refactor: extract shared format-region helper into system-lib

prog-json and prog-yaml each carried a byte-identical cj/--<lang>-format-region that runs a formatter over the buffer via call-process-region and replaces it on exit 0. Hoist it to system-lib as cj/format-region-with-program with a generic output buffer, and point both formatters at it. Adds the first direct unit coverage of the helper (Normal, Boundary, Error).

1 files changed, 4 insertions, 27 deletions

diff --git a/modules/prog-json.el b/modules/prog-json.el
index 953b5f79b..e7abd1828 100644
--- a/modules/prog-json.el
+++ b/modules/prog-json.el
@@ -9,7 +9,7 @@
 ;; Eager reason: none necessary; currently eager but should load by JSON major
 ;;   mode (Phase 6 deferral candidate).
 ;; Top-level side effects: one add-hook, package configuration via use-package.
-;; Runtime requires: none (configures packages via use-package).
+;; Runtime requires: system-lib (cj/format-region-with-program).
 ;; Direct test load: yes.
 ;;
 ;; JSON editing with tree-sitter highlighting, one-key formatting, and
@@ -27,6 +27,8 @@
 
 ;;; Code:
 
+(require 'system-lib)
+
 (defvar json-ts-mode-map)
 
 ;; -------------------------------- JSON Mode ----------------------------------
@@ -41,38 +43,13 @@
 ;; -------------------------------- Formatting ---------------------------------
 ;; pretty-print with sorted keys, bound to standard format key
 
-(defun cj/--json-format-region (program &rest args)
-  "Replace the buffer with PROGRAM ARGS run over its contents, via argv.
-Runs PROGRAM (with ARGS) on the whole buffer through
-`call-process-region' — no shell, so no quoting or word-splitting.
-The buffer is replaced only when PROGRAM exits zero; on a non-zero
-exit the buffer is left untouched and an error is signalled with
-the program's stderr text.  Point is preserved as closely as the
-reformatted size allows.  Returns t on success."
-  (let* ((point (point))
-         (src (current-buffer))
-         (out (generate-new-buffer " *json-format-out*"))
-         (status (apply #'call-process-region
-                        (point-min) (point-max) program
-                        nil out nil args)))
-    (unwind-protect
-        (if (and (integerp status) (zerop status))
-            (progn
-              (with-current-buffer src
-                (replace-buffer-contents out)
-                (goto-char (min point (point-max))))
-              t)
-          (user-error "%s failed: %s" program
-                      (string-trim (with-current-buffer out (buffer-string)))))
-      (kill-buffer out))))
-
 (defun cj/json-format-buffer ()
   "Format the current JSON buffer with sorted keys.
 Uses jq if available for reliable formatting, otherwise falls
 back to the built-in `json-pretty-print-buffer-ordered'."
   (interactive)
   (if (executable-find "jq")
-      (cj/--json-format-region "jq" "--sort-keys" ".")
+      (cj/format-region-with-program "jq" "--sort-keys" ".")
     (json-pretty-print-buffer-ordered)))
 
 (defun cj/json-setup ()