test: make subr mocks variadic for native-comp, add arity meta-test

Re-enabling native-comp surfaced a suite-wide fragility. When a test redefines a C primitive (or a native-compiled function), native-comp routes native callers through a trampoline that calls the mock with the primitive's maximum arity. A fixed-arity mock narrower than the primitive then throws wrong-number-of-arguments, intermittently, as the eln-cache fills.

I swept every arity-narrow subr mock to append &rest _ (188 sites, preserving any named args the body uses), and added tests/test-meta-subr-mock-arity.el, which fails make test on any subr mock too narrow for the primitive's arity. The rule isn't "never mock a subr". The suite mocks message and completing-read freely. It's "a subr mock must accept the primitive's arity."

Background, the three failure modes, and the research are in docs/native-comp-subr-mocking.org.

1 files changed, 6 insertions, 6 deletions

diff --git a/tests/test-video-audio-recording-test-mic.el b/tests/test-video-audio-recording-test-mic.el
index 60b9eb0b..64ef0eaa 100644
--- a/tests/test-video-audio-recording-test-mic.el
+++ b/tests/test-video-audio-recording-test-mic.el
@@ -36,11 +36,11 @@
         (let ((temp-file nil))
           ;; Mock make-temp-file to capture filename
           (cl-letf (((symbol-function 'make-temp-file)
-                     (lambda (prefix _dir-flag suffix)
+                     (lambda (prefix _dir-flag suffix &rest _)
                        (setq temp-file (concat prefix "12345" suffix))
                        temp-file))
                     ((symbol-function 'shell-command)
-                     (lambda (_cmd) 0)))
+                     (lambda (_cmd &rest _) 0)))
             (cj/recording-test-mic)
             (should (string-match-p "\\.wav$" temp-file)))))
     (test-mic-teardown)))
@@ -54,7 +54,7 @@
         (let ((commands nil))
           ;; Mock shell-command to capture all commands
           (cl-letf (((symbol-function 'shell-command)
-                     (lambda (cmd) (push cmd commands) 0)))
+                     (lambda (cmd &rest _) (push cmd commands) 0)))
             (cj/recording-test-mic)
             (should (= 2 (length commands)))
             ;; First command should be ffmpeg (stored last in list due to push)
@@ -74,7 +74,7 @@
         (let ((commands nil))
           ;; Capture all shell commands
           (cl-letf (((symbol-function 'shell-command)
-                     (lambda (cmd) (push cmd commands) 0)))
+                     (lambda (cmd &rest _) (push cmd commands) 0)))
             (cj/recording-test-mic)
             (should (= 2 (length commands)))
             ;; Second command should be ffplay
@@ -93,7 +93,7 @@
           (cl-letf (((symbol-function 'message)
                      (lambda (fmt &rest args) (push (apply #'format fmt args) messages)))
                     ((symbol-function 'shell-command)
-                     (lambda (_cmd) 0)))
+                     (lambda (_cmd &rest _) 0)))
             (cj/recording-test-mic)
             (should (>= (length messages) 3))
             ;; Check for recording message
@@ -135,7 +135,7 @@
         (setq cj/recording-mic-device "test-mic-device")
         ;; Mock shell-command to fail
         (cl-letf (((symbol-function 'shell-command)
-                   (lambda (_cmd) 1)))  ;; Non-zero exit code
+                   (lambda (_cmd &rest _) 1)))  ;; Non-zero exit code
           ;; Should complete without crashing (ffmpeg errors are ignored)
           ;; No error is raised - function just completes
           (cj/recording-test-mic)