Skip install step when a package has nothing to install

colcon_cargo/task/cargo/build.py

@@ -1,6 +1,7 @@
 # Copyright 2018 Easymov Robotics
 # Licensed under the Apache License, Version 2.0
 
+import json
 from pathlib import Path
 import shutil
 
@@ -80,12 +81,12 @@ async def build(  # noqa: D102
         if rc and rc.returncode:
             return rc.returncode
 
+        # colcon-ros-cargo overrides install command to return None.
+        # We also need to check if the package has any binaries, because if it
+        # has no binaries then cargo install will return an error.
         cmd = self._install_cmd(cargo_args)
-
-        self.progress('install')
-
-        # colcon-ros-cargo overrides install command to return None
-        if cmd is not None:
+        if cmd is not None and await self._has_binaries(env):
+            self.progress('install')
             rc = await run(
                 self.context, cmd, cwd=self.context.pkg.path, env=env)
             if rc and rc.returncode:
@@ -126,3 +127,42 @@ def _install_cmd(self, cargo_args):
             '--path', '.',
             '--root', args.install_base,
         ] + cargo_args
+
+    # Identify if there are any binaries to install for the current package
+    async def _has_binaries(self, env):
+        cmd = [
+            CARGO_EXECUTABLE,
+            'metadata',
+            '--no-deps',
+            '--format-version', '1',
+        ]
+
+        rc = await run(
+            self.context,
+            cmd,
+            cwd=self.context.pkg.path,
+            capture_output=True,
+            env=env
+        )
+        if rc is None or rc.returncode != 0:
+            raise RuntimeError(
+                "Could not inspect package using 'cargo metadata'"
+            )
+
+        if rc.stdout is None:
+            raise RuntimeError(
+                "Failed to capture stdout from 'cargo metadata'"
+            )
+
+        metadata = json.loads(rc.stdout)
+        for package in metadata.get('packages', {}):
+            for target in package.get('targets', {}):
+                for crate_type in target.get('crate_types', {}):
+                    if crate_type == 'bin':
+                        # If any one binary exists in the package then we
+                        # should go ahead and run cargo install
+                        return True
+
+        # If no binary target exists in the whole package, then skip running
+        # cargo install because it would produce an error.
+        return False

test/rust-pure-library/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "rust-pure-library"
+version = "0.1.0"
+authors = ["Luca Della Vedova<[email protected]>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

test/rust-pure-library/src/lib.rs

@@ -0,0 +1 @@
+pub struct Type;

test/test_build.py

@@ -19,8 +19,10 @@
 import pytest
 
 TEST_PACKAGE_NAME = 'rust-sample-package'
+PURE_LIBRARY_PACKAGE_NAME = 'rust-pure-library'
 
 test_project_path = Path(__file__).parent / TEST_PACKAGE_NAME
+pure_library_path = Path(__file__).parent / PURE_LIBRARY_PACKAGE_NAME
 
 
 @pytest.fixture(autouse=True)
@@ -107,6 +109,43 @@ def test_build_and_test_package():
         event_loop.close()
 
 
+@pytest.mark.skipif(
+    not shutil.which('cargo'),
+    reason='Rust must be installed to run this test')
+def test_skip_pure_library_package():
+    event_loop = new_event_loop()
+    asyncio.set_event_loop(event_loop)
+
+    try:
+        cpi = CargoPackageIdentification()
+        package = PackageDescriptor(pure_library_path)
+        cpi.identify(package)
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            tmpdir = Path(tmpdir)
+            # TODO(luca) Also test clean build and cargo args
+            context = TaskContext(pkg=package,
+                                  args=SimpleNamespace(
+                                      path=str(pure_library_path),
+                                      build_base=str(tmpdir / 'build'),
+                                      install_base=str(tmpdir / 'install'),
+                                      clean_build=None,
+                                      cargo_args=None,
+                                  ),
+                                  dependencies={}
+                                  )
+
+            task = CargoBuildTask()
+            task.set_context(context=context)
+
+            # Make sure the task succeeds, even though there is no binary
+            rc = event_loop.run_until_complete(task.build())
+            assert not rc
+
+    finally:
+        event_loop.close()
+
+
 # Check the testing result file, expect cargo test and doc test to fail
 # but fmt to succeed
 def check_result_file(path):