terser and uglify-es don't add sourcemap entries where the original sourcemap doesn't have an entry. This will cause the unmapped range to appear to be mapped to the preceding range.
To fix
$ diff -u node_modules/uglify-es/lib/sourcemap.js sourcemap.js
--- node_modules/uglify-es/lib/sourcemap.js 2019-11-05 12:39:49.000000000 -0500
+++ sourcemap.js 2019-11-21 17:13:05.000000000 -0500
@@ -75,6 +75,10 @@
column: orig_col
});
if (info.source === null) {
+ generator.addMapping({
+ generated : { line: gen_line + options.dest_line_diff, column: gen_col },
+ source : null,
+ });
return;
}
source = info.source;