capture errors from cargo metadata (#254)

Author: h-vetinari

setuptools_rust/build.py

@@ -210,9 +210,21 @@ def build_extension(
 
         # Execute cargo
         try:
-            output = subprocess.check_output(command, env=env, encoding="latin-1")
+            output = subprocess.check_output(
+                command, env=env, encoding="latin-1", stderr=subprocess.PIPE
+            )
         except subprocess.CalledProcessError as e:
-            raise CompileError(f"cargo failed with code: {e.returncode}\n{e.output}")
+            raise CompileError(
+                f"""
+                cargo failed with code: {e.returncode}
+
+                Output captured from stderr:
+                {e.stderr}
+
+                Output captured from stdout:
+                {e.stdout}
+                """
+            )
 
         except OSError:
             raise DistutilsExecError(

setuptools_rust/extension.py

@@ -240,7 +240,32 @@ def _metadata(self) -> "_CargoMetadata":
             ]
             if self.cargo_manifest_args:
                 metadata_command.extend(self.cargo_manifest_args)
-            self._cargo_metadata = json.loads(subprocess.check_output(metadata_command))
+
+            try:
+                payload = subprocess.check_output(
+                    metadata_command, encoding="latin-1", stderr=subprocess.PIPE
+                )
+            except subprocess.CalledProcessError as e:
+                raise DistutilsSetupError(
+                    f"""
+                    cargo metadata failed with code: {e.returncode}
+
+                    Output captured from stderr:
+                    {e.stderr}
+
+                    Output captured from stdout:
+                    {e.stdout}
+                    """
+                )
+            try:
+                self._cargo_metadata = json.loads(payload)
+            except json.decoder.JSONDecodeError as e:
+                raise DistutilsSetupError(
+                    f"""
+                    Error parsing output of cargo metadata as json; received:
+                    {payload}
+                    """
+                ) from e
         return self._cargo_metadata
 
     def _uses_exec_binding(self) -> bool: