build: delete all junctions before calling "git clean"

git clean can't deal with junctions and in case there is a loop
it follows them forever (or until stack overflow).
git-for-windows/git#5320

To work around this try to delete all junctions in the clean
re-try code path.

Fixes #108

msys2_autobuild/build.py

@@ -144,6 +144,21 @@ def chmod(p: PathLike) -> None:
                 chmod(fpath)
 
 
+def remove_junctions(topdir: PathLike) -> None:
+    # work around a git issue where it can't handle junctions
+    # https://github.com/git-for-windows/git/issues/5320
+    if not hasattr(os.path, 'isjunction'):  # Python 3.12 only
+        return
+    for root, dirs, _ in os.walk(topdir):
+        no_junctions = []
+        for d in dirs:
+            if not os.path.isjunction(os.path.join(root, d)):
+                no_junctions.append(d)
+            else:
+                os.remove(os.path.join(root, d))
+        dirs[:] = no_junctions
+
+
 def reset_git_repo(path: PathLike):
 
     def clean():
@@ -160,6 +175,7 @@ def clean():
                 if not made_writable:
                     print("Trying to make files writable")
                     make_tree_writable(path)
+                    remove_junctions(path)
                     made_writable = True
             except OSError as e:
                 print("Making files writable failed", e)

tests/main_test.py

@@ -7,7 +7,7 @@
 
 from msys2_autobuild.utils import parse_optional_deps
 from msys2_autobuild.queue import parse_buildqueue, get_cycles
-from msys2_autobuild.build import make_tree_writable
+from msys2_autobuild.build import make_tree_writable, remove_junctions
 
 
 def test_make_tree_writable():
@@ -37,6 +37,21 @@ def test_make_tree_writable():
         assert os.access(nested_junction, os.W_OK) and os.access(nested_junction, os.R_OK)
 
 
+def test_remove_junctions():
+    with tempfile.TemporaryDirectory() as tempdir:
+        nested_dir = Path(tempdir) / "nested"
+        nested_junction = nested_dir / "junction"
+        nested_dir.mkdir()
+
+        # Create a junction loop if possible, to make sure we ignore it
+        if hasattr(os.path, 'isjunction') and os.name == 'nt':
+            import _winapi
+            _winapi.CreateJunction(str(nested_dir), str(nested_junction))
+
+        remove_junctions(tempdir)
+        assert not nested_junction.exists()
+
+
 def test_parse_optional_deps():
     assert parse_optional_deps("a:b,c:d,a:x") == {'a': ['b', 'x'], 'c': ['d']}