[lldb] Consult summary provider before printing children of root references

[kastiglione]

Summary

When printing the root of a value, if it's a reference its children are unconditionally
printed - in contrast to pointers whose children are only printed if a sufficient
pointer depth is given.

However, the children are printed even when there's a summary provider that says not to.
If a summary provider exists, this change consults it to determine if children should be
printed.

For example, given a variable of type std::string &, this change has the following
effect:

Before:

(lldb) p string_ref
(std::string &) string_ref = "one two three four five six seven eight nine ten": {
  __r_ = {
    std::__1::__compressed_pair_elem<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::__rep, 0, false> = {
      __value_ = {
         = {
          __l = (__data_ = "one two three four five six seven eight nine ten", __size_ = 48, __cap_ = 64, __is_long_ = 1)
          __s = (__data_ = "@\0p\U00000001\0`\0\00\0\0\0\0\0\0\0@", __padding_ = "\x80t<", __size_ = '\0', __is_long_ = '\x01')
          __r = {
            __words ={...}
          }
        }
      }
    }
  }
}

After:

(lldb) p string_ref
(std::string &) string_ref = "one two three four five six seven eight nine ten"

rdar://73248786

[Michael137]

makes sense

[bulbazord]

LGTM

lldb/source/DataFormatters/ValueObjectPrinter.cpp

bool ValueObjectPrinter::ShouldPrintChildren(
   if (is_uninit)
     return false;
 
   // if the user has specified an element count, always print children as it is
   // explicit user demand being honored
   if (m_options.m_pointer_as_array)
     return true;
 
-  TypeSummaryImpl *entry = GetSummaryFormatter();
-
   if (m_options.m_use_objc)
     return false;
 
+  bool print_children = true;
+  if (TypeSummaryImpl *type_summary = GetSummaryFormatter())
+    print_children = type_summary->DoesPrintChildren(m_valobj);
+
   if (is_failed_description || !HasReachedMaximumDepth()) {
     // We will show children for all concrete types. We won't show pointer
     // contents unless a pointer depth has been specified. We won't reference
     // contents unless the reference is the root object (depth of zero).
 
     // Use a new temporary pointer depth in case we override the current
     // pointer depth below...
 
     if (is_ptr || is_ref) {
       // We have a pointer or reference whose value is an address. Make sure
       // that address is not NULL
       AddressType ptr_address_type;
       if (m_valobj->GetPointerValue(&ptr_address_type) == 0)
         return false;
 
       const bool is_root_level = m_curr_depth == 0;
 
-      if (is_ref && is_root_level) {
+      if (is_ref && is_root_level && print_children) {
         // If this is the root object (depth is zero) that we are showing and
         // it is a reference, and no pointer depth has been supplied print out
         // what it references. Don't do this at deeper depths otherwise we can
         // end up with infinite recursion...
         return true;
       }
 
       return curr_ptr_depth.CanAllowExpansion();
     }
 
-    return (!entry || entry->DoesPrintChildren(m_valobj) || m_summary.empty());
+    return print_children || m_summary.empty();
   }
   return false;
 }
 
 bool ValueObjectPrinter::ShouldExpandEmptyAggregates() {
   TypeSummaryImpl *entry = GetSummaryFormatter();
 
   if (!entry)

lldb/test/API/functionalities/data-formatter/root-reference-children/Makefile

+CXX_SOURCES := main.cpp
+
+include Makefile.rules

lldb/test/API/functionalities/data-formatter/root-reference-children/TestRootReferenceChildren.py

+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class TestCase(TestBase):
+    def test(self):
+        self.build()
+        lldbutil.run_to_source_breakpoint(
+            self, "break here", lldb.SBFileSpec("main.cpp")
+        )
+
+        self.dbg.HandleCommand(
+            f"type summary add --expand -s 'some summary' SummaryAndChildren"
+        )
+        self.dbg.HandleCommand(f"type summary add -s 'some summary' SummaryOnly")
+
+        self.expect(
+            "v summary_and_children_ref", substrs=["some summary", "child = 30"]
+        )
+        self.expect(
+            "v summary_only_ref", patterns=["some summary", "(?s)^(?!.*child = )"]
+        )
+        self.expect(
+            "v children_only_ref", patterns=["(?s)^(?!.*some summary)", "child = 30"]
+        )

lldb/test/API/functionalities/data-formatter/root-reference-children/main.cpp

+#include <stdio.h>
+
+struct SummaryAndChildren {
+  int child = 30;
+};
+
+struct SummaryOnly {
+  int child = 30;
+};
+
+struct ChildrenOnly {
+  int child = 30;
+};
+
+int main() {
+  SummaryAndChildren summary_and_children;
+  SummaryOnly summary_only;
+  ChildrenOnly children_only;
+  auto &summary_and_children_ref = summary_and_children;
+  auto &summary_only_ref = summary_only;
+  auto &children_only_ref = children_only;
+  printf("break here\n");
+  return 0;
+}