[bug #62706] Restrict second expansion to targets which are being built.

[Dmitry Goncharov]

Follow-up Comment #2, bug #62706 (project make):

This is a more detailed description of point 2 above (2. Causes all
prerequisites to be second expanded in the same order they are being built.)

++++
$ cat makefile
.SECONDEXPANSION:
all: hello.tsk bye.tsk
hello.tsk: $$(info 2nd expansion of prereqs of $$@); $(info $@)
bye.tsk: $$(info 2nd expansion of prereqs of $$@); $(info $@)
$ # this is patched make
$ ~/src/make/l64/make
2nd expansion of prereqs of hello.tsk
hello.tsk
2nd expansion of prereqs of bye.tsk
bye.tsk
make: Nothing to be done for 'all'.
$ # this is make-4.3
$ make
2nd expansion of prereqs of bye.tsk
2nd expansion of prereqs of hello.tsk
hello.tsk
bye.tsk
make: Nothing to be done for `all'.
$
----

We can see that make-4.3 builds 'hello.tsk' before building
'bye.tsk'. The order of secondary expanding prerequisites is the
opposite, first the prerequisites of 'bye.tsk' are expanded, then the
prerequisites of 'hello.tsk'.

The proposed behavior is to secondary expand the prerequisites of
'hello.tsk", build 'hello.tsk', secondary expand the prerequisites of
'bye.tsk', build 'bye.tsk'.

If however the makefile is changed like
++++
$ cat makefile
.SECONDEXPANSION:
all: $$(info 2nd expansion for all) hello.tsk bye.tsk; $(info $@)
hello.tsk: $$(info 1st 2nd expansion of prereqs of $$@) $$(info 2nd 2nd
expansion of prereqs of $$@); $(info $@)
bye.tsk: $$(info 1st 2nd expansion of prereqs of $$@) $$(info 2nd 2nd
expansion of prereqs of $$@); $(info $@)
$ ~/src/make/l64/make
2nd expansion for all
1st 2nd expansion of prereqs of hello.tsk
2nd 2nd expansion of prereqs of hello.tsk
hello.tsk
1st 2nd expansion of prereqs of bye.tsk
2nd 2nd expansion of prereqs of bye.tsk
bye.tsk
all
make: 'all' is up to date.
$ make
2nd expansion for all
1st 2nd expansion of prereqs of bye.tsk
2nd 2nd expansion of prereqs of bye.tsk
1st 2nd expansion of prereqs of hello.tsk
2nd 2nd expansion of prereqs of hello.tsk
hello.tsk
bye.tsk
all
make: `all' is up to date.
$

----
Then $$(info 2nd expansion for all) is secondary expanded
before the prerequisites of hello.tsk and bye.tsk are secondary
expanded. The patch keeps this aspect of behavior is intact.



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