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Tips and Tricks for Contributint to Rune

Currently the main effort is building the bootstrap Rune compiler: rewriting the Rune compiler in Rune. Here are some tips for working on this effort.

  1. Use "make -j10" or something like that in the top level Rune directory to build Rune. Debugging is simpler using make.
  2. In bootstrap/database or bootstrap/parsegen, also use make.
  3. If the C Rune compiler fails in a way that looks like a bug, ping [email protected]. There are lots of C Rune compiler bugs remaining, and some will be fixed, while others we will work around.
  4. Avoid poorly tested features of Rune. In particular, try to use cascade-delete classes rather than ref-counted classes, and try to use classes rather than structs.
  5. Run "make" a lot. Sometimes the Rune compiler loses its mind and starts giving incorrect feedback, making it impossible to fix the error, because you have no idea where it is. It is nice in these cases to revert the last few lines changed and to try again. Usually, the error is real, but the reporting is borked.
  6. You can debug your Rune binary with gdb, but there are a lot of gotchas:
    1. The LLVM compiler optimizes out a TON of parameters. If you follow the explicit advice of the LLVM gurus, you'll avoid writing all your parameters to local variable storage like C/C++ front-ends do. This makes life hard for the LLVM back-end folks, but today, they punish those who follow their advice by optimizing out parameters entirely, making debugging much harder. To see what is available, use "info locals" in gdb.
    2. Use the bulitin helper functions! You can type 'source prettyprint.py' if your are in the top-level Rune directory, and then when you print an object, you'll see its fields.
    3. Use the "show" methods, e.g. call pegparser_Peg_show(parser) will show you the contents of parser assuming Clang has not optimized it away.
    4. Write dump methods for your classes, and use the ones that already exist. They are invaluable for debugging in gdb.
  7. The Rune C compiler is NOT memory safe. In particular, it passes all tuples, structures and arrays by reference, een if the called function may realloc the arrays containing them. This is mostly a problem when writing copy methods for classes: DO NOT PASS ARRAYs, TUPLES, or STRUCTs to copy constructors. The auto-generated allocation function may move the arrays holding the data, causing your program to crash randomly. The work-around is to assign the tuple/array/struct to a local variable, which in the C Rune compiler forces a copy, and to pass the copy to the copy-constructor.
  8. There is a global 'counter' variable which can be used in condition expressions on GDB breakpoints.