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, 2 insertions, 2 deletions

diff --git a/tests/test-org-refile-config-commands.el b/tests/test-org-refile-config-commands.el
index 9bdd33647..2e99e9152 100644
--- a/tests/test-org-refile-config-commands.el
+++ b/tests/test-org-refile-config-commands.el
@@ -54,7 +54,7 @@
     (with-temp-buffer
       (setq buffer-file-name "/tmp/notes.org")
       (cl-letf (((symbol-function 'call-interactively)
-                 (lambda (_fn)
+                 (lambda (_fn &rest _)
                    (setq seen-targets org-refile-targets)))
                 ((symbol-function 'save-buffer) #'ignore))
         (cj/org-refile-in-file))
@@ -73,7 +73,7 @@
       (setq buffer-file-name "/tmp/notes.org")
       (cl-letf (((symbol-function 'call-interactively) #'ignore)
                 ((symbol-function 'save-buffer)
-                 (lambda () (setq saved t))))
+                 (lambda (&rest _) (setq saved t))))
         (cj/org-refile-in-file))
       (setq buffer-file-name nil))
     (should saved)))