Fix #20004 - generate DW_TAG_enumerator for enum members in DWARF debug info

Previously, D enum types were emitted as DWARF forward references with no
children. The backend's SEenumlist was never populated and SENforward was
never cleared for D enums.

Populate the SEenumlist with enum member symbols and clear SENforward
in visitEnum for all integer-based enums, so that ubyte, ulong, etc.
enum base types also get correct DWARF output with member names and values.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: dkorpel

changelog/dmd.dwarf-enum-members.dd

@@ -0,0 +1,6 @@
+DWARF debug info now includes enum members
+
+The DMD compiler now generates `DW_TAG_enumerator` entries for D enum members in DWARF debug info.
+Previously, enum types were always emitted as forward references with no member information.
+
+Debuggers can now inspect enum member names and values for `int`-based enums.

compiler/src/dmd/glue/toctype.d

@@ -14,7 +14,11 @@ module dmd.glue.toctype;
 import core.stdc.stdio;
 import core.stdc.stdlib;
 
-import dmd.backend.cc : Classsym, Symbol;
+import dmd.backend.cc : Classsym, SENforward, Symbol;
+import dmd.backend.cdef : SC;
+import dmd.backend.dlist : list_append;
+import dmd.backend.el : el_long;
+import dmd.backend.symbol : symbol_name;
 import dmd.backend.ty;
 import dmd.backend.type;
 
@@ -256,6 +260,21 @@ type* Type_toCtype(Type t)
             else if (symMemtype.toBasetype().ty == Tint32)
             {
                 t.ctype = type_enum(sym.toPrettyChars(true), Type_toCtype(symMemtype));
+                if (driverParams.symdebug && sym.members)
+                {
+                    Symbol* s = cast(Symbol*)(cast(type*)t.ctype).Ttag;
+                    s.Senum.SEflags &= ~SENforward;
+                    type* memctype = Type_toCtype(symMemtype);
+                    foreach (m; *sym.members)
+                    {
+                        EnumMember em = m.isEnumMember();
+                        if (!em)
+                            continue;
+                        Symbol* sf = symbol_name(em.ident.toString(), SC.enum_, memctype);
+                        sf.Svalue = el_long(totym(symMemtype.toBasetype()), em.value().toInteger());
+                        list_append(&s.Senum.SEenumlist, sf);
+                    }
+                }
             }
             else
             {

compiler/test/dshell/extra-files/dwarf/excepted_results/issue20004.txt

@@ -0,0 +1,9 @@
+DW_TAG_enumeration_type
+DW_AT_name        : issue20004.Color
+DW_TAG_enumerator
+DW_AT_name        : red
+DW_AT_const_value : 0
+DW_AT_name        : green
+DW_AT_const_value : 1
+DW_AT_name        : blue
+DW_AT_const_value : 2

compiler/test/dshell/extra-files/dwarf/issue20004.d

@@ -0,0 +1,4 @@
+enum Color { red, green, blue }
+void main() {
+    Color c = Color.red;
+}