Add morphlib.util.find_root and find_leaf functions

These will be used to find workspace and system branch root directories.

Also accidentally removed some whitespace from ends of lines. Too lazy
to split that into a separate commit.

1 files changed, 53 insertions, 6 deletions

diff --git a/morphlib/util.py b/morphlib/util.py
index a9c22217..ead0bafe 100644
--- a/morphlib/util.py
+++ b/morphlib/util.py
@@ -197,28 +197,28 @@ def copyfileobj(inputfp, outputfp, blocksize=1024*1024):  # pragma: no cover
     while 1:
         inbuf = inputfp.read(blocksize)
         if not inbuf: break
-        if not buf: 
+        if not buf:
             buf = inbuf
         else:
             buf += inbuf
-            
+
         # Combine "short" reads
         if (len(buf) < blocksize):
             continue
-            
+
         buflen = len(buf)
         if buf == "\x00" * buflen:
             outputfp.seek(buflen, os.SEEK_CUR)
             buf = None
             # flag sparse=True, that we seek()ed, but have not written yet
             # The filesize is wrong until we write
-            sparse = True 
+            sparse = True
         else:
             outputfp.write(buf)
             buf = None
             # We wrote, so clear sparse.
             sparse = False
-            
+
     if buf:
         outputfp.write(buf)
     elif sparse:
@@ -244,7 +244,7 @@ def on_same_filesystem(path_a, path_b): # pragma: no cover
 def unify_space_requirements(tmp_path, tmp_min_size,
                              cache_path, cache_min_size): # pragma: no cover
     """Adjust minimum sizes when paths share a disk.
-    
+
        Given pairs of path and minimum size, return the minimum sizes such
        that when the paths are on the same disk, the sizes are added together.
 
@@ -280,3 +280,50 @@ def check_disk_available(tmp_path, tmp_min_size,
                          'space or reduce the disk space required by the '
                          'tempdir-min-space and cachedir-min-space '
                          'configuration options.')
+
+
+
+
+def find_root(dirname, subdir_name):
+    '''Find parent of a directory, at or above a given directory.
+
+    The sought-after directory is indicated by the existence of a
+    subdirectory of the indicated name. For example, dirname might
+    be the current working directory of the process, and subdir_name
+    might be ".morph"; then the returned value would be the Morph
+    workspace root directory, which has a subdirectory called
+    ".morph".
+
+    Return path to desired directory, or None if not found.
+
+    '''
+
+    dirname = os.path.normpath(os.path.abspath(dirname))
+    while not os.path.isdir(os.path.join(dirname, subdir_name)):
+        if dirname == '/':
+            return None
+        dirname = os.path.dirname(dirname)
+    return dirname
+
+
+def find_leaf(dirname, subdir_name):
+    '''This is like find_root, except it looks towards leaves.
+
+    It only looks in a subdirectory if it is the only subdirectory.
+    If there are no subdirectories, or more than one, fail.
+    (Subdirectories whose name starts with a dot are ignored for this.)
+
+    '''
+
+    while True:
+        if os.path.exists(os.path.join(dirname, subdir_name)):
+            return dirname
+        pathnames = [
+            os.path.join(dirname, x)
+            for x in os.listdir(dirname)
+            if not x.startswith('.')]
+        subdirs = [x for x in pathnames if os.path.isdir(x)]
+        if len(subdirs) != 1:
+            return None
+        dirname = subdirs[0]
+