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I want to see the source code of the function other-buffer. When I use M-x- xref-find-definitions, Emacs shows:visit tags table (default TAGS). Then I press RET, Emacs shows:File /TAGS does not exist.
What should I do if I want to see the source code?
I'm reading an introduction book and I got stuck with the expression:
(other-buffer (current-buffer) t)
This is why I want to see the source code. And this is my second day learning Emacs.

System: macOS

Lluvio Liu
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2 Answers2

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Usually the way to do that is to type M-x describe-function in the minibuffer, then enter other-buffer. That will show you a help window on the function with the documentation on that function. At the top is usually a link to the source code of the function you can click on to get there. other-buffer is implemented in the C source code though so you unless you installed emacs from source you probably can't get to it this way.

John Kitchin
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  • There's been discussion about *always* installing the C-sources precisely for this use case. Disk space is cheap after all (but the distributions would probably just strip it out again ) – rpluim Jan 14 '21 at 10:48
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    See also `M-x find-function RET`. – Basil Jan 14 '21 at 11:26
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Unless you've compiled your Emacs you have to download the C source code separately. If you're on GNU, some distros allow downloading the source code using the package manager, which makes upgrading a bit easier. For example here's a tutorial for installing the source code on Fedora.

Once you have the source code tree in a directory, say ~/src/emacs-27.1/src, add

(setq find-function-C-source-directory (concat "~/src/emacs-" emacs-version "/src"))

to your init.el. The (concat "~/src/emacs-" emacs-version "/src") bit evaluates to "~/src/emacs-27.1/src" (assuming your Emacs is version 27.1), so you don't need to update this setting when you upgrade Emacs. The variable find-function-C-source-directory stores the directory Emacs looks into for the C source files (see C-hv find-function-C-source-directory).

Since you're on MacOS I can't suggest anything in particular but to try

git clone https://git.savannah.gnu.org/git/emacs.git

That should get you the full source tree. Place it on a directory of your choice and set find-function-C-source-directory, then both xref-find-definitions and links in describe-function/describe-variable (C-h f/C-h v) and should work.

Arch Stanton
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