Stop re-indexing on every find-file in projects with a .projectile

CHANGELOG.md

@@ -31,6 +31,7 @@
 
 ### Bugs fixed
 
+- [#2196](https://github.com/bbatsov/projectile/pull/2196): With the default in-memory cache, a project with a `.projectile` no longer throws its cache away and re-indexes on every `projectile-find-file` ([#2193](https://github.com/bbatsov/projectile/issues/2193)).
 - [#2195](https://github.com/bbatsov/projectile/pull/2195): `projectile-dispatch` can be extended with `transient-insert-suffix`/`transient-append-suffix` as soon as `transient` is loaded, instead of failing with "Not a transient prefix command" until the menu had been opened once ([#2194](https://github.com/bbatsov/projectile/discussions/2194)).
 - [#2191](https://github.com/bbatsov/projectile/pull/2191): The test suite passes under native compilation with an empty eln cache, as in distro package builds, instead of failing two dirconfig specs with `native-lisp-load-failed` ([#2100](https://github.com/bbatsov/projectile/issues/2100)).
 - [#2190](https://github.com/bbatsov/projectile/pull/2190): Alien indexing no longer hands git exclude pathspecs to an `fd` whose `projectile-git-fd-args` lacks `--strip-cwd-prefix`, which made it fail with `No valid search paths given` ([#2187](https://github.com/bbatsov/projectile/issues/2187)).

projectile.el

@@ -2588,10 +2588,28 @@ is tracked in `projectile--current-project'."
           (run-hook-with-args 'projectile-project-changed-functions
                               project-root previous))))))
 
+(defun projectile--dirconfig-newer-than-cache-p (project-root)
+  "Return non-nil if PROJECT-ROOT's dirconfig changed after its files were cached.
+When the files are cached in memory, what counts is when that cache was
+filled; otherwise it's the persistent cache file, if there is one.  With
+no cache at all there is nothing to be stale."
+  (let ((dirconfig (projectile-dirconfig-file project-root))
+        (cache-time (gethash project-root projectile-projects-cache-time)))
+    (if cache-time
+        ;; The cache time is in whole seconds, so an edit in the second the
+        ;; cache was filled counts as newer: re-indexing once too often
+        ;; beats serving a file list that ignores the edit.
+        (when-let* ((attributes (file-attributes dirconfig)))
+          (time-less-p cache-time (file-attribute-modification-time attributes)))
+      (let ((cache-file (projectile-project-cache-file project-root)))
+        (and (file-exists-p cache-file)
+             (file-newer-than-file-p dirconfig cache-file))))))
+
 (defun projectile-maybe-invalidate-cache (force)
   "Invalidate if FORCE or project's dirconfig newer than cache."
-  (when (or force (file-newer-than-file-p (projectile-dirconfig-file)
-                                          (projectile-project-cache-file)))
+  (when (or force
+            (when-let* ((project-root (projectile-project-root)))
+              (projectile--dirconfig-newer-than-cache-p project-root)))
     (projectile-invalidate-cache nil)))
 
 

test/projectile-root-test.el

@@ -56,8 +56,54 @@
     (expect (projectile-maybe-invalidate-cache t) :to-be-truthy))
   (it "should invalidate cache if dirconfig is newer than cache"
     (spy-on 'projectile-invalidate-cache :and-return-value t)
-    (spy-on 'file-newer-than-file-p :and-return-value t)
-    (expect (projectile-maybe-invalidate-cache nil) :to-be-truthy)))
+    (spy-on 'projectile--dirconfig-newer-than-cache-p :and-return-value t)
+    (expect (projectile-maybe-invalidate-cache nil) :to-be-truthy))
+  (it "leaves an in-memory cache alone when the dirconfig predates it (#2193)"
+    (projectile-test-with-stub-root "project" (".projectile")
+      (let ((root (projectile-project-root)))
+        (set-file-times (projectile-dirconfig-file root) (seconds-to-time 1000))
+        (puthash root 2000 projectile-projects-cache-time)
+        (spy-on 'projectile-invalidate-cache)
+        (projectile-maybe-invalidate-cache nil)
+        (expect 'projectile-invalidate-cache :not :to-have-been-called)))))
+
+(describe "projectile--dirconfig-newer-than-cache-p"
+  :var (root)
+  (it "keeps an in-memory cache filled after the dirconfig was written"
+    (projectile-test-with-stub-root "project" (".projectile")
+      (setq root (projectile-project-root))
+      (set-file-times (projectile-dirconfig-file root) (seconds-to-time 1000))
+      (puthash root 2000 projectile-projects-cache-time)
+      ;; No cache file: the in-memory cache never writes one.
+      (expect (file-exists-p (projectile-project-cache-file root)) :to-be nil)
+      (expect (projectile--dirconfig-newer-than-cache-p root) :to-be nil)))
+
+  (it "detects a dirconfig edited after the in-memory cache was filled"
+    (projectile-test-with-stub-root "project" (".projectile")
+      (setq root (projectile-project-root))
+      (set-file-times (projectile-dirconfig-file root) (seconds-to-time 3000))
+      (puthash root 2000 projectile-projects-cache-time)
+      (expect (projectile--dirconfig-newer-than-cache-p root) :to-be-truthy)))
+
+  (it "falls back to the cache file when nothing is cached in memory"
+    (projectile-test-with-stub-root "project" (".projectile" ".projectile-cache.eld")
+      (setq root (projectile-project-root))
+      (set-file-times (projectile-project-cache-file root) (seconds-to-time 2000))
+      (set-file-times (projectile-dirconfig-file root) (seconds-to-time 3000))
+      (expect (projectile--dirconfig-newer-than-cache-p root) :to-be-truthy)
+      (set-file-times (projectile-dirconfig-file root) (seconds-to-time 1000))
+      (expect (projectile--dirconfig-newer-than-cache-p root) :to-be nil)))
+
+  (it "has nothing to invalidate when there is no cache at all"
+    (projectile-test-with-stub-root "project" (".projectile")
+      (setq root (projectile-project-root))
+      (expect (projectile--dirconfig-newer-than-cache-p root) :to-be nil)))
+
+  (it "has nothing to invalidate when there is no dirconfig"
+    (projectile-test-with-stub-root "project" ("a.el")
+      (setq root (projectile-project-root))
+      (puthash root 2000 projectile-projects-cache-time)
+      (expect (projectile--dirconfig-newer-than-cache-p root) :to-be nil))))
 
 (describe "projectile-root-top-down"
   (it "identifies the root directory of a project by top-down search"