refactor(web/cgit-tvl): Move cgit config back out of module

It occured to me yesterday that with the config inside of the module
it is kind of difficult to test cgit locally.

This moves it back to a separate location (//web/cgit-tvl) and makes
the most important things configurable via overrides.

Change-Id: I9b0f4c60b75c31441e1718e63b5b55aba3100aae
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5893
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

web/cgit-tvl/default.nix

@@ -0,0 +1,73 @@
+# Wrapper for running cgit through thttpd with TVL-specific
+# configuration.
+#
+# In practice this is only used for //ops/modules/cgit, but exposing
+# it here makes it easy to experiment with cgit locally.
+{ depot, lib, pkgs, ... }:
+
+let
+  cgitConfig = repo: pkgs.writeText "cgitrc" ''
+    # Global configuration
+    virtual-root=/
+    enable-http-clone=0
+    readme=:README.md
+    about-filter=${depot.tools.cheddar.about-filter}/bin/cheddar-about
+    source-filter=${depot.tools.cheddar}/bin/cheddar
+    enable-log-filecount=1
+    enable-log-linecount=1
+    enable-follow-links=1
+    enable-blame=1
+    mimetype-file=${pkgs.mime-types}/etc/mime.types
+    logo=https://static.tvl.fyi/${depot.web.static.drvHash}/logo-animated.svg
+
+    # Repository configuration
+    repo.url=depot
+    repo.path=${repo}
+    repo.desc=monorepo for the virus lounge
+    repo.owner=The Virus Lounge
+    repo.clone-url=https://code.tvl.fyi/depot.git
+  '';
+
+  thttpdConfig = port: pkgs.writeText "thttpd.conf" ''
+    port=${toString port}
+    dir=${depot.third_party.cgit}/cgit
+    nochroot
+    novhost
+    cgipat=**.cgi
+  '';
+
+  # Patched version of thttpd that serves cgit.cgi as the index and
+  # sets the environment variable for pointing cgit at the correct
+  # configuration.
+  #
+  # Things are done this way because recompilation of thttpd is much
+  # faster than cgit.
+  thttpdConfigPatch = repo: pkgs.writeText "thttpd_cgit_conf.patch" ''
+    diff --git a/libhttpd.c b/libhttpd.c
+    index c6b1622..eef4b73 100644
+    --- a/libhttpd.c
+    +++ b/libhttpd.c
+    @@ -3055,4 +3055,6 @@ make_envp( httpd_conn* hc )
+
+         envn = 0;
+    +    // force cgit to load the correct configuration
+    +    envp[envn++] = "CGIT_CONFIG=${cgitConfig repo}";
+         envp[envn++] = build_env( "PATH=%s", CGI_PATH );
+     #ifdef CGI_LD_LIBRARY_PATH
+  '';
+
+  thttpdCgit = repo: pkgs.thttpd.overrideAttrs (old: {
+    patches = [
+      ./thttpd_cgi_idx.patch
+      (thttpdConfigPatch repo)
+    ];
+  });
+
+in
+lib.makeOverridable
+  ({ port ? 2448
+   , repo ? "/var/lib/gerrit/git/depot.git/"
+   }: pkgs.writeShellScript "cgit-launch" ''
+    exec ${thttpdCgit repo}/bin/thttpd -D -C ${thttpdConfig port}
+  '')
+{ }

web/cgit-tvl/thttpd_cgi_idx.patch

@@ -0,0 +1,13 @@
+diff --git a/config.h b/config.h
+index 65ab1e3..cde470f 100644
+--- a/config.h
++++ b/config.h
+@@ -327,7 +327,7 @@
+ /* CONFIGURE: A list of index filenames to check.  The files are searched
+ ** for in this order.
+ */
+-#define INDEX_NAMES "index.html", "index.htm", "index.xhtml", "index.xht", "Default.htm", "index.cgi"
++#define INDEX_NAMES "cgit.cgi"
+ 
+ /* CONFIGURE: If this is defined then thttpd will automatically generate
+ ** index pages for directories that don't have an explicit index file.