Problem with .phony .secondary between 3.79.1 and 3.81

[Andy Juniper]

I need some help with the behaviour .phony .secondary targets, and the 
way that this has changed between 3.79.1 and 3.81.

I have a .phony target (i.e. a target which never exists as a real file) 
which I only want to be 'built' if something that depends on it needs to 
be rebuilt (i.e. a secondary).

This can be demonstrated with a simple makefile:

.PHONY: all
all: fileb

.PHONY: prepare
.SECONDARY: prepare
prepare:
   @echo $@

filea: prepare filea.dep
   @echo $@
   @touch $@

fileb: prepare filea fileb.dep
   @echo $@
   @touch $@

In 3.79.1, this works as expected and the "prepare" target is only 
rebuilt if filea or fileb are rebuilt.  Running make a second time just 
reports that there is nothing to be done.

But in 3.81, running make a second time will rebuild everything again.

In this example, it's not a problem, but in the original case, the 
prepare target deleted the build directory and thus everything above it 
needed to be rebuilt.


Running 3.81 with -d shows the following debug of interest:

Updating goal targets....
Considering target file `all'.
File `all' does not exist.
 Considering target file `fileb'.
   Considering target file `prepare'.
    File `prepare' does not exist.
    Finished prerequisites of target file `prepare'.
   Must remake target `prepare'.


So my questions are:
- was the behaviour which made this work in 3.79.1 accidental or deliberate?
- how to recreate this behaviour in 3.81?
- is there a fix for 3.81 which will recreate the required behaviour?


thanks,
Andy Juniper
address@hidden