[aot] Deprecate filename arg in ti.aot.Module.save() (taichi-dev#6554)

Issue: #

### Brief Summary
`filename` argument in `ti.aot.Module.save()` has been no-op for a long
time. This PR deprecates it and annouce that it'll be removed in v1.4.0
release.

Also added a test file called `test_deprecation.py` which is designed to
be the place to check all DeprecationWarnings so that before every
release we can just check here to see if we can safely remove any
deprecated apis.

python/taichi/aot/module.py

@@ -1,3 +1,4 @@
+import warnings
 from contextlib import contextmanager
 from glob import glob
 from pathlib import Path, PurePosixPath
@@ -199,14 +200,18 @@ def add_kernel_template(self, kernel_fn):
         kt = KernelTemplate(kernel_fn, self)
         yield kt
 
-    def save(self, filepath, filename):
+    def save(self, filepath, filename=None):
         """
         Args:
           filepath (str): path to a folder to store aot files.
           filename (str): filename prefix for stored aot files.
         """
+        if filename is not None:
+            warnings.warn(
+                "Specifying filename is no-op and will be removed in release v1.4.0",
+                DeprecationWarning)
         filepath = str(PurePosixPath(Path(filepath)))
-        self._aot_builder.dump(filepath, filename)
+        self._aot_builder.dump(filepath, "")
 
     def archive(self, filepath: str):
         """

tests/python/test_aot.py

@@ -48,7 +48,7 @@ def init():
         m = ti.aot.Module(ti.opengl)
         m.add_field('density', density)
         m.add_kernel(init)
-        m.save(tmpdir, '')
+        m.save(tmpdir)
         with open(os.path.join(tmpdir, 'metadata.json')) as json_file:
             res = json.load(json_file)
             range_hint = res['aot_data']['kernels']['init']['tasks'][0][
@@ -70,7 +70,7 @@ def init(x: ti.f32, density1: ti.types.ndarray(field_dim=2)):
     with tempfile.TemporaryDirectory() as tmpdir:
         m = ti.aot.Module(ti.lang.impl.current_cfg().arch)
         m.add_kernel(init, {'density1': density1})
-        m.save(tmpdir, '')
+        m.save(tmpdir)
         with open(os.path.join(tmpdir, 'metadata.json')) as json_file:
             res = json.load(json_file)
             buffer_binds = res['aot_data']['kernels']['init']['tasks'][0][
@@ -96,7 +96,7 @@ def init():
         m = ti.aot.Module(ti.lang.impl.current_cfg().arch)
         m.add_field('density', density)
         m.add_kernel(init)
-        m.save(tmpdir, '')
+        m.save(tmpdir)
         with open(os.path.join(tmpdir, 'metadata.json')) as json_file:
             json.load(json_file)
 
@@ -117,7 +117,7 @@ def foo(n: ti.template()):
         with m.add_kernel_template(foo) as kt:
             kt.instantiate(n=6)
             kt.instantiate(n=8)
-        m.save(tmpdir, '')
+        m.save(tmpdir)
         with open(os.path.join(tmpdir, 'metadata.json')) as json_file:
             json.load(json_file)
 
@@ -228,7 +228,7 @@ def init():
         m.add_field("grid_m", grid_m)
         m.add_kernel(substep)
         m.add_kernel(init)
-        m.save(tmpdir, '')
+        m.save(tmpdir)
         with open(os.path.join(tmpdir, 'metadata.json')) as json_file:
             json.load(json_file)
 
@@ -409,7 +409,7 @@ def initialize():
         m.add_kernel(initialize)
         m.add_kernel(substep)
 
-        m.save(tmpdir, '')
+        m.save(tmpdir)
         with open(os.path.join(tmpdir, 'metadata.json')) as json_file:
             json.load(json_file)
 
@@ -503,7 +503,7 @@ def substep(x: ti.types.ndarray(element_dim=1),
         }
         m.add_kernel(substep, template_args=template_args)
 
-        m.save(tmpdir, '')
+        m.save(tmpdir)
         with open(os.path.join(tmpdir, 'metadata.json')) as json_file:
             json.load(json_file)
 
@@ -570,7 +570,7 @@ def init_data(test_vec: ivec3):
         # note ti.aot.Module(ti.opengl) is no-op according to its docstring.
         m = ti.aot.Module(ti.lang.impl.current_cfg().arch)
         m.add_graph("g_init", g_init)
-        m.save(tmpdir, '')
+        m.save(tmpdir)
         with open(os.path.join(tmpdir, 'metadata.json'), "r") as json_file:
             json.load(json_file)
 
@@ -596,4 +596,4 @@ def test(a: ti.types.ndarray(), c: ti.u8):
     m = ti.aot.Module(ti.lang.impl.current_cfg().arch, caps=['spirv_has_int8'])
     m.add_graph('g_init', g)
     with tempfile.TemporaryDirectory() as tmpdir:
-        m.save(tmpdir, '')
+        m.save(tmpdir)

tests/python/test_deprecation.py

@@ -0,0 +1,21 @@
+import tempfile
+
+import pytest
+
+import taichi as ti
+from tests import test_utils
+
+
+@test_utils.test(arch=[ti.vulkan, ti.opengl, ti.cuda, ti.cpu])
+def test_deprecated_aot_save_filename():
+    density = ti.field(float, shape=(4, 4))
+
+    with tempfile.TemporaryDirectory() as tmpdir:
+        m = ti.aot.Module(ti.lang.impl.current_cfg().arch)
+        m.add_field('density', density)
+        with pytest.warns(
+                DeprecationWarning,
+                match=
+                r'Specifying filename is no-op and will be removed in release v1.4.0'
+        ):
+            m.save(tmpdir, 'filename')