feat(dev-fkeys): revert projectile cache on failed-and-modified compile

Without this, a one-off typo at projectile's compile/test/run prompt poisons the per-project cache: every subsequent invocation pre-fills the broken value. I hit it during the Phase 2a live-test, where projectile's "All tests" prompt was replaying `go test ../.` and there was no clean way to get the prior known-good back.

Three pieces of machinery, all in `dev-fkeys.el`:

`cj/--projectile-capture-cmd' captures the current cached cmd at the project root before each invocation, stashing a plist with :map / :root / :prior in `cj/--projectile-revert-state'.

`cj/--projectile-revert-on-fail' is a `compilation-finish-functions' hook that reads that state. If the compile failed AND the cmd was modified from the captured prior value AND the prior was non-nil, it puts the prior back in projectile's cmd-map. Test-fails-because-of-real-bug (cmd unchanged through the run) leaves the cache alone. The hook self-removes on first invocation regardless of outcome and clears the state.

`cj/--projectile-around-revert' is the around-advice that wires the two together. I added the advice to all three projectile cmd-runners — `projectile-compile-project', `projectile-test-project', `projectile-run-project' — so the auto-revert applies whether the user invoked via F4 / F6 or directly via `M-x'.

Plus the manual escape-hatch: `cj/projectile-reset-cmds' clears compile/test/run cache for the current project. Bound to `C-; P' under the personal keymap. Use when projectile's auto-derived default was wrong from the start and you want to start fresh — the next F4 / F6 invocation re-derives projectile's project-type default.

TDD: 18 new tests across 4 files, one per helper. The around-advice tests build the capture/install/orig-fn flow against stub cmd-maps and verify state captured, hook installed, orig-fn invoked. The revert hook tests cover failure-and-modified (revert), success (leave alone), failure-but-unchanged (leave alone), nil prior (leave alone), nil state (no-op), and self-removal. The reset-cmds tests cover the all-three-maps clear, no-cached-entry no-op, and no-project user-error.

4 files changed, 312 insertions, 0 deletions

diff --git a/tests/test-dev-fkeys--projectile-around-revert.el b/tests/test-dev-fkeys--projectile-around-revert.el
new file mode 100644
index 00000000..bdcb11a1
--- /dev/null
+++ b/tests/test-dev-fkeys--projectile-around-revert.el
@@ -0,0 +1,76 @@
+;;; test-dev-fkeys--projectile-around-revert.el --- Tests for cj/--projectile-around-revert -*- lexical-binding: t -*-
+
+;;; Commentary:
+;; Tests for the around-advice that wires the capture / finish-hook pair
+;; to projectile cmd runners. The advice:
+;;
+;; 1. Captures the prior cached cmd via `cj/--projectile-capture-cmd'.
+;; 2. Adds `cj/--projectile-revert-on-fail' to `compilation-finish-functions'.
+;; 3. Calls ORIG-FN with ARGS so projectile's normal flow proceeds.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'dev-fkeys)
+
+(defvar projectile-compile-cmd-map nil)
+
+;;; Normal Cases
+
+(ert-deftest test-dev-fkeys-projectile-around-revert-invokes-orig-fn ()
+  "Normal: advice calls the wrapped function with its args."
+  (let ((calls nil)
+        (cj/--projectile-revert-state nil)
+        (compilation-finish-functions nil)
+        (projectile-compile-cmd-map (make-hash-table :test 'equal)))
+    (cl-letf (((symbol-function 'cj/--f4-project-root) (lambda () "/p/")))
+      (cj/--projectile-around-revert
+       'projectile-compile-cmd-map
+       (lambda (&rest args) (push args calls))
+       'arg1 'arg2))
+    (should (equal calls '((arg1 arg2))))))
+
+(ert-deftest test-dev-fkeys-projectile-around-revert-captures-prior ()
+  "Normal: advice captures the prior cmd into the revert state."
+  (let ((cj/--projectile-revert-state nil)
+        (compilation-finish-functions nil)
+        (projectile-compile-cmd-map (make-hash-table :test 'equal)))
+    (puthash "/p/" "make build" projectile-compile-cmd-map)
+    (cl-letf (((symbol-function 'cj/--f4-project-root) (lambda () "/p/")))
+      (cj/--projectile-around-revert
+       'projectile-compile-cmd-map
+       (lambda (&rest _) nil)))
+    (should (equal (plist-get cj/--projectile-revert-state :prior)
+                   "make build"))))
+
+(ert-deftest test-dev-fkeys-projectile-around-revert-installs-finish-hook ()
+  "Normal: advice adds the revert-on-fail hook to compilation-finish-functions."
+  (let ((cj/--projectile-revert-state nil)
+        (compilation-finish-functions nil)
+        (projectile-compile-cmd-map (make-hash-table :test 'equal)))
+    (cl-letf (((symbol-function 'cj/--f4-project-root) (lambda () "/p/")))
+      (cj/--projectile-around-revert
+       'projectile-compile-cmd-map
+       (lambda (&rest _) nil)))
+    (should (member #'cj/--projectile-revert-on-fail
+                    compilation-finish-functions))))
+
+;;; Boundary Cases
+
+(ert-deftest test-dev-fkeys-projectile-around-revert-no-project-still-runs-orig-fn ()
+  "Boundary: no project root → capture is a no-op, orig-fn still runs.
+The state stays nil so the finish hook will be a no-op too."
+  (let ((calls 0)
+        (cj/--projectile-revert-state nil)
+        (compilation-finish-functions nil))
+    (cl-letf (((symbol-function 'cj/--f4-project-root) (lambda () nil)))
+      (cj/--projectile-around-revert
+       'projectile-compile-cmd-map
+       (lambda (&rest _) (cl-incf calls))))
+    (should (= calls 1))
+    (should (null cj/--projectile-revert-state))))
+
+(provide 'test-dev-fkeys--projectile-around-revert)
+;;; test-dev-fkeys--projectile-around-revert.el ends here
diff --git a/tests/test-dev-fkeys--projectile-capture-cmd.el b/tests/test-dev-fkeys--projectile-capture-cmd.el
new file mode 100644
index 00000000..92309198
--- /dev/null
+++ b/tests/test-dev-fkeys--projectile-capture-cmd.el
@@ -0,0 +1,70 @@
+;;; test-dev-fkeys--projectile-capture-cmd.el --- Tests for cj/--projectile-capture-cmd -*- lexical-binding: t -*-
+
+;;; Commentary:
+;; Tests for the prior-cmd capture helper used by the auto-revert advice.
+;; Captures the current cached cmd at the project root into
+;; `cj/--projectile-revert-state' so a later finish-hook can restore it
+;; if the compile fails after the cmd was modified.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'dev-fkeys)
+
+;; Test stub: projectile cmd-maps as defvars so `boundp' is non-nil and
+;; `let'-binding has a target. In real use, projectile defines these.
+(defvar projectile-compile-cmd-map nil)
+(defvar projectile-test-cmd-map nil)
+(defvar projectile-run-cmd-map nil)
+
+;;; Normal Cases
+
+(ert-deftest test-dev-fkeys-projectile-capture-cmd-stores-prior-value ()
+  "Normal: captures the cached cmd at the project root into the state plist."
+  (let* ((cj/--projectile-revert-state nil)
+         (projectile-compile-cmd-map (make-hash-table :test 'equal)))
+    (puthash "/p/" "make build" projectile-compile-cmd-map)
+    (cl-letf (((symbol-function 'cj/--f4-project-root) (lambda () "/p/")))
+      (cj/--projectile-capture-cmd 'projectile-compile-cmd-map))
+    (should (equal (plist-get cj/--projectile-revert-state :map)
+                   'projectile-compile-cmd-map))
+    (should (equal (plist-get cj/--projectile-revert-state :root) "/p/"))
+    (should (equal (plist-get cj/--projectile-revert-state :prior) "make build"))))
+
+(ert-deftest test-dev-fkeys-projectile-capture-cmd-no-prior-stores-nil ()
+  "Normal: when no cmd is cached, captures :prior nil — distinct from
+\"didn't capture at all\" because :map and :root are still set."
+  (let* ((cj/--projectile-revert-state nil)
+         (projectile-test-cmd-map (make-hash-table :test 'equal)))
+    (cl-letf (((symbol-function 'cj/--f4-project-root) (lambda () "/p/")))
+      (cj/--projectile-capture-cmd 'projectile-test-cmd-map))
+    (should (eq (plist-get cj/--projectile-revert-state :map)
+                'projectile-test-cmd-map))
+    (should (null (plist-get cj/--projectile-revert-state :prior)))))
+
+;;; Boundary Cases
+
+(ert-deftest test-dev-fkeys-projectile-capture-cmd-nil-root-leaves-state-nil ()
+  "Boundary: when no project root resolves, state stays nil so the
+finish hook treats it as a no-op."
+  (let ((cj/--projectile-revert-state nil)
+        (projectile-compile-cmd-map (make-hash-table :test 'equal)))
+    (cl-letf (((symbol-function 'cj/--f4-project-root) (lambda () nil)))
+      (cj/--projectile-capture-cmd 'projectile-compile-cmd-map))
+    (should (null cj/--projectile-revert-state))))
+
+;;; Error Cases
+
+(ert-deftest test-dev-fkeys-projectile-capture-cmd-unbound-map-leaves-state-nil ()
+  "Error: when the cmd-map symbol is unbound (projectile not loaded),
+state stays nil and no error is raised."
+  (let ((cj/--projectile-revert-state nil))
+    (cl-letf (((symbol-function 'cj/--f4-project-root) (lambda () "/p/")))
+      ;; Use a clearly-unbound symbol to simulate projectile-not-loaded.
+      (cj/--projectile-capture-cmd 'cj-test--definitely-not-bound-xyzzy))
+    (should (null cj/--projectile-revert-state))))
+
+(provide 'test-dev-fkeys--projectile-capture-cmd)
+;;; test-dev-fkeys--projectile-capture-cmd.el ends here
diff --git a/tests/test-dev-fkeys--projectile-reset-cmds.el b/tests/test-dev-fkeys--projectile-reset-cmds.el
new file mode 100644
index 00000000..6fb1cc17
--- /dev/null
+++ b/tests/test-dev-fkeys--projectile-reset-cmds.el
@@ -0,0 +1,62 @@
+;;; test-dev-fkeys--projectile-reset-cmds.el --- Tests for cj/projectile-reset-cmds -*- lexical-binding: t -*-
+
+;;; Commentary:
+;; Tests for the manual escape-hatch command that clears projectile's
+;; per-project compile / test / run cache for the current project. Use
+;; case: projectile's auto-derived default was wrong to begin with and
+;; you want to reset to projectile's default-derived cmd at the next
+;; prompt.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'dev-fkeys)
+
+(defvar projectile-compile-cmd-map nil)
+(defvar projectile-test-cmd-map nil)
+(defvar projectile-run-cmd-map nil)
+
+;;; Normal Cases
+
+(ert-deftest test-dev-fkeys-projectile-reset-cmds-clears-all-three-maps ()
+  "Normal: clears compile, test, and run cache entries for the current root.
+Other projects' entries are left alone."
+  (let ((projectile-compile-cmd-map (make-hash-table :test 'equal))
+        (projectile-test-cmd-map    (make-hash-table :test 'equal))
+        (projectile-run-cmd-map     (make-hash-table :test 'equal)))
+    (puthash "/p/" "make"      projectile-compile-cmd-map)
+    (puthash "/p/" "make test" projectile-test-cmd-map)
+    (puthash "/p/" "./run.sh"  projectile-run-cmd-map)
+    (puthash "/other/" "untouched" projectile-compile-cmd-map)
+    (cl-letf (((symbol-function 'cj/--f4-project-root) (lambda () "/p/")))
+      (cj/projectile-reset-cmds))
+    (should-not (gethash "/p/" projectile-compile-cmd-map))
+    (should-not (gethash "/p/" projectile-test-cmd-map))
+    (should-not (gethash "/p/" projectile-run-cmd-map))
+    (should (string= (gethash "/other/" projectile-compile-cmd-map) "untouched"))))
+
+;;; Boundary Cases
+
+(ert-deftest test-dev-fkeys-projectile-reset-cmds-no-cached-entry-is-noop ()
+  "Boundary: project root has no cached entries → command runs cleanly,
+no error, maps stay empty."
+  (let ((projectile-compile-cmd-map (make-hash-table :test 'equal))
+        (projectile-test-cmd-map    (make-hash-table :test 'equal))
+        (projectile-run-cmd-map     (make-hash-table :test 'equal)))
+    (cl-letf (((symbol-function 'cj/--f4-project-root) (lambda () "/p/")))
+      (cj/projectile-reset-cmds))
+    (should (zerop (hash-table-count projectile-compile-cmd-map)))
+    (should (zerop (hash-table-count projectile-test-cmd-map)))
+    (should (zerop (hash-table-count projectile-run-cmd-map)))))
+
+;;; Error Cases
+
+(ert-deftest test-dev-fkeys-projectile-reset-cmds-no-project-signals-user-error ()
+  "Error: no project detected → user-error rather than silent no-op."
+  (cl-letf (((symbol-function 'cj/--f4-project-root) (lambda () nil)))
+    (should-error (cj/projectile-reset-cmds) :type 'user-error)))
+
+(provide 'test-dev-fkeys--projectile-reset-cmds)
+;;; test-dev-fkeys--projectile-reset-cmds.el ends here
diff --git a/tests/test-dev-fkeys--projectile-revert-on-fail.el b/tests/test-dev-fkeys--projectile-revert-on-fail.el
new file mode 100644
index 00000000..6fadd539
--- /dev/null
+++ b/tests/test-dev-fkeys--projectile-revert-on-fail.el
@@ -0,0 +1,104 @@
+;;; test-dev-fkeys--projectile-revert-on-fail.el --- Tests for cj/--projectile-revert-on-fail -*- lexical-binding: t -*-
+
+;;; Commentary:
+;; Tests for the compilation-finish hook that reverts projectile's
+;; per-project cache when a build/test failed AND the cmd was modified.
+;; Test-fails-because-of-real-bug (cmd unchanged) leaves the cache alone.
+;; The hook also self-removes from `compilation-finish-functions' on
+;; first invocation and clears `cj/--projectile-revert-state'.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'dev-fkeys)
+
+(defvar projectile-compile-cmd-map nil)
+
+;;; Normal Cases
+
+(ert-deftest test-dev-fkeys-projectile-revert-on-fail-failure-and-modified-reverts ()
+  "Normal: failure status + cmd modified from prior → revert to prior."
+  (let* ((projectile-compile-cmd-map (make-hash-table :test 'equal))
+         (cj/--projectile-revert-state
+          (list :map 'projectile-compile-cmd-map
+                :root "/p/"
+                :prior "make build")))
+    (puthash "/p/" "make buidl" projectile-compile-cmd-map)
+    (cj/--projectile-revert-on-fail nil "exited abnormally with code 2\n")
+    (should (string= (gethash "/p/" projectile-compile-cmd-map) "make build"))))
+
+(ert-deftest test-dev-fkeys-projectile-revert-on-fail-success-leaves-cache ()
+  "Normal: success status → no revert, cache keeps the modified cmd."
+  (let* ((projectile-compile-cmd-map (make-hash-table :test 'equal))
+         (cj/--projectile-revert-state
+          (list :map 'projectile-compile-cmd-map
+                :root "/p/"
+                :prior "make build")))
+    (puthash "/p/" "make build-fast" projectile-compile-cmd-map)
+    (cj/--projectile-revert-on-fail nil "finished\n")
+    (should (string= (gethash "/p/" projectile-compile-cmd-map) "make build-fast"))))
+
+(ert-deftest test-dev-fkeys-projectile-revert-on-fail-clears-state ()
+  "Normal: hook clears `cj/--projectile-revert-state' regardless of outcome."
+  (let* ((projectile-compile-cmd-map (make-hash-table :test 'equal))
+         (cj/--projectile-revert-state
+          (list :map 'projectile-compile-cmd-map :root "/p/" :prior "x")))
+    (cj/--projectile-revert-on-fail nil "finished\n")
+    (should (null cj/--projectile-revert-state))))
+
+(ert-deftest test-dev-fkeys-projectile-revert-on-fail-removes-itself ()
+  "Normal: hook removes itself from `compilation-finish-functions'."
+  (let* ((projectile-compile-cmd-map (make-hash-table :test 'equal))
+         (cj/--projectile-revert-state
+          (list :map 'projectile-compile-cmd-map :root "/p/" :prior "x"))
+         (compilation-finish-functions
+          (list #'cj/--projectile-revert-on-fail)))
+    (cj/--projectile-revert-on-fail nil "finished\n")
+    (should-not (member #'cj/--projectile-revert-on-fail
+                        compilation-finish-functions))))
+
+;;; Boundary Cases
+
+(ert-deftest test-dev-fkeys-projectile-revert-on-fail-failure-but-unchanged-no-revert ()
+  "Boundary: failure status + cmd unchanged from prior → no revert.
+This is the test-fails-because-of-real-bug case. Don't flap the cache.
+
+Components integrated:
+- `cj/--projectile-revert-on-fail' (unit under test)
+- `cj/--projectile-revert-state' (real, scoped via let)
+- `projectile-compile-cmd-map' (test stub)"
+  (let* ((projectile-compile-cmd-map (make-hash-table :test 'equal))
+         (cj/--projectile-revert-state
+          (list :map 'projectile-compile-cmd-map
+                :root "/p/"
+                :prior "pytest")))
+    (puthash "/p/" "pytest" projectile-compile-cmd-map)
+    (cj/--projectile-revert-on-fail nil "exited abnormally with code 1\n")
+    ;; Cache value still equals the prior value (unchanged through the run).
+    (should (string= (gethash "/p/" projectile-compile-cmd-map) "pytest"))))
+
+(ert-deftest test-dev-fkeys-projectile-revert-on-fail-failure-with-nil-prior-no-revert ()
+  "Boundary: failure with no prior cmd cached → don't store nil.
+A nil prior means projectile cached for the first time on this run; even
+if it failed, there's nothing to revert to."
+  (let* ((projectile-compile-cmd-map (make-hash-table :test 'equal))
+         (cj/--projectile-revert-state
+          (list :map 'projectile-compile-cmd-map
+                :root "/p/"
+                :prior nil)))
+    (puthash "/p/" "broken-cmd" projectile-compile-cmd-map)
+    (cj/--projectile-revert-on-fail nil "exited abnormally\n")
+    (should (string= (gethash "/p/" projectile-compile-cmd-map) "broken-cmd"))))
+
+;;; Error Cases
+
+(ert-deftest test-dev-fkeys-projectile-revert-on-fail-nil-state-is-noop ()
+  "Error: nil state (capture didn't run) → hook is a no-op, no error."
+  (let ((cj/--projectile-revert-state nil))
+    (cj/--projectile-revert-on-fail nil "exited abnormally\n")
+    (should (null cj/--projectile-revert-state))))
+
+(provide 'test-dev-fkeys--projectile-revert-on-fail)
+;;; test-dev-fkeys--projectile-revert-on-fail.el ends here