Make main.rkt the "shim" for command-server.rkt

Don't really need the shim.rkt file.

Author: greghendershott

racket-cmd.el

@@ -94,7 +94,7 @@ Before doing anything runs the hook `racket-stop-back-end-hook'."
                     :sentinel #'ignore))
            (local-p (racket--back-end-local-p back-end))
            (main-dot-rkt (expand-file-name
-                          "shim.rkt"
+                          "main.rkt"
                           (if local-p
                               racket--rkt-source-dir
                             (racket--ensure-updated-back-end-on-remote))))

racket/image.rkt

@@ -1,10 +1,11 @@
-;; Copyright (c) 2013-2022 by Greg Hendershott.
+;; Copyright (c) 2013-2025 by Greg Hendershott.
 ;; SPDX-License-Identifier: GPL-3.0-or-later
 
 #lang racket/base
 
-;;; Portions Copyright (C) 2012 Jose Antonio Ortega Ruiz.
+;; Portions Copyright (C) 2012 Jose Antonio Ortega Ruiz.
 
+;; Limit imports to those supplied by Minimal Racket!
 (require file/convertible
          racket/file
          racket/format

racket/main.rkt

@@ -3,28 +3,49 @@
 
 #lang racket/base
 
+;; This module acts as a "shim" or "launcher" for command-server.rkt.
+;;
+;; We dynamic-require command-server.rkt within an exn handler for
+;; missing modules, to provide a better error UX when people are using
+;; Minimal Racket; see issue #744. Any such error is written to stdout
+;; as a "notification" for the Emacs front end, which can display it
+;; in a dedicated buffer. Not only is this better than error text
+;; flashing by in the echo bar and hiding in the *Messages* buffer,
+;; our dedicated can supply a browse-url button to our docs section
+;; about Minimal Racket.
+;;
+;; Note that the exn handler is active only during the dynamic extent
+;; of the dynamic-require to extract the command-server-loop function.
+;; Subsequently we call that function without any such handler in
+;; effect.
+;;
+;; Use the same notification mechanism for other back end startup
+;; failures, such as when they need a newer version of Racket.
+
+;; Limit imports to those supplied by Minimal Racket!
 (require racket/match
-         racket/port
+         (only-in racket/port open-output-nowhere)
+         racket/runtime-path
          (only-in racket/string string-trim)
          (only-in racket/system system/exit-code)
          version/utils
-         "command-server.rkt"
          (only-in "image.rkt" set-use-svg?!))
 
-(provide main)
-
-;;;(require does-not-exist) ;;TESTING
+;; Write a "notification" for the Emacs front end and exit.
+(define (notify/exit kind data)
+  (writeln `(startup-error ,kind ,data))
+  (flush-output)
+  (exit 13))
 
 (define (assert-racket-version minimum-version)
   (define actual-version (version))
   (unless (version<=? minimum-version actual-version)
-    ;; Write a "notification" for the Emacs front end and exit.
-    (writeln `(startup-error
-               other
-               ,(format "Racket Mode needs Racket ~a or newer but ~a is ~a."
-                        minimum-version
-                        (find-executable-path (find-system-path 'exec-file))
-                        actual-version)))
+    (notify/exit
+     'other
+     (format "Racket Mode needs Racket ~a or newer but ~a is ~a."
+             minimum-version
+             (find-executable-path (find-system-path 'exec-file))
+             actual-version))
     (flush-output)
     (exit 14)))
 
@@ -39,7 +60,7 @@
                   (and (valid-version? ver)
                        (version<=? "15.0" ver))))))))
 
-(define (main)
+(module+ main
   (assert-racket-version (if (macos-sequoia-or-newer?)
                              "8.14.0.4" ;issue #722
                              "6.12"))   ;general requirement
@@ -49,14 +70,24 @@
     [(vector "--use-svg" )       (set-use-svg?! #t)]
     [(vector "--do-not-use-svg") (set-use-svg?! #f)]
     [v
-     (error '|Racket Mode back end|
-            "Bad command-line arguments:\n~s\n" v)])
+     (notify/exit
+      'other
+      (format "Bad command-line arguments:\n~s\n" v))])
+
+  (define-runtime-path command-server.rkt "command-server.rkt")
+  (define command-server-loop
+    (with-handlers ([exn:fail:syntax:missing-module?
+                     (λ (e)
+                       (notify/exit
+                        'missing-module
+                        (format "~a" (exn:fail:syntax:missing-module-path e))))])
+      (dynamic-require command-server.rkt 'command-server-loop)))
 
   ;; Save original current-{input output}-port to give to
-  ;; command-server-loop for command I/O.
+  ;; command-server-loop for command I/O ...
   (let ([stdin  (current-input-port)]
         [stdout (current-output-port)])
-    ;; Set no-ops so e.g. rando print can't bork the command I/O.
+    ;; ... and set no-ops so rando print can't bork the command I/O.
     (parameterize ([current-input-port  (open-input-bytes #"")]
                    [current-output-port (open-output-nowhere)])
       (command-server-loop stdin stdout))))