make directories a build dep

Author: coke

htmlify.p6

@@ -160,10 +160,11 @@ sub MAIN(
         $proc = Proc::Async.new($coffee-exe, './highlights/highlight-filename-from-stdin.coffee', :r, :w);
         $proc-supply = $proc.stdout.lines;
     }
-    say 'Creating html/subdirectories ...';
 
     for <programs type language routine images syntax> {
-        mkdir "html/$_" unless "html/$_".IO ~~ :e;
+        Build::Dependency::require(
+            'directory', "html/$_"
+        );
     }
 
     my $*DR = Perl6::Documentable::Registry.new;

lib/Build/Dependency.pm

@@ -7,3 +7,17 @@ multi sub require('executable', $exec-name, :$suggest) {
         die "Could not find $exec-name. Did you `$suggest`?";
     }
 }
+
+multi sub require('directory', $dir-name, :$create) {
+
+    my $io = $dir-name.IO;
+
+    return if $dir-name.IO ~~ :d;
+
+    if $dir-name.IO ~~ :e {
+        die "$dir-name already exists, but isn't a directory.";
+    }
+
+    note "Creating $dir-name";
+    mkdir $dir-name;
+}