147 lines
8.1 KiB
EmacsLisp
147 lines
8.1 KiB
EmacsLisp
;;; early-init.el --- Doom's universal bootstrapper -*- lexical-binding: t -*-
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;;; Commentary:
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;;
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;; This file, in summary:
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;; - Determines where `user-emacs-directory' is by:
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;; - Processing `--init-directory DIR' (backported from Emacs 29),
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;; - Processing `--profile NAME' (see
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;; `https://docs.doomemacs.org/-/developers' or docs/developers.org),
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;; - Or assume that it's the directory this file lives in.
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;; - Loads Doom as efficiently as possible, with only the essential startup
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;; optimizations, and prepares it for interactive or non-interactive sessions.
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;; - If Doom isn't present, then we assume that Doom is being used as a
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;; bootloader and the user wants to load a non-Doom config, so we undo all our
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;; global side-effects, load `user-emacs-directory'/early-init.el, and carry
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;; on as normal (without Doom).
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;; - Do all this without breaking compatibility with Chemacs.
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;;
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;; early-init.el was introduced in Emacs 27.1. It is loaded before init.el,
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;; before Emacs initializes its UI or package.el, and before site files are
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;; loaded. This is great place for startup optimizing, because only here can you
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;; *prevent* things from loading, rather than turn them off after-the-fact.
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;;
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;; Doom uses this file as its "universal bootstrapper" for both interactive and
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;; non-interactive sessions. That means: no matter what environment you want
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;; Doom in, load this file first.
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;;
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;;; Code:
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;; PERF: Garbage collection is a big contributor to startup times. This fends it
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;; off, but will be reset later by `gcmh-mode' (or in doom-cli.el, if in a
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;; noninteractive session). Not resetting it later causes stuttering/freezes.
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(setq gc-cons-threshold most-positive-fixnum)
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;; PERF: Don't use precious startup time checking mtime on elisp bytecode.
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;; Ensuring correctness is 'doom sync's job, not the interactive session's.
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;; Still, stale byte-code will cause *heavy* losses in startup efficiency, but
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;; performance is unimportant when Emacs is in an error state.
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(setq load-prefer-newer noninteractive)
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;; UX: Respect DEBUG envvar as an alternative to --debug-init, and to make
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;; startup sufficiently verbose from this point on.
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(when (getenv-internal "DEBUG")
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(setq init-file-debug t
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debug-on-error t))
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;;
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;;; Bootstrap
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(or
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;; PERF: `file-name-handler-alist' is consulted often. Unsetting it offers a
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;; notable saving in startup time. This is just a stopgap though; this
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;; optimization is continued more comprehensively in lisp/doom.el.
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(let (file-name-handler-alist)
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(let (;; FIX: Unset `command-line-args' in noninteractive sessions, to
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;; ensure upstream switches aren't misinterpreted.
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(command-line-args (unless noninteractive command-line-args))
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;; I avoid using `command-switch-alist' to process --profile (and
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;; --init-directory) because it is processed too late to change
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;; `user-emacs-directory' in time.
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(profile (or (cadr (member "--profile" command-line-args))
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(getenv-internal "DOOMPROFILE"))))
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(if (null profile)
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;; REVIEW: Backported from Emacs 29. Remove when 28 support is dropped.
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(let ((init-dir (or (cadr (member "--init-directory" command-line-args))
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(getenv-internal "EMACSDIR"))))
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(if (null init-dir)
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;; FIX: If we've been loaded directly (via 'emacs -batch -l
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;; early-init.el') or by a doomscript (like bin/doom), and Doom
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;; is in a non-standard location (and/or Chemacs is used), then
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;; `user-emacs-directory' will be wrong.
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(when noninteractive
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(setq user-emacs-directory
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(file-name-directory (file-truename load-file-name))))
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;; FIX: To prevent "invalid option" errors later.
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(push (cons "--init-directory" (lambda (_) (pop argv))) command-switch-alist)
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(setq user-emacs-directory (expand-file-name init-dir))))
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;; FIX: Discard the switch to prevent "invalid option" errors later.
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(push (cons "--profile" (lambda (_) (pop argv))) command-switch-alist)
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;; Running 'doom sync' or 'doom profile sync' (re)generates a light
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;; profile loader in $EMACSDIR/profiles/load.el (or
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;; $DOOMPROFILELOADFILE), after reading `doom-profile-load-path'. This
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;; loader requires `$DOOMPROFILE' be set to function.
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(setenv "DOOMPROFILE" profile)
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(or (load (expand-file-name
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(format (let ((lfile (getenv-internal "DOOMPROFILELOADFILE")))
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(if lfile
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(concat (let ((suffix ".el"))
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(if (string-suffix-p suffix lfile)
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(substring lfile 0 (- (length lfile) (length suffix)))
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lfile))
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".%d.elc")
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"profiles/load.%d.elc"))
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emacs-major-version)
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user-emacs-directory)
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'noerror (not init-file-debug) 'nosuffix)
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(user-error "Profiles not initialized yet; run 'doom sync' first"))))
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;; PERF: When `load'ing or `require'ing files, each permutation of
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;; `load-suffixes' and `load-file-rep-suffixes' (then `load-suffixes' +
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;; `load-file-rep-suffixes') is used to locate the file. Each permutation
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;; amounts to at least one file op, which is normally very fast, but can
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;; add up over the hundreds/thousands of files Emacs loads.
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;;
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;; To reduce that burden -- and since Doom doesn't load any dynamic modules
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;; this early -- I remove `.so' from `load-suffixes' and pass the
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;; `must-suffix' arg to `load'. See the docs of `load' for details.
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(if (let ((load-suffixes '(".elc" ".el")))
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;; I avoid `load's NOERROR argument because it suppresses other,
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;; legitimate errors (like permission or IO errors), which gets
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;; incorrectly interpreted as "this is not a Doom config".
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(condition-case-unless-debug _
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;; Load the heart of Doom Emacs.
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(load (expand-file-name "lisp/doom" user-emacs-directory)
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nil (not init-file-debug) nil 'must-suffix)
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;; Failing that, assume that we're loading a non-Doom config.
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(file-missing
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;; HACK: `startup--load-user-init-file' resolves $EMACSDIR from a
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;; lexical (and so, not-trivially-modifiable)
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;; `startup-init-directory', so Emacs will fail to locate the
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;; correct $EMACSDIR/init.el without help.
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(define-advice startup--load-user-init-file (:filter-args (args) reroute-to-profile)
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(list (lambda () (expand-file-name "init.el" user-emacs-directory))
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nil (nth 2 args)))
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;; (Re)set `user-init-file' for the `load' call further below, and
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;; do so here while our `file-name-handler-alist' optimization is
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;; still effective (benefits `expand-file-name'). BTW: Emacs resets
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;; `user-init-file' and `early-init-file' after this file is loaded.
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(setq user-init-file (expand-file-name "early-init" user-emacs-directory))
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;; COMPAT: I make no assumptions about the config we're going to
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;; load, so undo this file's global side-effects.
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(setq load-prefer-newer t)
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;; PERF: But make an exception for `gc-cons-threshold', which I
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;; think all Emacs users and configs will benefit from. Still,
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;; setting it to `most-positive-fixnum' is dangerous if downstream
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;; does not reset it later to something reasonable, so I use 16mb
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;; as a best fit guess. It's better than Emacs' 80kb default.
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(setq gc-cons-threshold (* 16 1024 1024))
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nil)))
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;; ...Otherwise, we're loading a Doom config, so continue as normal.
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(doom-require (if noninteractive 'doom-cli 'doom-start))))
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;; Then continue on to the config/profile we want to load.
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(load user-init-file 'noerror (not init-file-debug) nil 'must-suffix))
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;;; early-init.el ends here
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