Weird behavior in case of using archive rules for archives other than ar/.a, i.e. jar/.jar

[Christian Hujer]

Hello,

trying to use archive rules for jar (placeholder for any kind of
archive other than ar archive/ranlib static link library).

---begin Makefile---
#Weird1: Test.jar is remade all the time.

#Weird2: Using test.a(object1.o object2.o) directly works, but using
Test.jar(Class1.class Class2.class) directly doesn't, it would use ar
instead of jar.
.PHONY: all
#all: Test.jar(Class1.class Class2.class) test.a(object1.o object2.o)
all: Test.jar test.a
Test.jar: Test.jar(Class1.class Class2.class)
test.a: test.a(object1.o object2.o)

# Warning: This has a race condition, it might lead to jar cf being
called concurrently if make -j is used.
# A possible solution is to use ljar https://github.com/christianhujer/ljar
#%.jar: AR:=ljar
#%.jar: ARFLAGS:=uf
%.jar: AR:=jar
%.jar: ARFLAGS=$(if $(wildcard $@),u,c)f

%.class: %.java
        javac $^

%.java:
        echo "public class $* {}" >$@

#Weird3: Using %.c instead of explicit names will lead to make trying
to build a file named "Test.jar(Class1.class).c"
object1.c object2.c:
        echo "void $*(void) {}" >$@

.PHONY: clean
clean:
        $(RM) *.jar *.a *.class *.o *.c *.java
---end Makefile---

While Weird2 and Weird3 could be worked around in the Makefile, I
cannot find a workaround for Weird1:
I run make, I run make again, and while it doesn't touch test.a
(expected), it remakes Test.jar (unexpected).

Am I doing something wrong? Is this a bug? Or am I trying to use the
archive feature in a not (yet?) supported way?

I'm using GNU Make 4.0.

Best regards,

Christian Hujer