travis: upgrade c++ build to focal & llvm 10

[felixn]

Alternative PR to #2908, upgrading only the c++ build

The first build shows that openjdk8 is not available with Ubuntu focal:
https://travis-ci.org/github/antlr/antlr4/builds/746825671

The command "~/bin/install-jdk.sh --target "/home/travis/openjdk8" --workspace "/home/travis/.cache/install-jdk" --feature "8" --license "GPL" --cacerts" failed and exited with 3 during .

The second build shows the issues in the C++ runtime:
https://travis-ci.org/github/antlr/antlr4/builds/746909160

In file included from /tmp/BaseCppTest-main-1606808268300/TLexer.cpp:5:
In file included from /tmp/BaseCppTest-main-1606808268300/TLexer.h:7:
In file included from /home/travis/build/antlr/antlr4/runtime-testsuite/target/classes/Cpp/runtime/src/antlr4-runtime.h:126:
/home/travis/build/antlr/antlr4/runtime-testsuite/target/classes/Cpp/runtime/src/misc/InterpreterDataReader.h:20:5: error: call to implicitly-deleted default constructor of 'dfa::Vocabulary'
    InterpreterData() {}; // For invalid content.
    ^
/home/travis/build/antlr/antlr4/runtime-testsuite/target/classes/Cpp/runtime/src/Vocabulary.h:25:5: note: explicitly defaulted function was implicitly deleted here
    Vocabulary() = default;
    ^
/home/travis/build/antlr/antlr4/runtime-testsuite/target/classes/Cpp/runtime/src/Vocabulary.h:185:36: note: default constructor of 'Vocabulary' is implicitly deleted because field '_literalNames' of const-qualified type 'const std::vector<std::string>' (aka 'const vector<basic_string<char> >') would not be initialized
    std::vector<std::string> const _literalNames;
                                   ^
1 error generated.

The third build passes:
https://travis-ci.org/github/antlr/antlr4/builds/747024792?utm_source=github_status&utm_medium=notification

[felixn]

This is ready to merge, from my point of view.

[mike-lischke]

@parrt That's a minimal change, so I believe it is safe to merge.

[parrt]

Hmm... I think it would feel better if it didn't also change the Java version being used to test.

[mike-lischke]

All tests passed, so what suprise do you expect by that change?

[parrt]

well, we claim java 7 compatibility. Seems like we should stick to that version for tests.

[felixn]

Hi Terence,

unfortunately, the current Ubuntu LTS (20.04 / focal) Travis image does not support openjkd8 - that's why the first build failed.

Also, from my point of view, it's actually a good thing if we test with some varying Java versions (C++ with Java 11, others with Java 8) to increase test coverage.

Plus, Java 8 is "almost" EOL: "Java SE 8 has gone through the End of Public Updates process for legacy releases."
https://www.oracle.com/java/technologies/java-se-support-roadmap.html

But you're the big boss ;)
If you want, I can look for a Ubuntu version that supports the old Java 8 and the newer LLVM releases.

Cheers Felix

[parrt]

Well if there is no java 8 then I guess we have no choice. Ha ha. Merging. thanks for your efforts.