RakuAST: add support for supply blocks

- add RakuAST::StatementPrefix::Supply class
- adapt grammar and actions accordingly
- add tests, .rakufication and deparsing already handled by base class

This did *not* port the optimizations for single emit supplies.

  https://github.com/rakudo/rakudo/blob/main/src/Perl6/Actions.nqp#L2557-L2577

Feels this should be part of a more general optimization strategy
in RakuAST.

src/Raku/Grammar.nqp

@@ -1103,8 +1103,9 @@ grammar Raku::Grammar is HLL::Grammar does Raku::Common {
     token statement-prefix:sym<eager>   { <sym><.kok> <blorst> }
     token statement-prefix:sym<gather>  { <sym><.kok> <blorst> }
     token statement-prefix:sym<quietly> { <sym><.kok> <blorst> }
-    token statement-prefix:sym<try>     { <sym><.kok> <blorst> }
     token statement-prefix:sym<start>   { <sym><.kok> <blorst> }
+    token statement-prefix:sym<supply>  { <sym><.kok> <blorst> }
+    token statement-prefix:sym<try>     { <sym><.kok> <blorst> }
 
     # Prefixes that work differently on for loops
     token statement-prefix:sym<hyper>   { <sym><.kok> <blorst> }

src/Raku/ast/statementprefixes.rakumod

@@ -360,6 +360,52 @@ class RakuAST::StatementPrefix::Start
     }
 }
 
+# The `supply` statement prefix.
+class RakuAST::StatementPrefix::Supply
+  is RakuAST::StatementPrefix::Thunky
+  is RakuAST::SinkPropagator
+  is RakuAST::ImplicitBlockSemanticsProvider
+{
+    method type() { "supply" }
+
+    method propagate-sink(Bool $is-sunk) {
+        self.blorst.apply-sink(False);
+    }
+
+    method apply-implicit-block-semantics() {
+        self.blorst.set-fresh-variables(:match, :exception)
+          if nqp::istype(self.blorst, RakuAST::Block);
+    }
+
+    method IMPL-QAST-FORM-BLOCK(
+      RakuAST::IMPL::QASTContext  $context,
+                             str :$blocktype,
+             RakuAST::Expression :$expression
+    ) {
+        if nqp::istype(self.blorst, RakuAST::Block) {
+            self.blorst.IMPL-QAST-FORM-BLOCK($context, :$blocktype, :$expression)
+        }
+        else {
+            my $block := QAST::Block.new(
+                :blocktype('declaration_static'),
+                QAST::Stmts.new(
+                  RakuAST::VarDeclaration::Implicit::Special.new(:name('$/')).IMPL-QAST-DECL($context),
+                    RakuAST::VarDeclaration::Implicit::Special.new(:name('$!')).IMPL-QAST-DECL($context),
+                    self.blorst.IMPL-TO-QAST($context)
+                ));
+            $block.arity(0);
+            $block
+        }
+    }
+
+    method IMPL-EXPR-QAST(RakuAST::IMPL::QASTContext $context) {
+        QAST::Op.new(:op<call>,
+          :name<&SUPPLY>,
+          self.IMPL-CLOSURE-QAST($context)
+        )
+    }
+}
+
 # Done by all phasers. Serves as little more than a marker for phasers, for
 # easing locating them all.
 class RakuAST::StatementPrefix::Phaser

t/12-rakuast/statement-prefix.rakutest

@@ -1,7 +1,7 @@
 use v6.e.PREVIEW;
 use Test;
 
-plan 14;
+plan 16;
 
 my $ast;
 my $deparsed;
@@ -461,4 +461,70 @@ subtest 'A start has a fresh $!' => {
     }
 }
 
+subtest 'supply statement prefix with expression evaluates to Supply' => {
+    # supply emit(42)
+    ast RakuAST::StatementPrefix::Supply.new(
+      RakuAST::Statement::Expression.new(
+        expression => RakuAST::Call::Name.new(
+          name => RakuAST::Name.from-identifier("emit"),
+          args => RakuAST::ArgList.new(
+            RakuAST::IntLiteral.new(42)
+          )
+        )
+      )
+    );
+
+    # must be this number of tests
+    plan 7;
+
+    is-deeply $deparsed, 'supply emit(42)', 'deparse';
+
+    for
+      'AST', EVAL($ast),
+      'Str', EVAL($deparsed),
+      'Raku', EVAL(EVAL $raku)
+    -> $type, $supply {
+        isa-ok $supply, Supply, $type;
+        $supply.tap({ is $_, 42, 'emitted value ok' });
+    }
+}
+
+subtest 'supply statement prefix with block evaluates to Supply' => {
+    # supply { emit(42) }
+    ast RakuAST::StatementPrefix::Supply.new(
+      RakuAST::Block.new(
+        body => RakuAST::Blockoid.new(
+          RakuAST::StatementList.new(
+            RakuAST::Statement::Expression.new(
+              expression => RakuAST::Call::Name.new(
+                name => RakuAST::Name.from-identifier("emit"),
+                args => RakuAST::ArgList.new(
+                  RakuAST::IntLiteral.new(42)
+                )
+              )
+            )
+          )
+        )
+      )
+    );
+
+    # must be this number of tests
+    plan 7;
+
+    is-deeply $deparsed, q:to/CODE/.chomp, 'deparse';
+supply {
+    emit(42)
+}
+CODE
+
+    for
+      'AST', EVAL($ast),
+      'Str', EVAL($deparsed),
+      'Raku', EVAL(EVAL $raku)
+    -> $type, $supply {
+        isa-ok $supply, Supply, $type;
+        $supply.tap({ is $_, 42, 'emitted value ok' });
+    }
+}
+
 # vim: expandtab shiftwidth=4