bug#9306: Java build errors due to trailing colon in CLASSPATH

[Daniel Richard G.]

I am using Automake 1.11.1, and have recently encountered a subtle issue
that causes compilation of some Java programs to fail.

Here is a typical build failure, produced from a minimal test case I've
assembled, using OpenJDK on Ubuntu's Natty release:

make[3]: Entering directory `/tmp/automake-java-bug/org/gnu/bug'
CLASSPATH=../../..:./../../..:$CLASSPATH javac -d ../../..    Library.java 
Application.java
./Library.java:5: duplicate class: org.gnu.bug.Library
public class Library
       ^
Application.java:9: cannot access Library
bad class file: RegularFileObject[./Library.java]
file does not contain class Library
Please remove or make sure it appears in the correct subdirectory of the 
classpath.
                Library lib = new Library();
                ^
2 errors
make[3]: *** [classdist_noinst.stamp] Error 1


If I copy-and-paste the javac invocation, edit it slightly, and run
it...

    env CLASSPATH=../../..:./../../..: javac -d ../../.. Library.java 
Application.java

...I get the same error. However, if I remove that trailing colon from
CLASSPATH, and try it again...

    env CLASSPATH=../../..:./../../.. javac -d ../../.. Library.java 
Application.java

...compilation succeeds. If I invoke the above build with

    env CLASSPATH=/does-not-exist make

then compilation likewise succeeds.

Note that I do not have CLASSPATH set in my environment. It would appear
that a trailing colon in the CLASSPATH environment variable has a
special meaning attached to it, which makes Automake's use of
CLASSPATH=mumblemumble:$$CLASSPATH in makefiles problematic.

(The straightforward solution would be to replace that construct with
CLASSPATH=mumblemumble$${CLASSPATH:+:$$CLASSPATH}, but whether all
shells can handle that is an open question.)

Attached is a tarball containing the minimal test case.


--Daniel


P.S.: Please Cc: any replies to me, as I am not subscribed to this list.


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automake-java-bug.tar.gz
Description: GNU Zip compressed data