bug#44319: make mode should recognize ::= as a macro assignment

bug#44319: make mode should recognize ::= as a macro assignment

[Robert Lange via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Using the following simple Makefile as an example:

Begin file Makefile
---
ELC_FILES ::= foo.elc

all: $(ELC_FILES)

.el.elc:
	$(EMACS) -batch -Q -L . -f batch-byte-compile "$<"
---
End file Makefile

I've tested this on Emacs 26.1 on Debian, as well as a self-compiled 27.1. When I use the GNU immediate assignment operator `:=` the macro name ELC_FILES is correctly shown in font-lock in the macro color. But if I use the POSIX standard `::=` (well, forthcoming POSIX standard, but  GNU emacs has supported it since v4.0) ELC_FILES is incorrectly shown in the target color.

Looking in lisp/progmodes/make-mode.el, the const makefile-macroassign-regex is pretty gnarly, but I *think* it should match a `::=`, so I'm assuming it's getting preempted by something else, probably the const makefile-dependency-regex. Unfortunately, that regexp is a bit more than I can interpret, and I don't dare change it because I'll almost certainly break some other obscure but legal cases.

I'd appreciate any insights anyone has on this.

--Rob Lange


---
In GNU Emacs 26.1 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.5)
 of 2019-09-22, modified by Debian built on x86-grnet-01
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description:	Debian GNU/Linux 10 (buster)

Recent messages:
Loading /etc/emacs/site-start.d/50texlive-lang-english.el (source)...done
Loading delsel...done
Loading diff-hl...done
Loading hl-line...done
Loading paren...done
Loading xt-mouse...done
Starting new Ispell process aspell with default dictionary...
Starting Emacs daemon.
When done with this frame, type C-x 5 0
Making completion list...

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Configured features:
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ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 THREADS LIBSYSTEMD LCMS2

Important settings:
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  value of $LC_MONETARY: en_US.utf8
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Major mode: Lisp Interaction

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Load-path shadows:
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Memory information:
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bug#44319: make mode should recognize ::= as a macro assignment

[Lars Ingebrigtsen]

Robert Lange <rlange@corusa.net> writes:

> I've tested this on Emacs 26.1 on Debian, as well as a self-compiled
> 27.1. When I use the GNU immediate assignment operator `:=` the macro
> name ELC_FILES is correctly shown in font-lock in the macro color. But
> if I use the POSIX standard `::=` (well, forthcoming POSIX standard,
> but GNU emacs has supported it since v4.0) ELC_FILES is incorrectly
> shown in the target color.

Yup.  This bug is still present in Emacs 28.

> Looking in lisp/progmodes/make-mode.el, the const
> makefile-macroassign-regex is pretty gnarly, but I *think* it should
> match a `::=`, so I'm assuming it's getting preempted by something
> else, probably the const makefile-dependency-regex. Unfortunately,
> that regexp is a bit more than I can interpret, and I don't dare
> change it because I'll almost certainly break some other obscure but
> legal cases.

The bug seemed to be in makefile-match-dependency, which checked for
":=", but not for "::=", and I've now fixed this on the trunk.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no