[java] [regression from 6.55] UseDiamondOperator false-positive with Java 8 code

[kohlschuetter]

Affects PMD Version:
7.0.0-SNAPSHOT

Rule:
UseDiamondOperator

Description:
A class member that initializes an anonymous inner class with generics must not use the diamond operator (for code that targets Java 8).

Code Sample demonstrating the issue:

from https://github.com/kohlschutter/junixsocket/blob/72110d0/junixsocket-tipc/src/main/java/org/newsclub/net/unix/tipc/AFTIPCSelectorProvider.java

  static final AFAddressFamily<@NonNull AFTIPCSocketAddress> AF_TIPC = AFAddressFamily
      .registerAddressFamilyImpl("tipc", AFTIPCSocketAddress.addressFamily(),
          new AFAddressFamilyConfig<AFTIPCSocketAddress>() {   // here

          /// ...
         });

Expected outcome:

PMD reports a violation at the line marked with "// here"", but that's wrong. That's a false positive.

Running PMD through: CLI

Only occurs with "aux-classpath" set. Download junixsocket-selftest-2.6.2-jar-with-dependencies.jar to reproduce. Use attached pmd-ruleset.xml.zip

pmd check AFTIPCSelectorProvider.java --aux-classpath=junixsocket-selftest-2.6.2-jar-with-dependencies.jar --use-version=java-8 -f text -R pmd-ruleset.xml

Warning shown:

AFTIPCSelectorProvider.java:128:	UseDiamondOperator:	Explicit type arguments can be replaced by a diamond: `new AFTIPCSocketPair<>(s1, s2)`

After changing to the diamond operator, compilation for Java 8 fails with:

[ERROR] .../AFTIPCSelectorProvider.java:[48,36] cannot infer type arguments for org.newsclub.net.unix.AFAddressFamilyConfig<A>
  reason: '<>' with anonymous inner classes is not supported in -source 8
    (use -source 9 or higher to enable '<>' with anonymous inner classes)

[oowekyala]

I cannot reproduce this. When I try with PMD 7 snapshot (built locally), the rule behaves as expected:

# java 8
$ sandbox/pmd-bin-7.0.0-SNAPSHOT/bin/pmd check -d ~/Downloads/AFTIPCSelectorProvider.java --aux-classpath ~/Downloads/junixsocket-selftest-2.6.2-jar-with-dependencies.jar -R category/java/codestyle.xml/UseDiamondOperator --no-progress  --use-version java-8 --no-cache
[main] INFO net.sourceforge.pmd.cli.commands.internal.AbstractPmdSubcommand - Log level is at INFO
/home/clem/Downloads/AFTIPCSelectorProvider.java:128:	UseDiamondOperator:	Explicit type arguments can be replaced by a diamond: `new AFTIPCSocketPair<>(s1, s2)`
# java 9
$ sandbox/pmd-bin-7.0.0-SNAPSHOT/bin/pmd check -d ~/Downloads/AFTIPCSelectorProvider.java --aux-classpath ~/Downloads/junixsocket-selftest-2.6.2-jar-with-dependencies.jar -R category/java/codestyle.xml/UseDiamondOperator --no-progress  --use-version java-9 --no-cache
[main] INFO net.sourceforge.pmd.cli.commands.internal.AbstractPmdSubcommand - Log level is at INFO
/home/clem/Downloads/AFTIPCSelectorProvider.java:48:	UseDiamondOperator:	Explicit type arguments can be replaced by a diamond: `new AFAddressFamilyConfig<>()`
/home/clem/Downloads/AFTIPCSelectorProvider.java:128:	UseDiamondOperator:	Explicit type arguments can be replaced by a diamond: `new AFTIPCSocketPair<>(s1, s2)`

I got the same results with the released binary for PMD7 RC3 (there has been no changes to the rule since).

Can you give more info to reproduce this?

[kohlschuetter]

My bad, can no longer reproduce either. I think I missed the "targetJdk" config in my POM.
Thanks for the fast response, though!