Error "Symbol's function definition is void: json-parse-string" in Emacs 27.2

[taquangtrung]

Hi,

I'm using Emacs 27.2 and when double-clicking to a node, Org-roam UI failed to open the file in Emacs, and threw this error:

Error (websocket): in callback `on-message': Symbol's function definition is void: json-parse-string

I checked the library /usr/local/share/emacs/27.2/lisp/json.el.gz and couldn't find the function json-parse-string.

Could you advise where that function comes from?

[tefkah]

It says here in the Elisp manual that you need an Emacs compiled with JSON support, which most ways of obtaining Emacs should come with. Notable exception is probably the Windows versions, maybe this thread can help? Let me know if it does, I will add it to the readme.

https://www.reddit.com/r/emacs/comments/d52vlg/anyone_compiled_emacs_on_windows_with_jansson/

[nobiot]

Windows binary from the official site has no problem on 27.2, which I use; at least I don't have this issue.

[nobiot]

Looking at this path, though, it's not a Windows system.

/usr/local/share/emacs/27.2/lisp/json.el.gz

[tefkah]

Yeah that makes sense. Then maybe on of the package managers does not include Emacs with JSON support?

[taquangtrung]

@ThomasFKJorna @nobiot : Thank you for the pointer!

I'm using Linux 20.2 and compile Emacs 27.2 from source code. I just realized from this website (https://www.masteringemacs.org/article/speed-up-emacs-libjansson-native-elisp-compilation) that I need to install libjansson before running configure Emacs to have native JSON support.

$ sudo apt-get install -y libjansson4 libjansson-dev

$ ./configure
# output of configure
# ...
# Does Emacs use -ljansson?                               yes

Now everything works fine. The function json-parse-string comes from emacs/src/json.c.

[tefkah]

Great!

[santosardr]

Despite being closed, I want to confirm this problem in Ubuntu 22.04 LTS. I compiled GNU Emacs 30.0.50 on two machines with 20.04 and 22.04. I perceived the problem only at the 22.04 LTS. However, I am still trying to figure out the reason.