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use-inference.mk revision 1.1 
      1 # $NetBSD: use-inference.mk,v 1.1 2020/08/09 16:32:28 rillig Exp $
      2 #
      3 # Demonstrate that .USE rules do not have an effect on inference rules.
      4 # At least not in the special case where the inference rule does not
      5 # have any associated commands.
      6 
      7 .SUFFIXES:
      8 .SUFFIXES: .from .to
      9 
     10 all: use-inference.to
     11 
     12 verbose: .USE
     13 	@echo 'Verbosely making $@ out of $>'
     14 
     15 .from.to: verbose
     16 # Since this inference rule does not have any associated commands, it
     17 # is ignored.
     18 #
     19 #	@echo 'Building $@ from $<'
     20 
     21 use-inference.from:		# assume it exists
     22 	@echo 'Building $@ from nothing'
     23 
     24 # Possible but unproven explanation:
     25 #
     26 # The main target is "all", which depends on "use-inference.to".
     27 # The inference connects the .from to the .to file, otherwise make
     28 # would not know that the .from file would need to be built.
     29 #
     30 # The .from file is then built.
     31 #
     32 # After this, make stops since it doesn't know how to make the .to file.
     33 # This is strange since make definitely knows about the .from.to suffix
     34 # inference rule.  But it seems to ignore it, maybe because it doesn't
     35 # have any associated commands.
     36