Handle nested build paths

Author: stefanv

spin/cmds/meson.py

@@ -293,7 +293,10 @@ def build(
     Which can then be used to build (`spin-clang build`), to test (`spin-clang test ...`), etc.
 
     """
+    abs_build_dir = os.path.abspath(build_dir)
     install_dir = _get_install_dir(build_dir)
+    abs_install_dir = os.path.abspath(install_dir)
+
     cfg = get_config()
     distname = cfg.get("project.name", None)
     if distname and _is_editable_install_of_same_source(distname):
@@ -355,7 +358,7 @@ def build(
             "--destdir",
             install_dir
             if os.path.isabs(install_dir)
-            else os.path.join("..", install_dir),
+            else os.path.relpath(abs_install_dir, abs_build_dir),
         ],
         output=(not quiet) and verbose,
     )

spin/tests/test_build_cmds.py

@@ -159,18 +159,18 @@ def test_lldb():
 @skip_py_lt_311  # python command does not run on older pythons
 def test_parallel_builds():
     spin("build")
-    spin("build", "-C", "parallel-build")
+    spin("build", "-C", "parallel/build")
     p = spin("python", "--", "-c", "import example_pkg; print(example_pkg.__file__)")
     example_pkg_path = stdout(p).split("\n")[-1]
     p = spin(
         "python",
         "-C",
-        "parallel-build",
+        "parallel/build",
         "--",
         "-c",
         "import example_pkg; print(example_pkg.__file__)",
     )
     example_pkg_parallel_path = stdout(p).split("\n")[-1]
     assert "build-install" in example_pkg_path
-    assert "parallel-build-install" in example_pkg_parallel_path
-    assert "parallel-build-install" not in example_pkg_path
+    assert "parallel/build-install" in example_pkg_parallel_path
+    assert "parallel/build-install" not in example_pkg_path