/usr/share/gps/docgen2/index_entry.tmpl is in gnat-gps-common 5.3dfsg-1ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | @@SET@@ NAMESTR = $1
@@SET@@ LOCSTR = $2
@@SET@@ TYPSTR = $3
new Array ('@_REPLACE_ALL(([.])/.<wbr/>):REPLACE_ALL((_)/_<wbr/>):NAMESTR_@', '@_LOCSTR_@', '@_TYPSTR_@'),
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