Have Repository::FileSystem automatically precompile files

We now precompile loaded modules automatically. However, we cannot do this
anymore as soon as we encounter a 'use lib' as this changes the precompilation
store used. Consider:
    use Test;
    use lib 'foo';
    use Test::Util; # which again uses Test
Test::Util would be loaded from a different precompilation store that contains
a different precompiled version of Test to the one already loaded.

src/core/CompUnit/PrecompilationRepository.pm

@@ -1,11 +1,21 @@
-role CompUnit::PrecompilationRepository {
-    method load(CompUnit::PrecompilationId $id) returns CompUnit {
-        CompUnit
+{
+    my $i;
+    role CompUnit::PrecompilationRepository {
+        has $!i = $i++;
+
+        method load(CompUnit::PrecompilationId $id) returns CompUnit {
+            CompUnit
+        }
+
+        method may-precomp() {
+            $i < 3 # number of next repo after None and the first Default
+        }
     }
 }
 
 BEGIN CompUnit::PrecompilationRepository::<None> := CompUnit::PrecompilationRepository.new;
 
+class CompUnit { ... }
 class CompUnit::PrecompilationRepository::Default does CompUnit::PrecompilationRepository {
     has CompUnit::PrecompilationStore $.store;
 
@@ -27,6 +37,36 @@ class CompUnit::PrecompilationRepository::Default does CompUnit::PrecompilationR
             CompUnit::Handle
         }
     }
+
+    method precompile(CompUnit:D $compunit, CompUnit::PrecompilationId $id) {
+        my $io = self.store.destination($*PERL.compiler.id, $id);
+        my $path = $compunit.path;
+        die "Cannot pre-compile over a newer existing file: $io"
+          if $io.e && $io.modified > $path.modified;
+
+        my Mu $opts := nqp::atkey(%*COMPILING, '%?OPTIONS');
+        my $lle = !nqp::isnull($opts) && !nqp::isnull(nqp::atkey($opts, 'll-exception'))
+          ?? ' --ll-exception'
+          !! '';
+        %*ENV<RAKUDO_PRECOMP_WITH> = CREATE-INCLUDE-SPECS(@*INC);
+
+RAKUDO_MODULE_DEBUG("Precomping with %*ENV<RAKUDO_PRECOMP_WITH>")
+  if $*RAKUDO_MODULE_DEBUG;
+
+        my $cmd = "$*EXECUTABLE$lle --target={$*VM.precomp-target} --output=$io $path";
+        my $proc = shell("$cmd 2>&1", :out, :!chomp);
+        %*ENV<RAKUDO_PRECOMP_WITH>:delete;
+
+        my $result = '';
+        $result ~= $_ for $proc.out.lines;
+        $proc.out.close;
+        if $proc.status -> $status {  # something wrong
+            $result ~= "Return status $status\n";
+            fail $result if $result;
+        }
+        note $result if $result;
+        True
+    }
 }
 
 # vim: ft=perl6 expandtab sw=4

src/core/CompUnit/PrecompilationStore/File.pm

@@ -22,13 +22,20 @@ class CompUnit::PrecompilationStore::File does CompUnit::PrecompilationStore {
         $path ~~ :e ?? $path.Str !! Str
     }
 
+    method destination(CompUnit::PrecompilationId $compiler-id,
+                       CompUnit::PrecompilationId $precomp-id)
+        returns IO::Path
+    {
+        my $dest = self!dir($compiler-id, $precomp-id);
+        $dest.mkdir;
+        $dest.child($precomp-id.IO)
+    }
+
     method store(CompUnit::PrecompilationId $compiler-id,
                  CompUnit::PrecompilationId $precomp-id,
                  Str:D $path)
     {
-        my $dest = self!dir($compiler-id, $precomp-id);
-        $dest.mkdir;
-        $path.IO.copy($dest.child($precomp-id.IO));
+        $path.IO.copy(self.destination($compiler-id, $precomp-id));
     }
 
     method delete(CompUnit::PrecompilationId $compiler-id, CompUnit::PrecompilationId $precomp-id)

src/core/CompUnit/Repository/FileSystem.pm

@@ -1,5 +1,6 @@
 class CompUnit::Repository::FileSystem does CompUnit::Repository::Locally does CompUnit::Repository {
     has %!loaded;
+    has $!precomp;
 
     my %extensions =
       Perl6 => <pm6 pm>,
@@ -25,9 +26,11 @@ class CompUnit::Repository::FileSystem does CompUnit::Repository::Locally does C
         my $base := $!prefix.abspath ~ $dir-sep ~ $name.subst(:g, "::", $dir-sep) ~ '.';
         my $compunit;
 
+        return %!loaded{$name} if %!loaded{$name}:exists;
+
         if $handle {
             return %!loaded{$name} = %seen{$base} = CompUnit.new(
-              $base, :name($name), :extension(''), :has-precomp, :$handle, :repo(self)
+                $base, :name($name), :extension(''), :has-precomp, :$handle, :repo(self)
             );
         }
         else {
@@ -40,7 +43,7 @@ class CompUnit::Repository::FileSystem does CompUnit::Repository::Locally does C
                                     !! $!prefix.abspath ~ $dir-sep ~ $file;
 
                     $compunit = %seen{$path} = CompUnit.new(
-                      $path, :name($name), :extension(''), :has_source, :repo(self)
+                        $path, :name($name), :extension(''), :has-source, :repo(self)
                     ) if IO::Path.new-from-absolute-path($path).f;
                 }
             }
@@ -64,8 +67,16 @@ class CompUnit::Repository::FileSystem does CompUnit::Repository::Locally does C
         }
 
         if $compunit {
-            $compunit.load(:$line);
-            return %!loaded{$compunit.name} = $compunit;
+            if $precomp.may-precomp and $precomp.precompile($compunit, $id) {
+                $handle = $precomp.load($id);
+                return %!loaded{$name} = %seen{$base} = CompUnit.new(
+                    $base, :name($name), :extension(''), :has-precomp, :$handle, :repo(self)
+                );
+            }
+            else {
+                $compunit.load(:$line);
+                return %!loaded{$compunit.name} = $compunit;
+            }
         }
 
         return self.next-repo.need($spec, $precomp, :$line) if self.next-repo;
@@ -108,13 +119,14 @@ class CompUnit::Repository::FileSystem does CompUnit::Repository::Locally does C
     }
 
     method precomp-repository() returns CompUnit::PrecompilationRepository {
-        CompUnit::PrecompilationRepository::Default.new(
+        $!precomp := CompUnit::PrecompilationRepository::Default.new(
             :store(
                 CompUnit::PrecompilationStore::File.new(
                     :prefix(self.prefix.child('.precomp')),
                 )
             ),
-        );
+        ) unless $!precomp;
+        $!precomp
     }
 }