wrap: Use MESON_PACKAGE_CACHE_DIR as default packagecache path

Allow packagecache to contain already extracted directory to match what
some distro does with Cargo source packages in /usr/share/cargo/registry.

Note that there is no need to lock the cache directory because we
download into a temporary name and atomically rename afterward. It means
we could be downloading the same file twice, but at least integrity is
guaranteed.

Fixes: #12211

docs/markdown/Wrap-dependency-system-manual.md

@@ -109,6 +109,12 @@ project's `subprojects/packagecache` directory, it will be used instead
 of downloading the file, even if `--wrap-mode` option is set to
 `nodownload`. The file's hash will be checked.
 
+Since *1.3.0* if the `MESON_PACKAGE_CACHE_DIR` environment variable is set, it is used instead of
+the project's `subprojects/packagecache`. This allows sharing the cache across multiple
+projects. In addition it can contain an already extracted source tree as long as it
+has the same directory name as the `directory` field in the wrap file. In that
+case, the directory will be copied into `subprojects/` before applying patches.
+
 ### Specific to VCS-based wraps
 - `url` - name of the wrap-git repository to clone. Required.
 - `revision` - name of the revision to checkout. Must be either: a

docs/markdown/snippets/meson_home.md

@@ -0,0 +1,7 @@
+## New environment variable `MESON_PACKAGE_CACHE_DIR`
+
+If the `MESON_PACKAGE_CACHE_DIR` environment variable is set, it is used instead of the
+project's `subprojects/packagecache`. This allows sharing the cache across multiple
+projects. In addition it can contain an already extracted source tree as long as it
+has the same directory name as the `directory` field in the wrap file. In that
+case, the directory will be copied into `subprojects/` before applying patches.

mesonbuild/wrap/wrap.py

@@ -289,7 +289,7 @@ class Resolver:
 
     def __post_init__(self) -> None:
         self.subdir_root = os.path.join(self.source_dir, self.subdir)
-        self.cachedir = os.path.join(self.subdir_root, 'packagecache')
+        self.cachedir = os.environ.get('MESON_PACKAGE_CACHE_DIR') or os.path.join(self.subdir_root, 'packagecache')
         self.wraps: T.Dict[str, PackageDefinition] = {}
         self.netrc: T.Optional[netrc] = None
         self.provided_deps: T.Dict[str, PackageDefinition] = {}
@@ -462,7 +462,17 @@ class Resolver:
             if not os.path.isdir(self.dirname):
                 raise WrapException('Path already exists but is not a directory')
         else:
-            if self.wrap.type == 'file':
+            # Check first if we have the extracted directory in our cache. This can
+            # happen for example when MESON_PACKAGE_CACHE_DIR=/usr/share/cargo/registry
+            # on distros that ships Rust source code.
+            # TODO: We don't currently clone git repositories into the cache
+            # directory, but we should to avoid cloning multiple times the same
+            # repository. In that case, we could do something smarter than
+            # copy_tree() here.
+            cached_directory = os.path.join(self.cachedir, self.directory)
+            if os.path.isdir(cached_directory):
+                self.copy_tree(cached_directory, self.dirname)
+            elif self.wrap.type == 'file':
                 self.get_file()
             else:
                 self.check_can_download()

test cases/unit/116 meson package cache dir/cache_dir/bar/meson.build

@@ -0,0 +1 @@
+project('bar')

test cases/unit/116 meson package cache dir/meson.build

@@ -0,0 +1,4 @@
+project('meson package cache dir')
+
+subproject('foo')
+subproject('bar')

test cases/unit/116 meson package cache dir/subprojects/bar.wrap

@@ -0,0 +1,3 @@
+[wrap-file]
+directory = bar
+

test cases/unit/116 meson package cache dir/subprojects/foo.wrap

@@ -0,0 +1,5 @@
+[wrap-file]
+directory = foo
+source_url = http://server.invalid/foo.zip
+source_filename = foo.zip
+source_hash = c5dd7e8fca93045f736c83700686722b0fbc20b7dc4597b295060684c5b05b72

unittests/platformagnostictests.py

@@ -18,6 +18,7 @@ import pickle
 import tempfile
 import subprocess
 import textwrap
+import shutil
 from unittest import skipIf, SkipTest
 from pathlib import Path
 
@@ -261,3 +262,12 @@ class PlatformAgnosticTests(BasePlatformTests):
 
         self.assertEqual(data['modules'], expected)
         self.assertEqual(data['count'], 68)
+
+    def test_meson_package_cache_dir(self):
+        # Copy testdir into temporary directory to not pollute meson source tree.
+        testdir = os.path.join(self.unit_test_dir, '116 meson package cache dir')
+        srcdir = os.path.join(self.builddir, 'srctree')
+        shutil.copytree(testdir, srcdir)
+        builddir = os.path.join(srcdir, '_build')
+        self.change_builddir(builddir)
+        self.init(srcdir, override_envvars={'MESON_PACKAGE_CACHE_DIR': os.path.join(srcdir, 'cache_dir')})