Use cons cells as projectile-project-root-cache keys

Per-function entries are now keyed on (FUNC . DIR), and the overall
failure marker on ('none . DIR), instead of formatted strings.  Same
equal semantics, no per-call format allocation, and lambda functions
in projectile-project-root-functions hash by identity instead of by
their printed repr.

3 files changed, 10 insertions, 12 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 24b0cd1..2b64613 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 ### Changes
 
+* `projectile-project-root-cache` now keys entries on cons cells (`(FUNC . DIR)` for per-function results, `('none . DIR)` for the overall failure marker) instead of formatted strings. This is internal state, but third-party code that reaches into the cache directly will need to update.
 * `projectile-parse-dirconfig-file' now returns a `projectile-dirconfig' struct (with `keep', `ignore', `ensure', and `prefixless-ignore' slots) instead of a positional 3-tuple. External callers should use the accessors (`projectile-dirconfig-keep' etc.) rather than `car'/`cadr'/`caddr'.
 * Soft-deprecate prefix-less ignore entries in `.projectile'. Lines without a `+'/`-'/`!' prefix are still treated as ignore patterns for backward compatibility, but a one-time warning is now shown for each project that uses them. Set `projectile-warn-on-prefixless-dirconfig-lines' to nil to silence.
 
diff --git a/projectile.el b/projectile.el
index cd3ea2a..bcd8302 100644
--- a/projectile.el
+++ b/projectile.el
@@ -1457,15 +1457,14 @@ If DIR is not supplied it's set to the current directory by default."
     (when (and (fboundp 'tramp-archive-file-name-p)
                (tramp-archive-file-name-p dir))
       (setq dir (file-name-directory (tramp-archive-file-name-archive dir))))
-    ;; the cached value will be 'none in the case of no project root (this is to
-    ;; ensure it is not reevaluated each time when not inside a project) so
-    ;; replace this 'none value with nil so a nil value is used instead
+    ;; The cached value is 'none when no project root was found (so we don't
+    ;; reevaluate every time when not inside a project); we map that back to
+    ;; nil for callers.  Cache keys are conses: (FUNC . DIR) for per-function
+    ;; results, ('none . DIR) for the overall failure marker.
     (let ((result (or
        ;; if we've already failed to find a project dir for this
        ;; dir, and cached that failure, don't recompute
-       (let* ((cache-key (format "projectilerootless-%s" dir))
-              (cache-value (gethash cache-key projectile-project-root-cache)))
-         cache-value)
+       (gethash (cons 'none dir) projectile-project-root-cache)
        ;; if the file isn't local, and we're not connected, don't try to
        ;; find a root now, but don't cache failure, as we might
        ;; re-connect.  The `is-local' and `is-connected' variables are
@@ -1482,7 +1481,7 @@ If DIR is not supplied it's set to the current directory by default."
        ;; through the project root functions until we find a project dir
        (seq-some
         (lambda (func)
-          (let* ((cache-key (format "%s-%s" func dir))
+          (let* ((cache-key (cons func dir))
                  (cache-value (gethash cache-key projectile-project-root-cache)))
             (if (and cache-value (file-exists-p cache-value))
                 cache-value
@@ -1493,9 +1492,7 @@ If DIR is not supplied it's set to the current directory by default."
        ;; if we get here, we have failed to find a root by all
        ;; conventional means, and we assume the failure isn't transient
        ;; / network related, so cache the failure
-       (let ((cache-key (format "projectilerootless-%s" dir)))
-         (puthash cache-key 'none projectile-project-root-cache)
-         'none))))
+       (puthash (cons 'none dir) 'none projectile-project-root-cache))))
       (unless (eq result 'none) result))))
 
 (defun projectile-ensure-project (dir)
diff --git a/test/projectile-test.el b/test/projectile-test.el
index b62224a..f099d5f 100644
--- a/test/projectile-test.el
+++ b/test/projectile-test.el
@@ -1236,7 +1236,7 @@ Just delegates OPERATION and ARGS for all operations except for`shell-command`'.
       ("projectA/src/")
       (let* ((projectile-project-root-functions '())
              (dir "projectA/src")
-             (cache-key (format "projectilerootless-%s" dir))
+             (cache-key (cons 'none dir))
              (projectile-project-root-cache (make-hash-table :test 'equal)))
         (expect (gethash cache-key projectile-project-root-cache) :to-be nil)
         (expect (projectile-project-root dir) :to-be nil)
@@ -1257,7 +1257,7 @@ Just delegates OPERATION and ARGS for all operations except for`shell-command`'.
                  (lambda (&rest args) (eql 1 (length args)))))
         (let* ((projectile-project-root-functions '())
                (dir "projectA/src")
-               (cache-key (format "projectilerootless-%s" dir))
+               (cache-key (cons 'none dir))
                (projectile-project-root-cache (make-hash-table :test 'equal)))
           (expect (gethash cache-key projectile-project-root-cache) :to-be nil)
           (expect (projectile-project-root dir) :to-be nil)