Refine PADDLE_ENFORCE Error Messages. test=develop (#30149)

Improve some error messages in parallel_executor.cc, conditional_block_op.cc, recurrent_op.cc

paddle/fluid/framework/parallel_executor.cc

@@ -167,7 +167,9 @@ class ParallelExecutorPrivate {
         nccl_id = new ncclUniqueId();
         PADDLE_ENFORCE_EQ(
             platform::dynload::ncclGetUniqueId(nccl_id), ncclSuccess,
-            platform::errors::PreconditionNotMet("Get NCCL unique ID failed."));
+            platform::errors::PreconditionNotMet(
+                "PaddlePaddle failed to get NCCL unique ID. It may due to your "
+                "system settings or NCCL library error, please debug on NCCL"));
         VLOG(10) << "can't find nccl_id_var:" << var_name
                  << ", nccl_id:" << nccl_id;
       }

paddle/fluid/operators/controlflow/conditional_block_op.cc

@@ -57,8 +57,10 @@ class ConditionalBlockOp : public ConditionalOp {
     if (need_run) {
       auto *scope_var = scope.FindVar(Output(ConditionalOp::kScope));
       PADDLE_ENFORCE_NOT_NULL(
-          scope_var, platform::errors::PreconditionNotMet(
-                         "Scope must be set in conditional_block_op."));
+          scope_var,
+          platform::errors::PreconditionNotMet(
+              "Expect Scope variable to be set in conditional_block_op, but "
+              "got a null Scope variable. Please set the Scope variable."));
       auto *scopes = scope_var->GetMutable<std::vector<framework::Scope *>>();
       scopes->resize(1);
       scopes->front() = &scope.NewScope();
@@ -119,12 +121,16 @@ class ConditionalBlockGradOp : public ConditionalOp {
 
       auto *scope_var = scope.FindVar(Input(ConditionalOp::kScope));
       PADDLE_ENFORCE_NOT_NULL(
-          scope_var, platform::errors::PreconditionNotMet(
-                         "Scope must be set in conditional block op."));
+          scope_var,
+          platform::errors::PreconditionNotMet(
+              "Expect Scope variable to be set in conditional_block_op, but "
+              "got a null Scope variable. Please set the Scope variable."));
       auto &scopes = scope_var->Get<std::vector<framework::Scope *>>();
-      PADDLE_ENFORCE_GT(scopes.size(), 0,
+      PADDLE_ENFORCE_GT(
+          scopes.size(), 0,
           platform::errors::InvalidArgument(
-                            "Scope must be set in conditional block op."));
+              "Expect Scope variable contains at least 1 scope, but got: %d",
+              scopes.size()));
       framework::Scope &cur_scope = *scopes[0];
 
       framework::Executor exec(dev_place);

paddle/fluid/operators/recurrent_op.cc

@@ -161,7 +161,9 @@ int64_t RecurrentBase::GetSequenceLength(const framework::Scope &scope) const {
   }
   PADDLE_ENFORCE_GE(seq_len, 0,
                     platform::errors::InvalidArgument(
-                        "RecurrentOp gets invalid sequence length."));
+                        "RecurrentOp gets invalid sequence length. Expected "
+                        "seq_len >= 0. Received seq_len = %d",
+                        seq_len));
   return seq_len;
 }