Function: dtrt-indent-mode

dtrt-indent-mode is an interactive and natively compiled function defined in dtrt-indent.el.

Signature

(dtrt-indent-mode &optional ARG)

Documentation

Toggle dtrt-indent mode.

With no argument, this command toggles the mode. Non-null prefix argument turns on the mode. Null prefix argument turns off the mode.

When dtrt-indent mode is enabled, the proper indentation offset and indent-tabs-mode(var)/indent-tabs-mode(fun) will be guessed for newly opened files and adjusted transparently.

This is a minor mode. If called interactively, toggle the Dtrt-Indent mode mode. If the prefix argument is positive, enable the mode, and if it is zero or negative, disable the mode.

If called from Lisp, toggle the mode if ARG is toggle. Enable the mode if ARG is nil, omitted, or is a positive number. Disable the mode if ARG is a negative number.

To check whether the minor mode is enabled in the current buffer, evaluate the variable dtrt-indent-mode(var)/dtrt-indent-mode(fun).

The mode's hook is called both when the mode is enabled and when it is disabled.

Key Bindings

This command is not in any keymaps.

Source Code

;; Defined in /nix/store/xl774j723v677bsfsybzln3vi6w0fpm3-emacs-packages-deps/share/emacs/site-lisp/elpa/dtrt-indent-20260709.2011/dtrt-indent.el
;;; dtrt-indent.el --- Adapt to foreign indentation offsets -*- lexical-binding: t; -*-

;; Copyright (C) 2003, 2007, 2008 Julian Scheid
;; Copyright (C) 2014-2025 Reuben Thomas

;; Author: Julian Scheid <julians37@googlemail.com>
;; Maintainer: Reuben Thomas <rrt@sc3d.org>
;; URL: https://github.com/jscheid/dtrt-indent
;; Package-Version: 20260709.2011
;; Package-Revision: nil
;; Keywords: convenience files languages c
;; Package-Requires: ((emacs "28.1"))

;; This file is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 2, or (at your option)
;; any later version.

;; This file is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with this software; see the file COPYING.  If not, write to
;; the Free Software Foundation, Inc., 51 Franklin Street, Fifth
;; Floor, Boston, MA 02110-1301 USA

;;; Commentary:

;; A minor mode that guesses the indentation offset and
;; `indent-tabs-mode' originally used for creating source code files and
;; transparently adjusts the corresponding settings in Emacs, making it
;; more convenient to edit others' files.
;;
;; This hooks into many major modes - c-mode, java-mode and ruby-mode, to
;; name but a few - and makes an educated guess on which offset is
;; appropriate by analyzing indentation levels in the file.  Modes that have
;; their own indentation offset guessing, such as python-mode, are not dealt
;; with.  In modes based on SMIE, dtrt-indent delegates to smie-config-guess.
;;
;; Heuristics are used to estimate the proper indentation offset and
;; therefore this system is not infallible, however adjustments will
;; only be made if the guess is considered reliable.  This way it
;; should leave you off no worse than before.
;;
;; To install, M-x customize-variable dtrt-indent-global-mode, and turn on
;; "Dtrt Indent Global Mode".
;;
;; The default settings have been carefully chosen and tested to work
;; reliably on a wide range of source files.  However, if it doesn't work
;; for you they can be fine tuned using M-x customize-group dtrt-indent.
;; You can use `dtrt-indent-diagnosis' to see dtrt-indent's
;; measurements, `dtrt-indent-highlight' to show indentation that was
;; considered,and `dtrt-indent-undo' to undo any changes it makes.
;;
;;
;; Heuristics
;;
;; We now describe the inner workings of dtrt-indent and how it arrives
;; at a conclusion on whether or not to change the indentation settings,
;; and to which value.
;;
;; Lines Analyzed
;;
;; In order to limit performance degradation due to the analysis, only a
;; fixed number of lines will be analyzed.  If the size of the file is
;; less than this number of lines, the whole file will be analyzed;
;; otherwise, the given number of lines at the beginning of the file are
;; analyzed.
;;
;; Certain lines are ignored during analysis:
;;
;; * Empty lines.
;; * Lines that are not indented (indentation offset 0).
;; * Lines that are the continuation of a multi-line comment or a
;;   multi-line statement or expression.
;; * Lines that only contain a single character can be ignored; by
;;   default, however, they are included.
;;
;; If, after ignoring any lines that are not eligible, the number of
;; relevant lines is smaller than a given threshold then the file is
;; treated as not fit for analysis and no guess will be made.
;;
;; Configuration settings used at this stage:
;; `dtrt-indent-min-relevant-lines', `dtrt-indent-max-lines',
;; `dtrt-indent-ignore-single-chars-flag'
;;
;; Histogram Generation
;;
;; For the remaining lines - those eligible within the fixed range - a
;; histogram is generated.  The histogram informs dtrt-indent about how
;; many lines are indented with one space, how many with two spaces, how
;; many with three spaces, etc.
;;
;; Offset Assessment
;;
;; Using the histogram, dtrt-indent determines for each of the potential
;; indentation offsets (by default, 2 through 8) how many lines are
;; indented with a multiple of that offset.
;;
;; Offsets for which the histogram doesn't contain enough distinct
;; indentations might be ignored; by default, however, a single
;; indentation per offset is accepted.
;;
;; After this step, dtrt-indent has a map of probabilities for each of
;; the potential offsets.
;;
;; Configuration settings used at this stage: `dtrt-indent-min-offset',
;; `dtrt-indent-max-offset', `dtrt-indent-min-matching-indentations'
;;
;; Offset Merging
;;
;; As a next step, offsets that are a factor of another offset with
;; similar probability are discarded; this is necessary because in a file
;; that has been indented with, say, 4 spaces per level, 2 spaces per
;; level could otherwise be wrongly guessed.
;;
;; Configuration settings used at this stage:
;; `dtrt-indent-max-merge-deviation'
;;
;; Final Evaluation
;;
;; Finally, dtrt-indent looks at the highest probability of all
;; potential offsets; if that probablity is below a given threshold, the
;; guess is deemed unreliable and no settings are changed.
;;
;; If the analysis yielded a best guess that exceeds the absolute
;; threshold, that guess is deemed reliable and the indentation setting
;; will be modified.
;;
;; Configuration settings used at this stage: `dtrt-indent-min-quality'.
;;
;; `indent-tabs-mode' Setting
;;
;; For determining hard vs. soft tabs, dtrt-indent counts the number of
;; lines out of the eligible lines in the fixed segment that are
;; indented using hard tabs, and the number of lines indented using
;; spaces.  If either count is significantly higher than the other count,
;; `indent-tabs-mode' will be modified.
;;
;; Configuration settings used at this stage:
;; `dtrt-indent-min-soft-tab-superiority',
;; `dtrt-indent-min-hard-tab-superiority'
;;
;; Files not touched by dtrt-indent:
;;
;; - Files that specify the corresponding variable
;;   (e.g. c-basic-offset) as a File Variable.
;;
;; - Files that specify dtrt-indent-mode: 0 as a File Variable.
;;
;; - Files with a major mode that dtrt-indent doesn't hook into.
;;
;; - Files for which the indentation offset cannot be guessed
;;   reliably.
;;
;; - Files for which `dtrt-indent-explicit-offset' is true; this can be
;; - used in `.dir-locals.el' files, for example.
;;
;; Limitations:
;;
;; - dtrt-indent can't deal well with files that use variable
;;   indentation offsets, e.g. files that use varying indentation
;;   based on the outer construct.
;;
;; - dtrt-indent currently only supports a limited number of languages
;;   (major-modes).
;;
;; - dtrt-indent only guesses the indendation offset, not the
;;   indentation style.  For instance, it does not detect whether a
;;   C-like file uses hanging braces or not.
;;
;; - dtrt-indent can't deal well with files that mix hard tabs with
;; - spaces for indentation.
;;
;; TODO:
;;
;; - verbose and diagnostics messages
;; - make sure variable documentation match their function
;; - make sure defaults are sensible
;; - bulk (real world) tests
;; - functional tests
;; - unit tests

;;; Code:

;;;###autoload
(define-minor-mode dtrt-indent-mode
  "Toggle dtrt-indent mode.
With no argument, this command toggles the mode.  Non-null prefix
argument turns on the mode.  Null prefix argument turns off the
mode.

When dtrt-indent mode is enabled, the proper indentation offset
and `indent-tabs-mode' will be guessed for newly opened files and
adjusted transparently."
  :lighter dtrt-indent-lighter
  :group 'dtrt-indent
  (if dtrt-indent-mode
      (if (and (boundp 'smie-grammar) (not (null smie-grammar)) (not (eq smie-grammar 'unset)))
          (progn
            (when (and (not (bound-and-true-p smie-config--buffer-local))
                       (fboundp 'smie-config-guess))
              (smie-config-guess))
            (when (bound-and-true-p dtrt-indent-run-after-smie)
              (dtrt-indent-try-set-offset)))
        (dtrt-indent-try-set-offset))
    (dtrt-indent-undo)))