From 966c92f39a8884f7a988733d675500780d57a4bf Mon Sep 17 00:00:00 2001
From: Guillaume Giudicelli <guillaume.giudicelli@inl.gov>
Date: Wed, 26 Jun 2024 15:07:39 -0600
Subject: [PATCH] Add support for FV variables for projection aux refs #22373

---
 framework/include/auxkernels/ProjectionAux.h | 3 ++-
 framework/src/auxkernels/ProjectionAux.C     | 2 +-
 test/tests/auxkernels/projection_aux/tests   | 2 +-
 3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/framework/include/auxkernels/ProjectionAux.h b/framework/include/auxkernels/ProjectionAux.h
index 5c9c9d21b5e3..a9936f301ae9 100644
--- a/framework/include/auxkernels/ProjectionAux.h
+++ b/framework/include/auxkernels/ProjectionAux.h
@@ -33,7 +33,8 @@ class ProjectionAux : public AuxKernel
   const VariableValue & _v;
 
   /// A reference to the variable to project from
-  const MooseVariable & _source_variable;
+  /// We must use a field variable to support finite volume variables
+  const MooseVariableFieldBase & _source_variable;
 
   /// The system owning the source variable
   const System & _source_sys;
diff --git a/framework/src/auxkernels/ProjectionAux.C b/framework/src/auxkernels/ProjectionAux.C
index 23ccda850bcc..2a7f0b060f9f 100644
--- a/framework/src/auxkernels/ProjectionAux.C
+++ b/framework/src/auxkernels/ProjectionAux.C
@@ -43,7 +43,7 @@ ProjectionAux::validParams()
 ProjectionAux::ProjectionAux(const InputParameters & parameters)
   : AuxKernel(parameters),
     _v(coupledValue("v")),
-    _source_variable(*getVar("v", 0)),
+    _source_variable(*getFieldVar("v", 0)),
     _source_sys(_c_fe_problem.getSystem(coupledName("v")))
 {
   // Output some messages to user
diff --git a/test/tests/auxkernels/projection_aux/tests b/test/tests/auxkernels/projection_aux/tests
index e85ee2e61740..8c45b1347fed 100644
--- a/test/tests/auxkernels/projection_aux/tests
+++ b/test/tests/auxkernels/projection_aux/tests
@@ -7,7 +7,7 @@
       type = 'CSVDiff'
       input = '1d.i'
       csvdiff = '1d_constant.csv'
-      cli_args = 'Outputs/file_base=1d_constant'
+      cli_args = 'AuxVariables/base_elem/type=MooseVariableFVReal Outputs/file_base=1d_constant'
       detail = "a constant to all variable families supported in 1d at various orders,"
     []
     [1d_linear]