Fix indentation in multi-line match expressions. Fixes #98

elixir-smie.el

@@ -42,7 +42,7 @@
        (statements (statement)
                    (statement ";" statements))
        (statement ("def" non-block-expr "do" statements "end")
-                  (non-block-expr "fn" match-statement "end")
+                  (non-block-expr "fn" match-statements "end")
                   (non-block-expr "do" statements "end")
                   ("if" non-block-expr "do" statements "else" statements "end")
                   ("if" non-block-expr "do" statements "end")
@@ -76,9 +76,11 @@
        (left "*" "/"))))))
 
 (defvar elixir-smie--operator-regexp
-  (regexp-opt '("<<<" ">>>" "^^^" "~~~" "&&&" "|||" "===" "!==" "==" "!=" "<="
-                ">=" "<" ">" "&&" "||" "<>" "++" "--" "//"
-                "/>" "=~" "|>" "->")))
+  (rx (or "<<<" ">>>" "^^^" "~~~" "&&&" "|||" "===" "!==" "==" "!=" "<="
+          ">=" "<" ">" "&&" "||" "<>" "++" "--" "//" "/>" "=~" "|>")))
+
+(defvar elixir-smie--block-operator-regexp
+  (rx "->"))
 
 (defvar elixir-smie--spaces-til-eol-regexp
   (rx (and (1+ space) eol))
@@ -96,6 +98,40 @@
   (not (or (memq (char-before) '(?\{ ?\[))
            (looking-back elixir-smie--operator-regexp (- (point) 3) t))))
 
+(defun elixir-smie--semi-ends-match ()
+  "Return non-nil if the current line concludes a match block."
+  (save-excursion
+    ;; Warning: Recursion.
+    ;; This is easy though.
+
+    ;; 1. If we're at a blank line, move forward a character. This takes us to
+    ;;    the next line.
+    ;; 2. If we're not at the end of the buffer, call this function again.
+    ;;    (Otherwise, return nil.)
+
+    ;; The point here is that we want to treat blank lines as a single semi-
+    ;; colon when it comes to detecting the end of match statements. This could
+    ;; also be handled by a `while' expression or some other looping mechanism.
+    (flet ((self-call ()
+                      (if (< (point) (point-max))
+                          (elixir-smie--semi-ends-match)
+                        nil)))
+      (cond
+       ((and (eolp) (bolp))
+        (forward-char)
+        (self-call))
+       ((looking-at elixir-smie--spaces-til-eol-regexp)
+        (move-beginning-of-line 2)
+        (self-call))
+       ;; And if we're NOT on a blank line, move to the end of the line, and see
+       ;; if we're looking back at a block operator.
+       (t (move-end-of-line 1)
+          (looking-back elixir-smie--block-operator-regexp))))))
+
+(defun elixir-smie--same-line-as-parent (parent-pos child-pos)
+  "Return non-nil if `child-pos' is on same line as `parent-pos'."
+  (= (line-number-at-pos parent-pos) (line-number-at-pos child-pos)))
+
 (defun elixir-smie-forward-token ()
   (cond
    ;; If there is nothing but whitespace between the last token and eol, emit
@@ -105,7 +141,12 @@
     ";")
    ((and (looking-at "[\n#]") (elixir-smie--implicit-semi-p))
     (if (eolp) (forward-char 1) (forward-comment 1))
-    ";")
+    (if (elixir-smie--semi-ends-match)
+        "MATCH-STATEMENT-DELIMITER"
+      ";"))
+   ((looking-at elixir-smie--block-operator-regexp)
+    (goto-char (match-end 0))
+    "->")
    ((looking-at elixir-smie--operator-regexp)
     (goto-char (match-end 0))
     "OP")
@@ -117,7 +158,12 @@
     (cond
      ((and (> pos (line-end-position))
            (elixir-smie--implicit-semi-p))
-      ";")
+      (if (elixir-smie--semi-ends-match)
+          "MATCH-STATEMENT-DELIMITER"
+        ";"))
+     ((looking-back elixir-smie--block-operator-regexp (- (point) 3) t)
+      (goto-char (match-beginning 0))
+      "->")
      ((looking-back elixir-smie--operator-regexp (- (point) 3) t)
       (goto-char (match-beginning 0))
       "OP")
@@ -140,14 +186,62 @@
       ((smie-rule-sibling-p) nil)
       ((smie-rule-hanging-p) (smie-rule-parent elixir-smie-indent-basic))
       (t elixir-smie-indent-basic)))
+
+    (`(:before . "MATCH-STATEMENT-DELIMITER")
+     (cond
+      ((and (not (smie-rule-sibling-p))
+            (smie-rule-hanging-p))
+       (smie-rule-parent elixir-smie-indent-basic))))
+      ;; ((and (smie-rule-hanging-p)
+      ;;       (smie-rule-sibling-p))
+      ;;  (smie-rule-parent))))
+
+    (`(:after . "MATCH-STATEMENT-DELIMITER")
+     (cond
+      ;; We don't want to specify any rules for the first `->' after `do' or
+      ;; `fn', since SMIE will look at the BNF to see how to handle indentation
+      ;; in that case.
+      ((smie-rule-hanging-p)
+       (smie-rule-parent elixir-smie-indent-basic))))
+
+    (`(:before . "->")
+     (cond
+      ((smie-rule-hanging-p)
+       (smie-rule-parent elixir-smie-indent-basic))))
+
+    (`(:after . "->")
+     (cond
+      ;; This first condition is kind of complicated so I'll try to make this
+      ;; comment as clear as possible.
+
+      ;; "If `->' is the last thing on the line, and its parent token
+      ;; is `fn' ..."
+      ((and (smie-rule-hanging-p)
+            (smie-rule-parent-p "fn"))
+       ;; "... and if:
+
+       ;; 1. `smie--parent' is non-nil
+       ;; 2. the `->' token in question is on the same line as its parent (if
+       ;;    the logic has gotten this far, its parent will be `fn')
+
+       ;; ... then indent the line after the `->' aligned with the
+       ;; parent, offset by `elixir-smie-indent-basic'."
+       (if (and smie--parent (elixir-smie--same-line-as-parent
+                              (nth 1 smie--parent)
+                              (point)))
+           (smie-rule-parent elixir-smie-indent-basic)))
+      ;; Otherwise, if just indent by two.
+      ((smie-rule-hanging-p)
+       elixir-smie-indent-basic)))
+
     (`(:before . ";")
      (cond
       ((smie-rule-parent-p "after" "catch" "def" "defmodule" "defp" "do" "else"
                            "fn" "if" "rescue" "try" "unless")
        (smie-rule-parent elixir-smie-indent-basic))))
     (`(:after . ";")
      (if (smie-rule-parent-p "if")
-         (smie-rule-parent 0)))))
+         (smie-rule-parent)))))
 
 (define-minor-mode elixir-smie-mode
   "SMIE-based indentation and syntax for Elixir"