feat: make VCS marker detection order configurable

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### New features
 
+* [#1984](https://github.com/bbatsov/projectile/pull/1984): Add `projectile-vcs-markers` to make VCS detection order configurable.
 * [#1964](https://github.com/bbatsov/projectile/issues/1964): Implement `project-name` and `project-buffers` methods for the `project.el` integration, so that code using `project.el` APIs returns correct results for Projectile-managed projects.
 * [#1837](https://github.com/bbatsov/projectile/issues/1837): Add `eat` project terminal commands with keybindings `x x` and `x 4 x`.
 * Add keybinding `A` (in the projectile command map) and a menu entry for `projectile-add-known-project`.

doc/modules/ROOT/pages/configuration.adoc

@@ -723,6 +723,39 @@ uses the project root directory name, but you can provide your own:
 NOTE: If the variable `projectile-project-name` is set (e.g. via
 `.dir-locals.el`), it takes precedence over the function.
 
+== VCS detection order
+
+Projectile automatically detects which version control system a project uses
+by checking for marker directories (`.git`, `.hg`, `.jj`, etc.).  The variable
+`projectile-vcs-markers` controls the detection order — earlier entries take
+priority:
+
+[source,elisp]
+----
+;; Default value — git is detected before jj
+(setq projectile-vcs-markers
+  '((".git"      . git)
+    (".hg"       . hg)
+    (".fslckout" . fossil)
+    ("_FOSSIL_"  . fossil)
+    (".bzr"      . bzr)
+    ("_darcs"    . darcs)
+    (".pijul"    . pijul)
+    (".sl"       . sapling)
+    (".jj"       . jj)
+    (".svn"      . svn)))
+----
+
+This is useful for colocated repositories where multiple VCS markers are
+present.  For example, https://martinvonz.github.io/jj/[Jujutsu] colocated
+repos contain both `.jj` and `.git`.  To detect them as `jj` instead of `git`:
+
+[source,elisp]
+----
+;; Prefer jj over git for colocated repos
+(push '(".jj" . jj) projectile-vcs-markers)
+----
+
 == Dirty projects
 
 `projectile-browse-dirty-projects` (kbd:[s-p V]) shows projects with

projectile.el

@@ -3925,38 +3925,43 @@ it acts on the current project.
 Expands wildcards using `file-expand-wildcards' before checking."
   (file-expand-wildcards (projectile-expand-root file dir)))
 
+(defcustom projectile-vcs-markers
+  '((".git"      . git)
+    (".hg"       . hg)
+    (".fslckout" . fossil)
+    ("_FOSSIL_"  . fossil)
+    (".bzr"      . bzr)
+    ("_darcs"    . darcs)
+    (".pijul"    . pijul)
+    (".svn"      . svn)
+    (".sl"       . sapling)
+    (".jj"       . jj))
+  "Ordered alist mapping VCS marker filenames to VCS symbols.
+Earlier entries take priority over later ones.  To prefer jj over
+git in colocated repos, move the \".jj\" entry before \".git\".
+Keys should be kept in sync with `projectile-project-root-files-bottom-up'."
+  :group 'projectile
+  :type '(alist :key-type string :value-type symbol)
+  :package-version '(projectile . "2.10.0"))
+
 (defun projectile-project-vcs (&optional project-root)
   "Determine the VCS used by the project if any.
 PROJECT-ROOT is the targeted directory.  If nil, use
 the variable `projectile-project-root'."
   (or project-root (setq project-root (projectile-acquire-root)))
-  (cond
+  (or
    ;; first we check for a VCS marker in the project root itself
-   ((projectile-file-exists-p (expand-file-name ".git" project-root)) 'git)
-   ((projectile-file-exists-p (expand-file-name ".hg" project-root)) 'hg)
-   ((projectile-file-exists-p (expand-file-name ".fslckout" project-root)) 'fossil)
-   ((projectile-file-exists-p (expand-file-name "_FOSSIL_" project-root)) 'fossil)
-   ((projectile-file-exists-p (expand-file-name ".bzr" project-root)) 'bzr)
-   ((projectile-file-exists-p (expand-file-name "_darcs" project-root)) 'darcs)
-   ((projectile-file-exists-p (expand-file-name ".pijul" project-root)) 'pijul)
-   ((projectile-file-exists-p (expand-file-name ".svn" project-root)) 'svn)
-   ((projectile-file-exists-p (expand-file-name ".sl" project-root)) 'sapling)
-   ((projectile-file-exists-p (expand-file-name ".jj" project-root)) 'jj)
+   (cl-loop for (marker . vcs) in projectile-vcs-markers
+            when (projectile-file-exists-p (expand-file-name marker project-root))
+            return vcs)
    ;; then we check if there's a VCS marker up the directory tree
    ;; that covers the case when a project is part of a multi-project repository
    ;; in those cases you can still use the VCS to get a list of files for
    ;; the project in question
-   ((projectile-locate-dominating-file project-root ".git") 'git)
-   ((projectile-locate-dominating-file project-root ".hg") 'hg)
-   ((projectile-locate-dominating-file project-root ".fslckout") 'fossil)
-   ((projectile-locate-dominating-file project-root "_FOSSIL_") 'fossil)
-   ((projectile-locate-dominating-file project-root ".bzr") 'bzr)
-   ((projectile-locate-dominating-file project-root "_darcs") 'darcs)
-   ((projectile-locate-dominating-file project-root ".pijul") 'pijul)
-   ((projectile-locate-dominating-file project-root ".svn") 'svn)
-   ((projectile-locate-dominating-file project-root ".sl") 'sapling)
-   ((projectile-locate-dominating-file project-root ".jj") 'jj)
-   (t 'none)))
+   (cl-loop for (marker . vcs) in projectile-vcs-markers
+            when (projectile-locate-dominating-file project-root marker)
+            return vcs)
+   'none))
 
 (defun projectile--test-name-for-impl-name (impl-file-path)
   "Determine the name of the test file for IMPL-FILE-PATH.

test/projectile-test.el

@@ -2553,6 +2553,34 @@ projectile-process-current-project-buffers-current to have similar behaviour"
         (projectile-project-buffer-p (current-buffer) project-root cache)
         (expect 'file-truename :to-have-been-called-times 1)))))
 
+(describe "projectile-project-vcs"
+  (it "returns git for a repo with only .git"
+    (projectile-test-with-sandbox
+      (projectile-test-with-files
+       (".git/")
+       (expect (projectile-project-vcs default-directory) :to-equal 'git))))
+  (it "returns jj for a repo with only .jj"
+    (projectile-test-with-sandbox
+      (projectile-test-with-files
+       (".jj/")
+       (expect (projectile-project-vcs default-directory) :to-equal 'jj))))
+  (it "defaults to git before jj for colocated repos"
+    (projectile-test-with-sandbox
+      (projectile-test-with-files
+       (".git/" ".jj/")
+       (expect (projectile-project-vcs default-directory) :to-equal 'git))))
+  (it "respects custom marker order: jj before git"
+    (projectile-test-with-sandbox
+      (projectile-test-with-files
+       (".git/" ".jj/")
+       (let ((projectile-vcs-markers '((".jj" . jj) (".git" . git))))
+         (expect (projectile-project-vcs default-directory) :to-equal 'jj)))))
+  (it "returns none when no VCS marker is present"
+    (let* ((tmpdir (make-temp-file "projectile-test-" t))
+           (default-directory tmpdir))
+      (unwind-protect
+          (expect (projectile-project-vcs default-directory) :to-equal 'none)
+        (delete-directory tmpdir t)))))
 ;; A bunch of tests that make sure Projectile commands handle
 ;; gracefully the case of being run outside of a project.
 (assert-friendly-error-when-no-project projectile-project-info)