We've had some recent discussions about code style. I have a propasal
For the purpose of this proposal I will assume that there is consensus on the
following ideas.
- Having multiple code styles is bad.
- Therefore, reducing the number of code styles in our code is a win (though
there are some caveats relating to how we get to that state, which I discuss
below).
- The standard Mozilla style is good enough. (It's not perfect, and it should
continue to evolve, but if you have any pet peeves please mention them in a
different thread to this one.)
With these ideas in mind, a goal is clear: convert non-Mozilla-style code to
Mozilla-style code, within reason.
There are two notions that block this goal.
- Our rule of thumb is to follow existing style in a file. From the style
guide:
The following norms should be followed for new code, and for Tower of Babel
code that needs cleanup. For existing code, use the prevailing style in a
file or module, or ask the owner if you are on someone else's turf and it's
not clear what style to use.
This implies that large-scale changes to convert existing code to standard
style are discouraged. (I'd be interested to hear if people think this
implication is incorrect, though in my experience it is not.)
I propose that we officially remove this implicit discouragement, and even
encourage changes that convert non-Mozilla-style code to Mozilla-style (with
some exceptions; see below). When modifying badly-styled code, following
existing style is still probably best.
However, large-scale style fixes have the following downsides.
- They complicate |hg blame|, but plenty of existing refactorings (e.g.
removing old types) have done likewise, and these are bearable if they
aren't too common. Therefore, style conversions should do entire files in
a single patch, where possible, and such patches should not make any
non-style changes. (However, to ease reviewing, it might be worth
putting fixes to separate style problems in separate patches. E.g. all
indentation fixes could be in one patch, separate from other changes.
These would be combined before landing. See bug 956199 for an example.)
- They can bitrot patches. This is hard to avoid.
However, I imagine changes would happen in a piecemeal fashion, e.g. one
module or directory at a time, or even one file at a time. (Again, see bug
956199 for an example.) A gigantic change-all-the-code patch seems
unrealistic.
- There is an semi-official policy that the owner of a module can dictate its
style. Examples: SpiderMonkey, Storage, MFBT.
There appears to be no good reason for this and I propose we remove it.
Possibly with the exception of SpiderMonkey (and XPConnect?), due to it being
an old and large module with its own well-established style.
Also, we probably shouldn't change the style of imported third-party code;
even if we aren't tracking upstream, we might still want to trade patches.
(Indeed, it might even be worth having some kind of marking at the top of
files to indicate this, a bit like a modeline?)
Finally, this is a proposal only to reduce the number of styles in our
codebase. There are other ideas floating around, such as using automated tools
to enforce consistency, but I consider them orthogonal to or
follow-ups/refinements of this proposal -- nothing can happen unless we agree
on a direction (fewer styles!) and a way to move in that direction (non-trivial
style changes are ok!)
Nick
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