sv62706_fix2.diff takes care of secondary expanding a prerequisite marked as intermediate by .SECONDARY or .INTERMEDIATE when an explicit or static pattern rule builds the prerequisite.
sv62706_test2.diff adds related tests.

Another thought on point 2 above.
Posix contains the following requirement.

"The make utility shall treat all prerequisites as targets themselves and recursively ensure that they are up-to-date, processing them in the order in which they appear in the rule."

Should word "processing" here be interpreted as any activity, including secondary expansion (which posix does not define), needed to bring a prerequisite up to date?

Secondary expansion of implicit rules in gnu make already satisfied these requirements. This patch makes explicit and static pattern rules to satisfy as well.

Second expand only the prerequisites of the targets being built.
Avoid second expanding the prerequisites of targets which are not being built.

There are multiple benefits.

1. Avoids redundant work of second expanding prerequisites of the targets which are not being built.

Example 1

.SECONDEXPANSION:
hello.tsk: $$(info 2nd exp for hello) $$(file <hello.d); $(info $@ from $^)
bye.tsk: $$(info 2nd exp for bye) $$(file <bye.d); $(info $@ from $^)
clean:; -rm -f hello.tsk bye.tsk

Assuming there are files 'hello.d' and 'bye.d' which contain the prerequisites of 'hello.tsk' and 'bye.tsk' respectively

$ make hello.tsk

second expands $$(file <hello.d), but does not second expand $$(file bye.d).

$ make clean

does not second expand either $$(file <hello.d) or $$(file <bye.d).


2. Causes all prerequisites to be second expanded in the same order they are being built. This fixes byte order dependent order of second expanding prerequisites. See sv 62175.

3. Eliminates redundant files from the make's database, which reduces the size of the hash table and memory consumption.

4. Prevents side effects from second expansion of unrelated prerequisites.  Even though we'd prefer makefiles which do not depend on side effects, the current behavior allows them.

Example 2

.SECONDEXPANSION:
hello.tsk:; cp hello.1 $@
unrelated: $$(shell touch hello.1);

The current behavior is to second expand $$(shell touch hello.1) during parse phase and thus create 'hello.1'. This allows 'cp hello.1 $@' to succeed.  The new behavior is such that when 'hello.tsk' is built, $$(shell touch hello.1) is not second expanded, and thus $$(shell touch hello.1) fails.

Another size effect is that, because the prerequisites of unrelated targets are not second expanded, those prerequisites may end up being treated as intermediates, where before this commit they would be treated as explicitly defined.

Example 3

.SECONDEXPANSION:
dep:=hello.x
all: hello.z
%.z: %.x; @echo $@
%.x: ;
unrelated: $$(dep)

In example 3 the old behavior is to second expand $$(dep) at parse time and thus enter file 'hello.x' to make's database prevent 'hello.x' from being intermediate. The new behavior is $$(dep) is not expanded and 'hello.x' is not entered and thus 'hello.x' is intermediate.

Both of this examples are artificially created to demonstrate side effects and are not very realistic.  Normally, an automatic variable would be second expanded, otherwise, there is really no point to second expand prerequisites at all.

i checked automake and cmake and found no dependency on such side effects. As far as i can see, most projects do not use second expansion.

However, if make has to retain side effects, it is possible to introduce another special target with the new behavior.



5. Implicit rules have behaved in this manner since day 1. This patch causes explicit and static pattern rules behave like implicit rules and do the required work only.