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.  Introduce a new function that checks whether
a file is under a path in the same way, removing usage of Path
from the biggest hotspot.

Signed-off-by: Paolo Bonzini <[email protected]>

mesonbuild/interpreter/interpreter.py

@@ -20,7 +20,7 @@
 from .. import mesonlib
 from ..mesonlib import (EnvironmentVariables, ExecutableSerialisation, MesonBugException, MesonException, HoldableObject,
                         FileMode, MachineChoice, listify,
-                        extract_as_list, has_path_sep, path_is_in_root, PerMachine)
+                        path_starts_with, extract_as_list, has_path_sep, path_is_in_root, PerMachine)
 from ..options import OptionKey
 from ..programs import ExternalProgram, NonExistingExternalProgram
 from ..dependencies import Dependency
@@ -3135,29 +3135,31 @@ def do_validate_within_subproject(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 path_starts_with(norm, self.environment.build_dir):
                 return
-            if srcdir not in norm.parents:
+
+            if not path_starts_with(norm, self.environment.source_dir):
                 # 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(self.environment.source_dir, self.root_subdir, '')
+            if not path_starts_with(norm, project_root):
+                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 path_starts_with(norm, subproject_dir):
+                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)
 

mesonbuild/utils/universal.py

@@ -135,6 +135,7 @@ class _VerPickleLoadable(Protocol):
     'listify_array_value',
     'partition',
     'path_is_in_root',
+    'path_starts_with',
     'pickle_load',
     'Popen_safe',
     'Popen_safe_logged',
@@ -1126,6 +1127,27 @@ def determine_worker_count(varnames: T.Optional[T.List[str]] = None) -> int:
             num_workers = 1
     return num_workers
 
+def path_starts_with(name: str, path: str) -> bool:
+    '''Checks if @name is a file under the directory @path. Both @name and @path should be
+       adequately normalized, and either both or none should be absolute.'''
+    assert os.path.isabs(name) == os.path.isabs(path)
+    if is_windows():
+        name = name.replace('\\', '/')
+        path = path.replace('\\', '/')
+
+    split_name = name.split('/')
+    split_path = path.split('/')
+    while not split_path[-1]:
+        del split_path[-1]
+
+    if len(split_name) < len(split_path):
+        return False
+    for i, component in enumerate(split_path):
+        if component != split_name[i]:
+            return False
+    return True
+
+
 def has_path_sep(name: str, sep: str = '/\\') -> bool:
     'Checks if any of the specified @sep path separators are in @name'
     for each in sep: