GNU bug report logs - #79626
30.1; Java programming modes handling of "var" keyword

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Robert Brown <robert.brown <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 30.1; Java programming modes handling of "var" keyword
Date: Tue, 14 Oct 2025 14:25:11 -0400

[Message part 1 (text/plain, inline)]

When fontifying the following Java code:

package mystuff;
import static foo.bar.Struct;
class MyClass {
    void func() {
        var foo = 100;
    }
}

java-mode and java-ts-mode display the "var" Java keyword right before "foo"
using font-lock-type-face.  In comparison, cc-mode fontifies semantically
similar uses of "auto" to omit a type using font-lock-keyword-face.

"var" is a keyword in Java, not a type, just as "auto" is a keyword in C++,
so
it would be better to fontify it using font-lock-keyword-face.


In GNU Emacs 30.1 (build 4, x86_64-pc-linux-gnu) of 2025-02-23 built on
 chuwi
System Description: Ubuntu 24.04.3 LTS

Configured using:
 'configure --without-x
 --prefix=/home/brown/local/software/package/emacs-30.1'

Configured features:
DBUS GMP GNUTLS LIBSELINUX LIBSYSTEMD LIBXML2 MODULES NATIVE_COMP NOTIFY
INOTIFY PDUMPER SECCOMP SOUND THREADS TREE_SITTER XIM ZLIB

Important settings:
  value of $LC_COLLATE: C
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Completion List

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  minibuffer-regexp-mode: t
  buffer-read-only: t
  line-number-mode: t
  cursor-face-highlight-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
/home/brown/local/software/source/slime/slime-tests hides
/home/brown/.emacs.d/elpa/slime-20240323.141/slime-tests
/home/brown/local/software/source/slime/slime-autoloads hides
/home/brown/.emacs.d/elpa/slime-20240323.141/slime-autoloads
/home/brown/local/software/source/slime/slime hides
/home/brown/.emacs.d/elpa/slime-20240323.141/slime
/home/brown/lib/emacs/lisp/yow hides
/home/brown/local/software/package/emacs-30.1/share/emacs/30.1/lisp/obsolete/yow

Features:
(shadow sort mail-extr cl-extra warnings display-line-numbers ebuff-menu
emacsbug message yank-media puny dired dnd dired-loaddefs rfc822 mml
mml-sec epa derived epg rfc6068 epg-config gnus-util
text-property-search time-date mm-decode mm-bodies mm-encode mail-parse
rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mail-utils mule-util apropos crm thingatpt
help-fns radix-tree help-mode cap-words superword subword cc-mode
cc-fonts cc-guess cc-menus cc-cmds java-ts-mode c-ts-common treesit
term/xterm xterm company-oddmuse company-keywords company-etags etags
fileloop generator xref project ring company-gtags company-dabbrev-code
company-dabbrev company-files company-clang company-capf company-cmake
company-semantic company-template company-bbdb company pcase cc-styles
cc-align cc-engine cc-vars cc-defs regexp-opt rx dash-autoloads
ement-autoloads persist-autoloads plz-autoloads slime-company-autoloads
slime-autoloads macrostep-autoloads svg-lib-autoloads
taxy-magit-section-autoloads taxy-autoloads info tool-bar
magit-section-autoloads llama-autoloads package browse-url url url-proxy
url-privacy url-expand url-methods url-history url-cookie
generate-lisp-file url-domsuf url-util mailcap url-handlers url-parse
auth-source cl-seq eieio eieio-core cl-macs icons password-cache json
subr-x map byte-opt gv bytecomp byte-compile url-vars cl-loaddefs cl-lib
rmc iso-transl tooltip cconv eldoc paren electric uniquify ediff-hook
vc-hooks lisp-float-type elisp-mode tabulated-list replace newcomment
text-mode lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow
isearch easymenu timer select mouse jit-lock font-lock syntax font-core
term/tty-colors frame minibuffer nadvice seq simple cl-generic
indonesian philippine cham georgian utf-8-lang misc-lang vietnamese
tibetan thai tai-viet lao korean japanese eucjp-ms cp51932 hebrew greek
romanian slovak czech european ethiopic indian cyrillic chinese
composite emoji-zwj charscript charprop case-table epa-hook
jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button loaddefs
theme-loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget keymap
hashtable-print-readable backquote threads dbusbind inotify multi-tty
make-network-process native-compile emacs)

Memory information:
((conses 16 155709 250114) (symbols 48 12179 99) (strings 32 41281 14457)
 (string-bytes 1 1412937) (vectors 16 18140) (vector-slots 8 213127 63218)
 (floats 8 72 88) (intervals 56 827 426) (buffers 992 15))

[Message part 2 (text/html, inline)]

Message #8 received at 79626 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Robert Brown <robert.brown <at> gmail.com>,
 Theodor Thornhill <theo <at> thornhill.no>, Yuan Fu <casouri <at> gmail.com>
Cc: 79626 <at> debbugs.gnu.org
Subject: Re: bug#79626: 30.1; Java programming modes handling of "var" keyword
Date: Tue, 14 Oct 2025 22:28:47 +0300

> From: Robert Brown <robert.brown <at> gmail.com>
> Date: Tue, 14 Oct 2025 14:25:11 -0400
> 
> When fontifying the following Java code:
> 
> package mystuff;
> import static foo.bar.Struct;
> class MyClass {
>     void func() {
>         var foo = 100;
>     }
> }
> 
> java-mode and java-ts-mode display the "var" Java keyword right before "foo"
> using font-lock-type-face.  In comparison, cc-mode fontifies semantically
> similar uses of "auto" to omit a type using font-lock-keyword-face.
> 
> "var" is a keyword in Java, not a type, just as "auto" is a keyword in C++, so
> it would be better to fontify it using font-lock-keyword-face.

Thanks.

If you enable treesit-explore-mode, you will see that the Javae
tree-sitter grammar identifies 'var' as 'type_identifier' node.  So
maybe the the problem is in the grammar library, not in Emacs?  Or
maybe we should add "var" to java-ts-mode--keywords?  Theodor and
Yuan, WDYT?

Message #11 received at 79626 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Yuan Fu <casouri <at> gmail.com>, theo <at> thornhill.no
Cc: robert.brown <at> gmail.com, 79626 <at> debbugs.gnu.org
Subject: Re: bug#79626: 30.1; Java programming modes handling of "var" keyword
Date: Sat, 01 Nov 2025 11:00:22 +0200

Ping!  Yuan and Theo, could you please chime in on this issue?

> Cc: 79626 <at> debbugs.gnu.org
> Date: Tue, 14 Oct 2025 22:28:47 +0300
> From: Eli Zaretskii <eliz <at> gnu.org>
> 
> > From: Robert Brown <robert.brown <at> gmail.com>
> > Date: Tue, 14 Oct 2025 14:25:11 -0400
> > 
> > When fontifying the following Java code:
> > 
> > package mystuff;
> > import static foo.bar.Struct;
> > class MyClass {
> >     void func() {
> >         var foo = 100;
> >     }
> > }
> > 
> > java-mode and java-ts-mode display the "var" Java keyword right before "foo"
> > using font-lock-type-face.  In comparison, cc-mode fontifies semantically
> > similar uses of "auto" to omit a type using font-lock-keyword-face.
> > 
> > "var" is a keyword in Java, not a type, just as "auto" is a keyword in C++, so
> > it would be better to fontify it using font-lock-keyword-face.
> 
> Thanks.
> 
> If you enable treesit-explore-mode, you will see that the Javae
> tree-sitter grammar identifies 'var' as 'type_identifier' node.  So
> maybe the the problem is in the grammar library, not in Emacs?  Or
> maybe we should add "var" to java-ts-mode--keywords?  Theodor and
> Yuan, WDYT?
> 
> 
> 
> 

Message #16 received at 79626-done <at> debbugs.gnu.org (full text, mbox):

From: Yuan Fu <casouri <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: robert.brown <at> gmail.com, theo <at> thornhill.no, 79626-done <at> debbugs.gnu.org
Subject: Re: bug#79626: 30.1; Java programming modes handling of "var" keyword
Date: Sun, 2 Nov 2025 14:33:25 -0800

> On Nov 1, 2025, at 2:00 AM, Eli Zaretskii <eliz <at> gnu.org> wrote:
> 
> Ping!  Yuan and Theo, could you please chime in on this issue?
> 
>> Cc: 79626 <at> debbugs.gnu.org
>> Date: Tue, 14 Oct 2025 22:28:47 +0300
>> From: Eli Zaretskii <eliz <at> gnu.org>
>> 
>>> From: Robert Brown <robert.brown <at> gmail.com>
>>> Date: Tue, 14 Oct 2025 14:25:11 -0400
>>> 
>>> When fontifying the following Java code:
>>> 
>>> package mystuff;
>>> import static foo.bar.Struct;
>>> class MyClass {
>>>    void func() {
>>>        var foo = 100;
>>>    }
>>> }
>>> 
>>> java-mode and java-ts-mode display the "var" Java keyword right before "foo"
>>> using font-lock-type-face.  In comparison, cc-mode fontifies semantically
>>> similar uses of "auto" to omit a type using font-lock-keyword-face.
>>> 
>>> "var" is a keyword in Java, not a type, just as "auto" is a keyword in C++, so
>>> it would be better to fontify it using font-lock-keyword-face.
>> 
>> Thanks.
>> 
>> If you enable treesit-explore-mode, you will see that the Javae
>> tree-sitter grammar identifies 'var' as 'type_identifier' node.  So
>> maybe the the problem is in the grammar library, not in Emacs?  Or
>> maybe we should add "var" to java-ts-mode--keywords?  Theodor and
>> Yuan, WDYT?

Thanks for the ping. I thought there’s only one report on java-ts-mode. So the java grammar is correct, Java treats the var syntax as a type, rather than a keyword. It’s a special non-determined type that will be figured out by the compiler. I added a special rule to fontify it.

Yuan

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