javacomp-script, javacomp: Add support for javac versions > 11

[Bruno Haible]

It was reported in <https://savannah.gnu.org/bugs/?63385> that Gnulib's
Java support does not work for javac versions 12..17.

At the time the 'javacomp-script' and 'javacomp' modules were written, each
major Java release required extra support code, so it was natural to limit
the support to the known versions. But nowadays, a new major Java release
occurs every 6 months [1], and the previous approach has three problems:

  * After a new Java release is made, the time that elapses until
      - support for it gets added to gnulib,
      - a new gettext release is made that includes that support,
      - the distros pull this new release,
      - the user updates to this release and benefits from the support,
    will most often be longer than 6 months, possibly two years or so.
    That is, gettext will almost always be out-of-date.

  * Adding new support to gnulib is a (small) manual effort, that includes
    finding some piece of code that compiles with "javac -source N" but not
    with "javac -source N-1".

  * Bugs can be made in these code snippets. For example, I thought that
    to detect '-source 11' as opposed to '-source 10', this code would work [2]:

       class conftest { Readable r = (var b) -> 0; }

    But it does not always work, namely in JDK 11 no error is shown for this:

      $ jdk-10.0.2/bin/javac -d . -source 10 -target 10 conftest.java 
      conftest.java:1: error: 'var' is not allowed here
      class conftest { Readable r = (var b) -> 0; }
                                     ^
      1 error
      $ jdk-11.0.2/bin/javac -d . -source 10 -target 10 conftest.java 
      warning: [options] bootstrap class path not set in conjunction with 
-source 10
      1 warning
      $ jdk-12.0.2/bin/javac -d . -source 10 -target 10 conftest.java 
      warning: [options] bootstrap class path not set in conjunction with 
-source 10
      conftest.java:1: error: var syntax in implicit lambdas are not supported 
in -source 10
      class conftest { Readable r = (var b) -> 0; }
                                         ^
        (use -source 11 or higher to enable var syntax in implicit lambdas)
      1 error
      1 warning

With these two patches, I'm adding support for the newer javac versions, 
assuming
they follow the same patterns at seen in versions 11..20.

[1] https://en.wikipedia.org/wiki/Java_version_history
[2] https://en.wikipedia.org/wiki/Java_version_history#Java_11


2023-06-10  Bruno Haible  <bruno@clisp.org>

        javacomp-script, javacomp: Add support for javac versions > 11.
        Reported by Adrian Bunk <bunk-gnu@fs.tum.de> in
        <https://savannah.gnu.org/bugs/?63385>.
        * m4/javacomp.m4 (gt_JAVACOMP): When the java version is > 11, use that
        version as target_version, not 11. When the java version is > 17, don't
        warn. Remove goodcode, failcode variables. Don't bail out if the
        source-version argument or the target-version argument is in the range
        12..99. Use a heuristic that works with javac versions 11..20 at least.
        Update comments.
        * lib/javacomp.h (compile_java_class): State that source-version and
        target-version may be larger than 11.
        * lib/javacomp.c (default_target_version): Accommodate versions up to
        99.
        (SOURCE_VERSION_BOUND): Increase to 94.
        (source_version_index): Accept versions up to 99.
        (get_goodcode_snippet, get_failcode_snippet): Remove functions.
        (TARGET_VERSION_BOUND): Increase to 94.
        (target_version_index): Accept versions up to 99.
        (corresponding_classfile_version): Remove function.
        (execute_and_read_line): New function, based on lib/javaversion.c.
        (get_compiler_version): New function.
        (is_envjavac_usable): Add parameters source_option_out,
        target_option_out. Use a heuristic that works with javac versions 11..20
        at least. Call cleanup_temp_dir.
        (is_javac_usable): Likewise.
        (compile_java_class): Update.

2023-06-10  Bruno Haible  <bruno@clisp.org>

        javacomp-script, javacomp: Remove support for javac versions < 1.6.
        * m4/javacomp.m4 (gt_JAVACOMP): State that the minimum source_version
        and the minimum target_version are 1.6. Map smaller values to 1.6.
        Complain if the java version is < 1.6. Use 1.6 as default, instead of
        1.1. Don't bother trying the -target option alone.
        * lib/javacomp.h (compile_java_class): State that the minimum
        source_version and the minimum target_version are 1.6.
        * lib/javacomp.c (default_target_version): Complain if the java version
        is < 1.6. Use 1.6 as default, instead of 1.1.
        (SOURCE_VERSION_BOUND, source_version_index, get_goodcode_snippet,
        get_failcode_snippet): Adjust to the new minimum source_version = 1.6.
        (TARGET_VERSION_BOUND, target_version_index,
        corresponding_classfile_version): Adjust to the new minimum
        target_version = 1.6.
        (get_source_version_for_javac): Remove function.
        (is_envjavac_usable): Remove source_version_for_javac parameter. Don't
        bother trying the -target option alone.
        (is_javac_usable): Likewise.
        (compile_java_class): Map source_version < 1.6 to 1.6. Map
        target_version < 1.6 to 1.6. Use source_version instead of calling
        get_source_version_for_javac.

0001-javacomp-script-javacomp-Remove-support-for-javac-ve.patch
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0002-javacomp-script-javacomp-Add-support-for-javac-versi.patch
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