Repository: numba/numba

Issue:
Ellipsis indexing and assignment not working when needed number of `:` is zero
I was trying to index using `...` on both sides of assignment so I could use the same function for inputs with 1, 2, or N dimensions.

Here is code for the MCVE (using `numba` 0.39.0):
```python
import numpy as np
import numba

def func(A, B, indices):
    rv = A.copy()
    for i in range(indices.size):
        index = indices[i]
        rv[..., index] = B[..., index]
    return rv

jitted = numba.njit(func)

A = np.ones((3, 5))
B = 2 * np.ones((3, 5))
indices = np.array([0, 2])

jitted(A[0], B[0], indices)  # <-- raises.  traceback below
```
Let's compare results using `numpy` and `numba`:
```python
In [2]: func(A, B, indices)
Out[2]: 
array([[2., 1., 2., 1., 1.],
       [2., 1., 2., 1., 1.],
       [2., 1., 2., 1., 1.]])

In [3]: func(A[0], B[0], indices)
Out[3]: array([2., 1., 2., 1., 1.])

In [4]: jitted(A, B, indices)
Out[4]: 
array([[2., 1., 2., 1., 1.],
       [2., 1., 2., 1., 1.],
       [2., 1., 2., 1., 1.]])

In [5]: jitted(A[0], B[0], indices)  # <-- raises.  traceback below
```
Traceback:
<details>

```python-traceback
---------------------------------------------------------------------------
NotImplementedError                       Traceback (most recent call last)
~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/targets/base.py in cast(self, builder, val, fromty, toty)
    674         try:
--> 675             impl = self._casts.find((fromty, toty))
    676             return impl(self, builder, fromty, toty, val)

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/targets/base.py in find(self, sig)
     47         if out is None:
---> 48             out = self._find(sig)
     49             self._cache[sig] = out

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/targets/base.py in _find(self, sig)
     56         else:
---> 57             raise NotImplementedError(self, sig)
     58 

NotImplementedError: (<numba.targets.base.OverloadSelector object at 0x1059269e8>, (array(float64, 0d, C), float64))

During handling of the above exception, another exception occurred:

NotImplementedError                       Traceback (most recent call last)
~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/errors.py in new_error_context(fmt_, *args, **kwargs)
    576     try:
--> 577         yield
    578     except NumbaError as e:

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/lowering.py in lower_block(self, block)
    253                                    loc=self.loc, errcls_=defaulterrcls):
--> 254                 self.lower_inst(inst)
    255 

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/lowering.py in lower_inst(self, inst)
    357             assert signature is not None
--> 358             return self.lower_setitem(inst.target, inst.index, inst.value, signature)
    359 

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/lowering.py in lower_setitem(self, target_var, index_var, value_var, signature)
    429 
--> 430         return impl(self.builder, (target, index, value))
    431 

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/targets/base.py in __call__(self, builder, args)
   1078     def __call__(self, builder, args):
-> 1079         return self._imp(self._context, builder, self._sig, args)
   1080 

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/targets/arrayobj.py in setitem_array(context, builder, sig, args)
    481     # Store source value the given location
--> 482     val = context.cast(builder, val, valty, aryty.dtype)
    483     store_item(context, builder, aryty, val, dataptr)

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/targets/base.py in cast(self, builder, val, fromty, toty)
    678             raise NotImplementedError(
--> 679                 "Cannot cast %s to %s: %s" % (fromty, toty, val))
    680 

NotImplementedError: Cannot cast array(float64, 0d, C) to float64: %".417" = load {i8*, i8*, i64, i64, double*, [0 x i64], [0 x i64]}, {i8*, i8*, i64, i64, double*, [0 x i64], [0 x i64]}* %"$22.9"

During handling of the above exception, another exception occurred:

LoweringError                             Traceback (most recent call last)
<ipython-input-6-e6ce0775290a> in <module>()
----> 1 jitted(A[0], B[0], indices)

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/dispatcher.py in _compile_for_args(self, *args, **kws)
    366                     e.patch_message(''.join(e.args) + help_msg)
    367             # ignore the FULL_TRACEBACKS config, this needs reporting!
--> 368             raise e
    369 
    370     def inspect_llvm(self, signature=None):

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/dispatcher.py in _compile_for_args(self, *args, **kws)
    323                 argtypes.append(self.typeof_pyval(a))
    324         try:
--> 325             return self.compile(tuple(argtypes))
    326         except errors.TypingError as e:
    327             # Intercept typing error that may be due to an argument

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/dispatcher.py in compile(self, sig)
    651 
    652                 self._cache_misses[sig] += 1
--> 653                 cres = self._compiler.compile(args, return_type)
    654                 self.add_overload(cres)
    655                 self._cache.save_overload(sig, cres)

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/dispatcher.py in compile(self, args, return_type)
     81                                       args=args, return_type=return_type,
     82                                       flags=flags, locals=self.locals,
---> 83                                       pipeline_class=self.pipeline_class)
     84         # Check typing error if object mode is used
     85         if cres.typing_error is not None and not flags.enable_pyobject:

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/compiler.py in compile_extra(typingctx, targetctx, func, args, return_type, flags, locals, library, pipeline_class)
    871     pipeline = pipeline_class(typingctx, targetctx, library,
    872                               args, return_type, flags, locals)
--> 873     return pipeline.compile_extra(func)
    874 
    875 

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/compiler.py in compile_extra(self, func)
    365         self.lifted = ()
    366         self.lifted_from = None
--> 367         return self._compile_bytecode()
    368 
    369     def compile_ir(self, func_ir, lifted=(), lifted_from=None):

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/compiler.py in _compile_bytecode(self)
    802         """
    803         assert self.func_ir is None
--> 804         return self._compile_core()
    805 
    806     def _compile_ir(self):

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/compiler.py in _compile_core(self)
    789         self.define_pipelines(pm)
    790         pm.finalize()
--> 791         res = pm.run(self.status)
    792         if res is not None:
    793             # Early pipeline completion

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/compiler.py in run(self, status)
    251                     # No more fallback pipelines?
    252                     if is_final_pipeline:
--> 253                         raise patched_exception
    254                     # Go to next fallback pipeline
    255                     else:

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/compiler.py in run(self, status)
    243                 try:
    244                     event(stage_name)
--> 245                     stage()
    246                 except _EarlyPipelineCompletion as e:
    247                     return e.result

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/compiler.py in stage_nopython_backend(self)
    676         """
    677         lowerfn = self.backend_nopython_mode
--> 678         self._backend(lowerfn, objectmode=False)
    679 
    680     def stage_compile_interp_mode(self):

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/compiler.py in _backend(self, lowerfn, objectmode)
    626             self.library.enable_object_caching()
    627 
--> 628         lowered = lowerfn()
    629         signature = typing.signature(self.return_type, *self.args)
    630         self.cr = compile_result(

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/compiler.py in backend_nopython_mode(self)
    613                 self.return_type,
    614                 self.calltypes,
--> 615                 self.flags)
    616 
    617     def _backend(self, lowerfn, objectmode):

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/compiler.py in native_lowering_stage(targetctx, library, interp, typemap, restype, calltypes, flags)
    990 
    991     lower = lowering.Lower(targetctx, library, fndesc, interp)
--> 992     lower.lower()
    993     if not flags.no_cpython_wrapper:
    994         lower.create_cpython_wrapper(flags.release_gil)

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/lowering.py in lower(self)
    171         if self.generator_info is None:
    172             self.genlower = None
--> 173             self.lower_normal_function(self.fndesc)
    174         else:
    175             self.genlower = self.GeneratorLower(self)

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/lowering.py in lower_normal_function(self, fndesc)
    212         # Init argument values
    213         self.extract_function_arguments()
--> 214         entry_block_tail = self.lower_function_body()
    215 
    216         # Close tail of entry block

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/lowering.py in lower_function_body(self)
    237             bb = self.blkmap[offset]
    238             self.builder.position_at_end(bb)
--> 239             self.lower_block(block)
    240 
    241         self.post_lower()

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/lowering.py in lower_block(self, block)
    252             with new_error_context('lowering "{inst}" at {loc}', inst=inst,
    253                                    loc=self.loc, errcls_=defaulterrcls):
--> 254                 self.lower_inst(inst)
    255 
    256     def create_cpython_wrapper(self, release_gil=False):

~/miniconda3/envs/numba3/lib/python3.7/contextlib.py in __exit__(self, type, value, traceback)
    128                 value = type()
    129             try:
--> 130                 self.gen.throw(type, value, traceback)
    131             except StopIteration as exc:
    132                 # Suppress StopIteration *unless* it's the same exception that

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/errors.py in new_error_context(fmt_, *args, **kwargs)
    583         from numba import config
    584         tb = sys.exc_info()[2] if config.FULL_TRACEBACKS else None
--> 585         six.reraise(type(newerr), newerr, tb)
    586 
    587 

~/miniconda3/envs/numba3/lib/python3.7/site-packages/numba/six.py in reraise(tp, value, tb)
    657         if value.__traceback__ is not tb:
    658             raise value.with_traceback(tb)
--> 659         raise value
    660 
    661 else:

LoweringError: Failed at nopython (nopython mode backend)
Cannot cast array(float64, 0d, C) to float64: %".417" = load {i8*, i8*, i64, i64, double*, [0 x i64], [0 x i64]}, {i8*, i8*, i64, i64, double*, [0 x i64], [0 x i64]}* %"$22.9"

File "<ipython-input-1-f6cc8d5fb861>", line 8:
def func(A, B, indices):
    <source elided>
        index = indices[i]
        rv[..., index] = B[..., index]
        ^
[1] During: lowering "rv[$22.13] = $22.9" at <ipython-input-1-f6cc8d5fb861> (8)
-------------------------------------------------------------------------------
This should not have happened, a problem has occurred in Numba's internals.

Please report the error message and traceback, along with a minimal reproducer
at: https://github.com/numba/numba/issues/new

If more help is needed please feel free to speak to the Numba core developers
directly at: https://gitter.im/numba/numba

Thanks in advance for your help in improving Numba!
```

</details>


Discussion:
Thanks for the report, I can reproduce. According to the trace back it seems like casting a 0d array to a scalar is not working and this is required for the `setitem` of the index of `rv` to some part of `B`.

Resolving patch:
diff --git a/numba/typing/arraydecl.py b/numba/typing/arraydecl.py
--- a/numba/typing/arraydecl.py
+++ b/numba/typing/arraydecl.py
@@ -144,7 +144,11 @@ def check_contiguity(outer_indices):
             elif not check_contiguity(right_indices[::-1]):
                 layout = 'A'
 
-        res = ary.copy(ndim=ndim, layout=layout)
+        if ndim == 0:
+            # Implicitly convert to a scalar if the output ndim==0
+            res = ary.dtype
+        else:
+            res = ary.copy(ndim=ndim, layout=layout)
 
     # Re-wrap indices
     if isinstance(idx, types.BaseTuple):


Test patch:
diff --git a/numba/tests/test_fancy_indexing.py b/numba/tests/test_fancy_indexing.py
--- a/numba/tests/test_fancy_indexing.py
+++ b/numba/tests/test_fancy_indexing.py
@@ -117,6 +117,16 @@ def test_getitem_tuple_and_ellipsis(self):
 
         self.check_getitem_indices(arr, indices)
 
+    def test_ellipsis_getsetitem(self):
+        # See https://github.com/numba/numba/issues/3225
+        @jit(nopython=True)
+        def foo(arr, v):
+            arr[..., 0] = arr[..., 1]
+
+        arr = np.arange(2)
+        foo(arr, 1)
+        self.assertEqual(arr[0], arr[1])
+
     @tag('important')
     def test_getitem_array(self):
         # Test advanced indexing with a single array index
@@ -187,7 +197,7 @@ def check(arr, ind):
         # 3. nd array index
         # 4. reflected list
         # 5. tuples
-        
+
         test_indices = []
         test_indices.append(1)
         test_indices.append(np.array([1, 5, 1, 11, 3]))
@@ -195,7 +205,7 @@ def check(arr, ind):
         test_indices.append([1, 5, 1, 11, 3])
         test_indices.append((1, 5, 1))
         test_indices.append(((1, 5, 1), (11, 3, 2)))
-    
+
         for dt in [np.int64, np.complex128]:
             A = np.arange(12, dtype=dt).reshape((4, 3))
             for ind in test_indices:
@@ -212,7 +222,7 @@ def check(arr, ind):
         # check float indexing raises
         with self.assertRaises(TypingError):
             cfunc(A, [1.7])
-       
+
         # check unsupported arg raises
         with self.assertRaises(TypingError):
             take_kws = jit(nopython=True)(np_take_kws)
diff --git a/numba/tests/test_indexing.py b/numba/tests/test_indexing.py
--- a/numba/tests/test_indexing.py
+++ b/numba/tests/test_indexing.py
@@ -679,7 +679,7 @@ def run(a):
             cfunc = compile_func(a)
             for i, j in itertools.product(bounds, bounds):
                 x = cfunc(a, i, j)
-                self.assertPreciseEqual(pyfunc(a, i, j), cfunc(a, i, j))
+                np.testing.assert_equal(pyfunc(a, i, j), cfunc(a, i, j))
 
         run(np.arange(16, dtype='i4').reshape(4, 4))
         run(np.arange(27, dtype='i4').reshape(3, 3, 3))