#+title: Magit-Section Developer Manual
:PREAMBLE:
#+author: Jonas Bernoulli
#+email: emacs.magit@jonas.bernoulli.dev
#+date: 2015-{{{year}}}

#+texinfo_dir_category: Emacs
#+texinfo_dir_title: Magit-Section: (magit-section).
#+texinfo_dir_desc: Use Magit sections in your own packages.
#+subtitle: for version 4.7.0

#+setupfile: .orgconfig

This package implements the main user interface of Magit — the
collapsible sections that make up its buffers.  This package used
to be distributed as part of Magit but how it can also be used by
other packages that have nothing to do with Magit or Git.

To learn more about the section abstraction and available commands and
user options see [[info:magit#Sections]].  This manual documents how you
can use sections in your own packages.

#+texinfo: @noindent
This manual is for Magit-Section version 4.7.0.

#+texinfo: @insertcopying
:END:
* Introduction

This package implements the main user interface of Magit — the
collapsible sections that make up its buffers.  This package used
to be distributed as part of Magit but how it can also be used by
other packages that have nothing to do with Magit or Git.

To learn more about the section abstraction and available commands
and user options see [[info:magit#Sections]].  This manual documents
how you can use sections in your own packages.

When the documentation leaves something unaddressed, then please
consider that Magit uses this library extensively and search its
source for suitable examples before asking me for help.  Thanks!

* Creating Sections

- Macro: magit-insert-section [name] (type &optional value hide) &rest body ::

  Create a section object of type CLASS, storing VALUE in its
  ~value~ slot, and insert the section at point.  CLASS is a
  subclass of `magit-section' or has the form ~(eval FORM)~, in
  which case FORM is evaluated at runtime and should return a
  subclass.  In other places a sections class is often referred
  to as its "type".

  Many commands behave differently depending on the class of the
  current section and sections of a certain class can have their
  own keymap, which is specified using the `keymap' class slot.
  The value of that slot should be a variable whose value is a
  keymap.

  For historic reasons Magit and Forge in most cases use symbols
  as CLASS that don't actually identify a class and that lack the
  appropriate package prefix.  This works due to some undocumented
  kludges, which are not available to other packages.

  When optional HIDE is non-~nil~ collapse the section body by
  default, i.e., when first creating the section, but not when
  refreshing the buffer.  Else expand it by default.  This can be
  overwritten using ~magit-section-set-visibility-hook~.  When a
  section is recreated during a refresh, then the visibility of
  predecessor is inherited and HIDE is ignored (but the hook is
  still honored).

  BODY is any number of forms that actually insert the section's
  heading and body.  Optional NAME, if specified, has to be a
  symbol, which is then bound to the object of the section being
  inserted.

  Before BODY is evaluated the ~start~ of the section object is set
  to the value of `point' and after BODY was evaluated its ~end~ is
  set to the new value of ~point~; BODY is responsible for moving
  ~point~ forward.

  If it turns out inside BODY that the section is empty, then
  ~magit-cancel-section~ can be used to abort and remove all traces
  of the partially inserted section.  This can happen when creating
  a section by washing Git's output and Git didn't actually output
  anything this time around.

- Function: magit-insert-heading [child-count] &rest args ::

  Insert the heading for the section currently being inserted.

  This function should only be used inside ~magit-insert-section~.

  When called without any arguments, then just set the ~content~
  slot of the object representing the section being inserted to
  a marker at ~point~.  The section should only contain a single
  line when this function is used like this.

  When called with arguments ARGS, which have to be strings, or
  ~nil~, then insert those strings at point.  The section should not
  contain any text before this happens and afterwards it should
  again only contain a single line.  If the ~face~ property is set
  anywhere inside any of these strings, then insert all of them
  unchanged.  Otherwise use the `magit-section-heading' face for
  all inserted text.

  The ~content~ property of the section object is the end of the
  heading (which lasts from ~start~ to ~content~) and the beginning
  of the the body (which lasts from ~content~ to ~end~).  If the
  value of ~content~ is ~nil~, then the section has no heading and
  its body cannot be collapsed.  If a section does have a heading,
  then its height must be exactly one line, including a trailing
  newline character.  This isn't enforced, you are responsible for
  getting it right.  The only exception is that this function does
  insert a newline character if necessary.

  If provided, optional CHILD-COUNT must evaluate to an integer or
  boolean.  If ~t~, then the count is determined once the children have been
  inserted, using ~magit-insert-child-count~ (which see).  For historic
  reasons, if the heading ends with ":", the count is substituted for
  that, at this time as well.  If ~magit-section-show-child-count~ is ~nil~,
  no counts are inserted

- Macro: magit-insert-section-body &rest body ::

  Use BODY to insert the section body, once the section is expanded.
  If the section is expanded when it is created, then this is
  like ~progn~.  Otherwise BODY isn't evaluated until the section
  is explicitly expanded.

- Function: magit-cancel-section ::

  Cancel inserting the section that is currently being inserted.
  Remove all traces of that section.

- Function: magit-wash-sequence function ::

  Repeatedly call FUNCTION until it returns ~nil~ or the end of the
  buffer is reached.  FUNCTION has to move point forward or return
  ~nil~.

You have to define some function that calls ~magit-insert-section~ to
populate a buffer with sections.  After doing so, that function also
has to call a few other functions, to put the sections in a good
initial state.  You will likely need these lines:

#+begin_src emacs-lisp
  (let ((magit-section-cache-visibility nil))
    (magit-section-show magit-root-section))
  (magit-section-update-highlight)
  (set-buffer-modified-p nil)
#+end_src

Magit does that in ~magit-refresh-buffer~.  Look at that function for
inspiration, and also check out how that function is being used in in
~magit-mode.el~.  The code in that library is to specialized to Magit's
needs to be made part of the ~magit-section~ package, but a magit-like
package will likely have to perform mode and buffer setup in a similar
fashion.

* Core Functions

- Function: magit-current-section ::

  Return the section at point or where the context menu was invoked.
  When using the context menu, return the section that the user
  clicked on, provided the current buffer is the buffer in which
  the click occurred.  Otherwise return the section at point.

- Function magit-section-at &optional position ::

  Return the section at POSITION, defaulting to point.  Default to
  point even when the context menu is used.

- Function: magit-section-ident section ::

  Return an unique identifier for SECTION. The return value has the
  form ~((TYPE . VALUE)...)~.

- Function: magit-section-ident-value value ::

  Return a constant representation of VALUE.

  VALUE is the value of a ~magit-section~ object.  If that is an
  object itself, then that is not suitable to be used to identify
  the section because two objects may represent the same thing but
  not be equal.  If possible a method should be added for such
  objects, which returns a value that is equal.  Otherwise the
  catch-all method is used, which just returns the argument
  itself.

- Function: magit-get-section ident &optional root ::

  Return the section identified by IDENT.
  IDENT has to be a list as returned by ~magit-section-ident~.
  If optional ROOT is non-~nil~, then search in that section tree
  instead of in the one whose root ~magit-root-section~ is.

- Function: magit-section-lineage section &optional raw ::

  Return the lineage of SECTION.
  If optional RAW is non-~nil~, return a list of section objects,
  beginning with SECTION, otherwise return a list of section types.

- Function: magit-section-content-p section ::

  Return non-~nil~ if SECTION has content or an unused washer function.

The next two functions are replacements for the Emacs functions that
have the same name except for the ~magit-~ prefix.  Like
~magit-current-section~ they do not act on point, the cursors position,
but on the position where the user clicked to invoke the context menu.

If your package provides a context menu and some of its commands act
on the "thing at point", even if just as a default, then use the
prefixed functions to teach them to instead use the click location
when appropriate.

- Function magit-point ::

  Return point or the position where the context menu was invoked.
  When using the context menu, return the position the user clicked
  on, provided the current buffer is the buffer in which the click
  occurred.  Otherwise return the same value as ~point~.

- Function magit-thing-at-point thing &optional no-properties ::

  Return the THING at point or where the context menu was invoked.
  When using the context menu, return the thing the user clicked
  on, provided the current buffer is the buffer in which the click
  occurred.  Otherwise return the same value as ~thing-at-point~.
  For the meaning of THING and NO-PROPERTIES see that function.

* Matching Functions

- Function: magit-section-match condition &optional (section (magit-current-section)) ::

  Return ~t~ if SECTION matches CONDITION.

  SECTION defaults to the section at point.  If SECTION is not
  specified and there also is no section at point, then return
  ~nil~.

  CONDITION can take the following forms:

  - ~(CONDITION...)~ matches if any of the CONDITIONs matches.
  - ~[CLASS...]~ matches if the section's class is the same
                  as the first CLASS or a subclass of that;
                  the section's parent class matches the
                  second CLASS; and so on.

  - ~[* CLASS...]~ matches sections that match [CLASS...] and
                  also recursively all their child sections.
  - ~CLASS~ matches if the section's class is the same
                  as CLASS or a subclass of that; regardless
                  of the classes of the parent sections.

  Each CLASS should be a class symbol, identifying a class that
  derives from ~magit-section~.  For backward compatibility CLASS
  can also be a "type symbol".  A section matches such a symbol
  if the value of its ~type~ slot is ~eq~.  If a type symbol has
  an entry in ~magit--section-type-alist~, then a section also
  matches that type if its class is a subclass of the class that
  corresponds to the type as per that alist.

  Note that it is not necessary to specify the complete section
  lineage as printed by ~magit-describe-section-briefly~, unless
  of course you want to be that precise.

- Function: magit-section-value-if condition &optional section ::

  If the section at point matches CONDITION, then return its value.

  If optional SECTION is non-~nil~ then test whether that matches
  instead.  If there is no section at point and SECTION is ~nil~,
  then return ~nil~.  If the section does not match, then return
  ~nil~.

  See ~magit-section-match~ for the forms CONDITION can take.

- Macro: magit-section-case &rest clauses ::

  Choose among clauses on the type of the section at point.

  Each clause looks like ~(CONDITION BODY...)~.  The type of the
  section is compared against each CONDITION; the BODY forms of the
  first match are evaluated sequentially and the value of the last
  form is returned.  Inside BODY the symbol ~it~ is bound to the
  section at point.  If no clause succeeds or if there is no
  section at point, return ~nil~.

  See ~magit-section-match~ for the forms CONDITION can take.
  Additionally a CONDITION of ~t~ is allowed in the final clause, and
  matches if no other CONDITION match, even if there is no section
  at point.

* Copying
:PROPERTIES:
:COPYING:    t
:END:

#+begin_quote
Copyright (C) 2015-{{{year}}} Jonas Bernoulli <emacs.magit@jonas.bernoulli.dev>

You can redistribute this document and/or modify it under the terms
of the GNU General Public License as published by the Free Software
Foundation, either version 3 of the License, or (at your option) any
later version.

This document 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.
#+end_quote

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