Support indenting backquote substitutions in cl-indent

* lisp/emacs-lisp/cl-indent.el
(lisp-indent-backquote-substitution-mode): New user option.
(common-lisp-indent-function-1, common-lisp-loop-part-indentation)
(common-lisp-indent-function): Support normally indenting
backquote substitutions.
(extended-loop-p): Rename to `lisp-extended-loop-p'.

2 files changed, 60 insertions, 11 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index a9cf1b0f88f..fb2291c534c 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,12 @@
+2015-03-15  Daniel Colascione  <dancol@dancol.org>
+
+        * emacs-lisp/cl-indent.el
+        (lisp-indent-backquote-substitution-mode): New user option.
+        (common-lisp-indent-function-1, common-lisp-loop-part-indentation)
+        (common-lisp-indent-function): Support normally indenting
+        backquote substitutions.
+        (extended-loop-p): Rename to `lisp-extended-loop-p'.
+
 2015-03-14  Michael R. Mauger  <michael@mauger.com>
 
         * progmodes/sql.el: Version 3.5
diff --git a/lisp/emacs-lisp/cl-indent.el b/lisp/emacs-lisp/cl-indent.el
index 1bcfb6df2cf..5e75406cf22 100644
--- a/lisp/emacs-lisp/cl-indent.el
+++ b/lisp/emacs-lisp/cl-indent.el
@@ -138,6 +138,19 @@ If non-nil, alignment is done with the first parameter
   :type 'boolean
   :group 'lisp-indent)
 
+(defcustom lisp-indent-backquote-substitution-mode t
+  "How to indent substitutions in backquotes.
+If `t', the default, indent substituted forms normally.
+If `nil', do not apply special indentation rule to substituted
+forms.  If `corrected', subtract the `,' or `,@' from the form
+column, indenting as if this character sequence were not present.
+In any case, do not backtrack beyond a backquote substitution.
+
+Until Emacs 25.1, the `nil' behavior was hard-wired."
+  :version "25.1"
+  :type '(choice (const corrected) (const nil) (const t))
+  :group 'lisp-indent)
+
 
 (defvar lisp-indent-defun-method '(4 &lambda &body)
   "Defun-like indentation method.
@@ -145,7 +158,7 @@ This applies when the value of the `common-lisp-indent-function' property
 is set to `defun'.")
 
 
-(defun extended-loop-p (loop-start)
+(defun lisp-extended-loop-p (loop-start)
   "True if an extended loop form starts at LOOP-START."
   (condition-case ()
       (save-excursion
@@ -170,11 +183,22 @@ the standard lisp indent package."
   "Compute the indentation of loop form constituents."
   (let* ((loop-indentation (save-excursion
                              (goto-char (elt state 1))
-                             (current-column))))
+                             (current-column))))
+    (when (and (eq lisp-indent-backquote-substitution-mode 'corrected))
+      (save-excursion
+        (goto-char (elt state 1))
+        (incf loop-indentation
+              (cond ((eq (char-before) ?,) -1)
+                    ((and (eq (char-before) ?@)
+                          (progn (backward-char)
+                                 (eq (char-before) ?,)))
+                     -2)
+                    (t 0)))))
+
     (goto-char indent-point)
     (beginning-of-line)
     (list
-     (cond ((not (extended-loop-p (elt state 1)))
+     (cond ((not (lisp-extended-loop-p (elt state 1)))
             (+ loop-indentation lisp-simple-loop-indentation))
            ((looking-at "^\\s-*\\(:?\\sw+\\|;\\)")
             (+ loop-indentation lisp-loop-keyword-indentation))
@@ -264,9 +288,15 @@ at `common-lisp-indent-function' and, if set, use its value
 instead."
   ;; FIXME: why do we need to special-case loop?
   (if (save-excursion (goto-char (elt state 1))
-                      (looking-at (if (derived-mode-p 'emacs-lisp-mode)
-                                      "(\\(cl-\\)?[Ll][Oo][Oo][Pp]"
-                                    "([Ll][Oo][Oo][Pp]")))
+                      (and (looking-at (if (derived-mode-p 'emacs-lisp-mode)
+                                           "(\\(cl-\\)?loop"
+                                         "([Ll][Oo][Oo][Pp]"))
+                           (or lisp-indent-backquote-substitution-mode
+                               (not
+                                (or (and (eq (char-before) ?@)
+                                         (progn (backward-char)
+                                                (eq (char-before) ?,)))
+                                    (eq (char-before) ?,))))))
       (common-lisp-loop-part-indentation indent-point state)
     (common-lisp-indent-function-1 indent-point state)))
 
@@ -373,11 +403,21 @@ instead."
                         (not (eq (char-after (- containing-sexp 2)) ?\#)))
                    ;; No indentation for "'(...)" elements
                    (setq calculated (1+ sexp-column)))
-                  ((or (eq (char-after (1- containing-sexp)) ?\,)
-                       (and (eq (char-after (1- containing-sexp)) ?\@)
-                            (eq (char-after (- containing-sexp 2)) ?\,)))
-                   ;; ",(...)" or ",@(...)"
-                   (setq calculated normal-indent))
+                  ((when
+                       (or (eq (char-after (1- containing-sexp)) ?\,)
+                           (and (eq (char-after (1- containing-sexp)) ?\@)
+                                (eq (char-after (- containing-sexp 2)) ?\,)))
+                     ;; ",(...)" or ",@(...)"
+                     (when (eq lisp-indent-backquote-substitution-mode
+                               'corrected)
+                       (incf sexp-column -1)
+                       (when (eq (char-after (1- containing-sexp)) ?\@)
+                         (incf sexp-column -1)))
+                     (cond (lisp-indent-backquote-substitution-mode
+                            (setf tentative-calculated normal-indent)
+                            (setq depth lisp-indent-maximum-backtracking)
+                            nil)
+                           (t (setq calculated normal-indent)))))
                   ((eq (char-after (1- containing-sexp)) ?\#)
                    ;; "#(...)"
                    (setq calculated (1+ sexp-column)))