The problem we were trying to address with this change is that bsd make (bmake) and GNU make both have a := operator, but they behave differently. We originally added ::= to match the gmake behavior. The idea with :::= is to match the bmake behavior. There is then some further confusion because bmake also has the variable .MAKE.SAVE_DOLLARS. So, extracting from the etherpad of 2021-08-12:
Options: 1. Add :::= with behavior of BSD := with $$ always preserved (.MAKE.SAVE_DOLLARS either doesn't affect :::= or is an extension) 2. Add :::= with behavior of BSD := with $$ never preserved (.MAKE.SAVE_DOLLARS is an extension, nominally required to be false by default if implemented so existing scripts don't break if implementation applies it to additional assignment types other than :::=, imo) 3. Add :::= with behavior of BSD := with .MAKE.SAVE_DOLLARS, default true 4. Add :::= with behavior of BSD := with .MAKE.SAVE_DOLLARS, default false 5. Don't add :::= I believe we opted for #4. On Tue, Sep 7, 2021 at 5:19 PM Paul Smith via austin-group-l at The Open Group <austin-group-l@opengroup.org> wrote: > On Thu, 2021-08-12 at 15:19 +0000, Austin Group Bug Tracker wrote: > > After page 2894 line 97263 add: > > > > <blockquote>The following form defines a delayed-expansion macro > > (replacing any previous definition of the macro named by > > <i>string1</i>): > > > > <tt><i>string1</i> :::= <b>[</b><i>string2</i><b>]</b></tt> > > > > by immediately expanding macros in <i>string2</i>, if any, before > > assigning the value.</blockquote> > > > > On page 2895 line 97310, change: > > > > <blockquote>The macro $$ shall be replaced by the single > > character > > '$'.</blockquote> > > > > to: > > > > <blockquote>The string "$$" shall be replaced by the single > > character > > '$', except during the immediate expansion performed for the :::= > > operator, > > where it shall be left unmodified.</blockquote> > > So I took a look at implementing this in GNU make since it seems to > have been adopted. > > I just can't understand the point of this change. Can someone provide > me with some example(s) of this :::= operator showing how it might be > used and what problems it is trying to solve? The idea behind this > completely escapes me so I'm wondering if I'm somehow misinterpreting > the text above defining how :::= is supposed to work. > > I can sort of understand why someone might want to immediately expand a > variable but then treat the expansion as delayed-expansion (although as > I pointed out in the issue comments, you can already do this without > this new operator you just have to use two variables, and I haven't had > anyone ask me for this capability). > > But what is the point of having an immediately expanded variable where > variables are expanded but "$$" is preserved? This I can't really > fathom. > > Also, it's not clear to me whether preserving the '$$' only applies to > the unexpanded string, or also applies to the expansion of variables > contained in the string. > > For example, what would be the expected result of this: > > foo = one$$two > bar :::= $(foo) three$$four > all:;@echo '$(bar)' > > Is the internal value of the "bar" variable 'one$$two three$$four', so > that the result of running make is: > > one$two three$four > > or is the internal value of the "bar" variable 'one$two three$$four', > so that the result of running make is: > > onewo three$four > > >
