* fix for #39310 by fixing various small issues in tabstractrecordsymtable.has_single_field:

- initialize the returned def to a safe default
  - correctly reset the found symbol for each loop
  - reset the result when descending into a record
+ added test

compiler/symtable.pas

@@ -1633,6 +1633,7 @@ implementation
         sym: tfieldvarsym;
       begin
         result:=false;
+        def:=generrordef;
         { If a record contains a union, it does not contain a "single
           non-composite field" in the context of certain ABIs requiring
           special treatment for such records }
@@ -1642,8 +1643,8 @@ implementation
         { a record/object can contain other things than fields }
         currentsymlist:=symlist;
         { recurse in arrays and records }
-        sym:=nil;
         repeat
+          sym:=nil;
           { record has one field? }
           for i:=0 to currentsymlist.Count-1 do
             begin
@@ -1674,7 +1675,12 @@ implementation
                 end;
               { if the array element is again a record, continue descending }
               if currentdef.typ=recorddef then
+                begin
+                  { the record might be empty, so reset the result until we've
+                    really found something }
+                  result:=false;
                   currentsymlist:=trecorddef(currentdef).symtable.SymList
+                end
               else
                 begin
                   { otherwise we found the type of the single element }

tests/webtbs/tw39310.pp

@@ -0,0 +1,21 @@
+{ %NORUN }
+
+{$MODESWITCH ADVANCEDRECORDS}
+Program tw39310;
+
+Type
+  Rec0 = record
+  end;
+
+  Rec1 = record
+    r:Rec0;
+    Procedure Proc;
+  end;
+
+Procedure Rec1.Proc;
+  begin
+  end;
+
+Begin
+End.
+