[flang][hlfir] Added a TODO note for parameterized array component shapes.

[vzakhari]

Summary

Without the TODO, MLIR verifier fails because of invalid hlfir.declare
or fir.alloca that lowering produces.

[clementval]

LG

flang/lib/Lower/ConvertExprToHLFIR.cpp

if (componentSym.Rank() == 0 ||
       return mlir::Value{};
 
     fir::FirOpBuilder &builder = getBuilder();
     mlir::Location loc = getLoc();
     mlir::Type idxTy = builder.getIndexType();
     llvm::SmallVector<mlir::Value> extents;
     auto seqTy = hlfir::getFortranElementOrSequenceType(fieldType)
                      .cast<fir::SequenceType>();
-    for (auto extent : seqTy.getShape())
+    for (auto extent : seqTy.getShape()) {
+      if (extent == fir::SequenceType::getUnknownExtent()) {
+        // We have already generated invalid hlfir.declare
+        // without the type parameters and probably invalid storage
+        // for the variable (e.g. fir.alloca without type parameters).
+        // So this TODO here is a little bit late, but it matches
+        // the non-HLFIR path.
+        TODO(loc, "array component shape depending on length parameters");
+      }
       extents.push_back(builder.createIntegerConstant(loc, idxTy, extent));
+    }
     if (!hasNonDefaultLowerBounds(componentSym))
       return builder.create<fir::ShapeOp>(loc, extents);
 
     llvm::SmallVector<mlir::Value> lbounds;
     if (const auto *objDetails =
             componentSym.detailsIf<Fortran::semantics::ObjectEntityDetails>())
       for (const Fortran::semantics::ShapeSpec &bounds : objDetails->shape())
         if (auto lb = bounds.lbound().GetExplicit())