(file-start-mode-alist): New variable.

(magic-mode-regexp-match-limit): Doc fix.
(set-auto-mode): Handle file-start-mode-alist.
A little cleanup of structure.

diff --git a/lisp/files.el b/lisp/files.el
index 1b6a94766d30c0c2aa09f951ee19fba414037a02..85478ac40a0ef1036b68a47ce8ba7fee5c500b0d 100644 (file)
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -2151,8 +2151,21 @@ If FUNCTION is nil, then it is not called.  (That is a way of saying
 \"allow `auto-mode-alist' to decide for these files.\")")
 (put 'magic-mode-alist 'risky-local-variable t)
 
+(defvar file-start-mode-alist
+  nil
+  "Like `magic-mode-alist' but has lower priority than `auto-mode-alist'.
+Each element looks like (REGEXP . FUNCTION) or (MATCH-FUNCTION . FUNCTION).
+After visiting a file, if REGEXP matches the text at the beginning of the
+buffer, or calling MATCH-FUNCTION returns non-nil, `normal-mode' will
+call FUNCTION, provided that `magic-mode-alist' and `auto-mode-alist'
+have not specified a mode for this file.
+
+If FUNCTION is nil, then it is not called.")
+(put 'file-start-mode-alist 'risky-local-variable t)
+
 (defvar magic-mode-regexp-match-limit 4000
-  "Upper limit on `magic-mode-alist' regexp matches.")
+  "Upper limit on `magic-mode-alist' regexp matches.
+Also applies to `file-start-mode-alist'.")
 
 (defun set-auto-mode (&optional keep-mode-if-same)
   "Select major mode appropriate for current buffer.
@@ -2207,10 +2220,10 @@ only set the major mode, if that would change it."
              (or (set-auto-mode-0 mode keep-mode-if-same)
                  ;; continuing would call minor modes again, toggling them off
                  (throw 'nop nil))))))
+    ;; If we didn't, look for an interpreter specified in the first line.
+    ;; As a special case, allow for things like "#!/bin/env perl", which
+    ;; finds the interpreter anywhere in $PATH.
     (unless done
-      ;; If we didn't, look for an interpreter specified in the first line.
-      ;; As a special case, allow for things like "#!/bin/env perl", which
-      ;; finds the interpreter anywhere in $PATH.
       (setq mode (save-excursion
                   (goto-char (point-min))
                   (if (looking-at auto-mode-interpreter-regexp)
@@ -2223,7 +2236,7 @@ only set the major mode, if that would change it."
       ;; If we found an interpreter mode to use, invoke it now.
       (if done
          (set-auto-mode-0 (cdr done) keep-mode-if-same)))
-    ;; If we didn't, match the buffer beginning against magic-mode-alist.
+    ;; Next try matching the buffer beginning against magic-mode-alist.
     (unless done
       (if (setq done (save-excursion
                       (goto-char (point-min))
@@ -2236,39 +2249,55 @@ only set the major mode, if that would change it."
                                          (if (functionp re)
                                              (funcall re)
                                            (looking-at re)))))))
-         (set-auto-mode-0 done keep-mode-if-same)
-       ;; Compare the filename against the entries in auto-mode-alist.
-       (if buffer-file-name
-           (let ((name buffer-file-name))
-             ;; Remove backup-suffixes from file name.
-             (setq name (file-name-sans-versions name))
-             (while name
-               ;; Find first matching alist entry.
-               (setq mode
-                     (if (memq system-type '(vax-vms windows-nt cygwin))
-                         ;; System is case-insensitive.
-                         (let ((case-fold-search t))
-                           (assoc-default name auto-mode-alist
-                                          'string-match))
-                       ;; System is case-sensitive.
-                       (or
-                        ;; First match case-sensitively.
-                        (let ((case-fold-search nil))
-                          (assoc-default name auto-mode-alist
-                                         'string-match))
-                        ;; Fallback to case-insensitive match.
-                        (and auto-mode-case-fold
-                             (let ((case-fold-search t))
-                               (assoc-default name auto-mode-alist
-                                              'string-match))))))
-               (if (and mode
-                        (consp mode)
-                        (cadr mode))
-                   (setq mode (car mode)
-                         name (substring name 0 (match-beginning 0)))
-                 (setq name))
-               (when mode
-                 (set-auto-mode-0 mode keep-mode-if-same)))))))))
+         (set-auto-mode-0 done keep-mode-if-same)))
+    ;; Next compare the filename against the entries in auto-mode-alist.
+    (unless done
+      (if buffer-file-name
+         (let ((name buffer-file-name))
+           ;; Remove backup-suffixes from file name.
+           (setq name (file-name-sans-versions name))
+           (while name
+             ;; Find first matching alist entry.
+             (setq mode
+                   (if (memq system-type '(vax-vms windows-nt cygwin))
+                       ;; System is case-insensitive.
+                       (let ((case-fold-search t))
+                         (assoc-default name auto-mode-alist
+                                        'string-match))
+                     ;; System is case-sensitive.
+                     (or
+                      ;; First match case-sensitively.
+                      (let ((case-fold-search nil))
+                        (assoc-default name auto-mode-alist
+                                       'string-match))
+                      ;; Fallback to case-insensitive match.
+                      (and auto-mode-case-fold
+                           (let ((case-fold-search t))
+                             (assoc-default name auto-mode-alist
+                                            'string-match))))))
+             (if (and mode
+                      (consp mode)
+                      (cadr mode))
+                 (setq mode (car mode)
+                       name (substring name 0 (match-beginning 0)))
+               (setq name))
+             (when mode
+               (set-auto-mode-0 mode keep-mode-if-same)
+               (setq done t))))))
+    ;; Next try matching the buffer beginning against file-start-mode-alist.
+    (unless done
+      (if (setq done (save-excursion
+                      (goto-char (point-min))
+                      (save-restriction
+                        (narrow-to-region (point-min)
+                                          (min (point-max)
+                                               (+ (point-min) magic-mode-regexp-match-limit)))
+                        (assoc-default nil file-start-mode-alist
+                                       (lambda (re dummy)
+                                         (if (functionp re)
+                                             (funcall re)
+                                           (looking-at re)))))))
+         (set-auto-mode-0 done keep-mode-if-same)))))
 
 ;; When `keep-mode-if-same' is set, we are working on behalf of
 ;; set-visited-file-name.  In that case, if the major mode specified is the