[bug #48970] unclear which prerequisites included in $? for intermediate targets

[Sam Fok]

URL:
  <http://savannah.gnu.org/bugs/?48970>

                 Summary: unclear which prerequisites included in $? for
intermediate targets
                 Project: make
            Submitted by: fragapanagos
            Submitted on: Thu 01 Sep 2016 07:22:48 PM GMT
                Severity: 3 - Normal
              Item Group: Documentation
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
       Component Version: 3.81
        Operating System: POSIX-Based
           Fixed Release: None
           Triage Status: None

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Details:

I have the following Makefile with intermediate target ${LIST}.

------------------------------

TGT := tgt
LIST := list

all: ${TGT}

${TGT}: ${LIST}
        touch `cat ${LIST}`
        touch $@

${LIST}: foo1.in foo2.in
        echo $(?:in=out) > ${LIST}

foo%.in:
        touch foo$*.in

clean:
        rm -f foo*
        rm -f ${LIST}
        rm -f ${TGT}

.PHONY: all clean
.INTERMEDIATE: ${LIST}

------------------------------

When any of ${LIST}'s prerequisite's is newer than ${TGT}, the ${LIST} recipe
is executed. However, if .INTERMEDIATE file ${LIST} does not exist, it is
unclear from the documentation which ${LIST} prerequisite would be included in
${?} in the ${LIST} recipe. Would it be only the prerequisites that were newer
than ${TGT} or all prerequisites because ${LIST} does not exist? The following
shell session illustrates the confusion.

------------------------------
$ ls # to show directory state.
Makefile
$ make
touch foo1.in
touch foo2.in
echo foo1.out foo2.out > list
touch `cat list`
touch tgt
rm list
$ make # to show that make ran successfully
make: Nothing to be done for `all'.
$ touch foo1.in # update foo1.in to be newer than tgt
$ make
echo foo1.out foo2.out > list
touch `cat list`
touch tgt

------------------------------

Since list's prerequisite foo1.in was newer than tgt, list's recipe was
executed. However, I expected only foo1.in to be included in ${?} because
foo1.in alone was newer than tgt and so foo1.in alone caused list's recipe to
be executed.

On intermediate files, the documentation states that 

"
The first difference is what happens if the intermediate file does not exist.
If an ordinary file b does not exist, and make considers a target that depends
on b, it invariably creates b and then updates the target from b. But if b is
an intermediate file, then make can leave well enough alone. It won’t bother
updating b, or the ultimate target, unless some prerequisite of b is newer
than that target or there is some other reason to update that target.
"

There is no mention of which prerequisites of b will be considered to be newer
than b. The documentation for $? also does not mention intermediate targets.





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