Allow PyPipeline and PyFunc to realize() scalar buffers (halide#6674)

python_bindings/correctness/complexstub_generator.cpp

@@ -35,6 +35,7 @@ class ComplexStub : public Halide::Generator<ComplexStub> {
     Output<Buffer<float, 3>> typed_buffer_output{"typed_buffer_output"};
     Output<Buffer<void, 3>> untyped_buffer_output{"untyped_buffer_output"};
     Output<Buffer<uint8_t, 3>> static_compiled_buffer_output{"static_compiled_buffer_output"};
+    Output<float> scalar_output{"scalar_output"};
 
     void configure() {
         // Pointers returned by add_input() are managed by the Generator;
@@ -72,6 +73,8 @@ class ComplexStub : public Halide::Generator<ComplexStub> {
         static_compiled_buffer_output = static_compiled_buffer;
 
         (*extra_func_output)(x, y) = cast<double>((*extra_func_input)(x, y, 0) + 1);
+
+        scalar_output() = float_arg + int_arg;
     }
 
     void schedule() {

python_bindings/correctness/pystub.py

@@ -184,6 +184,7 @@ def test_complexstub():
         typed_buffer_output,
         untyped_buffer_output,
         static_compiled_buffer_output,
+        scalar_output,
         extra_func_output) = r
 
     b = simple_output.realize([32, 32, 3], target)
@@ -249,6 +250,10 @@ def test_complexstub():
                 actual = b[x, y, c]
                 assert expected == actual, "Expected %s Actual %s" % (expected, actual)
 
+    b = scalar_output.realize([], target)
+    assert b.type() == hl.Float(32)
+    assert b[()] == 34.25
+
     b = extra_func_output.realize([32, 32], target)
     assert b.type() == hl.Float(64)
     for x in range(32):

python_bindings/src/PyFunc.cpp

@@ -122,15 +122,12 @@ void define_func(py::module &m) {
                 },
                 py::arg("dst"), py::arg("target") = Target())
 
-            // This will actually allow a list-of-buffers as well as a tuple-of-buffers, but that's OK.
-            .def(
-                "realize",
-                [](Func &f, std::vector<Buffer<>> buffers, const Target &t) -> void {
-                    py::gil_scoped_release release;
-                    f.realize(Realization(buffers), t);
-                },
-                py::arg("dst"), py::arg("target") = Target())
-
+            // It's important to have this overload of realize() go first:
+            // passing an empty list [] is ambiguous in Python, and could match to
+            // either list-of-sizes or list-of-buffers... but the former is useful
+            // (it allows realizing a 0-dimensional/scalar buffer) and the former is
+            // not (it will always assert-fail). Putting this one first allows it to
+            // be the first one chosen by the bindings in this case.
             .def(
                 "realize",
                 [](Func &f, const std::vector<int32_t> &sizes, const Target &target) -> py::object {
@@ -143,6 +140,15 @@ void define_func(py::module &m) {
                 },
                 py::arg("sizes") = std::vector<int32_t>{}, py::arg("target") = Target())
 
+            // This will actually allow a list-of-buffers as well as a tuple-of-buffers, but that's OK.
+            .def(
+                "realize",
+                [](Func &f, std::vector<Buffer<>> buffers, const Target &t) -> void {
+                    py::gil_scoped_release release;
+                    f.realize(Realization(buffers), t);
+                },
+                py::arg("dst"), py::arg("target") = Target())
+
             .def("defined", &Func::defined)
             .def("name", &Func::name)
             .def("dimensions", &Func::dimensions)

python_bindings/src/PyPipeline.cpp

@@ -101,14 +101,12 @@ void define_pipeline(py::module &m) {
                 },
                 py::arg("dst"), py::arg("target") = Target())
 
-            // This will actually allow a list-of-buffers as well as a tuple-of-buffers, but that's OK.
-            .def(
-                "realize", [](Pipeline &p, std::vector<Buffer<>> buffers, const Target &t) -> void {
-                    py::gil_scoped_release release;
-                    p.realize(Realization(buffers), t);
-                },
-                py::arg("dst"), py::arg("target") = Target())
-
+            // It's important to have this overload of realize() go first:
+            // passing an empty list [] is ambiguous in Python, and could match to
+            // either list-of-sizes or list-of-buffers... but the former is useful
+            // (it allows realizing a 0-dimensional/scalar buffer) and the former is
+            // not (it will always assert-fail). Putting this one first allows it to
+            // be the first one chosen by the bindings in this case.
             .def(
                 "realize", [](Pipeline &p, std::vector<int32_t> sizes, const Target &target) -> py::object {
                     std::optional<Realization> r;
@@ -120,6 +118,14 @@ void define_pipeline(py::module &m) {
                 },
                 py::arg("sizes") = std::vector<int32_t>{}, py::arg("target") = Target())
 
+            // This will actually allow a list-of-buffers as well as a tuple-of-buffers, but that's OK.
+            .def(
+                "realize", [](Pipeline &p, std::vector<Buffer<>> buffers, const Target &t) -> void {
+                    py::gil_scoped_release release;
+                    p.realize(Realization(buffers), t);
+                },
+                py::arg("dst"), py::arg("target") = Target())
+
             .def(
                 "infer_input_bounds", [](Pipeline &p, const py::object &dst, const Target &target) -> void {
                     // dst could be Buffer<>, vector<Buffer>, or vector<int>