bug#28926: 26.0.90; java-mode hangs on "<"

[detlevvandaele <detlev.vandaele@gmail.com>]

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Hello,

recently I've been trying to get a decent java environment set-up for
emacs, and I've noticed that whenever I open a java buffer and type
"<" for the first time, the emacs process hangs indefinitely.

Quitting out with C-g then inserts the character, and no further issues
arise so long as the buffer is not reverted (meaning I can then insert
as many "<" as I want without hanging).
Reverting the buffer or opening a new java buffer re-introduces the issue.

I can personally reproduce this bug on both my macbook pro running macOS High
Sierra and my Arch Linux machine with emacs version 26.0.90.
The bug does not seem to occur on emacs 25.3.2 on either OS.

Steps to reproduce:
1. Start emacs -Q
2. Open an arbitrary java file (e.g. test.java)
3. Type an opening "<"

Alternatively:
1. Start emacs -Q
2. Open up the *scratch* buffer
3. Activate java-mode (M-x java-mode)
4. Type an opening "<"

Perceived result: emacs hangs indefinitely until the current command is quit.
Expected result: immediate insertion of the "<" character without freezing/hanging.


In GNU Emacs 26.0.90 (build 2, x86_64-apple-darwin17.0.0, NS appkit-1561.00 Version 10.13 (Build 17A405))
of 2017-10-13 built on Detlevs-MBP.kelder.zeus.ugent.be
Repository revision: 716b84034d10b8cae5d721173108c4c299f66ed0
Windowing system distributor 'Apple', version 10.3.1561

Configured using:
'configure --with-ns --with-gnutls --with-mailutils --with-modules
--with-dbus --with-imagemagick --with-jpeg'

Configured features:
JPEG RSVG DBUS NOTIFY ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS
MODULES LCMS2

Important settings:
value of $LANG: en_BE.UTF-8
locale-coding-system: utf-8-unix

Major mode: Emacs-Lisp

Minor modes in effect:
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recentf-mode: t
global-semanticdb-minor-mode: t
global-semantic-idle-scheduler-mode: t
semantic-mode: t
ivy-mode: t
shell-dirtrack-mode: t
savehist-mode: t
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diff-auto-refine-mode: t
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perspeen-mode: t
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git-gutter-mode: t
projectile-mode: t
show-paren-mode: t
smartparens-mode: t
global-undo-tree-mode: t
undo-tree-mode: t
which-key-mode: t
yas-global-mode: t
yas-minor-mode: t
company-quickhelp-mode: t
company-quickhelp-local-mode: t
global-company-mode: t
company-mode: t
global-flycheck-mode: t
flycheck-mode: t
which-function-mode: t
global-aggressive-indent-mode: t
aggressive-indent-mode: t
indent-guide-global-mode: t
indent-guide-mode: t
global-hl-line-mode: t
delete-selection-mode: t
override-global-mode: t
cl-old-struct-compat-mode: t
tooltip-mode: t
global-eldoc-mode: t
eldoc-mode: t
electric-indent-mode: t
mouse-wheel-mode: t
menu-bar-mode: t
file-name-shadow-mode: t
global-font-lock-mode: t
font-lock-mode: t
auto-composition-mode: t
auto-encryption-mode: t
auto-compression-mode: t
size-indication-mode: t
column-number-mode: t
line-number-mode: t
global-visual-line-mode: t
visual-line-mode: t
transient-mark-mode: t

Load-path shadows:
None found.

Features:
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Memory information:
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