depfixer: silence fix_jar() and make it do something

fix_jar() tries to remove an existing Class-Path entry from the jar
manifest by postprocessing the manifest and passing it to `jar -um`.
However, `jar -um` can only add/replace manifest entries, not remove
them, and it also complains loudly when replacing an entry:

    Dec 13, 2022 7:11:19 PM java.util.jar.Attributes read
    WARNING: Duplicate name in Manifest: Manifest-Version.
    Ensure that the manifest does not have duplicate entries, and
    that blank lines separate individual sections in both your
    manifest and in the META-INF/MANIFEST.MF entry in the jar file.

Thus fix_jar() produces one such warning for each entry in the manifest
and accomplishes nothing else.

Use jar -uM instead.  This completely removes the manifest from the jar
and allows adding it back as a normal zip member, fixing fix_jar() and
avoiding the warnings.

Fixes: https://github.com/mesonbuild/meson/issues/10491
Fixes: c70a051e93 ("java: remove manifest classpath from installed jar")

mesonbuild/scripts/depfixer.py

@@ -465,7 +465,12 @@ def fix_jar(fname: str) -> None:
             if not line.startswith('Class-Path:'):
                 f.write(line)
         f.truncate()
-    subprocess.check_call(['jar', 'ufm', fname, 'META-INF/MANIFEST.MF'])
+    # jar -um doesn't allow removing existing attributes.  Use -uM instead,
+    # which a) removes the existing manifest from the jar and b) disables
+    # special-casing for the manifest file, so we can re-add it as a normal
+    # archive member.  This puts the manifest at the end of the jar rather
+    # than the beginning, but the spec doesn't forbid that.
+    subprocess.check_call(['jar', 'ufM', fname, 'META-INF/MANIFEST.MF'])
 
 def fix_rpath(fname: str, rpath_dirs_to_remove: T.Set[bytes], new_rpath: T.Union[str, bytes], final_path: str, install_name_mappings: T.Dict[str, str], verbose: bool = True) -> None:
     global INSTALL_NAME_TOOL  # pylint: disable=global-statement

test cases/unit/110 classpath/com/mesonbuild/Simple.java

@@ -0,0 +1,7 @@
+package com.mesonbuild;
+
+class Simple {
+    public static void main(String [] args) {
+        System.out.println("Java is working.\n");
+    }
+}

test cases/unit/110 classpath/meson.build

@@ -0,0 +1,14 @@
+project('simplejava', 'java')
+
+one = jar('one', 'com/mesonbuild/Simple.java',
+  main_class : 'com.mesonbuild.Simple',
+  install : true,
+  install_dir : get_option('bindir'),
+)
+
+two = jar('two', 'com/mesonbuild/Simple.java',
+  main_class : 'com.mesonbuild.Simple',
+  install : true,
+  install_dir : get_option('bindir'),
+  link_with : one,
+)

unittests/helpers.py

@@ -5,6 +5,7 @@ import unittest
 import functools
 import re
 import typing as T
+import zipfile
 from pathlib import Path
 from contextlib import contextmanager
 
@@ -176,6 +177,22 @@ def get_rpath(fname: str) -> T.Optional[str]:
         return None
     return final
 
+def get_classpath(fname: str) -> T.Optional[str]:
+    with zipfile.ZipFile(fname) as zip:
+        with zip.open('META-INF/MANIFEST.MF') as member:
+            contents = member.read().decode().strip()
+    lines = []
+    for line in contents.splitlines():
+        if line.startswith(' '):
+            # continuation line
+            lines[-1] += line[1:]
+        else:
+            lines.append(line)
+    manifest = {
+        k.lower(): v.strip() for k, v in [l.split(':', 1) for l in lines]
+    }
+    return manifest.get('class-path')
+
 def get_path_without_cmd(cmd: str, path: str) -> str:
     pathsep = os.pathsep
     paths = OrderedSet([Path(p).resolve() for p in path.split(pathsep)])

unittests/machinefiletests.py

@@ -42,6 +42,7 @@ import mesonbuild.modules.pkgconfig
 
 
 from run_tests import (
+    Backend,
     get_fake_env
 )
 
@@ -368,6 +369,23 @@ class NativeFileTests(BasePlatformTests):
         self._single_implementation_compiler(
             'java', 'javac', 'javac 9.99.77', '9.99.77')
 
+    @skip_if_not_language('java')
+    def test_java_classpath(self):
+        if self.backend is not Backend.ninja:
+            raise SkipTest('Jar is only supported with Ninja')
+        testdir = os.path.join(self.unit_test_dir, '110 classpath')
+        self.init(testdir)
+        self.build()
+        one_build_path = get_classpath(os.path.join(self.builddir, 'one.jar'))
+        self.assertIsNone(one_build_path)
+        two_build_path = get_classpath(os.path.join(self.builddir, 'two.jar'))
+        self.assertEqual(two_build_path, 'one.jar')
+        self.install()
+        one_install_path = get_classpath(os.path.join(self.installdir, 'usr/bin/one.jar'))
+        self.assertIsNone(one_install_path)
+        two_install_path = get_classpath(os.path.join(self.installdir, 'usr/bin/two.jar'))
+        self.assertIsNone(two_install_path)
+
     @skip_if_not_language('swift')
     def test_swift_compiler(self):
         wrapper = self.helper_create_binary_wrapper(