[ONNX] Handling of unknown domains in ONNX models [r0.26] (#3632)

* Do not throw for unknown domains in ONNX models

* UT that makes sure onnx_importer does not throw for unknown domains

* Check if nGraph throws for unknown ONNX domain and op

src/ngraph/frontend/onnx_import/ops_bridge.cpp

@@ -178,7 +178,8 @@ namespace ngraph
             auto dm = m_map.find(domain);
             if (dm == std::end(m_map))
             {
-                throw error::UnknownDomain{domain};
+                NGRAPH_WARN << "Domain '" << domain << "' not recognized by nGraph";
+                return OperatorSet{};
             }
             if (domain == "" && version > OperatorsBridge::LATEST_SUPPORTED_ONNX_OPSET_VERSION)
             {

test/models/onnx/unknown_domain.prototxt

+ir_version: 4
+producer_name: "nGraph ONNX Importer"
+graph {
+  node {
+    input: "A"
+    input: "B"
+    output: "C"
+    op_type: "Add"
+  }
+  name: "compute_graph"
+  input {
+    name: "A"
+    type {
+      tensor_type {
+        elem_type: 1
+        shape {
+          dim {
+            dim_value: 2
+          }
+          dim {
+            dim_value: 2
+          }
+        }
+      }
+    }
+  }
+  input {
+    name: "B"
+    type {
+      tensor_type {
+        elem_type: 1
+        shape {
+          dim {
+            dim_value: 2
+          }
+          dim {
+            dim_value: 2
+          }
+        }
+      }
+    }
+  }
+  output {
+    name: "C"
+    type {
+      tensor_type {
+        elem_type: 1
+        shape {
+          dim {
+            dim_value: 2
+          }
+          dim {
+            dim_value: 2
+          }
+        }
+      }
+    }
+  }
+}
+opset_import {
+  domain: "unknown.domain"
+  version: 1
+}
+opset_import {
+  domain: ""
+  version: 7
+}

test/models/onnx/unknown_domain_add.prototxt

+ir_version: 4
+producer_name: "nGraph ONNX Importer"
+graph {
+  node {
+    input: "A"
+    input: "B"
+    output: "C"
+    op_type: "Add"
+    domain: "unknown.domain"
+  }
+  name: "compute_graph"
+  input {
+    name: "A"
+    type {
+      tensor_type {
+        elem_type: 1
+        shape {
+          dim {
+            dim_value: 2
+          }
+          dim {
+            dim_value: 2
+          }
+        }
+      }
+    }
+  }
+  input {
+    name: "B"
+    type {
+      tensor_type {
+        elem_type: 1
+        shape {
+          dim {
+            dim_value: 2
+          }
+          dim {
+            dim_value: 2
+          }
+        }
+      }
+    }
+  }
+  output {
+    name: "C"
+    type {
+      tensor_type {
+        elem_type: 1
+        shape {
+          dim {
+            dim_value: 2
+          }
+          dim {
+            dim_value: 2
+          }
+        }
+      }
+    }
+  }
+}
+opset_import {
+  domain: "unknown.domain"
+  version: 1
+}

test/onnx/onnx_import.in.cpp

@@ -268,6 +268,31 @@ NGRAPH_TEST(onnx_${BACKEND_NAME}, model_missing_op_domain)
     EXPECT_TRUE(test::all_close_f(expected_output.front(), outputs.front()));
 }
 
+NGRAPH_TEST(onnx_${BACKEND_NAME}, model_unknown_domain)
+{
+    // the importer should not throw when it encounters an unknown domain in the model
+    EXPECT_NO_THROW(onnx_import::import_onnx_model(
+        file_util::path_join(SERIALIZED_ZOO, "onnx/unknown_domain.prototxt")));
+}
+
+NGRAPH_TEST(onnx_${BACKEND_NAME}, model_op_in_unknown_domain)
+{
+    try
+    {
+        onnx_import::import_onnx_model(
+            file_util::path_join(SERIALIZED_ZOO, "onnx/unknown_domain_add.prototxt"));
+
+        FAIL() << "The onnx_importer did not throw for unknown domain and op";
+    }
+    catch (const ngraph::ngraph_error& e)
+    {
+        const std::string msg = e.what();
+
+        EXPECT_NE(msg.find("unknown.domain.Add"), std::string::npos)
+            << "The error message should contain domain and op name: unknown.domain.Add";
+    }
+}
+
 NGRAPH_TEST(onnx_${BACKEND_NAME}, model_missing_input)
 {
     onnx_import::register_operator(