Multiple input file support (idaholab#17989)

framework/include/base/MooseApp.h

@@ -187,7 +187,10 @@ class MooseApp : public ConsoleStreamInterface, public libMesh::ParallelObject
   /**
    * Returns the input file name that was set with setInputFileName
    */
-  std::string getInputFileName() const { return _input_filename; }
+  std::string getInputFileName() const
+  {
+    return _input_filenames.empty() ? "" : _input_filenames[0];
+  }
 
   /**
    * Override the selection of the output file base name.
@@ -271,7 +274,7 @@ class MooseApp : public ConsoleStreamInterface, public libMesh::ParallelObject
   Real getGlobalTimeOffset() const { return _global_time_offset; }
 
   /**
-   * Return the filename that was parsed
+   * Return the primary (first) filename that was parsed
    * Note: When stripLeadingPath is false, this function returns the same name as
    *       getInputFileName() method when the input file is not a link.
    */
@@ -885,8 +888,8 @@ class MooseApp : public ConsoleStreamInterface, public libMesh::ParallelObject
   /// The RankMap is a useful object for determining how
   const RankMap _rank_map;
 
-  /// Input file name used
-  std::string _input_filename;
+  /// Input file names used
+  std::vector<std::string> _input_filenames;
 
   /// The output file basename
   std::string _output_file_base;

framework/include/parser/Parser.h

@@ -63,15 +63,15 @@ class Parser : public ConsoleStreamInterface, public hit::Walker
   virtual ~Parser();
 
   /**
-   * Return the filename that was parsed
+   * Return the primary (first) filename that was parsed
    */
-  std::string getFileName(bool stripLeadingPath = true) const;
+  std::string getPrimaryFileName(bool stripLeadingPath = true) const;
 
   /**
    * Parse an input file consisting of hit syntax and setup objects
    * in the MOOSE derived application
    */
-  void parse(const std::string & input_filename);
+  void parse(const std::vector<std::string> & input_filenames);
 
   /**
    * This function attempts to extract values from the input file based on the contents of
@@ -216,8 +216,8 @@ class Parser : public ConsoleStreamInterface, public hit::Walker
   /// Object for holding the syntax parse tree
   std::unique_ptr<SyntaxTree> _syntax_formatter;
 
-  /// The input file name that is used for parameter extraction
-  std::string _input_filename;
+  /// The input file names that are used for parameter extraction
+  std::vector<std::string> _input_filenames;
 
   /// The set of all variables extracted from the input file
   std::set<std::string> _extracted_vars;

framework/src/actions/MeshOnlyAction.C

@@ -54,7 +54,7 @@ MeshOnlyAction::act()
 
   if (should_generate)
   {
-    mesh_file = _app.parser().getFileName();
+    mesh_file = _app.parser().getPrimaryFileName();
     size_t pos = mesh_file.find_last_of('.');
 
     // Default to writing out an ExodusII mesh base on the input filename.

framework/src/base/MooseApp.C

@@ -83,7 +83,11 @@ MooseApp::validParams()
 
   params.addCommandLineParam<bool>(
       "display_version", "-v --version", false, "Print application version");
-  params.addCommandLineParam<std::string>("input_file", "-i <input_file>", "Specify an input file");
+  params.addCommandLineParam<std::vector<std::string>>(
+      "input_file",
+      "-i <input_files>",
+      "Specify one or multiple input files. Multiple files get merged into a single simulation "
+      "input.");
   params.addCommandLineParam<std::string>(
       "mesh_only",
       "--mesh-only [mesh_file_name]",
@@ -868,11 +872,11 @@ MooseApp::setupOptions()
     Moose::out << "MooseApp Type: " << type() << std::endl;
     _ready_to_exit = true;
   }
-  else if (_input_filename != "" ||
+  else if (!_input_filenames.empty() ||
            isParamValid("input_file")) // They already specified an input filename
   {
-    if (_input_filename == "")
-      _input_filename = getParam<std::string>("input_file");
+    if (_input_filenames.empty())
+      _input_filenames = getParam<std::vector<std::string>>("input_file");
 
     if (isParamValid("recover"))
     {
@@ -897,7 +901,7 @@ MooseApp::setupOptions()
       _restart_recover_suffix = getParam<std::string>("recoversuffix");
     }
 
-    _parser.parse(_input_filename);
+    _parser.parse(_input_filenames);
 
     if (isParamValid("mesh_only"))
     {
@@ -929,7 +933,7 @@ MooseApp::setupOptions()
       }
       else if (isUltimateMaster())
       {
-        // if this app is a master, we use the input file name as the default file base
+        // if this app is a master, we use the first input file name as the default file base
         std::string base = getInputFileName();
         size_t pos = base.find_last_of('.');
         _output_file_base = base.substr(0, pos);
@@ -956,7 +960,8 @@ MooseApp::setupOptions()
 void
 MooseApp::setInputFileName(const std::string & input_filename)
 {
-  _input_filename = input_filename;
+  // for now we only permit single input to be set for multiapps
+  _input_filenames = {input_filename};
 }
 
 std::string
@@ -1317,7 +1322,7 @@ MooseApp::setStartTime(Real time)
 std::string
 MooseApp::getFileName(bool stripLeadingPath) const
 {
-  return _parser.getFileName(stripLeadingPath);
+  return _parser.getPrimaryFileName(stripLeadingPath);
 }
 
 OutputWarehouse &