[gdb/symtab] Revert "Change handling of DW_TAG_enumeration_type in DWARF scanner"

After adding dwarf assembly to test-case gdb.dwarf2/enum-type.exp that adds
this debug info:
...
 <1><11f>: Abbrev Number: 3 (DW_TAG_enumeration_type)
    <120>   DW_AT_specification: <0x130>
 <2><124>: Abbrev Number: 4 (DW_TAG_enumerator)
    <125>   DW_AT_name        : val1
    <12a>   DW_AT_const_value : 1
 <2><12b>: Abbrev Number: 0
 <1><12c>: Abbrev Number: 5 (DW_TAG_namespace)
    <12d>   DW_AT_name        : ns
 <2><130>: Abbrev Number: 6 (DW_TAG_enumeration_type)
    <131>   DW_AT_name        : e
    <133>   DW_AT_type        : <0x118>
    <137>   DW_AT_declaration : 1
...
I run into an assertion failure:
...
(gdb) file enum-type^M
Reading symbols from enum-type...^M
cooked-index.h:214: internal-error: get_parent: \
  Assertion `(flags & IS_PARENT_DEFERRED) == 0' failed.^M
...

This was reported in PR32160 comment 1.

This is a regression since commit 4e417d7bb1 ("Change handling of
DW_TAG_enumeration_type in DWARF scanner").

Fix this by reverting the commit.

[ Also drop the kfails for PR31900 and PR32158, which are regressions by that
same commit. ]

That allows us to look at the output of "maint print objfiles", and for val1
we get an entry without parent:
...
    [27] ((cooked_index_entry *) 0x7fbbb4002ef0)
    name:       val1
    canonical:  val1
    qualified:  val1
    DWARF tag:  DW_TAG_enumerator
    flags:      0x0 []
    DIE offset: 0x124
    parent:     ((cooked_index_entry *) 0)
...
which is incorrect, as noted in that same comment, but an improvement over the
assertion failure, and I don't think that ever worked.  This is to be
addressed in a follow-up patch.

Reverting the commit begs the question: what was it trying to fix in the first
place, and do we need a different fix?  I've investigated this and filed
PR32160 to track this.

My guess is that the commit was based on a misunderstand of what we track
in cooked_indexer::m_die_range_map.

Each DIE has two types of parent DIEs:
- a DIE that is the parent as indicated by the tree structure in which DIEs
  occur, and
- a DIE that represent the parent scope.

In most cases, these two are the same, but some times they're not.

The debug info above demonstrates such a case.  The DIE at 0x11f:
- has a tree-parent: the DIE representing the CU, and
- has a scope-parent: DIE 0x12c representing namespace ns.

In cooked_indexer::m_die_range_map, we track scope-parents, and the commit
tried to add a tree-parent instead.

So, I don't think we need a different fix, and propose we backport the reversal
for gdb 15.2.

Tested on x86_64-linux.

Approved-By: Tom Tromey <tom@tromey.com>

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31900
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32158
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32160
(cherry picked from commit a2860473ef)

gdb/dwarf2/read.c

@@ -16440,12 +16440,6 @@ cooked_indexer::index_dies (cutu_reader *reader,
 	  flags &= ~IS_STATIC;
 	  flags |= parent_entry->flags & IS_STATIC;
 	}
-      /* If the parent is an enum, but not an enum class, then use the
-	 grandparent instead.  */
-      if (this_parent_entry != nullptr
-	  && this_parent_entry->tag == DW_TAG_enumeration_type
-	  && !is_enum_class)
-	this_parent_entry = this_parent_entry->get_parent ();
 
       if (abbrev->tag == DW_TAG_namespace
 	  && m_language == language_cplus
@@ -16505,7 +16499,15 @@ cooked_indexer::index_dies (cutu_reader *reader,
 	      break;
 
 	    case DW_TAG_enumeration_type:
-	      info_ptr = recurse (reader, info_ptr, this_entry, fully);
+	      /* We need to recurse even for an anonymous enumeration.
+		 Which scope we record as the parent scope depends on
+		 whether we're reading an "enum class".  If so, we use
+		 the enum itself as the parent, yielding names like
+		 "enum_class::enumerator"; otherwise we inject the
+		 names into our own parent scope.  */
+	      info_ptr = recurse (reader, info_ptr,
+				  is_enum_class ? this_entry : parent_entry,
+				  fully);
 	      continue;
 
 	    case DW_TAG_module:

gdb/testsuite/gdb.dwarf2/enum-type-c++.exp

@@ -32,7 +32,6 @@ require {string equal [have_index $binfile] ""}
 set re_ws "\[ \t\]"
 
 # Regression test for PR31900.
-setup_kfail "gdb/31900" *-*-*
 set val1 ns::A::val1
 gdb_test_lines "maint print objfiles" \
     "val1 has a parent" \
@@ -44,7 +43,6 @@ gdb_test_lines "maint print objfiles" \
 gdb_test "print $val1" " = $val1"
 
 # Regression test for PR32158.
-setup_kfail "gdb/32158" *-*-*
 set val2 ns::ec::val2
 gdb_test_lines "maint print objfiles" \
     "val2 has correct parent" \

gdb/testsuite/gdb.dwarf2/enum-type.exp

@@ -65,6 +65,41 @@ Dwarf::assemble $asm_file {
 	    }
 	}
     }
+
+    cu {} {
+	DW_TAG_compile_unit {
+		{DW_AT_language @DW_LANG_C_plus_plus}
+		{DW_AT_name	tmp.c}
+		{DW_AT_comp_dir /tmp}
+	} {
+	    declare_labels integer_label forward
+
+	    integer_label: DW_TAG_base_type {
+		{DW_AT_byte_size 4 DW_FORM_sdata}
+		{DW_AT_encoding	 @DW_ATE_signed}
+		{DW_AT_name	 int}
+	    }
+
+	    DW_TAG_enumeration_type {
+		{DW_AT_specification :$forward}
+	    } {
+		DW_TAG_enumerator {
+		    {DW_AT_name val1}
+		    {DW_AT_const_value 1 DW_FORM_sdata}
+		}
+	    }
+
+	    DW_TAG_namespace {
+		{DW_AT_name ns}
+	    } {
+		forward: DW_TAG_enumeration_type {
+		    {DW_AT_name e}
+		    {DW_AT_type :$integer_label}
+		    {DW_AT_declaration 1 flag}
+		}
+	    }
+	}
+    }
 }
 
 if { [prepare_for_testing "failed to prepare" ${testfile} \