Generate Rakudo Flavor into the actual code

Adapt tools/build/gen-cat.nqp so that it will look for the string
 #RAKUDO_FLAVOR# in the source being processed.  If found, it will
look in the environment for the RAKUDO_FLAVOR variable.  If that is
set, then it will replace the #RAKUDO_FLAVOR# target with a
"' $flavor'".  If it is not found, it will generate an empty string
(as in "''") there.

This also adds the #RAKUDO_FLAVOR# string to Compiler.nqp's version
information, so that --version will show the flavor.

This grants the wish of the Rakudo Star people to be able to mark
their version of Rakudo with an additional "Star" label, by making
sure that the environment variable RAKUDO_FLAVOR is set to "Star"
**at the moment that Rakudo is being compiled**.

This also should fix any objections with users potentially getting
confused by which version of Rakudo they are using, as the flavor
is "burnt into" the actual binary code of the executor, and thus
cannot be changed at runtime.

Additionally, this should allow the flavor to become available in
other areas, perhaps in the form of a $*RAKU attribute, burnt into
in the same manner.

src/Perl6/Compiler.nqp

@@ -144,15 +144,8 @@ class Perl6::Compiler is HLL::Compiler {
     method version_string(:$shorten-versions, :$no-unicode) {
         my $config-version  := self.config()<version>;
         my $backend-version := nqp::getattr(self,HLL::Compiler,'$!backend').version_string;
-        my $execname        := nqp::execname;
-        my $path-sep        := nqp::gethllsym('default', 'SysConfig').path-sep;
-        my $install-dir     := nqp::substr($execname, 0, nqp::rindex($execname, $path-sep, nqp::rindex($execname, $path-sep) - 1));
-        my $flavor-file     := $install-dir ~ $path-sep ~ "etc" ~ $path-sep ~ "FLAVOR";
-        my $rakudo-core-flavor := " v";
-
         my $raku;
         my $rakudo;
-        my $rakudo-flavor;
 
         if $shorten-versions {
             my $index := nqp::index($config-version,"-");
@@ -173,24 +166,10 @@ class Perl6::Compiler is HLL::Compiler {
             $rakudo := "Rakudo™";
         }
 
-        # Support different flavors of Rakudo, i.e. Star.
-        # Rakudo flavor can be either set by an environment variable
-        # 'RAKUDO_FLAVOR' or by the special file '$RAKUDO_PREFIX/etc/FLAVOR'
-        if nqp::existskey(nqp::getenvhash(), 'RAKUDO_FLAVOR') {
-            $rakudo-flavor := " " ~ (nqp::getenvhash<RAKUDO_FLAVOR>) ~ $rakudo-core-flavor;
-        }
-        elsif nqp::stat($flavor-file, nqp::const::STAT_EXISTS) {
-            my $data := open($flavor-file, :r);
-            $rakudo-flavor :=  " " ~ ($data.get) ~ $rakudo-core-flavor;
-            close($data);
-        }
-        else {
-             $rakudo-flavor := $rakudo-core-flavor;
-        }
-
         "Welcome to "
           ~ $rakudo
-          ~ $rakudo-flavor
+          ~ #RAKUDO_FLAVOR#
+          ~ " v"
           ~ $config-version
           ~ ".\nImplementing the "
           ~ $raku
@@ -381,7 +360,6 @@ The following environment variables are respected:
   PERL6LIB      Modify the module search path (DEPRECATED)
   NQP_HOME      Override the path of the NQP runtime files
   RAKUDO_HOME   Override the path of the Rakudo runtime files
-  RAKUDO_FLAVOR Set derived Rakudo compiler, i.e. "Star"
 
 
 ♥); # end of usage statement

tools/build/gen-cat.nqp

@@ -40,7 +40,8 @@ sub MAIN(*@ARGS) {
                 $in_cond := 1;
                 $in_omit := $x[0] && $x[1] eq $backend || !$x[0] && $x[1] ne $backend;
                 print("\n");
-            } elsif $_ ~~ /^ '#?endif' / {
+            }
+            elsif $_ ~~ /^ '#?endif' / {
                 unless $in_cond {
                     stderr().say(
                         "#?endif without matching #?if in file $file, line $line"
@@ -49,15 +50,26 @@ sub MAIN(*@ARGS) {
                 $in_cond := 0;
                 $in_omit := 0;
                 print("\n");
-            } elsif $in_omit {
+            }
+            elsif $in_omit {
                 print("\n");
-            } else {
-                if $backend eq 'js' && $_ ~~ /'#?js: NFG'/ {
-                    print(subst($_, /nqp\:\:[chars|substr|iseq_s|iscclass]/,
-                        -> $op {$op ~ 'nfg'}, :global));
-                } else {
-                    print($_) unless nqp::eqat($_,"# vim:",0);
-                }
+            }
+            elsif nqp::index($_, '#RAKUDO_FLAVOR#') > -1 {
+                my str $flavor := nqp::ifnull(
+                  nqp::atkey(nqp::getenvhash, 'RAKUDO_FLAVOR'),
+                  ""
+                );
+                $flavor := " $flavor" if $flavor;
+                print(
+                  nqp::join("'$flavor'", nqp::split('#RAKUDO_FLAVOR#', $_))
+                );
+            }
+            elsif $backend eq 'js' && $_ ~~ /'#?js: NFG'/ {
+                print(subst($_, /nqp\:\:[chars|substr|iseq_s|iscclass]/,
+                    -> $op {$op ~ 'nfg'}, :global));
+            }
+            else {
+                print($_) unless nqp::eqat($_,"# vim:",0);
             }
             $line++;
         }