Add ghostel-pre-spawn-hook for env injection at spawn time

CHANGELOG.md

@@ -4,6 +4,19 @@ All notable changes to this project will be documented in this file.
 
 ## [Unreleased]
 
+### Added
+- `ghostel-pre-spawn-hook`, run inside `ghostel--spawn-pty` just
+  before `make-process` with `process-environment` dynamically
+  bound to the about-to-be-spawned env.  Hook functions can
+  `setenv` to inject entries the child inherits.  Intended for
+  integrations like with-editor — with a `with-editor-setup-environment`
+  exposed upstream, users can wire Magit's `EDITOR` plumbing into
+  ghostel buffers via
+  `(add-hook 'ghostel-pre-spawn-hook
+            #'with-editor-setup-environment)`.  Fires for both
+  `ghostel`/`ghostel-project` and `ghostel-exec` spawns;
+  `ghostel-compile` has its own `make-process` and is not covered.
+
 ### Fixed
 - Launching `M-x ghostel` from a TRAMP `default-directory` (e.g.
   after `find-file /ssh:host:`) now produces a usable remote shell.

lisp/ghostel.el

@@ -378,6 +378,18 @@ Errors in hook functions are demoted to messages via
 non-nil so the debugger can fire)."
   :type 'hook)
 
+(defcustom ghostel-pre-spawn-hook nil
+  "Hook run inside `ghostel--spawn-pty' just before `make-process'.
+Each function is called with no arguments in the buffer that will
+host the new process.  `process-environment' is dynamically bound
+to the env that will be passed to the child, so hook functions can
+inject or override entries with `setenv' and the spawned process
+inherits them.
+
+Use this hook for one-time pre-spawn setup; see `ghostel-environment'
+for static env entries that don't depend on runtime state."
+  :type 'hook)
+
 (defcustom ghostel-eval-cmds '(("find-file" find-file)
                                ("find-file-other-window" find-file-other-window)
                                ("dired" dired)
@@ -3534,25 +3546,30 @@ matches the PTY window size, and stores the process in
          (tramp-terminal-type (if remote-p
                                   (ghostel--remote-tramp-terminal-type
                                    extra-env)
-                                tramp-terminal-type))
-         (proc (make-process
-                :name "ghostel"
-                :buffer (current-buffer)
-                :command shell-command
-                :connection-type 'pty
-                :file-handler remote-p
-                :filter #'ghostel--filter
-                :sentinel #'ghostel--sentinel)))
-    (setq ghostel--process proc)
-    ;; Raw binary I/O — no encoding/decoding by Emacs
-    (set-process-coding-system proc 'binary 'binary)
-    ;; Set the PTY's actual window size (ioctl TIOCSWINSZ) so that
-    ;; the program's line editor (readline/ZLE) can render properly.
-    (set-process-window-size proc height width)
-    (set-process-query-on-exit-flag proc nil)
-    (process-put proc 'adjust-window-size-function
-                 #'ghostel--window-adjust-process-window-size)
-    proc))
+                                tramp-terminal-type)))
+    ;; Pre-spawn hook: runs while `process-environment' is dynamically
+    ;; bound to the about-to-be-spawned env, so hook functions can
+    ;; `setenv' to inject/override entries that the child inherits.
+    ;; See `ghostel-pre-spawn-hook'.
+    (run-hooks 'ghostel-pre-spawn-hook)
+    (let ((proc (make-process
+                 :name "ghostel"
+                 :buffer (current-buffer)
+                 :command shell-command
+                 :connection-type 'pty
+                 :file-handler remote-p
+                 :filter #'ghostel--filter
+                 :sentinel #'ghostel--sentinel)))
+      (setq ghostel--process proc)
+      ;; Raw binary I/O — no encoding/decoding by Emacs
+      (set-process-coding-system proc 'binary 'binary)
+      ;; Set the PTY's actual window size (ioctl TIOCSWINSZ) so that
+      ;; the program's line editor (readline/ZLE) can render properly.
+      (set-process-window-size proc height width)
+      (set-process-query-on-exit-flag proc nil)
+      (process-put proc 'adjust-window-size-function
+                   #'ghostel--window-adjust-process-window-size)
+      proc)))
 
 (defun ghostel--start-process ()
   "Start the shell process with a PTY.

test/ghostel-test.el

@@ -8315,6 +8315,47 @@ buffer eventually shows up."
             (should (equal (nth 1 captured) 80))))
       (kill-buffer buf))))
 
+(ert-deftest ghostel-test-pre-spawn-hook-injects-into-process-environment ()
+  "Hook `setenv' calls reach the spawned process via `process-environment'.
+`ghostel-pre-spawn-hook' fires with `process-environment' dynamically
+bound to the about-to-be-spawned env, so hook functions that call
+`setenv' inject entries the child process actually inherits.
+
+Contract relied on by integrations like with-editor: drive a real
+`/bin/sh' through `ghostel--start-process', have the hook `setenv' a
+sentinel value, and verify the value reached `make-process'.  Also
+verifies the hook fires in the spawning buffer with `default-directory'
+intact (with-editor's `with-editor--setup' reads `default-directory')."
+  (let ((captured-env nil)
+        captured-buffer
+        captured-default-directory
+        (orig-make-process (symbol-function #'make-process)))
+    (cl-letf (((symbol-function #'make-process)
+               (lambda (&rest plist)
+                 (setq captured-env process-environment)
+                 (apply orig-make-process plist))))
+      (with-temp-buffer
+        (setq-local ghostel--term-rows 24
+                    ghostel--term-cols 80)
+        (let* ((process-environment '("PATH=/usr/bin:/bin" "HOME=/tmp"))
+               (ghostel-shell "/bin/sh")
+               (ghostel-shell-integration nil)
+               (default-directory "/tmp/")
+               (test-buffer (current-buffer))
+               (ghostel-pre-spawn-hook
+                (list (lambda ()
+                        (setq captured-buffer (current-buffer))
+                        (setq captured-default-directory default-directory)
+                        (setenv "GHOSTEL_PRE_SPAWN_TEST" "ok"))))
+               (proc (ghostel--start-process)))
+          (unwind-protect
+              (progn
+                (should (eq captured-buffer test-buffer))
+                (should (equal captured-default-directory "/tmp/"))
+                (should (member "GHOSTEL_PRE_SPAWN_TEST=ok" captured-env)))
+            (when (process-live-p proc)
+              (delete-process proc))))))))
+
 ;; -----------------------------------------------------------------------
 ;; Test: ghostel-eshell integration
 ;; -----------------------------------------------------------------------