extmod/vfs_posix_file: Implement finaliser for files.

Prevent handle leaks when file objects aren't closed explicitly and
fix some MICROPY_CPYTHON_COMPAT issues: this wasn't properly adhered
to because #ifdef was used so it was always on, and closing files
multiple times should be avoided unconditionally.

2 files changed, 30 insertions, 0 deletions

diff --git a/tests/extmod/vfs_posix.py b/tests/extmod/vfs_posix.py
index d193236696..3c23140065 100644
--- a/tests/extmod/vfs_posix.py
+++ b/tests/extmod/vfs_posix.py
@@ -1,6 +1,7 @@
 # Test for VfsPosix
 
 try:
+    import gc
     import uos
 
     uos.VfsPosix
@@ -51,6 +52,34 @@ f = open(temp_dir + "/test", "r")
 print(f.read())
 f.close()
 
+# file finaliser, also see vfs_fat_finaliser.py
+names = [temp_dir + "/x%d" % i for i in range(4)]
+basefd = temp_dir + "/nextfd1"
+nextfd = temp_dir + "/nextfd2"
+
+with open(basefd, "w") as f:
+    base_file_no = f.fileno()
+
+for i in range(1024):  # move GC head forwards by allocating a lot of single blocks
+    []
+
+
+def write_files_without_closing():
+    for n in names:
+        open(n, "w").write(n)
+    sorted(list(range(128)), key=lambda x: x)  # use up Python and C stack so f is really gone
+
+
+write_files_without_closing()
+gc.collect()
+
+with open(nextfd, "w") as f:
+    next_file_no = f.fileno()
+    print("next_file_no <= base_file_no", next_file_no <= base_file_no)
+
+for n in names + [basefd, nextfd]:
+    uos.remove(n)
+
 # rename
 uos.rename(temp_dir + "/test", temp_dir + "/test2")
 print(uos.listdir(temp_dir))
diff --git a/tests/extmod/vfs_posix.py.exp b/tests/extmod/vfs_posix.py.exp
index eb9ab43106..99922e621d 100644
--- a/tests/extmod/vfs_posix.py.exp
+++ b/tests/extmod/vfs_posix.py.exp
@@ -4,6 +4,7 @@ True
 <class 'list'>
 <io.TextIOWrapper 2>
 hello
+next_file_no <= base_file_no True
 ['test2']
 ['test2']
 <class 'tuple'>