bootstrap: Removed second fetch and allow for SHA

This commit cleans up the second fetch, which potentially could have
changed content since first fetch.

Normal ref-space (similar to git clone) and user specified revision is
now fetched in same command.

This further allows to checkout tags in detached HEAD while still
referring to the tag name instead of FETCH_HEAD.

This commit also allows a user to specify a sha.
When specify a sha as revision, that sha must be valid in to the normal
ref-space.

Signed-off-by: Torsten Rasmussen <torsten.rasmussen@nordicsemi.no>

src/west/_bootstrap/main.py

@@ -91,32 +91,49 @@ def west_topdir(start=None):
         cur_dir = parent_dir
 
 
+def _is_sha(s):
+    try:
+        int(s, 16)
+    except ValueError:
+        return False
+
+    return len(s) == 40
+
+
 def clone(desc, url, rev, dest, exist_ok=False):
     if not exist_ok and os.path.exists(dest):
         raise WestError('refusing to clone into existing location ' + dest)
 
     print('=== Cloning {} from {}, rev. {} into {} ==='.format(desc, url, rev,
                                                                dest))
-    branch = False
+    local_rev = False
     subprocess.check_call(('git', 'init', dest))
-    os.chdir(dest)
-    subprocess.check_call(('git', 'remote', 'add', 'origin', '--', url))
-    subprocess.check_call(('git', 'fetch', 'origin', '--', rev))
+    subprocess.check_call(('git', '-C', dest, 'remote', 'add', 'origin',
+                           '--', url))
+    is_sha = _is_sha(rev)
+    if is_sha:
+        # Fetch the ref-space and hope the SHA is contained in that ref-space
+        subprocess.check_call(('git', '-C', dest, 'fetch', 'origin', '--tags',
+                               '--', 'refs/heads/*:refs/remotes/origin/*'))
+    else:
+        # Fetch the ref-space similar to git clone plus the ref given by user.
+        # Redundancy is ok, as example if user specify 'heads/master'.
+        # This allows users to specify: pull/<no>/head for pull requests
+        subprocess.check_call(('git', '-C', dest, 'fetch', 'origin', '--tags',
+                               '--', rev,
+                               'refs/heads/*:refs/remotes/origin/*'))
 
     try:
-        # Using show-ref to determine if rev is identical to a branch
-        subprocess.check_call(('git', 'show-ref', '--', rev))
-        branch = True
+        # Using show-ref to determine if rev is available in local repo.
+        subprocess.check_call(('git', '-C', dest, 'show-ref', '--', rev))
+        local_rev = True
     except subprocess.CalledProcessError:
         pass
 
-    if branch:
-        subprocess.check_call(('git', 'checkout', rev))
+    if local_rev or is_sha:
+        subprocess.check_call(('git', '-C', dest, 'checkout', rev))
     else:
-        subprocess.check_call(('git', 'checkout', 'FETCH_HEAD'))
-
-    # Fetch the rest of the ref-space, similar to git clone
-    subprocess.check_call(('git', 'fetch', '--tags', 'origin'))
+        subprocess.check_call(('git', '-C', dest, 'checkout', 'FETCH_HEAD'))
 
 
 #