From 6c7668c8a7e8666db0b79d7f90893bdae1d64da8 Mon Sep 17 00:00:00 2001
From: Axel Huebl <axel.huebl@plasma.ninja>
Date: Wed, 18 Sep 2024 13:25:30 -0700
Subject: [PATCH] `ParmParse:addFile`: User-Friendly Error (#4156)

## Summary

If a file added via `ParmParse:addFile` does not exist, we did not yet
receive a user-friendly error message. This fixes this in a way that
does not hammer the file system from all MPI ranks.

## Additional background

Follow-up to #2842 #2936 #3440

X-ref: https://github.com/ECP-WarpX/WarpX/issues/5283
https://github.com/ECP-WarpX/impactx/pull/704
---
 Src/Base/AMReX_ParmParse.cpp | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/Src/Base/AMReX_ParmParse.cpp b/Src/Base/AMReX_ParmParse.cpp
index 9d61fad89f..4e69901d5e 100644
--- a/Src/Base/AMReX_ParmParse.cpp
+++ b/Src/Base/AMReX_ParmParse.cpp
@@ -1069,12 +1069,23 @@ ParmParse::prefixedName (const std::string_view& str) const
 void
 ParmParse::addfile (std::string const& filename) {
 #ifdef AMREX_USE_MPI
+    // this is required because we will BCast the file content in sub-function calls
     if (ParallelDescriptor::Communicator() == MPI_COMM_NULL)
     {
         throw std::runtime_error("ParmParse::addfile: AMReX must be initialized");
     }
 #endif
 
+    // check the file exists and give a user-friendly error
+    if (ParallelDescriptor::IOProcessor())
+    {
+        AMREX_ALWAYS_ASSERT_WITH_MESSAGE(
+            FileExists(filename),
+            "ParmParse::addfile: file does not exist: " + filename
+        );
+    }
+
+    // add the file
     auto file = FileKeyword;
     std::vector<std::string> val{{filename}};
     addDefn(file, val, g_table);