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, 8 insertions, 8 deletions

diff --git a/tests/test-video-audio-recording-process-cleanup.el b/tests/test-video-audio-recording-process-cleanup.el
index 52177a17c..7cb261c16 100644
--- a/tests/test-video-audio-recording-process-cleanup.el
+++ b/tests/test-video-audio-recording-process-cleanup.el
@@ -53,7 +53,7 @@
         (setq cj/video-recording-ffmpeg-process fake-process)
         (cl-letf (((symbol-function 'cj/recording--wayland-p) (lambda () nil))
                   ((symbol-function 'signal-process)
-                   (lambda (pid sig)
+                   (lambda (pid sig &rest _)
                      (setq signaled-pid pid)
                      (setq signaled-sig sig)
                      0))
@@ -85,7 +85,7 @@ so ffmpeg sees EOF on its video input pipe and starts finalizing the file."
                        (push (cons 'pkill args) call-order))
                      0))
                   ((symbol-function 'signal-process)
-                   (lambda (_pid _sig)
+                   (lambda (_pid _sig &rest _)
                      (push 'signal call-order)
                      0))
                   ((symbol-function 'cj/recording--wait-for-exit)
@@ -114,7 +114,7 @@ so ffmpeg sees EOF on its video input pipe and starts finalizing the file."
                      (when (equal program "pkill")
                        (push args pkill-args-list))
                      0))
-                  ((symbol-function 'signal-process) (lambda (_pid _sig) 0))
+                  ((symbol-function 'signal-process) (lambda (_pid _sig &rest _) 0))
                   ((symbol-function 'cj/recording--wait-for-exit)
                    (lambda (_proc _timeout) t)))
           (cj/video-recording-stop)
@@ -140,7 +140,7 @@ so ffmpeg sees EOF on its video input pipe and starts finalizing the file."
                      (when (equal program "pkill")
                        (setq pkill-called t))
                      0))
-                  ((symbol-function 'signal-process) (lambda (_pid _sig) 0))
+                  ((symbol-function 'signal-process) (lambda (_pid _sig &rest _) 0))
                   ((symbol-function 'cj/recording--wait-for-exit)
                    (lambda (_proc _timeout) t)))
           (cj/video-recording-stop)
@@ -206,7 +206,7 @@ so ffmpeg sees EOF on its video input pipe and starts finalizing the file."
             (wait-timeout nil))
         (setq cj/video-recording-ffmpeg-process fake-process)
         (cl-letf (((symbol-function 'cj/recording--wayland-p) (lambda () nil))
-                  ((symbol-function 'signal-process) (lambda (_pid _sig) 0))
+                  ((symbol-function 'signal-process) (lambda (_pid _sig &rest _) 0))
                   ((symbol-function 'cj/recording--wait-for-exit)
                    (lambda (_proc timeout)
                      (setq wait-called t)
@@ -227,7 +227,7 @@ so ffmpeg sees EOF on its video input pipe and starts finalizing the file."
             (warning-shown nil))
         (setq cj/video-recording-ffmpeg-process fake-process)
         (cl-letf (((symbol-function 'cj/recording--wayland-p) (lambda () nil))
-                  ((symbol-function 'signal-process) (lambda (_pid _sig) 0))
+                  ((symbol-function 'signal-process) (lambda (_pid _sig &rest _) 0))
                   ((symbol-function 'cj/recording--wait-for-exit)
                    (lambda (_proc _timeout) nil))  ; Simulate timeout
                   ((symbol-function 'message)
@@ -247,7 +247,7 @@ so ffmpeg sees EOF on its video input pipe and starts finalizing the file."
       (let ((fake-process (make-process :name "test-audio" :command '("sleep" "1000")))
             (warning-shown nil))
         (setq cj/audio-recording-ffmpeg-process fake-process)
-        (cl-letf (((symbol-function 'signal-process) (lambda (_pid _sig) 0))
+        (cl-letf (((symbol-function 'signal-process) (lambda (_pid _sig &rest _) 0))
                   ((symbol-function 'cj/recording--wait-for-exit)
                    (lambda (_proc _timeout) nil))  ; Simulate timeout
                   ((symbol-function 'message)
@@ -268,7 +268,7 @@ so ffmpeg sees EOF on its video input pipe and starts finalizing the file."
             (wait-called nil)
             (wait-timeout nil))
         (setq cj/audio-recording-ffmpeg-process fake-process)
-        (cl-letf (((symbol-function 'signal-process) (lambda (_pid _sig) 0))
+        (cl-letf (((symbol-function 'signal-process) (lambda (_pid _sig &rest _) 0))
                   ((symbol-function 'cj/recording--wait-for-exit)
                    (lambda (_proc timeout)
                      (setq wait-called t)