emacs: resolve wrapper load-path at build time
Since the included package set is determined at build time we can also generate the `subdirs.el` file at build time. This improves startup time somewhat since we don't have to traverse the directory to add to `load-path`. For example, ``` sh-session $ bench './emacs-old -Q --batch --kill' './emacs-new -Q --batch --kill' benchmarking bench/./emacs-old -Q --batch --kill time 72.77 ms (71.66 ms .. 73.65 ms) 1.000 R² (0.999 R² .. 1.000 R²) mean 72.49 ms (72.06 ms .. 72.92 ms) std dev 746.5 μs (582.4 μs .. 1.008 ms) benchmarking bench/./emacs-new -Q --batch --kill time 40.56 ms (40.24 ms .. 40.86 ms) 1.000 R² (0.999 R² .. 1.000 R²) mean 40.30 ms (40.12 ms .. 40.51 ms) std dev 401.9 μs (311.1 μs .. 555.8 μs) ``` The change does not actually affect the content of `load-path`: ``` sh-session $ diff -s <(./emacs-old --batch --eval '(prin1 load-path)' | sed -E 's!/nix/store/[[:alnum:]]{32}-!!g') \ <(./emacs-new --batch --eval '(prin1 load-path)' | sed -E 's!/nix/store/[[:alnum:]]{32}-!!g') Files /dev/fd/63 and /dev/fd/62 are identical ``` So in principle the only observable effect should be the improved startup time.
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pkgs/build-support/emacs/mk-wrapper-subdirs.el
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pkgs/build-support/emacs/mk-wrapper-subdirs.el
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@ -0,0 +1,6 @@
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(defmacro mk-subdirs-expr (path)
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`(setq load-path
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(delete-dups (append '(,path)
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',(let ((default-directory path))
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(normal-top-level-add-subdirs-to-load-path))
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load-path))))
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@ -165,8 +165,13 @@ runCommand
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(add-to-list 'native-comp-eln-load-path "$out/share/emacs/native-lisp/")
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''}
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EOF
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# Link subdirs.el from the emacs distribution
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ln -s $emacs/share/emacs/site-lisp/subdirs.el -T $subdirs
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# Generate a subdirs.el that statically adds all subdirectories to load-path.
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$emacs/bin/emacs \
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--batch \
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--load ${./mk-wrapper-subdirs.el} \
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--eval "(prin1 (macroexpand-1 '(mk-subdirs-expr \"$out/share/emacs/site-lisp\")))" \
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> "$subdirs"
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# Byte-compiling improves start-up time only slightly, but costs nothing.
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$emacs/bin/emacs --batch -f batch-byte-compile "$siteStart" "$subdirs"
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