For the sake of reliability I wouldn't use pure `$<` anywhere. And if the answer to your question "Which one, listed in another rule, becomes $<?" isn't "All collected prerequisites, with duplicates purged" as I was believing until now, then I'm close to dropping make alltogether.
Am Mi., 27. Sept. 2023 um 17:05 Uhr schrieb Renaud Pacalet < renaud.paca...@telecom-paris.fr>: > > > On 9/27/23 17:01, Mark Piffer wrote: > > Is there a case (common or rare) where the answer to this question has > real world consequences? > > Yes, I think. If you don't know how $< is expanded you cannot reliably use > it in your recipe. I strongly suspect that it is expanded to the first > prerequisite of the rule with a recipe but is this always the case? I > couldn't find this in the manual. Moreover, what if the rule with a recipe > has no prerequisites? Which one, listed in another rule, becomes $<? > > > regards, > > Mark > > > >> Am 27.09.2023 um 12:17 schrieb Renaud Pacalet < > renaud.paca...@telecom-paris.fr>: > >> > >> Dear all, > >> > >> I read the manual carefully (especially section 4.11 "Multiple Rules > for One Target") and searched the help-make archives but couldn't find a > clear description of how $^ and $< are computed when there are several > rules for the same target and only one has a recipe. > >> > >> According the manual "All the prerequisites mentioned in all the rules > are merged into one list of prerequisites for the target". But when the > recipe gets expanded what is the order of prerequisites in $^ and, more > important, what is $<? Does it depend on the order of rules in the > Makefile(s)? On the type of rules (pattern, static pattern, explicit...)? > On which rule has a recipe? Is it deterministic? etc. > >> > >> I did some tests and came up with the following algorithm for $^ and $< > computation: > >> > >> 0. When the list of prerequisites of a rule is added to $^, the order > is preserved. > >> > >> 1. Initialize $^ with the list of prerequisites of the rule with a > recipe, implicit or not. > >> > >> 2. Consider all other applicable explicit or static pattern rules, in > their order of appearance in the Makefile(s), and for each of them append > its list of prerequisites to $^. > >> > >> 3. Ignore all other implicit rules (which seems to contradict 4.11). > >> > >> 4. Remove duplicates from $^, keeping only the first occurrence. > >> > >> 5. Set $< to the first prerequisite in $^. > >> > >> Can someone confirm? > >> > >> Renaud. > >> > > -- > Renaud Pacalet > Télécom Paris > Campus SophiaTech > 450 Route des Chappes, CS 50193 > 06904 Biot Sophia Antipolis cedex, FRANCE > Tel : +33 (0) 4 9300 8402 > Web : http://www.telecom-paris.fr/ >
