( Match-Anything Rules

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 10.5.5 Match-Anything Pattern Rules
 When a pattern rule's target is just `%', it matches any file name
 whatever.  We call these rules "match-anything" rules.  They are very
 useful, but it can take a lot of time for `make' to think about them,
 because it must consider every such rule for each file name listed
 either as a target or as a prerequisite.
    Suppose the makefile mentions `foo.c'.  For this target, `make'
 would have to consider making it by linking an object file `foo.c.o',
 or by C compilation-and-linking in one step from `foo.c.c', or by
 Pascal compilation-and-linking from `foo.c.p', and many other
    We know these possibilities are ridiculous since `foo.c' is a C
 source file, not an executable.  If `make' did consider these
 possibilities, it would ultimately reject them, because files such as
 `foo.c.o' and `foo.c.p' would not exist.  But these possibilities are so
 numerous that `make' would run very slowly if it had to consider them.
    To gain speed, we have put various constraints on the way `make'
 considers match-anything rules.  There are two different constraints
 that can be applied, and each time you define a match-anything rule you
 must choose one or the other for that rule.
    One choice is to mark the match-anything rule as "terminal" by
 defining it with a double colon.  When a rule is terminal, it does not
 apply unless its prerequisites actually exist.  Prerequisites that
 could be made with other implicit rules are not good enough.  In other
 words, no further chaining is allowed beyond a terminal rule.
    For example, the built-in implicit rules for extracting sources from
 RCS and SCCS files are terminal; as a result, if the file `foo.c,v' does
 not exist, `make' will not even consider trying to make it as an
 intermediate file from `foo.c,v.o' or from `RCS/SCCS/,v'.  RCS
 and SCCS files are generally ultimate source files, which should not be
 remade from any other files; therefore, `make' can save time by not
 looking for ways to remake them.
    If you do not mark the match-anything rule as terminal, then it is
 nonterminal.  A nonterminal match-anything rule cannot apply to a file
 name that indicates a specific type of data.  A file name indicates a
 specific type of data if some non-match-anything implicit rule target
 matches it.
    For example, the file name `foo.c' matches the target for the pattern
 rule `%.c : %.y' (the rule to run Yacc).  Regardless of whether this
 rule is actually applicable (which happens only if there is a file
 `foo.y'), the fact that its target matches is enough to prevent
 consideration of any nonterminal match-anything rules for the file
 `foo.c'.  Thus, `make' will not even consider trying to make `foo.c' as
 an executable file from `foo.c.o', `foo.c.c', `foo.c.p', etc.
    The motivation for this constraint is that nonterminal match-anything
 rules are used for making files containing specific types of data (such
 as executable files) and a file name with a recognized suffix indicates
 some other specific type of data (such as a C source file).
    Special built-in dummy pattern rules are provided solely to recognize
 certain file names so that nonterminal match-anything rules will not be
 considered.  These dummy rules have no prerequisites and no commands,
 and they are ignored for all other purposes.  For example, the built-in
 implicit rule
      %.p :
 exists to make sure that Pascal source files such as `foo.p' match a
 specific target pattern and thereby prevent time from being wasted
 looking for `foo.p.o' or `foo.p.c'.
    Dummy pattern rules such as the one for `%.p' are made for every
 suffix listed as valid for use in suffix rules ( Old-Fashioned
 Suffix Rules Suffix Rules.).
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