Travis: Automatically test KS submissions

With @SirCmpwn's permission, this should download and test any mod from
KerbalStuff. This is only triggered on PRs, and will automatically fetch
the latest stable netkan.exe for testing.

.gitignore

@@ -1,2 +1,3 @@
 .fatten.out
 *.ckan
+netkan.exe

.travis.yml

@@ -1,7 +1,7 @@
-language: c
+language: csharp
 
 install:
-    - sudo apt-get install python-demjson libtest-most-perl libjson-any-perl
+    - sudo apt-get install python-demjson libtest-most-perl libjson-any-perl libwww-mechanize-perl libipc-system-simple-perl
 
 script:
     - jsonlint -s -v NetKAN/*.netkan

t/kerbalstuff.t

@@ -0,0 +1,77 @@
+#!/usr/bin/perl -w
+use 5.010;
+use strict;
+use warnings;
+use autodie qw(:all);
+use Test::More;
+use IPC::System::Simple qw(capture);
+use WWW::Mechanize;
+
+my $pr_branch = $ENV{TRAVIS_PULL_REQUEST};
+my $netkan = "./netkan.exe";
+
+if (! $pr_branch or $pr_branch eq "false") {
+    plan skip_all => "Not a pull request";
+}
+
+if (! -x $netkan) {
+
+    # If we don't already have a netkan executable, then go download the latest.
+    # This includes unstable netkan.exe builds, as submissions may reference
+    # experimental features.
+
+    my $agent = WWW::Mechanize->new( agent => "NetKAN travis testing" );
+    $agent->get("https://github.com/KSP-CKAN/CKAN/releases");
+    $agent->follow_link(text => 'netkan.exe');
+
+    open(my $fh, '>', $netkan);
+    binmode($fh);
+    print {$fh} $agent->content;
+    close($fh);
+    chmod(0755, $netkan);
+}
+
+# TODO: What if our PR is against something other than master?
+my @changed_files = capture("git diff --name-only master");
+chomp(@changed_files);
+
+# Walk through our changed files. If any of them mention KS, then
+# run netkan over them. (We have @sircmpwn's permission to make KS
+# downloads during CI testing.)
+
+foreach my $file (@changed_files) {
+    if (is_ks_file($file)) {
+        netkan_validate($file);
+    }
+}
+
+done_testing;
+
+sub is_ks_file {
+    my ($file) = @_;
+
+    # Not a netkan file? Not something we want to test.
+    return 0 if ($file !~ m{\.netkan$});
+
+    local $/;   # Slurp mode.
+
+    open(my $fh, '<', $file);
+    my $content = <$fh>;
+    close($fh);
+
+    return $content =~ m{#/ckan/kerbalstuff};
+}
+
+# Simply checks to see if netkan.exe runs without errors on this file
+sub netkan_validate {
+    my ($file) = @_;
+
+    my $valid = eval {
+        system($netkan, $file);
+        return 1;
+    };
+
+    if ($@) { diag $@ }
+
+    ok($valid, $file);
+}