Extension "Count Nested Control Structures" -ENS fails on most Rust code

[snowpoke]

The extension fails often enough that the program won't finish in most larger crates.

How to reproduce

git clone https://github.com/rust-lang/cargo
cd cargo
git checkout tags/0.59.0
lizard -ENS

will cause the following output:

Error: Fail to parse file './src/cargo/core/source/source_id.rs'
======================================================
  NLOC    CCN   token  PARAM  length   NS   location  
------------------------------------------------------
       4      1     24      1       6     0 source_id@15-20@./src/cargo/core/source/mod.rs
       9      2    132      1      20     0 supports_checksums@24-43@./src/cargo/core/source/mod.rs
      12      4    121      1      15     0 update@47-61@./src/cargo/core/source/mod.rs
       5      1     64      3      23     0 finish_download@63-85@./src/cargo/core/source/mod.rs
       4      1     20      1       6     0 describe@89-94@./src/cargo/core/source/mod.rs
       7      1     54      2      11     0 add_to_yanked_whitelist@99-109@./src/cargo/core/source/mod.rs
       3      1     18      1       3     0 source_id@113-115@./src/cargo/core/source/mod.rs
       3      1     18      1       3     0 replaced_source_id@118-120@./src/cargo/core/source/mod.rs
       3      1     18      1       3     0 supports_checksums@123-125@./src/cargo/core/source/mod.rs
       3      1     18      1       3     0 requires_precise@128-130@./src/cargo/core/source/mod.rs
       3      1     41      3       3     0 query@133-135@./src/cargo/core/source/mod.rs
       3      1     41      3       3     0 fuzzy_query@138-140@./src/cargo/core/source/mod.rs
       3      1     23      1       3     0 update@143-145@./src/cargo/core/source/mod.rs
       3      1     27      2       3     0 download@148-150@./src/cargo/core/source/mod.rs
       3      1     36      3       3     0 finish_download@152-154@./src/cargo/core/source/mod.rs
       3      1     27      2       3     0 fingerprint@157-159@./src/cargo/core/source/mod.rs
       3      1     27      2       3     0 verify@162-164@./src/cargo/core/source/mod.rs
       3      1     18      1       3     0 describe@166-168@./src/cargo/core/source/mod.rs
       3      1     18      1       3     0 is_replaced@170-172@./src/cargo/core/source/mod.rs
       3      1     26      2       3     0 add_to_yanked_whitelist@174-176@./src/cargo/core/source/mod.rs
       3      1     27      2       3     0 is_yanked@178-180@./src/cargo/core/source/mod.rs
      15      1     34      0      15     0 new@261-275@./src/cargo/core/source/mod.rs
       8      1     36      2       8     0 get_mut@278-285@./src/cargo/core/source/mod.rs
Traceback (most recent call last):
  File "/home/snowpoke/.local/bin/lizard", line 8, in <module>
    sys.exit(main())
  File "/home/snowpoke/.local/lib/python3.9/site-packages/lizard.py", line 1043, in main
    warning_count = printer(result, options, schema, AllResult)
  File "/home/snowpoke/.local/lib/python3.9/site-packages/lizard.py", line 830, in print_result
    result = print_and_save_modules(result, scheme)
  File "/home/snowpoke/.local/lib/python3.9/site-packages/lizard.py", line 797, in print_and_save_modules
    for module_info in all_fileinfos:
  File "/home/snowpoke/.local/lib/python3.9/site-packages/lizard.py", line 545, in __call__
    return self.analyze_source_code(
  File "/home/snowpoke/.local/lib/python3.9/site-packages/lizard.py", line 565, in analyze_source_code
    for _ in reader(tokens, reader):
  File "/home/snowpoke/.local/lib/python3.9/site-packages/lizard_languages/code_reader.py", line 160, in __call__
    for token in tokens:
  File "/home/snowpoke/.local/lib/python3.9/site-packages/lizard_ext/extension_base.py", line 11, in __call__
    self._state(token)
  File "/home/snowpoke/.local/lib/python3.9/site-packages/lizard_ext/lizardns.py", line 104, in _block_ending
    self.structure_piles[-1] = 0
IndexError: list assignment index out of range

When lizard fails on Rust code, it always fails with the same error message as above.

If you need an example of a crate where lizard does not fail, there is https://github.com/ssokolow/rust-cli-boilerplate, where it computes NS values above 0 on most files and does not crash.