I think this is parse.y issue.

The lineno of NODE_RESCUE is 1 correctly with begin ... rescue ... end pattern.

$ cat a.rb
begin
  raise
rescue
  raise ""
end

$ ./miniruby -v --dump=parsetree a.rb|grep -e "NODE.*line"
# @ NODE_SCOPE (line: 6)
#     @ NODE_PRELUDE (line: 6)
#     |   @ NODE_RESCUE (line: 1)
#     |   |   @ NODE_VCALL (line: 2)
#     |   |   @ NODE_RESBODY (line: 4)
#     |   |   |   @ NODE_FCALL (line: 4)
#     |   |   |       @ NODE_ARRAY (line: 4)
#     |   |   |       |   @ NODE_STR (line: 4)

But the lineno of NODE_RESCUE is 2 with def ... rescue ... end pattern.

$ cat b.rb
def foo
  raise
rescue
  raise ""
end

$ ./miniruby -v --dump=parsetree b.rb|grep -e "NODE.*line"
# @ NODE_SCOPE (line: 6)
#     @ NODE_PRELUDE (line: 6)
#     |   @ NODE_DEFN (line: 1)
#     |       @ NODE_SCOPE (line: 5)
#     |       |   @ NODE_ARGS (line: 1)
#     |           @ NODE_RESCUE (line: 2)
#     |           |   @ NODE_VCALL (line: 2)
#     |           |   @ NODE_RESBODY (line: 4)
#     |           |   |   @ NODE_FCALL (line: 4)
#     |           |   |       @ NODE_ARRAY (line: 4)
#     |           |   |       |   @ NODE_STR (line: 4)

NODE_RESCUE and NODE_ENSURE of "k_begin bodystmt k_end" are given special treatment in parse.y.
https://svn.ruby-lang.org/cgi-bin/viewvc.cgi/trunk/parse.y?revision=58466&view=markup#l2466

How about do likewise for "k_def fname f_arglist bodystmt k_end"?
https://svn.ruby-lang.org/cgi-bin/viewvc.cgi/trunk/parse.y?revision=58466&view=markup#l2793