Make subset behave depending on what language revision created it

For the purpose of supporting language version dependent functionality a
new metamodel role is being introduced:
`Perl6::Metamodel::LanguageRevision`. It is in turn consumes
`Perl6::Metamodel::Versioning`.

SubsetHOW records the compiler version which created a subset type
object and then later checks against the version in order to determine
if old or new behaviour is expected.

src/Perl6/Actions.nqp

@@ -3567,11 +3567,9 @@ class Perl6::Actions is HLL::Actions does STDActions {
     sub check_default_value_type($/, $descriptor, $bind_constraint, $what) {
         my $matches;
         my $maybe := 0;
-        note("TRY check_default_value_type") if nqp::getenvhash<RAKUDO_DEBUG>;
         try {
             $matches := nqp::istype($descriptor.default, $bind_constraint);
             CATCH {
-                note("IN CATCH") if nqp::getenvhash<RAKUDO_DEBUG>;
                 $maybe := 1;
                 my $pl := nqp::getpayload($_);
                 if nqp::istype($pl, $*W.find_symbol(['Exception'])) {
@@ -3583,7 +3581,6 @@ class Perl6::Actions is HLL::Actions does STDActions {
             }
         }
         unless $matches {
-            note("NO MATCH $maybe") if nqp::getenvhash<RAKUDO_DEBUG>;
             $/.typed_sorry('X::Syntax::Variable::MissingInitializer',
                 type => nqp::how($bind_constraint).name($bind_constraint),
                 :$maybe,

src/Perl6/Metamodel/LanguageRevision.nqp

@@ -0,0 +1,20 @@
+# This role is for metaclasses with languare-revision dependent behavior.
+role Perl6::Metamodel::LanguageRevision
+    does Perl6::Metamodel::Versioning
+{
+    has $!lang_rev;
+
+    # The only allowed version format is 6.X
+    method set_language_version($obj, $ver) {
+        (nqp::iseq_i(nqp::chars($ver), 3) && nqp::eqat($ver, '6.', 0))
+            || nqp::die("Language version must be a string in '6.<rev>' format, got `$ver`.");
+        self.set_ver($obj, $ver);
+        $!lang_rev := nqp::substr($ver, 2, 1);
+    }
+
+    method lang-rev-before($rev) {
+        nqp::iseq_i(nqp::chars($rev), 1)
+            || nqp::die("Language revision must be a single letter, got `$rev`.");
+        nqp::iseq_i(nqp::cmp_s($!lang_rev, $rev), -1)
+    }
+}

src/Perl6/Metamodel/SubsetHOW.nqp

@@ -2,6 +2,7 @@ class Perl6::Metamodel::SubsetHOW
     does Perl6::Metamodel::Naming
     does Perl6::Metamodel::Documenting
     does Perl6::Metamodel::Stashing
+    does Perl6::Metamodel::LanguageRevision
 {
     # The subset type or nominal type that we refine.
     has $!refinee;
@@ -27,6 +28,9 @@ class Perl6::Metamodel::SubsetHOW
         my $metasubset := self.new(:refinee($refinee), :refinement($refinement));
         my $type := nqp::settypehll(nqp::newtype($metasubset, 'Uninstantiable'), 'perl6');
         $metasubset.set_name($type, $name);
+        # TODO This only works at compile time. To support run-time creation of subsets we need to find caller's CORE.
+        # Will be possible when nqp::p6callerrevision() is implemented.
+        $metasubset.set_language_version($metasubset, nqp::getcomp('perl6').language_version);
         nqp::settypecheckmode($type, 2);
         self.add_stash($type)
     }
@@ -77,7 +81,11 @@ class Perl6::Metamodel::SubsetHOW
 
     # Do check when we're on LHS of smartmatch (e.g. Even ~~ Int).
     method type_check($obj, $checkee) {
-        nqp::hllboolfor( nqp::istype($!refinee, $checkee), "perl6" )
+        nqp::hllboolfor(
+            (self.lang-rev-before('e') && nqp::istrue($checkee.HOW =:= self))
+                || nqp::istype($!refinee, $checkee),
+            "perl6"
+        )
     }
 
     # Here we check the value itself (when on RHS on smartmatch).

src/Perl6/World.nqp

@@ -2037,15 +2037,15 @@ class Perl6::World is HLL::World {
     method maybe-definite-how-base($v) {
         # returns the value itself, unless it's a DefiniteHOW, in which case,
         # it returns its base type. Behaviour available in 6.d and later only.
-        !  $*W.lang-ver-before('d') && nqp::eqaddr($v.HOW,
+        ! $*W.lang-ver-before('d') && nqp::eqaddr($v.HOW,
             $*W.find_symbol: ['Metamodel','DefiniteHOW'], :setting-only
         ) ?? $v.HOW.base_type: $v !! $v
     }
 
     method maybe-nominalize($v) {
-        # if $*W.lang-ver-before('e') {
-        #     return self.maybe-definite-how-base($v);
-        # }
+        if $*W.lang-ver-before('e') {
+            return self.maybe-definite-how-base($v);
+        }
         $v.HOW.archetypes.nominalizable ?? $v.HOW.nominalize($v) !! $v
     }
 

tools/templates/common_bootstrap_sources

@@ -4,6 +4,7 @@ src/Perl6/Metamodel/Naming.nqp
 src/Perl6/Metamodel/Documenting.nqp
 src/Perl6/Metamodel/Stashing.nqp
 src/Perl6/Metamodel/Versioning.nqp
+src/Perl6/Metamodel/LanguageRevision.nqp
 src/Perl6/Metamodel/TypePretense.nqp
 src/Perl6/Metamodel/MethodDelegation.nqp
 src/Perl6/Metamodel/BoolificationProtocol.nqp