Implement a use_warnings flag for the Mason compiler

This allows you to catch runtime warnings in all Mason templates by
enabling a global use_warnings switch, similar to the use_strict
switch. Unlike use_strict this is off by default, so it's fully
backwards compatible.

I have a huge codebase where I'd like to enable warnings by default, and
not have to turn them on one-by-one for each template, which would
be *really* painful.

lib/HTML/Mason/Compiler/ToObject.pm

@@ -46,6 +46,10 @@ BEGIN
          { parse => 'boolean', type => SCALAR, default => 1,
            descr => "Whether to turn on Perl's 'strict' pragma in components" },
 
+         use_warnings =>
+         { parse => 'boolean', type => SCALAR, default => 0,
+           descr => "Whether to turn on Perl's 'warnings' pragma in components" },
+
          define_args_hash =>
          { parse => 'string', type => SCALAR, default => 'auto',
            regex => qr/^(?:always|auto|never)$/,
@@ -67,6 +71,7 @@ use HTML::Mason::MethodMaker
                         preamble
                         subcomp_class
                         use_strict
+                        use_warnings
                         )
                     ],
       );
@@ -300,6 +305,7 @@ sub _make_main_header
 
     return join '', ( "package $pkg;\n",
                       $self->use_strict ? "use strict;\n" : "no strict;\n",
+                      $self->use_warnings ? "use warnings;\n" : "",
                       sprintf( "use vars qw(\%s);\n",
                                join ' ', '$m', $self->allow_globals ),
                       $self->_blocks('once'),
@@ -690,6 +696,11 @@ C<$m> in postamble code.
 True or false, default is true. Indicates whether or not a given
 component should C<use strict>.
 
+=item use_warnings
+
+True or false, default is false. Indicates whether or not a given
+component should C<use warnings>.
+
 =item named_component_subs
 
 When compiling a component, use uniquely named subroutines for the a

lib/HTML/Mason/Params.pod

@@ -1458,4 +1458,23 @@ may be more appropriate for in-depth debugging sessions.
 =back
 
 True or false, default is true. Indicates whether or not a given
-component should C<use strict>.
+component should C<use strict>.
+
+=head2 use_warnings
+
+=over 4
+
+=item * Perl name:           use_warnings
+
+=item * Apache name:         MasonUseWarnings
+
+=item * Type in httpd.conf:  boolean
+
+=item * Default:             1
+
+=item * Belongs to:          C<HTML::Mason::Compiler::ToObject>
+
+=back
+
+True or false, default is false. Indicates whether or not a given
+component should C<use warnings>.

t/06-compiler.t

@@ -1131,6 +1131,36 @@ EOF
                           expect_warnings => qr/Use of uninitialized value.+in addition/,
                         );
 
+#------------------------------------------------------------
+
+        $group->add_test( name => 'warnings_do_not_need_explicit_enabling_on_use_warnings',
+                          interp_params => { use_warnings => 1 },
+                          description => "Make sure that warnings _are_ generated on use_warnings for other bad use of uninit",
+                          component => <<'EOF',
+% my $x;
+use_warnings is <% $x + 2 %>
+EOF
+                          expect => <<'EOF',
+use_warnings is 2
+EOF
+                          expect_warnings => qr/Use of uninitialized value.+in addition/,
+                        );
+
+#------------------------------------------------------------
+
+        $group->add_test( name => 'warnings_do_not_need_explicit_enabling_without_autoflush_on_use_warnings',
+                          description => "Make sure that warnings _are_ generated on use_warnings for other bad use of uninit when enable_autoflush is off",
+                          interp_params => { enable_autoflush => 0, use_warnings => 1 },
+                          component => <<'EOF',
+% my $x;
+use_warnings is <% $x + 2 %>
+EOF
+                          expect => <<'EOF',
+use_warnings is 2
+EOF
+                          expect_warnings => qr/Use of uninitialized value.+in addition/,
+                        );
+
 #------------------------------------------------------------
 
         $group->add_test( name => 'unbalanced_content_block_error',