Start of dependency tracer work.

blender_asset_tracer/bpathlib.py

@@ -0,0 +1,62 @@
+"""Blender path support.
+
+Does not use pathlib, because we may have to handle POSIX paths on Windows
+or vice versa.
+"""
+
+import os.path
+import string
+
+
+class BlendPath(bytes):
+    """A path within Blender is always stored as bytes."""
+
+    def __new__(cls, path):
+        if isinstance(path, str):
+            # As a convenience, when a string is given, interpret as UTF-8.
+            return bytes.__new__(cls, path.encode('utf-8'))
+        return bytes.__new__(cls, path)
+
+    def __str__(self) -> str:
+        """Decodes the path as UTF-8, replacing undecodable bytes.
+
+        Undecodable bytes are ignored so this function can be safely used
+        for reporting.
+        """
+        return self.decode('utf8', errors='replace')
+
+    def is_blendfile_relative(self) -> bool:
+        return self[:2] == b'//'
+
+    def is_absolute(self) -> bool:
+        if self.is_blendfile_relative():
+            return False
+        if self[0:1] == b'/':
+            return True
+
+        # Windows style path starting with drive letter.
+        if (len(self) >= 3 and
+                (self.decode('utf8'))[0] in string.ascii_letters and
+                self[1:2] == b':' and
+                self[2:3] in {b'\\', b'/'}):
+            return True
+
+        return False
+
+    def absolute(self, root: bytes=None) -> 'BlendPath':
+        """Determine absolute path.
+
+        :param root: root directory to compute paths relative to.
+            For blendfile-relative paths, root should be the directory
+            containing the blendfile. If not given, blendfile-relative
+            paths cause a ValueError but filesystem-relative paths are
+            resolved based on the current working directory.
+        """
+        if self.is_absolute():
+            return self
+
+        if self.is_blendfile_relative():
+            my_relpath = self[2:]  # strip off leading //
+        else:
+            my_relpath = self
+        return BlendPath(os.path.join(root, my_relpath))