Fix default attribute values in shape inference (onnx#7602)

This is an attempt to fix onnx#7573

When using the default value for an attribute, there are two separate
scenarios:
* The attribute is not present
* The attribute is present but the numerical value for the attribute is
not set

The previous logic was using the schema default in both cases, but in
the second case one should use the protobuf default for the relevant
data type instead.

This change fixes the example reported in the issue.

---------

Signed-off-by: Matteo Salvarezza <matteos@wolfram.com>
Co-authored-by: Matteo Salvarezza <matteos@wolfram.com>
Co-authored-by: Andreas Fehlner <fehlner@arcor.de>
Co-authored-by: Justin Chu <justinchuby@users.noreply.github.com>

Author: 4 people

onnx/defs/shape_inference.h

@@ -161,22 +161,31 @@ inline int64_t getAttribute(const InferenceContext& ctx, const std::string& attr
   const auto* attr_proto = ctx.getAttribute(attributeName);
   if ((nullptr != attr_proto) && attr_proto->has_i())
     return attr_proto->i();
-  return defaultValue;
+  else if (nullptr != attr_proto)
+    return 0; // protobuf default for integers
+  else
+    return defaultValue;
 }
 
 inline int64_t getAttribute(const DataPropagationContext& ctx, const std::string& attributeName, int64_t defaultValue) {
   const auto* attr_proto = ctx.getAttribute(attributeName);
   if ((nullptr != attr_proto) && attr_proto->has_i())
     return attr_proto->i();
-  return defaultValue;
+  else if (nullptr != attr_proto)
+    return 0; // protobuf default for integers
+  else
+    return defaultValue;
 }
 
 inline std::string
 getAttribute(const InferenceContext& ctx, const std::string& attributeName, const std::string& defaultValue) {
   const auto* attr_proto = ctx.getAttribute(attributeName);
   if ((nullptr != attr_proto) && attr_proto->has_s())
     return attr_proto->s();
-  return defaultValue;
+  else if (nullptr != attr_proto)
+    return ""; // protobuf default for strings
+  else
+    return defaultValue;
 }
 
 inline TensorShapeProto::Dimension operator*(

onnx/test/shape_inference_test.py

@@ -11,6 +11,7 @@
 
 import numpy as np
 import pytest
+from google.protobuf import text_format
 from parameterized import parameterized
 
 import onnx.shape_inference
@@ -10855,6 +10856,61 @@ def test_issue_constantofshape_6135(self, _, version):
             opset_imports=[helper.make_opsetid(ONNX_DOMAIN, version)],
         )
 
+    def test_protobuf_default(self) -> None:
+        model_text = """
+            ir_version: 8
+            producer_name: "test"
+            graph {
+              node {
+                input: "in"
+                output: "out"
+                op_type: "Flatten"
+                attribute {
+                  name: "axis"
+                  type: INT
+                }
+              }
+              name: "g"
+              input {
+                name: "in"
+                type {
+                  tensor_type {
+                    elem_type: 1
+                    shape {
+                      dim {
+                        dim_value: 2
+                      }
+                      dim {
+                        dim_value: 3
+                      }
+                    }
+                  }
+                }
+              }
+              output {
+                name: "out"
+                type {
+                  tensor_type {
+                    elem_type: 1
+                    shape {
+                      dim {
+                        dim_value: 1
+                      }
+                      dim {
+                        dim_value: 6
+                      }
+                    }
+                  }
+                }
+              }
+            }
+            opset_import {
+              version: 18
+            }
+        """
+        model = text_format.Parse(model_text, onnx.ModelProto())
+        self._assert_inferred(model, [])
+
 
 class TestCustomSchemaShapeInference(TestShapeInferenceHelper):
     custom_op_type: str = "CustomOp"