cargo: include the implicit feature for dependencies in the manifest

Make the implicit `xyz = ["dep:xyz"]` declaration explicit in the Manifest.
This also makes it possible to implement correctly the part of the spec where
"If you specify the optional dependency with the dep: prefix anywhere in
the [features] table, that disables the implicit feature."

Signed-off-by: Paolo Bonzini <[email protected]>

Author: bonzini

mesonbuild/cargo/interpreter.py

@@ -499,9 +499,6 @@ def _enable_feature(self, pkg: PackageState, feature: str) -> None:
         if feature in cfg.features:
             return
         cfg.features.add(feature)
-        # A feature can also be a dependency.
-        if feature in pkg.manifest.dependencies:
-            self._add_dependency(pkg, feature)
         # Recurse on extra features and dependencies this feature pulls.
         # https://doc.rust-lang.org/cargo/reference/features.html#the-features-section
         for f in pkg.manifest.features.get(feature, []):

mesonbuild/cargo/manifest.py

@@ -7,6 +7,7 @@
 
 import collections
 import dataclasses
+import itertools
 import os
 import typing as T
 
@@ -518,7 +519,7 @@ def from_raw(cls, raw: raw.Manifest, path: str, workspace: T.Optional[Workspace]
         def dependencies_from_raw(x: T.Dict[str, T.Any]) -> T.Dict[str, Dependency]:
             return {k: Dependency.from_raw(k, v, member_path, workspace) for k, v in x.items()}
 
-        return _raw_to_dataclass(raw, cls, f'Cargo.toml package {pkg.name}',
+        data = _raw_to_dataclass(raw, cls, f'Cargo.toml package {pkg.name}',
                                  raw_from_workspace=workspace.inheritable if workspace else None,
                                  ignored_fields=['badges', 'workspace'],
                                  package=ConvertValue(lambda _: pkg),
@@ -533,6 +534,21 @@ def dependencies_from_raw(x: T.Dict[str, T.Any]) -> T.Dict[str, Dependency]:
                                  example=ConvertValue(lambda x: [Example.from_raw(b, pkg) for b in x]),
                                  target=ConvertValue(lambda x: {k: dependencies_from_raw(v.get('dependencies', {})) for k, v in x.items()}))
 
+        # If you specify the optional dependency with the dep: prefix anywhere in the [features]
+        # table, that disables the implicit feature.
+        deps = set(feature[4:]
+                   for feature in itertools.chain.from_iterable(data.features.values())
+                   if feature.startswith('dep:'))
+
+        for name, dep in itertools.chain(data.dependencies.items(),
+                                         data.dev_dependencies.items(),
+                                         data.build_dependencies.items()):
+            if dep.optional and name not in deps:
+                data.features.setdefault(name, [])
+                data.features[name].append(f'dep:{name}')
+                deps.add(name)
+
+        return data
 
 @dataclasses.dataclass
 class Workspace:

unittests/cargotests.py

@@ -299,6 +299,26 @@ class CargoTomlTest(unittest.TestCase):
         crate-type = ["lib"] # ignored
     ''')
 
+    CARGO_TOML_RUSTIX = textwrap.dedent('''\
+        [package]
+        name = "rustix"
+        edition = "2021"
+        rust-version = "1.63"
+        version = "0.38.34"
+
+        [dependencies]
+        alloc = { version = "1.0.0", optional = true, package = "rustc-std-workspace-alloc" }
+        libc = { version = "0.2.0", optional = true, package = "libc" }
+        libc_errno = { version = "0.3.8", optional = true, package = "errno" }
+
+        [features]
+        alloc = []
+        default = ["std"]
+        rustc-dep-of-std = ["dep:alloc"]
+        std = ["alloc"]
+        use-libc = ["libc_errno", "libc"]
+    ''')
+
     CARGO_TOML_WS = textwrap.dedent('''\
         [workspace]
         resolver = "2"
@@ -558,6 +578,21 @@ def test_cargo_toml_system_deps(self) -> None:
         self.assertEqual(len(manifest.system_dependencies['pango'].feature_overrides), 1)
         self.assertEqual(manifest.system_dependencies['pango'].feature_overrides['v1_42'], {'version': '1.42'})
 
+    def test_cargo_toml_dep_features(self) -> None:
+        with tempfile.TemporaryDirectory() as tmpdir:
+            fname = os.path.join(tmpdir, 'Cargo.toml')
+            with open(fname, 'w', encoding='utf-8') as f:
+                f.write(self.CARGO_TOML_RUSTIX)
+            manifest_toml = load_toml(fname)
+            manifest = Manifest.from_raw(manifest_toml, 'Cargo.toml')
+
+        # not included because 'alloc = []' exists
+        self.assertNotIn('dep:alloc', manifest.features['alloc'])
+        # included because no libc feature exists
+        self.assertIn('dep:libc', manifest.features['libc'])
+        # included with the dependency name, not the package name
+        self.assertIn('dep:libc_errno', manifest.features['libc_errno'])
+
     def test_cargo_toml_features(self) -> None:
         with tempfile.TemporaryDirectory() as tmpdir:
             fname = os.path.join(tmpdir, 'Cargo.toml')