Regenerate cpanfile on make

Makefile.PL

@@ -98,6 +98,7 @@ sub get_perl_filename {
         # installed.
 
         my $make_readme_md = File::Spec->catfile(qw(support readme.pl));
+        my $make_cpanfile = File::Spec->catfile(qw(support cpanfile.pl));
         return <<EOT;
 authortest:
 \tRELEASE_TESTING=1 prove -lvj4 xt
@@ -111,8 +112,11 @@ README.md: @{[$VERSION_FROM]} Makefile.PL $make_readme_md
 README: @{[$VERSION_FROM]} Makefile.PL $make_readme_md
 \t"$secure_perl_path" "$make_readme_md" -i "\$<" -o "\$@" -f text --appveyor hopenbuild/Data-Hopen --travis hopenbuild/Data-Hopen
 
-all :: README.md README
-dist :: README.md README
+cpanfile: @{[$VERSION_FROM]} Makefile.PL $make_cpanfile MYMETA.json
+\t"$secure_perl_path" "$make_cpanfile"
+
+all :: README.md README cpanfile
+dist :: README.md README cpanfile
 
 # Uninstallation: mimic what the normal "uninstall" target does, but actually
 # carry out the actions.

support/cpanfile.pl

@@ -0,0 +1,21 @@
+#!/usr/bin/env perl
+package # hide from PAUSE
+    makecpanfile;
+
+# Make a cpanfile from the dependencies in Makefile.PL.
+# Modified from https://github.com/miyagawa/cpanfile/blob/master/README.md
+# by miyagawa.  Assumes MYMETA.json has already been created.
+use strict;
+use warnings;
+
+use CPAN::Meta;
+use File::Slurp qw(write_file);
+use Module::CPANfile;
+
+my $meta = CPAN::Meta->load_file("MYMETA.json");
+my $file = Module::CPANfile->from_prereqs($meta->prereqs);
+my $contents = <<EOT . $file->to_string;
+# Auto-generated from Makefile.PL by cpanfile-from-Makefile-PL
+EOT
+    # Note: No timestamp so that the header line doesn't show up in the git diff
+write_file('cpanfile', $contents);