rust plugin: genericize fetching cargo deps

To support workspaces, simply issue "cargo fetch" from the
build directory.  Should support both workspaces and non-worskpace
use. `cargo fetch` will honor Cargo.lock by default.

Update tests accordingly.

Signed-off-by: Chris Patterson <[email protected]>

Author: Chris Patterson

snapcraft/plugins/rust.py

@@ -158,21 +158,11 @@ def _fetch_rust(self) -> None:
             self.run(add_target_cmd, env=self._build_env())
 
     def _fetch_cargo_deps(self):
-        if self.options.source_subdir:
-            sourcedir = os.path.join(self.sourcedir, self.options.source_subdir)
-        else:
-            sourcedir = self.sourcedir
-
-        fetch_cmd = [
-            self._cargo_cmd,
-            "fetch",
-            "--manifest-path",
-            os.path.join(sourcedir, "Cargo.toml"),
-        ]
+        fetch_cmd = [self._cargo_cmd, "fetch"]
         toolchain = self._get_toolchain()
         if toolchain is not None:
             fetch_cmd.insert(1, "+{}".format(toolchain))
-        self.run(fetch_cmd, env=self._build_env())
+        self.run(fetch_cmd, env=self._build_env(), cwd=self.builddir)
 
     def _get_target(self) -> str:
         # Cf. rustc --print target-list

tests/unit/plugins/test_rust.py

@@ -193,8 +193,6 @@ def test_cross_compile(self, mock_download):
                         plugin._cargo_cmd,
                         "+stable",
                         "fetch",
-                        "--manifest-path",
-                        os.path.join(plugin.sourcedir, "Cargo.toml"),
                     ],
                     cwd=plugin.builddir,
                     env=plugin._build_env(),
@@ -259,8 +257,6 @@ def test_cross_compile_with_rust_toolchain_file(self, mock_download):
                     [
                         plugin._cargo_cmd,
                         "fetch",
-                        "--manifest-path",
-                        os.path.join(plugin.sourcedir, "Cargo.toml"),
                     ],
                     cwd=plugin.builddir,
                     env=plugin._build_env(),
@@ -348,8 +344,6 @@ def test_pull(self, script_mock):
                         plugin._cargo_cmd,
                         "+stable",
                         "fetch",
-                        "--manifest-path",
-                        os.path.join(plugin.sourcedir, "Cargo.toml"),
                     ],
                     cwd=plugin.builddir,
                     env=plugin._build_env(),
@@ -385,8 +379,6 @@ def test_pull_with_rust_toolchain_file(self, script_mock):
                     [
                         plugin._cargo_cmd,
                         "fetch",
-                        "--manifest-path",
-                        os.path.join(plugin.sourcedir, "Cargo.toml"),
                     ],
                     cwd=plugin.builddir,
                     env=plugin._build_env(),
@@ -428,8 +420,6 @@ def test_pull_with_channel(self, script_mock):
                         plugin._cargo_cmd,
                         "+nightly",
                         "fetch",
-                        "--manifest-path",
-                        os.path.join(plugin.sourcedir, "Cargo.toml"),
                     ],
                     cwd=plugin.builddir,
                     env=plugin._build_env(),
@@ -471,8 +461,6 @@ def test_pull_with_revision(self, script_mock):
                         plugin._cargo_cmd,
                         "+1.13.0",
                         "fetch",
-                        "--manifest-path",
-                        os.path.join(plugin.sourcedir, "Cargo.toml"),
                     ],
                     cwd=plugin.builddir,
                     env=plugin._build_env(),
@@ -513,8 +501,6 @@ def test_pull_with_source_and_source_subdir(self, script_mock):
                         plugin._cargo_cmd,
                         "+stable",
                         "fetch",
-                        "--manifest-path",
-                        os.path.join(plugin.sourcedir, "test-subdir", "Cargo.toml"),
                     ],
                     cwd=plugin.builddir,
                     env=plugin._build_env(),