Bug 1629708 - Port emacs docs to the in-tree docs. r=sylvestre

Differential Revision: https://phabricator.services.mozilla.com/D71052

--HG--
extra : moz-landing-system : lando

docs/contributing/editor.rst

@@ -82,6 +82,140 @@ also do that automatically:
 
     let g:syntastic_javascript_eslint_exec = 'eslint_d'
 
+Emacs
+-----
+
+Mozilla-specific packages
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+dxr.el
+^^^^^^
+
+dxr.el is an elisp package that enables searching of DXR Code Indexer results
+from within emacs. Using this can sometimes be easier than doing localized code
+indexing with rtags, as rtags processing of code trees can be very processing
+intensive.
+
+dxr.el is available via `github repo <https://github.com/tromey/dxr.el>`__, or
+via the Marmalade package manager.
+
+ESLint
+~~~~~~
+
+See `the devtools documentation <https://wiki.mozilla.org/DevTools/CodingStandards#Running_ESLint_in_Emacs>`__
+that describes how to integrate ESLint into Emacs.
+
+C/C++ Development Packages
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+General Guidelines to Emacs C++ Programming
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The following guides give an overview of the C++ editing capabilities of emacs.
+
+It is worth reading through these guides to see what features are available.
+The rest of this section is dedicated to Mozilla/Gecko specific setup for
+packages.
+
+
+  * `C/C++ Development Environment for Emacs <https://tuhdo.github.io/c-ide.html>`__
+  * `Emacs as C++ IDE <https://syamajala.github.io/c-ide.html>`__
+
+rtags (LLVM/Clang-based Code Indexing)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Instructions for the installation of rtags are available at the
+`rtags github repo <https://github.com/Andersbakken/rtags>`__.
+
+rtags requires a :ref:`compilation database <CompileDB back-end / compileflags>`.
+
+In order for rtags to index correctly, included files need to be copied and
+unified compilation files need to be created. Either run a full build of the
+tree, or if you only want indexes to be generated for the moment, run the
+following commands (assuming you're in the gecko repo root):
+
+.. code::
+    cd gecko_build_directory
+    make export
+    ./config.status
+
+To increase indexing speed, it's best to remove unified build files and test
+files from database updates. This can be done by creating a :code:`~/.rdmrc`
+file with the following contents, with :code:`[src_dir]` replaced with either
+the repo or build directory for your checkout:
+
+.. code::
+
+    -X */[src_dir]/*Unified*;*/[src_dir]/*/test/*;*/[src_dir]/*/tests/*
+
+Once the rdm daemon is running, the compilation database can be added to rtags
+like so:
+
+.. code::
+
+    rc -J [gecko_build_directory]/compile_commands.json
+
+Note that this process will take a while initially. However, once the database
+is built, it will only require incremental updates. As long as the rdm daemon
+is running in the background, the database will be updated based on changes to
+files.
+
+irony (LLVM/Clang-based Code Completion)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Instructions on the installation of irony-mode are available at the
+`irony-mode github repo <https://github.com/Sarcasm/irony-mode>`__.
+
+irony-mode requires a :ref:`compilation database <CompileDB back-end / compileflags>`.
+
+Note that irony-mode, by default, uses elisp to parse the
+:code:`compile_commands.json` file. As gecko is a very large codebase, this
+file can easily be multiple megabytes, which can make irony-mode take multiple
+seconds to load on a gecko file.
+
+It is recommended to use `this fork of irony-mode <https://github.com/Hylen/irony-mode/tree/compilation-database-guessing-4-pull-request>`__,
+which requires the boost System and Filesystem libraries.
+
+`Checking the bug to get this patch into the mainline of irony-mode <https://github.com/Sarcasm/irony-mode/issues/176>`__
+is recommended, to see if the fork can be used or if the mainline repo can be
+used. Using the Boost version of the irony-mode server brings file load times
+to under 1s.
+
+Projectile (Project Management)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Instructions on the installation of projectile are available at the
+`projectile github repo <https://github.com/bbatsov/projectile>`__.
+
+Projectile comes preconfigured for many project types. Since, gecko uses its
+own special build system (mach), a new project type needs to be added. This can
+be done via adding the following elisp configuration command to your emacs
+configuration file.
+
+.. code::
+
+    (projectile-register-project-type 'gecko
+                                      '("mach" "moz.build")
+                                      "python mach --log-no-times build"
+                                      "python mach mochitest"
+                                      "python mach run")
+
+Assuming projectile-global-mode is on, this will allow projectile to run the
+correct commands whenever it is working in a gecko repo.
+
+gdb
+^^^
+
+Emacs comes with great integration with gdb, especially when using
+`gdb-many-windows <https://www.gnu.org/software/emacs/manual/html_node/emacs/GDB-User-Interface-Layout.html>`__.
+
+However, when gdb is invoked via mach, some special arguments
+need to be passed in order to make sure the correct display mode is used. To
+use M-x gdb with mach on firefox, use the following command:
+
+.. code::
+
+    gecko_repo_directory/mach run --debug --debugparams=-i=mi
 
 Eclipse
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