Op(fetch) error message enhancement. (#23542)

paddle/fluid/operators/controlflow/fetch_op.cc

@@ -31,24 +31,39 @@ class FetchOp : public framework::OperatorBase {
  private:
   void RunImpl(const framework::Scope &scope,
                const platform::Place &place) const override {
+    OP_INOUT_CHECK(HasInputs("X"), "Input", "X", "Fetch");
+    OP_INOUT_CHECK(HasOutputs("Out"), "Output", "Out", "Fetch");
+
     auto fetch_var_name = Input("X");
     auto *fetch_var = scope.FindVar(fetch_var_name);
-    PADDLE_ENFORCE(fetch_var != nullptr,
-                   "Cannot find fetch variable in scope, fetch_var_name is %s",
-                   fetch_var_name);
+    PADDLE_ENFORCE_NOT_NULL(
+        fetch_var,
+        platform::errors::NotFound(
+            "Input variable(%s) cannot be found in scope for operator 'Fetch'.",
+            fetch_var_name));
 
-    auto out_name = this->Output("Out");
+    auto out_name = Output("Out");
     auto *out_var = scope.FindVar(out_name);
-    PADDLE_ENFORCE(out_var != nullptr,
-                   "Cannot find out_var in scope, out_var_name is %s",
-                   out_name);
-
-    auto col = static_cast<size_t>(Attr<int>("col"));
+    PADDLE_ENFORCE_NOT_NULL(out_var, platform::errors::NotFound(
+                                         "Output variable(%s) cannot be found "
+                                         "in scope for operator 'Fetch'.",
+                                         out_name));
+
+    int col = Attr<int>("col");
+    PADDLE_ENFORCE_GE(
+        col, 0, platform::errors::InvalidArgument(
+                    "Expected the column index (the attribute 'col' of "
+                    "operator 'Fetch') of current fetching variable to be "
+                    "no less than 0. But received column index = %d.",
+                    col));
+
+    VLOG(3) << "Fetch variable " << fetch_var_name << " to variable "
+            << out_name << "'s " << col << " column.";
 
     auto *fetch_list = out_var->GetMutable<framework::FeedFetchList>();
     auto &src_item = fetch_var->Get<framework::FeedFetchType>();
 
-    if (col >= fetch_list->size()) {
+    if (static_cast<size_t>(col) >= fetch_list->size()) {
       fetch_list->resize(col + 1);
     }
     auto &dst_item = fetch_list->at(col);
@@ -81,17 +96,19 @@ class FetchOp : public framework::OperatorBase {
       dst_item.Resize({0});
     }
     dst_item.set_lod(src_item.lod());
-
-    VLOG(3) << "Fetch variable " << fetch_var_name << " to " << out_name;
   }
 };
 
 class FetchOpInfoMaker : public framework::OpProtoAndCheckerMaker {
  public:
   void Make() override {
-    AddInput("X", "The input of fetch op");
-    AddOutput("Out", "The output of fetch op");
-    AddAttr<int>("col", "(int) The column of fetch");
+    AddInput("X",
+             "(LoDTensor) The resulted LoDTensor which is expected to return "
+             "to users.");
+    AddOutput("Out",
+              "(vector<LoDTensor>) A fetching list of LoDTensor which may have "
+              "different dimension, shape and data type.");
+    AddAttr<int>("col", "(int) The column index of fetching object.");
     AddComment(R"DOC(
 Fetch Operator.