Fix crashes when trying to compile CORE:: name references

lib/CodeGen.cs

@@ -3800,7 +3800,7 @@ public class DowncallReceiver : CallReceiver {
 
                 if (file != null) {
                     for (SubInfo csr2 = from;
-                            csr2.unit == from.unit && // modify this unit only
+                            csr2.used_in_scope != null && // modify only open units
                             !csr2.used_in_scope.ContainsKey(lkey);
                             csr2 = csr2.outer, levels--) {
 
@@ -3862,6 +3862,7 @@ public class DowncallReceiver : CallReceiver {
                     ret.Add(kv.Key);
                     ret.Add(kv.Value.pos);
                 }
+                s.used_in_scope = null;
                 return ret.ToArray();
             } else if (cmd == "unit_stubbed_stashes") {
                 RuntimeUnit u = (RuntimeUnit)Handle.Unbox(args[1]);

src/niecza

@@ -69,6 +69,93 @@ augment grammar STD::Regex {
 }
 
 augment grammar STD {
+my package DEBUG { our constant symtab = 0 };
+method is_name($longname, $curlex = $*CURLEX) {
+    my $deb = $*DEBUG +& DEBUG::symtab;
+    self.deb("is_name $longname") if $deb;
+    if defined($longname.index("::(")) {
+        self.deb("computed name gets a free pass") if $deb;
+        return True;
+    }
+    my @parts = $longname.split('::');
+    shift @parts if @parts[0] eq '';
+    pop @parts if @parts && @parts[*-1] eq ''; # doesn't change ref validity
+
+    @parts[*-1] = $/ ~ @parts[*-1] if @parts && @parts[0] ~~ s/^(\W\W?)//;
+
+    self.deb("reparsed: @parts.perl()") if $deb;
+    return True if !@parts;
+
+    my ($pkg, $sub);
+
+    given @parts[0] {
+        when 'OUR' {
+            $pkg = $curlex<!sub>.cur_pkg;
+            shift @parts;
+            goto "packagey";
+        }
+        when 'PROCESS' | 'GLOBAL' {
+            $pkg = $*unit.abs_pkg(shift @parts);
+            goto "packagey";
+        }
+        when 'MY'      { $sub = $curlex<!sub>;                 goto "lexy"; }
+        when 'OUTER'   { $sub = $curlex<!sub>.?outer;          goto "lexy"; }
+        when 'UNIT'    { $sub = $curlex<!sub>.?to_unit;        goto "lexy"; }
+        when 'CORE'    { $sub = $curlex<!sub>.?true_setting;   goto "lexy"; }
+        when 'SETTING' { $sub = $curlex<!sub>.?to_unit.?outer; goto "lexy"; }
+
+        when 'COMPILING' | 'DYNAMIC' | 'CALLER' | 'CLR' { return True }
+
+        default {
+            my @lexical = self.lookup_lex(@parts[0], $curlex);
+            if !@lexical || @parts[0] eq 'PARENT' {
+                return False if @parts == 1; # $x doesn't mean GLOBAL
+                $pkg = (@parts[0] ~~ /^\W/) ??
+                    $curlex<!sub>.cur_pkg !!
+                    $*unit.abs_pkg('GLOBAL');
+            } elsif @lexical[0] eq 'package' {
+                $pkg = @lexical[4];
+                shift @parts;
+            } else {
+                return @parts == 1;
+            }
+            goto "packagey";
+        }
+    }
+
+lexy:
+    shift @parts;
+    return False unless $sub;
+    return True unless @parts;
+    given @parts[0] {
+        when 'OUTER'   { $sub = $sub.?outer;          goto "lexy"; }
+        when 'UNIT'    { $sub = $sub.?to_unit;        goto "lexy"; }
+        when 'SETTING' { $sub = $sub.?to_unit.?outer; goto "lexy"; }
+        when 'CALLER'  { return True; }
+    }
+
+    my @lex = $sub.lookup_lex(@parts[0], $*FILE<name>, self.lineof(self.pos));
+    unless @lex {
+        self.deb("Lexical @parts[0] not found") if $deb;
+        return False;
+    }
+    if @lex[0] eq 'package' {
+        shift @parts;
+        $pkg = @lex[4];
+        goto "packagey";
+    }
+    else {
+        return @parts == 1;
+    }
+
+packagey:
+    for @parts {
+        return False if !$pkg || !$*unit.exists($pkg.who, $_);
+        $pkg = $*unit.get($pkg.who, $_);
+    }
+
+    return True;
+}
 method nibble ($lang) {
     temp %*RX; # prevent up-vars from leaking
     self.cursor_fresh($lang).nibbler;