[neopallium]

I used c2rust to start rewriting OpenJpeg into Rust code [0].

It was easy to get the Rust code compiled and working as a drop-in-replacement for the C Library. This has been a big help with refactoring the unsafe Rust code into safe Rust (manual work). OpenJpeg has a great testsuite that has allowed testing that each refactor step doesn't add new bugs (has happened at least 3 times).

The original run of c2rust generated 96,842 lines of Rust code (about 1 year ago), now it is down to 46,873 lines code. A lot of the extra 50k lines of code were from C macros that got expanded and from constant lookup tables (C code had 10-30 values per line, Rust 1 value 1 line).

For anyone looking to use c2rust to port C code to Rust, I recommend the following:

  1. Setup some automated testing if it doesn't exist already.
  2. Do refactoring in small amounts, run the tests and commit the changes before doing more refactoring.
  3. Use "search/replace" tools (`sed`) to help with rewriting common patterns.  Make sure to follow #2 when doing this.
  4. Don't re-organize the code until after most of the unsafe code has been rewritten.  This will allow easier side-by-side comparison with the original C code.
  5. c2rust expands macros and constants from `#define`.  Being able to do side-by-side comparison of the C code will help with adding constants back in and removing expanded code with Rust macros or just normal Rust functions.

[0] https://github.com/Neopallium/openjpeg/tree/master/openjp2-r...