Fix bug when expanding an Ast leaf which is a single token

cc ircmaxell/php-compiler#29

src/Expansion.php

@@ -232,6 +232,9 @@ private function mutate(TokenStream $ts, Ast $context, Engine $engine) : TokenSt
 
                     $delimiters = $result->{'delimiters'};
 
+                    // normalize when context is a single token
+                    if ($context instanceof Token) $context = [[$context]];
+
                     // normalize associative arrays
                     if (array_values($context) !== $context) $context = [$context];
 

tests/phpt/issues/ircmaxell-php-compiler#29.phpt

@@ -0,0 +1,51 @@
+--TEST--
+Test for bug found at https://github.com/ircmaxell/php-compiler/pull/29 --pretty-print
+--FILE--
+<?php
+
+$(macro :unsafe :recursive) {
+    $(optional(buffer('unsigned')) as unsigned) compile {
+        $(
+            repeat(
+                either(
+                    chain(
+                        T_VARIABLE as result,
+                        token('='),
+                        either(
+                            chain(
+                                T_VARIABLE as binary_left,
+                                either(token('^') as binary_xor) as binary_op,
+                                either(T_VARIABLE as binary_variable, T_LNUMBER as binary_number) as binary_right
+                            ) as binary
+                        ),
+                        token(';')
+                    ) as assignop
+                )
+            ) as stmts
+        )
+    }
+} >> {
+    $(stmts ... {
+        $(assignop ? ... {
+            $(binary ? ... {
+                $(binary_op ... {
+                    $(binary_xor ? ... {
+                        $(result) = $this->context->builder->bitwiseXor($(binary_left), $__right);
+                    })
+                })
+            })
+        })
+    })
+}
+
+compile {
+    $result = $value ^ 1;
+}
+
+?>
+--EXPECTF--
+<?php
+
+$result = $this->context->builder->bitwiseXor($value, $__right);
+
+?>