dh_setup_copyright: Strip trailing '/@/...' from Rust CUs

https://github.com/rust-lang/rust/pull/92024 appends a build-specific
suffix to each compilation unit name in order to ensure they're all
unique. Thus, in order to get the original filenames, we need to strip
that suffix off.

In order to ensure the SBOM contains the right paths, we also write the
modified sources back to the bin2sources file.

infrastructure/apertis-issues#456



Signed-off-by: Ryan Gonzalez <ryan.gonzalez@collabora.com>

dh_setup_copyright

@@ -198,9 +198,15 @@ sub process_external_sources {
 	my $added_referenced_srcpackages = 0;
 
 	my $sources = decode_json $sources_data;
+	my $sources_changed = 0;
 
 	while (my ($file, $info) = each %$sources) {
 		foreach my $unit (@{$info->{'units'}}) {
+			if (($unit->{'comp_name'} =~ s|/@/.*||) && !$sources_changed) {
+				print "Stripping trailing '/@/...' from Rust compilation units\n";
+				$sources_changed = 1;
+			}
+
 			my $comp_dir = $unit->{'comp_dir'};
 			my $comp_name = $unit->{'comp_name'};
 
@@ -229,6 +235,13 @@ sub process_external_sources {
 		}
 	}
 
+	if ($sources_changed) {
+		print "Saving edited dwarf2sources output\n";
+		open my $sources_handle, '>', $fname_list or die "Failed to open $fname_list: $!";
+		print $sources_handle encode_json($sources);
+		close $sources_handle;
+	}
+
 	if (%$external_sources_to_packages) {
 		my $count = scalar %$external_sources_to_packages;
 		print "Adding metadata for $count external source file(s)\n";