fix: Fix the bug that pdm plugins are invalid on ubuntu system python(#3289) (#3293)

* fix: Fix the bug that pdm plugins are invalid after installation on ubuntu.

* ensure backwards compatibility

* fix: undefined name

* make code runnable before python 3.10

* use "posix_prefix" as scheme on both plugin-installing and loading sides on ubuntu

Author: monchin

news/3289.bugfix.md

@@ -0,0 +1 @@
+Fix the bug that pdm plugins are invalid after installation on ubuntu system python.

src/pdm/core.py

@@ -316,7 +316,15 @@ def _add_project_plugins_library(self) -> None:
 
         base = str(project.root / ".pdm-plugins")
         replace_vars = {"base": base, "platbase": base}
-        scheme = "nt" if os.name == "nt" else "posix_prefix"
+
+        scheme_names = sysconfig.get_scheme_names()
+        if (sys.platform == "darwin" and "osx_framework_library" in scheme_names) or sys.platform == "linux":
+            scheme = "posix_prefix"
+        # sysconfig._get_default_scheme is a private function in 3.8 & 3.9
+        elif sys.version_info < (3, 10):
+            scheme = "nt" if os.name == "nt" else "posix_prefix"
+        else:
+            scheme = sysconfig.get_default_scheme()
         purelib = sysconfig.get_path("purelib", scheme, replace_vars)
         scripts = sysconfig.get_path("scripts", scheme, replace_vars)
         site.addsitedir(purelib)

src/pdm/models/in_process/sysconfig_get_paths.py

@@ -36,7 +36,9 @@ def get_paths(kind="default", vars=None):
             raise ValueError(f"{scheme} is not a valid scheme on the system, or user site may be disabled.")
         return sysconfig.get_paths(scheme, vars=vars)
     else:
-        if sys.platform == "darwin" and "osx_framework_library" in scheme_names and kind == "prefix":
+        if (
+            (sys.platform == "darwin" and "osx_framework_library" in scheme_names) or sys.platform == "linux"
+        ) and kind == "prefix":
             return sysconfig.get_paths("posix_prefix", vars=vars)
         return sysconfig.get_paths(vars=vars)