Skip cache for projectile-root-local (#1211)

projectile-root-local reads the buffer-local projectile-project-root
variable rather than inspecting its DIR argument, so caching its
result by (FUNC . DIR) was wrong: two buffers visiting the same
directory but with different file-local overrides would share the
first buffer's cached answer.  Skip the cache for this function
specifically - it's a single variable read, no FS work to amortize.

Adds a regression test that visits two buffers with different
file-local roots from the same default-directory and confirms each
sees its own override.

3 files changed, 34 insertions, 9 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2b64613..07e7a67 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,6 +18,7 @@
 
 ### Bugs fixed
 
+* [#1211](https://github.com/bbatsov/projectile/issues/1211): Fix file-local `projectile-project-root` overrides being ignored after the first buffer in a directory was visited. The cache used `(default-directory)` as part of the key but `projectile-root-local` reads a buffer-local variable, so two buffers in the same directory with different overrides got the first buffer's answer. Results from `projectile-root-local` are no longer cached.
 * [#1508](https://github.com/bbatsov/projectile/issues/1508): Fix dirconfig parser silently treating lines as ignore patterns when the `+`/`-`/`!` prefix or the comment character is preceded by whitespace; leading spaces and tabs are now skipped before prefix dispatch.
 * Fix `projectile-files-via-ext-command` executing empty string as shell command for non-git VCS sub-projects.
 * Fix `projectile-select-files` crashing on filenames with regexp metacharacters by using `string-search` instead of `string-match`.
diff --git a/projectile.el b/projectile.el
index bcd8302..0530925 100644
--- a/projectile.el
+++ b/projectile.el
@@ -1478,16 +1478,21 @@ If DIR is not supplied it's set to the current directory by default."
          (unless (or is-local is-connected)
            'none))
        ;; if the file is local or we're connected to it via TRAMP, run
-       ;; through the project root functions until we find a project dir
+       ;; through the project root functions until we find a project dir.
+       ;; `projectile-root-local' reads a buffer-local variable rather
+       ;; than inspecting DIR, so its result must not be cached - two
+       ;; buffers in the same directory can legitimately disagree.
        (seq-some
         (lambda (func)
-          (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
-              (let ((value (funcall func (file-truename dir))))
-                (puthash cache-key value projectile-project-root-cache)
-                value))))
+          (if (eq func 'projectile-root-local)
+              (funcall 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
+                (let ((value (funcall func (file-truename dir))))
+                  (puthash cache-key value projectile-project-root-cache)
+                  value)))))
         projectile-project-root-functions)
        ;; if we get here, we have failed to find a root by all
        ;; conventional means, and we assume the failure isn't transient
diff --git a/test/projectile-test.el b/test/projectile-test.el
index f099d5f..52f24b1 100644
--- a/test/projectile-test.el
+++ b/test/projectile-test.el
@@ -1264,7 +1264,26 @@ Just delegates OPERATION and ARGS for all operations except for`shell-command`'.
           ;; since the failure was transitory, there should be nothing cached
           (expect (gethash cache-key projectile-project-root-cache) :to-be nil)
           ;; and projectile-project-root should still return nil
-          (expect (projectile-project-root dir) :to-be nil)))))))
+          (expect (projectile-project-root dir) :to-be nil))))))
+
+  (it "honors a buffer-local projectile-project-root after it changes (#1211)"
+    (projectile-test-with-sandbox
+     (projectile-test-with-files
+      ("alpha/.projectile"
+       "beta/.projectile"
+       "host/notes.org")
+      (let* ((dir (expand-file-name "host/"))
+             (alpha-root (file-truename (expand-file-name "alpha/")))
+             (beta-root (file-truename (expand-file-name "beta/")))
+             (default-directory dir)
+             (projectile-project-root-cache (make-hash-table :test 'equal)))
+        ;; First "buffer": file-local override pointing at alpha.
+        (let ((projectile-project-root alpha-root))
+          (expect (projectile-project-root) :to-equal alpha-root))
+        ;; Second "buffer": same default-directory, different override.
+        ;; The cache must not return the previous buffer's answer.
+        (let ((projectile-project-root beta-root))
+          (expect (projectile-project-root) :to-equal beta-root)))))))
 
 (describe "projectile-file-exists-p"
   (it "returns t if file exists"