[llvm-dev] RFC: changing variable naming rules in LLVM codebase (original) (raw)

Rui Ueyama via llvm-dev llvm-dev at lists.llvm.org
Fri Feb 22 13:48:02 PST 2019

On Fri, Feb 22, 2019 at 12:39 PM Chandler Carruth via llvm-dev < llvm-dev at lists.llvm.org> wrote:

On Fri, Feb 22, 2019 at 5:59 AM via llvm-dev <llvm-dev at lists.llvm.org> wrote:

- Local variables and formal parameters should be lowercase, with one exception: Variables/parameters that have lambda/function type should follow the function-name spelling rules.

I really dislike this exception. Callable objects are objects and locally scoped, I would much prefer they look like variables. Also, what about callable objects that aren't lambdas? Or that use operator() for something other than emulating a function call? I think the simple rule is superior. - Initialisms and other abbreviations would be considered words for this purpose, so we have names such as: tli // Local variable for TargetLoweringInfo mcgm // Data member for CodeGenModule Agreed. - I don't have a good suggestion for file-static/global variables. Some people have suggested a "g" prefix for globals, or possibly an "s" prefix for class-static data. These are rare enough that I'm not sure we need special rules for naming them. They should also should typically be wrapped up in an actual API limiting how widely they are referenced. Regarding the transition: Some people have worried that the churn will cause blame issues. I respectfully point out that in my own archaeology I have to deal with lots of clang-format/indentation/other random semantically meaningless refactoring, this is just one more. Also the point is not to optimize for git-blame but to optimize for reading what is there at the moment. A more focused and shorter transition period will create a lot of short-term churn but get us to the good endpoint sooner. Doing conversions per-file or per-class (rather than per-function [too small] or per-library [too big]) are probably the way to go. Given we are changing the names used for data, and we try to practice good data-hiding, the impact of the conversion of any given class ought to be reasonably confined. I generally agree with this strategy. That said, I would still do it somewhat lazily rather than eagerly, but batched much as you're suggesting.

If we are going to update variable names in a batch, I'd like to nominate lld as a starter project. It is a middle-sized LLVM subproject which currently follows the today's LLVM naming convention, and because of its size it shouldn't be too hard to convert the entire code base in a single patch or a few patches.

If someone can make clang-tidy help with this, that's awesome.

I'm almost afraid to make the next suggestion, but here goes: In more complicated/wide-impact cases, it would be possible to stage a data-member name conversion into "small-bang" iterations using a C++ tactic like this: class Foo { int mbar; // The renamed member. int &Bar = mbar; // TEMPORARY alias using the old name. }; This would have to be done sparingly and for good reason, such as when the names are known across many components/subprojects and doing them all at once would be really too much. Someone would have to commit to getting it all done and removing the aliases in a reasonably short period of time. Needing to do this trick would be (IMO) strong evidence of poor software design and a place to focus some refactoring effort. Honestly, I don't think we need to do this. We routinely make wide-ranging API updates. If we need to do that, we do that. What we should do is encourage anyone that before they decide to do this to discuss it and see if there is a good way to hide this usage of a variable name behind a better API and make that widespread change instead. Then the name change is more local again.

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