From 38cc3be704518b12308e70da22494ddb1e7a2b2a Mon Sep 17 00:00:00 2001
From: anagainaru <ana.gainaru@gmail.com>
Date: Wed, 6 Nov 2024 12:08:03 -0500
Subject: [PATCH 1/2] Check for empty data entry for variables that are part of
 a derived variable

---
 source/adios2/engine/bp5/BP5Writer.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/source/adios2/engine/bp5/BP5Writer.cpp b/source/adios2/engine/bp5/BP5Writer.cpp
index 590c891a63..17d4df28e9 100644
--- a/source/adios2/engine/bp5/BP5Writer.cpp
+++ b/source/adios2/engine/bp5/BP5Writer.cpp
@@ -585,7 +585,7 @@ void BP5Writer::ComputeDerivedVariables()
             // extract the dimensions and data for each variable
             VariableBase *varBase = itVariable->second.get();
             auto mvi = WriterMinBlocksInfo(*varBase);
-            if (mvi->BlocksInfo.size() == 0)
+            if (!mvi || mvi->BlocksInfo.size() == 0)
             {
                 computeDerived = false;
                 break;

From 7eccd3bfa036c20137a64a3b7a5a0a2479a9fd29 Mon Sep 17 00:00:00 2001
From: anagainaru <ana.gainaru@gmail.com>
Date: Wed, 6 Nov 2024 12:58:33 -0500
Subject: [PATCH 2/2] Update the derived variable testing for when the
 component variables are not written

---
 .../derived/TestBPDerivedCorrectness.cpp      | 36 +++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/testing/adios2/derived/TestBPDerivedCorrectness.cpp b/testing/adios2/derived/TestBPDerivedCorrectness.cpp
index 4c3fadbb3b..f31c91234e 100644
--- a/testing/adios2/derived/TestBPDerivedCorrectness.cpp
+++ b/testing/adios2/derived/TestBPDerivedCorrectness.cpp
@@ -25,6 +25,42 @@ class DerivedCorrectnessP : public DerivedCorrectness,
     adios2::DerivedVarType GetThreads() { return GetParam(); };
 };
 
+TEST_P(DerivedCorrectnessP, BasicCorrectnessTest)
+{
+    adios2::DerivedVarType mode = GetParam();
+    adios2::ADIOS adios;
+    adios2::IO bpOut = adios.DeclareIO("BPNoData");
+    EXPECT_THROW(bpOut.DefineDerivedVariable("derived", "x= var1 \n sqrt(x)", mode),
+                 std::invalid_argument);
+
+    const size_t N = 10;
+    std::default_random_engine generator;
+    std::uniform_real_distribution<float> distribution(0.0, 10.0);
+    std::vector<float> simArray1(N);
+    std::vector<float> simArray2(N);
+    for (size_t i = 0; i < N; ++i)
+        simArray1[i] = distribution(generator);
+
+    auto U = bpOut.DefineVariable<float>("var1", {N}, {0}, {N});
+    auto V = bpOut.DefineVariable<float>("var2", {N}, {0}, {N});
+    bpOut.DefineDerivedVariable("derived", "x= var1 \n sqrt(x)", mode);
+    adios2::Engine bpFileWriter = bpOut.Open("BPNoData.bp", adios2::Mode::Write);
+
+    bpFileWriter.BeginStep();
+    bpFileWriter.Put(V, simArray1.data());
+    bpFileWriter.EndStep();
+    bpFileWriter.Close();
+
+    // check that no derived data was written
+    adios2::IO bpIn = adios.DeclareIO("BPReadExpression");
+    adios2::Engine bpFileReader = bpIn.Open("BPNoData.bp", adios2::Mode::Read);
+    bpFileReader.BeginStep();
+    auto derVar = bpIn.InquireVariable<float>("derived");
+    EXPECT_FALSE(derVar);
+    bpFileReader.EndStep();
+    bpFileReader.Close();
+}
+
 TEST_P(DerivedCorrectnessP, ScalarFunctionsCorrectnessTest)
 {
     const size_t Nx = 10, Ny = 3, Nz = 6;