interpreter: do not use pathlib in validate_within_subproject

pathlib's implementation of Path iteration is expensive;
"foo.parents" has quadratic complexity when building it:

        return self._path._from_parsed_parts(self._drv, self._root,
                                             self._tail[:-idx - 1])

and comparisons performed by "path in file.parents" potentially
have the same issue.  Use the newly introduced "is_parent_path"
function to check whether a file is under a path in the same way.
This removes Path from its hottest use.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

mesonbuild/interpreter/interpreter.py

@@ -19,7 +19,7 @@ from .. import envconfig
 from ..wrap import wrap, WrapMode
 from .. import mesonlib
 from ..mesonlib import (EnvironmentVariables, ExecutableSerialisation, MesonBugException, MesonException, HoldableObject,
-                        FileMode, MachineChoice, listify,
+                        FileMode, MachineChoice, is_parent_path, listify,
                         extract_as_list, has_path_sep, path_is_in_root, PerMachine)
 from ..options import OptionKey
 from ..programs import ExternalProgram, NonExistingExternalProgram
@@ -3133,8 +3133,8 @@ class Interpreter(InterpreterBase, HoldableObject):
     # subproject than it is defined in (due to e.g. a
     # declare_dependency).
     def validate_within_subproject(self, subdir, fname):
-        srcdir = Path(self.environment.source_dir)
-        builddir = Path(self.environment.build_dir)
+        srcdir = self.environment.source_dir
+        builddir = self.environment.build_dir
         if isinstance(fname, P_OBJ.DependencyVariableString):
             def validate_installable_file(fpath: Path) -> bool:
                 installablefiles: T.Set[Path] = set()
@@ -3155,34 +3155,36 @@ class Interpreter(InterpreterBase, HoldableObject):
             if validate_installable_file(norm):
                 return
 
-        def do_validate_within_subproject(norm: Path) -> None:
+        def do_validate_within_subproject(norm: str) -> None:
             if os.path.isdir(norm):
                 inputtype = 'directory'
             else:
                 inputtype = 'file'
-            if InterpreterRuleRelaxation.ALLOW_BUILD_DIR_FILE_REFERENCES in self.relaxations and builddir in norm.parents:
+            if InterpreterRuleRelaxation.ALLOW_BUILD_DIR_FILE_REFERENCES in self.relaxations and is_parent_path(builddir, norm):
                 return
-            if srcdir not in norm.parents:
+
+            if not is_parent_path(srcdir, norm):
                 # Grabbing files outside the source tree is ok.
                 # This is for vendor stuff like:
                 #
                 # /opt/vendorsdk/src/file_with_license_restrictions.c
                 return
-            project_root = Path(srcdir, self.root_subdir)
-            subproject_dir = project_root / self.subproject_dir
-            if norm == project_root:
-                return
-            if project_root not in norm.parents:
-                raise InterpreterException(f'Sandbox violation: Tried to grab {inputtype} {norm.name} outside current (sub)project.')
-            if subproject_dir == norm or subproject_dir in norm.parents:
-                raise InterpreterException(f'Sandbox violation: Tried to grab {inputtype} {norm.name} from a nested subproject.')
+
+            project_root = os.path.join(srcdir, self.root_subdir)
+            if not is_parent_path(project_root, norm):
+                name = os.path.basename(norm)
+                raise InterpreterException(f'Sandbox violation: Tried to grab {inputtype} {name} outside current (sub)project.')
+
+            subproject_dir = os.path.join(project_root, self.subproject_dir)
+            if is_parent_path(subproject_dir, norm):
+                name = os.path.basename(norm)
+                raise InterpreterException(f'Sandbox violation: Tried to grab {inputtype} {name} from a nested subproject.')
 
         fname = os.path.join(subdir, fname)
         if fname in self.validated_cache:
             return
 
-        # Use os.path.abspath() to eliminate .. segments, but do not resolve symlinks
-        norm = Path(os.path.abspath(Path(srcdir, fname)))
+        norm = os.path.abspath(os.path.join(srcdir, fname))
         do_validate_within_subproject(norm)
         self.validated_cache.add(fname)