refactor(system-lib): extract cj/executable-find-or-warn from mail-config

Phase 2 of utility-consolidation, first commit per the spec's recommended order. `cj/mail--executable-or-warn' was the right pattern -- check executable-find, return the path, otherwise emit a clear `display-warning' naming the feature -- but it was trapped in mail-config and only mail callers benefited. Lift it into `cj/executable-find-or-warn' in system-lib.el with one new argument: an optional GROUP symbol that flows through to `display-warning' (defaulting to `cj/system-lib') so per-feature warning filters keep working. Mail callers pass `mail-config' explicitly.

Migrate `cj/mail--mbsync-command' and `cj/mail-configure-smtpmail' to the new helper. Drop the local definition. Add `(require \='system-lib)' to mail-config.el per the spec's Phase 2 exit criterion ("consumer modules explicitly require system-lib").

Five Normal/Boundary tests cover the four return-shape cases (program found / program missing / warning content / default vs explicit group).

Other consumers (prog-*.el, dirvish-config.el, browser-config.el) still call `executable-find' directly. Migrating them is a follow-up commit, audited per call site -- the spec flags some `:if' silent checks as intentional and they should NOT switch to the warning helper.

1 files changed, 80 insertions, 0 deletions

diff --git a/tests/test-system-lib-executable-find-or-warn.el b/tests/test-system-lib-executable-find-or-warn.el
new file mode 100644
index 00000000..e9a540bd
--- /dev/null
+++ b/tests/test-system-lib-executable-find-or-warn.el
@@ -0,0 +1,80 @@
+;;; test-system-lib-executable-find-or-warn.el --- Tests for cj/executable-find-or-warn -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; `cj/executable-find-or-warn' generalizes the mail-specific
+;; `cj/mail--executable-or-warn' pattern.  Returns the program's
+;; executable path when found.  When the program is missing, returns
+;; nil AND emits a `display-warning' naming the feature that's
+;; unavailable, so the user gets a clear hint about what won't work.
+;; The optional GROUP argument controls `display-warning' grouping so
+;; per-feature filters keep working.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'system-lib)
+
+(defmacro test-system-lib-find-or-warn--with-stubs (executable-fn warning-capture &rest body)
+  "Run BODY with `executable-find' and `display-warning' stubbed.
+
+EXECUTABLE-FN replaces `executable-find' (takes a string program name,
+returns path or nil).  WARNING-CAPTURE is a symbol bound in BODY's scope
+to a list of (TYPE MESSAGE LEVEL) entries collected from
+`display-warning' calls."
+  (declare (indent 2))
+  `(let ((,warning-capture nil))
+     (cl-letf (((symbol-function 'executable-find) ,executable-fn)
+               ((symbol-function 'display-warning)
+                (lambda (type message &optional level)
+                  (push (list type message level) ,warning-capture))))
+       ,@body)))
+
+(ert-deftest test-cj-executable-find-or-warn-program-found-returns-path ()
+  "Normal: when the program exists, return its path and emit no warning."
+  (test-system-lib-find-or-warn--with-stubs
+      (lambda (prog) (when (string= prog "mbsync") "/usr/bin/mbsync"))
+      warnings
+    (let ((result (cj/executable-find-or-warn "mbsync" "mu4e mail sync")))
+      (should (equal result "/usr/bin/mbsync"))
+      (should-not warnings))))
+
+(ert-deftest test-cj-executable-find-or-warn-program-missing-returns-nil ()
+  "Normal: when the program is missing, return nil."
+  (test-system-lib-find-or-warn--with-stubs
+      (lambda (_prog) nil)
+      _warnings
+    (should-not (cj/executable-find-or-warn "missing-prog" "fake feature"))))
+
+(ert-deftest test-cj-executable-find-or-warn-missing-emits-warning ()
+  "Normal: a missing program produces a warning that names PROGRAM and FEATURE."
+  (test-system-lib-find-or-warn--with-stubs
+      (lambda (_prog) nil)
+      warnings
+    (cj/executable-find-or-warn "missing-prog" "fake feature")
+    (should (= 1 (length warnings)))
+    (let ((entry (car warnings)))
+      (should (string-match-p "missing-prog" (nth 1 entry)))
+      (should (string-match-p "fake feature" (nth 1 entry)))
+      (should (eq :warning (nth 2 entry))))))
+
+(ert-deftest test-cj-executable-find-or-warn-default-group ()
+  "Boundary: with no GROUP arg, the warning uses the default `cj/system-lib' symbol."
+  (test-system-lib-find-or-warn--with-stubs
+      (lambda (_prog) nil)
+      warnings
+    (cj/executable-find-or-warn "missing-prog" "feature")
+    (should (eq 'cj/system-lib (car (car warnings))))))
+
+(ert-deftest test-cj-executable-find-or-warn-explicit-group ()
+  "Normal: an explicit GROUP arg flows through to `display-warning'."
+  (test-system-lib-find-or-warn--with-stubs
+      (lambda (_prog) nil)
+      warnings
+    (cj/executable-find-or-warn "missing-prog" "feature" 'mail-config)
+    (should (eq 'mail-config (car (car warnings))))))
+
+(provide 'test-system-lib-executable-find-or-warn)
+;;; test-system-lib-executable-find-or-warn.el ends here