www: support publicinbox.cgit knob

For backwards-compatibility, this defaults to `first'.  When set
to `fallback', PublicInbox::WwwCoderepo is favored and cgit is
only used as a fallback.  Eventually, `rewrite' will also be
supported to rewrite cgit URLs to WwwCoderepo ones.

Of course, WwwCoderepo is still missing search and other key
features, but that's being worked on...

3 files changed, 44 insertions, 13 deletions

diff --git a/Documentation/public-inbox-config.pod b/Documentation/public-inbox-config.pod
index d8504e61..e926a27b 100644
--- a/Documentation/public-inbox-config.pod
+++ b/Documentation/public-inbox-config.pod
@@ -293,6 +293,32 @@ C<publicinbox.cgitbin>, but may be overridden.
 Default: basename of C<publicinbox.cgitbin>, /var/www/htdocs/cgit/
 or /usr/share/cgit/
 
+=item publicinbox.cgit
+
+Controls whether or not and how C<cgit> is used for serving coderepos.
+New in public-inbox 2.0.0 (PENDING).
+
+=over 8
+
+=item * first
+
+Try using C<cgit> as the first choice, this is the default.
+
+=item * fallback
+
+Fall back to using C<cgit> only if our native, inbox-aware
+git code repository viewer doesn't recognized the URL.
+
+=item * rewrite
+
+Rewrite C<cgit> URLs for our native, inbox-aware code repository viewer.
+This implies C<fallback> for URLs the native viewer does not recognize.
+
+=back
+
+Default: C<first>  (C<cgit> will be used iff C<publicinbox.cgitrc>
+is set and the C<cgit> binary exists).
+
 =item publicinbox.mailEditor
 
 See L<public-inbox-edit(1)>
diff --git a/lib/PublicInbox/Cgit.pm b/lib/PublicInbox/Cgit.pm
index 298663c7..336098ca 100644
--- a/lib/PublicInbox/Cgit.pm
+++ b/lib/PublicInbox/Cgit.pm
@@ -53,6 +53,7 @@ sub locate_cgit ($) {
 sub new {
         my ($class, $pi_cfg) = @_;
         my ($cgit_bin, $cgit_data) = locate_cgit($pi_cfg);
+        $cgit_bin // return; # fall back in WWW->cgit
         my $self = bless {
                 cmd => [ $cgit_bin ],
                 cgit_data => $cgit_data,
diff --git a/lib/PublicInbox/WWW.pm b/lib/PublicInbox/WWW.pm
index 470510ae..f861b192 100644
--- a/lib/PublicInbox/WWW.pm
+++ b/lib/PublicInbox/WWW.pm
@@ -194,12 +194,19 @@ sub r404 {
 
 sub news_cgit_fallback ($) {
         my ($ctx) = @_;
-        my $www = $ctx->{www};
-        my $env = $ctx->{env};
-        my $res = $www->news_www->call($env);
-        $res = $www->cgit->call($env, $ctx) if $res->[0] == 404;
+        my $res = $ctx->{www}->news_www->call($ctx->{env});
+
+        $res->[0] == 404 and ($ctx->{www}->{cgit_fallback} //= do {
+                my $c = $ctx->{www}->{pi_cfg}->{'publicinbox.cgit'} // 'first';
+                $c ne 'first' # `fallback' and `rewrite' => true
+        } // 0) and $res = $ctx->{www}->coderepo->srv($ctx);
+
         ref($res) eq 'ARRAY' && $res->[0] == 404 and
-                $res = $www->coderepo->srv($ctx);
+                $res = $ctx->{www}->cgit->call($ctx->{env}, $ctx);
+
+        ref($res) eq 'ARRAY' && $res->[0] == 404 &&
+                        !$ctx->{www}->{cgit_fallback} and
+                $res = $ctx->{www}->coderepo->srv($ctx);
         $res;
 }
 
@@ -484,17 +491,14 @@ sub news_www {
 
 sub cgit {
         my ($self) = @_;
-        $self->{cgit} //= do {
-                my $pi_cfg = $self->{pi_cfg};
-
-                if (defined($pi_cfg->{'publicinbox.cgitrc'})) {
+        $self->{cgit} //=
+                (defined($self->{pi_cfg}->{'publicinbox.cgitrc'}) ? do {
                         require PublicInbox::Cgit;
-                        PublicInbox::Cgit->new($pi_cfg);
-                } else {
+                        PublicInbox::Cgit->new($self->{pi_cfg});
+                } : undef) // do {
                         require Plack::Util;
                         Plack::Util::inline_object(call => sub { r404() });
-                }
-        }
+                };
 }
 
 sub coderepo {