[flang] add nested DEC STRUCTURE in DerivedTypeDetails component names

Currently, when a (legacy) DEC structure contained other DEC structure
declarations, the related component names were not added to the
containing DerivedTypeDetails component_names. This lead to bugs in
later phase when visiting the components (like in when lowering the
type to FIR/MLIR).

When an EntityDecl is visited and the scope is a DEC structure, add
the entity to the component names of this DEC structure.

Differential Revision: https://reviews.llvm.org/D154216

flang/lib/Lower/ConvertExprToHLFIR.cpp

@@ -719,6 +719,7 @@ class HlfirDesignatorBuilder {
     if (recordType.isDependentType())
       TODO(getLoc(), "Designate derived type with length parameters in HLFIR");
     mlir::Type fieldType = recordType.getType(partInfo.componentName);
+    assert(fieldType && "component name is not known");
     mlir::Type fieldBaseType =
         hlfir::getFortranElementOrSequenceType(fieldType);
     partInfo.componentShape = genComponentShape(componentSym, fieldBaseType);

flang/lib/Semantics/resolve-names.cpp

@@ -4354,6 +4354,10 @@ void DeclarationVisitor::Post(const parser::EntityDecl &x) {
   } else if (attrs.test(Attr::PARAMETER)) { // C882, C883
     Say(name, "Missing initialization for parameter '%s'"_err_en_US);
   }
+  if (auto *scopeSymbol{currScope().symbol()})
+    if (auto *details{scopeSymbol->detailsIf<DerivedTypeDetails>()})
+      if (details->isDECStructure())
+        details->add_component(symbol);
 }
 
 void DeclarationVisitor::Post(const parser::PointerDecl &x) {

flang/test/Semantics/struct02.f90

@@ -0,0 +1,21 @@
+! Test component name resolution with nested legacy DEC structures.
+!RUN: %flang_fc1 -fdebug-dump-symbols %s | FileCheck %s
+
+  structure /a/
+    integer :: a_first_comp
+    structure /b/ b1, b2(100)
+      integer :: i
+    end structure
+    structure /c/ z
+      integer :: i
+      structure /d/ d1, d2(10)
+        real :: x
+      end structure
+    end structure
+    integer :: a_last_comp
+  end structure
+end
+! CHECK:    /a/: DerivedType sequence components: a_first_comp,b1,b2,z,a_last_comp
+! CHECK:    /b/: DerivedType sequence components: i
+! CHECK:    /c/: DerivedType sequence components: i,d1,d2
+! CHECK:    /d/: DerivedType sequence components: x