Teko: Parser hooks missing for setting up an inner preconditioned KSP as a sub-block solver

[MalachiTimothyPhillips]

@trilinos/teko
@cgcgcg

The idea is essentially to use Teko as a preconditioner inside an "outer" KSP. For one of the Teko sub-blocks, I want to solve it using an "inner" preconditioned KSP that is invoked at every iteration. The "inner" KSP is working as expected. However, there doesn't seem to be a way to specify the preconditioner type for the inner KSP in Teko.

Example input:

<!-- Outer KSP settings -->
<ParameterList name="Belos-Tpetra">
  <!-- Flexible GMRES required here due to desire to use inner KSP in Teko -->
  <Parameter name="Flexible GMRES" type="bool" value="true"/>
  <Parameter name="Maximum Iterations" type="int" value="500"/>
  <Parameter name="Convergence Tolerance" type="double" value="1e-9"/>
  <Parameter name="Implicit Residual Scaling" type="string" value="None"/>
  <Parameter name="Explicit Residual Scaling" type="string" value="None"/>
  <!-- GMRES(infty) -> high orthogonalization cost, will remove once working -->
  <Parameter name="Num Blocks" type="int" value="500"/>
  <Parameter name="Maximum Restarts" type="int" value="1"/>
  <Parameter name="Orthogonalization" type="string" value="ICGS"/>
</ParameterList>

<!-- Teko-block preconditioner for the outer KSP -->
<ParameterList name="Teko-Tpetra">
  <ParameterList name="Teko-parameters">
    <ParameterList name="my_teko_preco">
      <Parameter name="Type" type="string" value="Block Gauss-Seidel"/>
      <Parameter name="Use Upper Triangle" type="bool" value="true"/>
      <!-- I want to use an inner KSP here as part of the Teko-block preconditioner -->
      <Parameter name="Inverse Type 1"  type="string" value="iterative_solver"/>
      <Parameter name="Inverse Type 2"  type="string" value="direct"/>
      <Parameter name="Inverse Type 3"  type="string" value="direct"/>
    </ParameterList>

    <!-- Iterative solver for block 1 -->
    <ParameterList name="iterative_solver">
      <ParameterList name="VerboseObject">
        <Parameter name="Verbosity Level" type="string" value="low"/>
      </ParameterList>
      <Parameter name="Type" type="string" value="Belos"/>
      <Parameter name="Solver Type" type="string" value="Pseudo Block GMRES"/>
      <ParameterList name="Solver Types">
        <ParameterList name="Pseudo Block GMRES">
          <Parameter name="Convergence Tolerance" type="double" value="1e-8"/>
          <Parameter name="Maximum Iterations" type="int" value="100"/>
          <Parameter name="Verbosity" type="int" value="41"/>
          <Parameter name="Output Frequency" type="int" value="1"/>
          <Parameter name="Output Style" type="int" value="1"/>
          <Parameter name="Num Blocks" type="int" value="40"/>
        </ParameterList>
      </ParameterList>
    
      <!-- BEGIN BAD XML CONTENT -->
      <!--
        Everything up until now works, however these blocks aren't valid.
        The following exception is thrown:

        Error, the parameter {name="Preconditioner Types",type="ParameterList",value="..."}
        in the parameter (sub)list "ANONYMOUS->Teko-Tpetra->Teko-parameters->iterative_solver"
        was not found in the list of valid parameters!
        
        The valid parameters and types are:
          {
            "Solver Type" : string = Pseudo Block GMRES
            "Convergence Test Frequency" : int = 1
            "Left Preconditioner If Unspecified" : bool = 0
            "Solver Types" : ParameterList = ...
            "VerboseObject" : ParameterList = ...
          }
      -->
      <Parameter name="Preconditioner Type" type="string" value="Ifpack2"/>
      <ParameterList name="Preconditioner Types">
        <ParameterList name="Ifpack2">
          <Parameter name="Prec Type" type="string" value="SCHWARZ"/>
          <ParameterList name="Ifpack2 Settings">
            <Parameter name="schwarz: use reordering" type="bool" value="true"/>
            <Parameter name="schwarz: overlap level" type="int" value="0"/>
            <Parameter name="schwarz: num iterations" type="int" value="2"/>
          </ParameterList>
        </ParameterList>
      </ParameterList>
      <!-- END BAD XML CONTENT -->
    </ParameterList>

    <!-- Direct solver for blocks 2, 3 -->
    <ParameterList name="direct">
      <Parameter name="Type" type="string" value="Amesos2"/>
    </ParameterList>
  </ParameterList>
</ParameterList>