viewdiff: add "b=" param when missing "diff --git" line

<2841d2de-32ad-eae8-6039-9251a40bb00e@tngtech.com> as posted to
git@vger contained an otherwise valid diff without a "diff
--git" line.  Generate a "b=" parameter in that case using the
"+++" line instead of the "diff --git" line.  SearchIdx.pm no
longer uses the "diff --git" line for filename information,
either.

1 files changed, 29 insertions, 2 deletions

diff --git a/lib/PublicInbox/ViewDiff.pm b/lib/PublicInbox/ViewDiff.pm
index 6a60d0dc..ff7d85f5 100644
--- a/lib/PublicInbox/ViewDiff.pm
+++ b/lib/PublicInbox/ViewDiff.pm
@@ -133,6 +133,17 @@ sub anchor1 ($$$$$) {
         undef
 }
 
+sub missing_diff_git_line ($$) {
+        my ($dctx, $pb) = @_;
+        # missing "diff --git ..."
+        $dctx->{path_b} = $pb;
+        $dctx->{Q} = '?b='.uri_escape_utf8($pb, UNSAFE);
+        my $pa = $dctx->{path_a};
+        if (defined($pa) && $pa ne $pb) {
+                $dctx->{Q} .= '&a='. uri_escape_utf8($pa, UNSAFE);
+        }
+}
+
 sub flush_diff ($$$) {
         my ($dst, $ctx, $linkify) = @_;
         my $diff = $ctx->{-diff};
@@ -192,8 +203,24 @@ sub flush_diff ($$$) {
                         $$dst .= '</span>';
                         $state = DSTATE_CTX;
                         $$dst .= $linkify->to_html($s);
-                } elsif ($s =~ m!^--- (?:$PATH_X)!o ||
-                         $s =~ m!^\+{3} (?:$PATH_X)!o)  {
+                } elsif ($s =~ m!^--- ($PATH_X)!o) {
+                        my $pa = $1;
+                        $pa = (split('/', git_unquote($pa), 2))[1];
+                        if (($dctx->{path_a} // '') ne $pa) {
+                                # missing "diff --git ..." ?
+                                $dctx->{path_a} = $pa;
+                        }
+                        # color only (no oid link) if missing dctx->{oid_*}
+                        $state <= DSTATE_STAT and
+                                to_state($dst, $state, DSTATE_HEAD);
+                        $$dst .= $linkify->to_html($s);
+                } elsif ($s =~ m!^\+{3} ($PATH_X)!o) {
+                        my $pb = $1;
+                        $pb = (split('/', git_unquote($pb), 2))[1];
+                        if (($dctx->{path_b} // '') ne $pb) {
+                                missing_diff_git_line($dctx, $pb);
+                        }
+
                         # color only (no oid link) if missing dctx->{oid_*}
                         $state <= DSTATE_STAT and
                                 to_state($dst, $state, DSTATE_HEAD);