-    else:
+    if os.path.isfile(executable):
         return executable
 
+    path = os.environ.get('PATH', os.defpath)
+    paths = path.split(os.pathsep)
+    for p in paths:
+        f = os.path.join(p, executable)
+        if os.path.isfile(f) and is_executable(f):
+            debug("find_executable(%s)" % executable, "found %s at %s" % (executable, f))
+            return f
+    return None
+
+
+def get_default_editor():
+    # Based on the git's own algorithm for identifying the editor.
+    # 'editor' (to please Debian-based systems) and 'nano' have been added.
+    proposed_editor_funs = [
+        ("$GIT_EDITOR", lambda: os.environ.get("GIT_EDITOR")),
+        ("git config core.editor", lambda: get_config_or_none("core.editor")),
+        ("editor", lambda: "editor"),
+        ("$VISUAL", lambda: os.environ.get("VISUAL")),
+        ("$EDITOR", lambda: os.environ.get("EDITOR")),
+        ("nano", lambda: "nano"),
+        ("vi", lambda: "vi")
+    ]
+
+    for name, fun in proposed_editor_funs:
+        editor = fun()
+        if not editor:
+            debug("get_default_editor()", "'%s' is undefined" % name)
+        elif not find_executable(editor):
+            debug("get_default_editor()", "'%s'%s is not available" % (name, (" (" + editor + ")") if editor != name else ""))
+        else:
+            debug("get_default_editor()", "'%s'%s is available" % (name, (" (" + editor + ")") if editor != name else ""))
+            return editor
+    raise MacheteException("Cannot determine editor. Set EDITOR environment variable or edit %s directly." % definition_file)
+
 
 def edit():
-    editor = os.environ.get("EDITOR")
-    if editor and find_executable(editor):
-        return run_cmd(editor, definition_file)
-    elif find_executable("vim"):
-        return run_cmd("vim", definition_file)
-    elif find_executable("nano"):
-        return run_cmd("nano", definition_file)
-    else:
-        raise MacheteException("Cannot determine editor. Set EDITOR environment variable or edit %s directly." % definition_file)
+    return run_cmd(get_default_editor(), definition_file)
 
 
 git_version = None