Support alignment for reader conditionals

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### New features
+
+* [#483](https://github.com/clojure-emacs/clojure-mode/issues/483): Support alignment for reader conditionals, with the new `clojure-align-reader-conditionals` user option.
+
 ## 5.9.1 (2018-08-27)
 
 * [#485](https://github.com/clojure-emacs/clojure-mode/issues/485): Fix a regression in `end-f-defun`.

clojure-mode.el

@@ -1090,6 +1090,12 @@ will align the values like this:
   :safe #'booleanp
   :type 'boolean)
 
+(defcustom clojure-align-reader-conditionals nil
+  "Whether to align reader conditionals, as if they were maps."
+  :package-version '(clojure-mode . "5.10")
+  :safe #'booleanp
+  :type 'boolean)
+
 (defcustom clojure-align-binding-forms
   '("let" "when-let" "when-some" "if-let" "if-some" "binding" "loop"
     "doseq" "for" "with-open" "with-local-vars" "with-redefs")
@@ -1104,6 +1110,10 @@ will align the values like this:
   :safe #'listp
   :type '(repeat string))
 
+(defvar clojure--beginning-of-reader-conditional-regexp
+  "#\\?@(\\|#\\?("
+  "Regexp denoting the beginning of a reader conditional.")
+
 (defun clojure--position-for-alignment ()
   "Non-nil if the sexp around point should be automatically aligned.
 This function expects to be called immediately after an
@@ -1118,32 +1128,36 @@ For instance, in a map literal point is left immediately before
 the first key; while, in a let-binding, point is left inside the
 binding vector and immediately before the first binding
 construct."
-  ;; Are we in a map?
-  (or (and (eq (char-before) ?{)
-           (not (eq (char-before (1- (point))) ?\#)))
-      ;; Are we in a cond form?
-      (let* ((fun    (car (member (thing-at-point 'symbol) clojure-align-cond-forms)))
-             (method (and fun (clojure--get-indent-method fun)))
-             ;; The number of special arguments in the cond form is
-             ;; the number of sexps we skip before aligning.
-             (skip   (cond ((numberp method) method)
-                           ((null method) 0)
-                           ((sequencep method) (elt method 0)))))
-        (when (and fun (numberp skip))
-          (clojure-forward-logical-sexp skip)
-          (comment-forward (point-max))
-          fun)) ; Return non-nil (the var name).
-      ;; Are we in a let-like form?
-      (when (member (thing-at-point 'symbol)
-                    clojure-align-binding-forms)
-        ;; Position inside the binding vector.
-        (clojure-forward-logical-sexp)
-        (backward-sexp)
-        (when (eq (char-after) ?\[)
-          (forward-char 1)
-          (comment-forward (point-max))
-          ;; Return non-nil.
-          t))))
+  (let ((point (point)))
+    ;; Are we in a map?
+    (or (and (eq (char-before) ?{)
+             (not (eq (char-before (1- point)) ?\#)))
+        ;; Are we in a reader conditional?
+        (and clojure-align-reader-conditionals
+             (looking-back clojure--beginning-of-reader-conditional-regexp (- (point) 4)))
+        ;; Are we in a cond form?
+        (let* ((fun    (car (member (thing-at-point 'symbol) clojure-align-cond-forms)))
+               (method (and fun (clojure--get-indent-method fun)))
+               ;; The number of special arguments in the cond form is
+               ;; the number of sexps we skip before aligning.
+               (skip   (cond ((numberp method) method)
+                             ((null method) 0)
+                             ((sequencep method) (elt method 0)))))
+          (when (and fun (numberp skip))
+            (clojure-forward-logical-sexp skip)
+            (comment-forward (point-max))
+            fun)) ; Return non-nil (the var name).
+        ;; Are we in a let-like form?
+        (when (member (thing-at-point 'symbol)
+                      clojure-align-binding-forms)
+          ;; Position inside the binding vector.
+          (clojure-forward-logical-sexp)
+          (backward-sexp)
+          (when (eq (char-after) ?\[)
+            (forward-char 1)
+            (comment-forward (point-max))
+            ;; Return non-nil.
+            t)))))
 
 (defun clojure--find-sexp-to-align (end)
   "Non-nil if there's a sexp ahead to be aligned before END.
@@ -1152,10 +1166,14 @@ Place point as in `clojure--position-for-alignment'."
   (let ((found))
     (while (and (not found)
                 (search-forward-regexp
-                 (concat "{\\|(" (regexp-opt
-                                  (append clojure-align-binding-forms
-                                          clojure-align-cond-forms)
-                                  'symbols))
+                 (concat (when clojure-align-reader-conditionals
+                           (concat clojure--beginning-of-reader-conditional-regexp
+                                   "\\|"))
+                         "{\\|("
+                         (regexp-opt
+                          (append clojure-align-binding-forms
+                                  clojure-align-cond-forms)
+                          'symbols))
                  end 'noerror))
 
       (let ((ppss (syntax-ppss)))

test/clojure-mode-indentation-test.el

@@ -485,7 +485,8 @@ x
   "Verify that all FORMs correspond to a properly indented sexps."
   (declare (indent defun))
   `(ert-deftest ,(intern (format "test-align-%s" name)) ()
-     (let ((clojure-align-forms-automatically t))
+     (let ((clojure-align-forms-automatically t)
+           (clojure-align-reader-conditionals t))
        ,@(mapcar (lambda (form)
                    `(with-temp-buffer
                       (clojure-mode)
@@ -596,6 +597,28 @@ x
  :b {:a  :a,
      :aa :a}}")
 
+(def-full-align-test reader-conditional
+  "#?(:clj  2
+   :cljs 2)")
+
+(def-full-align-test reader-conditional-splicing
+  "#?@(:clj  [2]
+    :cljs [2])")
+
+(ert-deftest reader-conditional-alignment-disabled-by-default ()
+  (let ((content "#?(:clj 2\n   :cljs 2)"))
+    (with-temp-buffer
+      (clojure-mode)
+      (insert content)
+      (call-interactively #'clojure-align)
+      (should (string= (buffer-string) content)))
+    (with-temp-buffer
+      (clojure-mode)
+      (setq-local clojure-align-reader-conditionals t)
+      (insert content)
+      (call-interactively #'clojure-align)
+      (should-not (string= (buffer-string) content)))))
+
 (ert-deftest clojure-align-remove-extra-commas ()
   (with-temp-buffer
     (clojure-mode)