bitbake: checksum: In FileChecksumCache don't follow directory symlinks

Before this patch, directory symlinks mathcing filename pattern (either
a file name or a glob pattern) were followed. However, directory
symlinks deeper in the search chain were omitted by os.walk(). Now
directory traversal behaves consistently, ignoring syminks on all
levels.

One reason for choosing not to "walk into" directory symlinks is that
dir symlinks in externalsrc.bbclass in oe-core are causing problems in
source tree checksumming.

[YOCTO #8853]

(Bitbake rev: 66dff37ebcd1dd14ebd6933d727df9cf0a641866)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/checksum.py

@@ -123,12 +123,14 @@ class FileChecksumCache(MultiProcessCache):
                 # Handle globs
                 for f in glob.glob(pth):
                     if os.path.isdir(f):
-                        checksums.extend(checksum_dir(f))
+                        if not os.path.islink(f):
+                            checksums.extend(checksum_dir(f))
                     else:
                         checksum = checksum_file(f)
                         checksums.append((f, checksum))
             elif os.path.isdir(pth):
-                checksums.extend(checksum_dir(pth))
+                if not os.path.islink(pth):
+                    checksums.extend(checksum_dir(pth))
             else:
                 checksum = checksum_file(pth)
                 checksums.append((pth, checksum))