Renamed module tracer → trace

This is consistent with the other module names.

blender_asset_tracer/trace/__init__.py

@@ -0,0 +1,49 @@
+import logging
+import pathlib
+import typing
+
+from blender_asset_tracer import blendfile
+from . import result, blocks2assets, file2blocks
+
+log = logging.getLogger(__name__)
+
+codes_to_skip = {
+    # These blocks never have external assets:
+    b'ID', b'WM', b'SN',
+
+    # These blocks are skipped for now, until we have proof they point to
+    # assets otherwise missed:
+    b'GR', b'WO', b'BR', b'LS',
+}
+
+
+def deps(bfilepath: pathlib.Path) -> typing.Iterator[result.BlockUsage]:
+    """Open the blend file and report its dependencies.
+
+    :param bfilepath: File to open.
+    """
+
+    log.info('opening: %s', bfilepath)
+    bfile = blendfile.open_cached(bfilepath)
+
+    # Sort the asset-holding blocks so that we can iterate over them
+    # in disk order, which is slightly faster than random order.
+    ahb = asset_holding_blocks(file2blocks.iter_blocks(bfile))
+    for block in sorted(ahb):
+        yield from blocks2assets.iter_assets(block)
+
+
+def asset_holding_blocks(blocks: typing.Iterable[blendfile.BlendFileBlock]) \
+        -> typing.Iterator[blendfile.BlendFileBlock]:
+    """Generator, yield data blocks that could reference external assets."""
+    for block in blocks:
+        assert isinstance(block, blendfile.BlendFileBlock)
+        code = block.code
+
+        # The longer codes are either arbitrary data or data blocks that
+        # don't refer to external assets. The former data blocks will be
+        # visited when we hit the two-letter datablocks that use them.
+        if len(code) > 2 or code in codes_to_skip:
+            continue
+
+        yield block