emacs: Add support for opam-switch-mode (#1654)

from erikmd/opam-switch-mode

CHANGES.md

@@ -19,6 +19,8 @@ unreleased
       local values in the completion options.  Alternatively, this
       behavior can be enabled permanently by customizing
       `merlin-construct-with-local-values` (#1644)
+    - emacs: add support for opam-switch-mode (#1654, fixes #1591).
+      See <https://github.com/ProofGeneral/opam-switch-mode>
 
 merlin 4.9
 ==========

README.md

@@ -105,6 +105,8 @@ Just add the following to your *.emacs* file:
 ;; (require 'merlin-iedit)       ; iedit.el editing of occurrences
 ;; (require 'merlin-company)     ; company.el completion
 ;; (require 'merlin-ac)          ; auto-complete.el completion
+;; To easily change opam switches and pick the ocamlmerlin binary accordingly,
+;; you can use the minor mode https://github.com/ProofGeneral/opam-switch-mode
 ```
 
 More comprehensive documentation can be found on the [emacs-from-scratch wiki](https://github.com/ocaml/merlin/wiki/emacs-from-scratch).
@@ -127,6 +129,8 @@ Emacs startup file is sufficient:
 ;; (require 'merlin-iedit)       ; iedit.el editing of occurrences
 ;; (require 'merlin-company)     ; company.el completion
 ;; (require 'merlin-ac)          ; auto-complete.el completion
+;; To easily change opam switches and pick the ocamlmerlin binary accordingly,
+;; you can use the minor mode https://github.com/ProofGeneral/opam-switch-mode
 ```
 
 ### Other Editors

emacs/merlin.el

@@ -258,8 +258,6 @@ The association list can contain the following optional keys:
 ;; Internal variables ;;
 ;;;;;;;;;;;;;;;;;;;;;;;;
 
-(defvar merlin-opam-bin-path nil)
-
 ;; If user did not specify its merlin-favourite-caml-mode, try to guess it from
 ;; the buffer being edited
 (defvar merlin-guessed-favorite-caml-mode nil)
@@ -512,7 +510,13 @@ argument (lookup appropriate binary, setup logging, pass global settings)"
   ;; Really start process
   (let ((binary      (merlin-command))
         ;; (flags       (merlin-lookup 'flags merlin-buffer-configuration))
-        (process-environment (cl-copy-list process-environment))
+        (process-environment
+         ;; for simplicity, we use a mere append here (leading to a
+         ;; duplicate binding), it does work because only the first
+         ;; occurrence is considered, one can check this by running
+         ;; (call-process "printenv" nil t)
+         (append (merlin-lookup 'env merlin-buffer-configuration)
+                 process-environment))
         (dot-merlin  (merlin-lookup 'dot-merlin merlin-buffer-configuration))
         ;; FIXME use logfile
         ;; (logfile     (or (merlin-lookup 'logfile merlin-buffer-configuration)
@@ -522,16 +526,6 @@ argument (lookup appropriate binary, setup logging, pass global settings)"
         (packages    (merlin--map-flatten (lambda (x) (cons "-I" x))
                                           merlin-buffer-packages-path))
         (filename    (buffer-file-name (buffer-base-buffer))))
-    ;; Update environment
-    (dolist (binding (merlin-lookup 'env merlin-buffer-configuration))
-      (let* ((equal-pos (string-match-p "=" binding))
-             (prefix (if equal-pos
-                       (substring binding 0 (1+ equal-pos))
-                       binding))
-             (is-prefix (lambda (x) (string-prefix-p prefix x))))
-        (setq process-environment (cl-delete-if is-prefix process-environment))
-        (when equal-pos
-          (setq process-environment (cons binding process-environment)))))
     ;; Compute verbosity
     (when (eq merlin-verbosity-context t)
       (setq merlin-verbosity-context (cons command args)))
@@ -611,6 +605,35 @@ argument (lookup appropriate binary, setup logging, pass global settings)"
         (kill-local-variable 'merlin-buffer-configuration)
         (kill-local-variable 'merlin-erroneous-buffer)))))
 
+(defcustom merlin-stop-server-on-opam-switch t
+  "If t, stops the Merlin server before the opam switch changes.
+If the user changes the opam switch using `opam-switch-set-switch'
+or an `\"OPSW\"' menu from `opam-switch-mode', this option asks to
+stop the Merlin server process, so that the next Merlin command
+starts a new server, typically with a different Merlin version
+from a different opam switch.
+
+See https://github.com/ProofGeneral/opam-switch-mode
+
+Note: `opam-switch-mode' triggers automatic changes for `exec-path' and
+`process-environment', which are useful to find the `\"ocamlmerlin\"'
+binary (its filename can be overriden in `merlin-command') and the
+binary of Merlin's subprocesses, in the ambient opam switch."
+  :type 'boolean)
+
+(defun merlin--stop-server-on-opam-switch ()
+  "Stop the Merlin server before the opam switch changes.
+This function is for the `opam-switch-mode' hook
+`opam-switch-before-change-opam-switch-hook', which runs just
+before the user changes the opam switch through `opam-switch-mode'."
+  (when (and merlin-mode merlin-stop-server-on-opam-switch)
+    (condition-case _sig
+        (merlin-stop-server)
+      (t (message "Info: (merlin-stop-server) failed in the previous opam switch")))))
+
+(add-hook 'opam-switch-before-change-opam-switch-hook
+          #'merlin--stop-server-on-opam-switch t)
+
 ;;;;;;;;;;;;;;;;;;;;
 ;; FILE SWITCHING ;;
 ;;;;;;;;;;;;;;;;;;;;
@@ -1910,7 +1933,8 @@ Empty string defaults to jumping to all these."
             (merlin-lookup 'do-not-cache-config merlin-buffer-configuration))
     (setq merlin-buffer-configuration (merlin--configuration)))
 
-  (let ((command (merlin-lookup 'command merlin-buffer-configuration)))
+  (let ((command (merlin-lookup 'command merlin-buffer-configuration))
+        bin-path)
     (unless command
       (setq
        command
@@ -1921,7 +1945,7 @@ Empty string defaults to jumping to all these."
          (with-temp-buffer
            (if (eq (call-process-shell-command
                     "opam var bin" nil (current-buffer) nil) 0)
-               (let ((bin-path
+               (let ((bin-dir
                       (replace-regexp-in-string "\n$" "" (buffer-string))))
                  ;; the opam bin dir needs to be on the path, so if merlin
                  ;; calls out to sub binaries (e.g. ocamlmerlin-reason), the
@@ -1930,21 +1954,17 @@ Empty string defaults to jumping to all these."
 
                  ;; this was originally done via `opam exec' but that does not
                  ;; work for opam 1, and added a performance hit
-                 (setq merlin-opam-bin-path (list (concat "PATH=" bin-path)))
-                 (concat bin-path "/ocamlmerlin"))
-
+                 (setq bin-path (list (concat "PATH=" bin-dir))))
              ;; best effort if opam is not available, lookup for the binary in
              ;; the existing env
-             (progn
-               (message "merlin-command: opam var failed (%S)"
-                        (buffer-string))
-               "ocamlmerlin"))))))
-
+             (message "merlin-command: opam var failed (%S)"
+                      (buffer-string)))
+           "ocamlmerlin"))))
       ;; cache command in merlin-buffer configuration to avoid having to shell
       ;; out to `opam` each time.
       (push (cons 'command command) merlin-buffer-configuration)
-      (when merlin-opam-bin-path
-        (push (cons 'env merlin-opam-bin-path) merlin-buffer-configuration)))
+      (when bin-path
+        (push (cons 'env bin-path) merlin-buffer-configuration)))
 
     command))
 

merlin.opam

@@ -51,8 +51,11 @@ Add opam emacs directory to your load-path by appending this to your .emacs:
     (add-hook 'tuareg-mode-hook 'merlin-mode t)
     (add-hook 'caml-mode-hook 'merlin-mode t)
     ;; Use opam switch to lookup ocamlmerlin binary
-    (setq merlin-command 'opam)))
-
+    (setq merlin-command 'opam)
+    ;; To easily change opam switches within a given Emacs session, you can
+    ;; install the minor mode https://github.com/ProofGeneral/opam-switch-mode
+    ;; and use one of its \"OPSW\" menus.
+    ))
 Take a look at https://github.com/ocaml/merlin for more information
 
 Quick setup with opam-user-setup