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Monday, February 10, 2014

emacs sql indent heuristic

I was using sql mode recently and was not happy with the indentation. I wanted something similar to python-mode's indentation, wherein the cursor will at most indent to the current scope and then cycle through all of the previous scopes.

I decided that the quickest way to satisfy my requirements for sane indentation was to assign a custom function to emac's indent-line-function function in sql-mode.

Here's a link to the gist

Here's the source:

(defun get-previous-indentation ()
  "Get the column of the previous indented line"
      (move-beginning-of-line nil)
   (skip-chars-backward "\n \t")

(defun get-current-indentation ()
  "Return column at current indentation"

(defun point-at-current-indentation ()
  "Return point at current indentation"  
   (move-to-column (get-current-indentation))

(defun point-at-column-on-line (col)
  "Returns the point at `col` on the current line"
      (move-to-column col)

(defun ig-move-line-to-column (col)
  "Move the line to col; fill with all spaces if moveing forward"
 (interactive "p")
  (let ((point-at-cur-indent (point-at-current-indentation))
  (col-at-cur-indent (get-current-indentation)))
    (cond (
     (= col 0)
     ;; delete to beginning of line or do nothing
     (if (= col-at-cur-indent 0)
    (delete-region point-at-cur-indent (point-at-column-on-line 0))))
     (< col col-at-cur-indent)
     ;; delete from our current point BACK to col
     (delete-region (point-at-column-on-line col) point-at-cur-indent))
     (> col col-at-cur-indent)
     ;; delete all text from indent to beginning of line
    (delete-region point-at-cur-indent (point-at-column-on-line 0))
    (move-beginning-of-line nil)
    ;; add spaces forward
    (insert-string (make-string col ?\s)))))))

(defun ig-indent-sql ()
  "Indent by `tab-width` at most 1 time greater than the previously indented line otherwise go to the beginning of the line indent forward by `tab-width`"
  (let ((previous (get-previous-indentation))
        (current (get-current-indentation)))
    (cond ( ;; exactly at previous line's indentation
           (= previous current)
     (ig-move-line-to-column (+ current tab-width)))

   ( ;; current is greater than previous
    (> current previous)
     ;; exactly at one indentation forward from previous lines indent
    (if (= tab-width (- current previous))
  ;; move line to beginning
        (ig-move-line-to-column 0)
      ;; go back to previous indentation level
      (ig-move-line-to-column previous)))

    (ig-move-line-to-column (+ current tab-width))))))

(add-hook 'sql-mode-hook
          (function (lambda ()
                      (make-local-variable 'indent-line-function)
                      (setq indent-line-function 'ig-indent-sql))))


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