[llvm] [CodingStandard] Add a rule about non-member definitions in CPP files (PR #126775)

[Mehdi Amini via llvm-commits]

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@@ -1640,6 +1640,10 @@ you have no immediate way to tell if this function is local to the file.  In
 contrast, when the function is marked static, you don't need to cross-reference
 faraway places in the file to tell that the function is local.
 
+Related to this issue, when non-member functions or variables are defined in a
+`.cpp`` file and need not be referenced outside that file, make them `static`.
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joker-eph wrote:

I don't quite see this as achieving what we want here actually: this is just saying to prefer using static instead of anonymous, but it does not say anything about the policy of making thing private as much as possible.


What about adding it at the end of the intro like this (last paragraph is added):

> After talking about namespaces in general, you may be wondering about anonymous
> namespaces in particular.  Anonymous namespaces are a great language feature
> that tells the C++ compiler that the contents of the namespace are only visible
> within the current translation unit, allowing more aggressive optimization and
> eliminating the possibility of symbol name collisions.  Anonymous namespaces are
> to C++ as "static" is to C functions and global variables.  While "``static``"
> is available in C++, anonymous namespaces are more general: they can make entire
classes private to a file.
> We aim to make private as much as possible every function or variable: if it is 
> defined in a `.cpp` file and need not be referenced outside that file, it should be 
> made private to this file.

That phrasing would cover also classes that can be put in anonymous namespaces as part of the intent to make things as private as possible.


https://github.com/llvm/llvm-project/pull/126775