The following improvements are made according to Ruby's behavior:
- Match location number to index.
- Remove duplicate most recent call output.
- Fix that first call is not output when array (unpacked) backtrace.
### Example
```ruby
def a; raise "error!" end
def b; a end
begin
b
rescue => e
e.backtrace if ARGV[0] == "unpack" # unpack backtrace
raise e
end
```
#### Before this patch:
```
$ bin/mruby example.rb unpack
trace (most recent call last):
[0] example.rb:2:in b
[1] example.rb:1:in a
example.rb:1: error! (RuntimeError)
```
#### After this patch:
```
$ bin/mruby example.rb unpack
trace (most recent call last):
[2] example.rb:4
[1] example.rb:2:in b
example.rb:1:in a: error! (RuntimeError)
```
The binary sizes (gems are only `mruby-bin-mruby`) are reduced slightly in
my environment than before the introduction of new specifiers/modifiers
(5116789a) with this change.
------------+-------------------+-------------------+--------
BINARY | BEFORE (5116789a) | AFTER (This PR) | RATIO
------------+-------------------+-------------------+--------
mruby | 593416 bytes | 593208 bytes | -0.04%
libmruby.a | 769048 bytes | 767264 bytes | -0.23%
------------+-------------------+-------------------+--------
BTW, I accidentally changed `tasks/toolchains/visualcpp.rake` at #4613,
so I put it back.
The addresses for packed inline symbols reference `mrb->symbuf` that
could be overridden by the later call of `mrb_sym2name_len`. Since
file names in call stack information are kept as symbols, keeping the
address in the C structures could cause problems like #4342.
This changes small incompatible changes in function prototypes:
* `mrb_parser_get_filename`: return value changed to `mrb_sym`.
* `mrb_debug_get_filename`: add `mrb_state*` as a first argument.
* `mrb_debug_get_line`: ditto.
I believe above functions are almost internal, and no third-party
mrbgem use them.
- Move calling `mrb_debug_get_filename()` to after `lineno` check.
- Remove unneeded array check in `print_backtrace()`.
- Add a few `const` qualifier.
Instead of preserving a backtrace in `mrb_state`, `mrb_exc_set`
keeps packed backtrace in an exception object. `#backtrace` unpacks
it to an array of strings.
It looks like the logic to reallocate the backtrace was flawed,
based on the wrong variable (loc_raw->i, which, as I have verified,
decreases from 16 to 0 instead of increasing)
I am not sure if this is the correct fix
Yukihiro "Matz" Matsumoto