[bug #48643] Irrelevant targets can confuse make on which pattern rule to select.

[Steven Simpson]

Follow-up Comment #3, bug #48643 (project make):

With the is_target test restored in implicit.c, "make check" fails:


features/patternrules ................................... Error running
/home/simpsons/Works/make/tests/../make (expected 0; got 512):
'/home/simpsons/Works/make/tests/../make' '-f'
'work/features/patternrules.mk.6'
FAILED (11/12 passed)


Seems to be in conflict with bug #17752 - the is_target test was removed to
resolve it, I gather.

I adapted a makefile from features/patternrules so that the intermediate can
have a specific suffix:


STEM = xyz
BIN = $(STEM)$(SFX)
COPY = $(STEM).cp
SRC = $(STEM).c
allbroken: $(COPY) $(BIN) ; @echo ok
$(SRC): ; @echo 'main(){}'
%.cp: %$(SFX) ; @echo $@ from $<
%$(SFX) : %.c ; @echo $@ from $<


Used with no builtin rules, if $(SFX) is non-empty, this works in 3.80, 3.81
and 4.3.  If $(SFX) is empty, only 3.81 fails.

So a %.sfx:%.c rule works, but %:%.c doesn't, because the target lacks a
suffix.  It seems this test eliminates the rule from the candidates:


          /* Rules that can match any filename and are not terminal
             are ignored if we're recursing, so that they cannot be
             intermediate files.  */
          if (recursions > 0 && target[1] == '\0' && !rule->terminal)
            continue;


This suggests that the test case in bug #17752 is a 'feature', as it tries to
use a rule "that can match any filename" to build an intermediate,
specifically, a builtin rule %:%.c.  The in_use flag prevents these repeating,
as in foo.c.c.c, but with umpteen builtin rules of this sort, every
arrangement of every subset of suffixes in these rules is tried, and that
takes a long time, which can result in some checks (variables/EXTRA_PREREQS)
being aborted.

I managed to introduce a new parameter to pattern_search, unsigned anydepth,
which is incremented on the recursive call only if such a rule is used.  The
test above then becomes:


          char anyrule = 0;
          if (target[1] == '\0' && !rule->terminal)
            {
              if (anydepth > 3)
                continue;
              anyrule = 1;
            }


anyrule is then stored in the tryrules entry, so it can be tested on
recursion:


                      if (pattern_search (int_file,
                                          0,
                                          depth + 1,
                                          recursions + 1,
                                          anydepth + !!tryrules[ri].anyrule))


This allows %:%.X rules to be applied at any depth, but limits the total
number on the stack.

For me, "make check" passes with the anydepth limit set to 0, 1, 2 or 3, but 4
took too long on the variables/EXTRA_PREREQS tests.

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