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.

1 files changed, 104 insertions, 0 deletions

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