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

[Steven Simpson]

Follow-up Comment #10, bug #48643 (project make):

[comment #9 comment #9:]
> Unfortunately it's exactly the is_target test that causes the problems.  The
rest of the changes, without that, don't seem to have any issues.
Okay, thanks.

I hope to get round to the documentation issue.  For now, I've had a look at
targets/INTERMEDIATE test 8, which is using this:


all: hello.z
%.z: test.x; touch $@
%.x: ;
.INTERMEDIATE: test.x


It then pre-creates hello.z, and asserts that nothing will be rebuilt, because
test.x is intermediate.

With the is_target test in place, execution reaches src/implicit.c line ~920:

          f->intermediate = !(pat->is_explicit || f->notintermediate);

f is pointing at the entry for "test.x", which already has its intermediate
flag set, but this line cancels it.  Later, the file struct is looked up
again:

          dep->file = lookup_file (s);

And so the file is seen as non-intermediate in src/remake.c:

          if (d_mtime == NONEXISTENT_MTIME && !d->file->intermediate)
            /* We must remake if this dep does not
               exist and is not intermediate.  */
            must_make = 1;


Without is_target, pat->file is null, so the f->intermediate assignment is
never carried out.  When the file is looked up later, f->intermediate hasn't
been reset, so test.x's intermediacy is preserved.

f->intermediate could be preserved like this:

          f->intermediate = f->intermediate || !(pat->is_explicit ||
f->notintermediate);


Then, without is_target, we get:

$ ~/Works/make/make -rRd
GNU Make 4.3.90
[snip]
Considering target file 'all'.
 File 'all' does not exist.
 Looking for an implicit rule for 'all'.
 No implicit rule found for 'all'.
  Considering target file 'hello.z'.
   Looking for an implicit rule for 'hello.z'.
   Trying pattern rule with stem 'hello'.
   Trying rule prerequisite 'test.x'.
   Found an implicit rule for 'hello.z'.
    Looking for an implicit rule for 'test.x'.
    Trying pattern rule with stem 'test'.
    Found an implicit rule for 'test.x'.
   Finished prerequisites of target file 'hello.z'.
   Prerequisite 'test.x' of target 'hello.z' does not exist.
  No need to remake target 'hello.z'.
 Finished prerequisites of target file 'all'.
Must remake target 'all'.
Successfully remade target file 'all'.
make: Nothing to be done for 'all'.


With is_target:

$ ~/Works/make/make -rRd
GNU Make 4.3.90
[snip]
Considering target file 'all'.
 File 'all' does not exist.
 Looking for an implicit rule for 'all'.
 No implicit rule found for 'all'.
  Considering target file 'hello.z'.
   Looking for an implicit rule for 'hello.z'.
   Trying pattern rule with stem 'hello'.
   Trying rule prerequisite 'test.x'.
   Trying pattern rule with stem 'hello'.
   Trying rule prerequisite 'test.x'.
   Looking for a rule with explicit file 'test.x'.
    Avoiding implicit rule recursion.
    Trying pattern rule with stem 'test'.
   Found an implicit rule for 'hello.z'.
   Finished prerequisites of target file 'hello.z'.
   Prerequisite 'test.x' of target 'hello.z' does not exist.
  No need to remake target 'hello.z'.
 Finished prerequisites of target file 'all'.
Must remake target 'all'.
Successfully remade target file 'all'.
make: Nothing to be done for 'all'.


So either way, test 8 passes.

In summary, the lack of is_target causes the .INTERMEDIATE rule to be mistaken
for a 'real' rule about test.x, and avoids the execution path that would reset
the intermediate flag.

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