ParseXS: refactor: set default alias at parse time

If the list of aliases for an XSUB doesn't include the XSUB's main name,
an extra alias entry is added, mapping the main name to ix 0.

Move this setting from the code generation phase to the end of the
parsing phase, because the AST should really be complete by the end of
parsing.

Also add a test for this behaviour.

Shouldn't affect hat code is generated.

Author: iabyn

dist/ExtUtils-ParseXS/lib/ExtUtils/ParseXS/Node.pm

@@ -379,6 +379,18 @@ sub parse {
                                && $_->{in_out} =~ /OUTLIST$/
                              }
                         @{$self->{decl}{params}{kids}};
+
+    # If any aliases have been declared, make the main sub name ix 0
+    # if not specified.
+
+    if (            $self->{map_alias_name_to_value}
+        and keys %{ $self->{map_alias_name_to_value} })
+    {
+        my $pname = $self->{decl}{full_perl_name};
+        $self->{map_alias_name_to_value}{$pname} = 0
+            unless defined $self->{map_alias_name_to_value}{$pname};
+    }
+
     1;
 }
 
@@ -567,10 +579,6 @@ sub boot_code {
         # For the main XSUB and for each alias name, generate a newXS() call
         # and 'XSANY.any_i32 = ix' line.
 
-        # Make the main name one of the aliases if it isn't already
-        $self->{map_alias_name_to_value}->{$pname} = 0
-            unless defined $self->{map_alias_name_to_value}{$pname};
-
         foreach my $xname (sort keys
                     %{ $self->{map_alias_name_to_value} })
         {

dist/ExtUtils-ParseXS/t/001-basic.t

@@ -4288,6 +4288,20 @@ EOF
             [ 0, 0, qr{\QCV * cv;}, "has cv declaration" ],
         ],
 
+        [
+            "ALIAS with main as default of 0",
+            [ Q(<<'EOF') ],
+                |void
+                |foo()
+                |    ALIAS:
+                |           bar = 2
+EOF
+            [ 0, 0, qr{"Foo::foo",.*\n.*= 0;},
+                   "has Foo::foo" ],
+            [ 0, 0, qr{"Foo::bar",.*\n.*= 2;},
+                   "has Foo::bar" ],
+        ],
+
         [
             "ALIAS multi-perl-line, blank lines",
             [ Q(<<'EOF') ],