[tor-bugs] #29209 [Core Tor/Tor]: Reduce visibility of more data type internals

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#29209: Reduce visibility of more data type internals
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 Reporter:  nickm                       |          Owner:  (none)
     Type:  task                        |         Status:  new
 Priority:  Medium                      |      Milestone:  Tor:
                                        |  0.4.1.x-final
Component:  Core Tor/Tor                |        Version:
 Severity:  Normal                      |     Resolution:
 Keywords:  technical-debt refactoring  |  Actual Points:  3.5
Parent ID:                              |         Points:  15
 Reviewer:  nickm                       |        Sponsor:  Sponsor31-can
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Comment (by catalyst):

 Replying to [comment:19 nickm]:
 > My understanding is that the leading underscore is also reserved for
 external identifiers; even if it's safe for struct members, it's something
 we don't want to encourage.
 We chatted a bit about this on IRC. I still like leading underscores for
 hiding struct members, because I think it makes it easier to search for
 inappropriate uses. (I also think it's easier to search for leading
 underscore than for some specific long suffix(es).)

 I think generally speaking we should avoid using identifiers with leading
 underscores in `.c` files, even when we use them for hiding struct
 members. Any `.c` file that uses the private members should only access
 them using helper macros defined in headers. These macros will hide the
 use of the leading underscores.

 It's fairly easy to write small Coccinelle scripts for matching
 * uses of identifiers starting with an underscore
 * uses of struct members starting with an underscore

 There are quite a few places where we already use identifiers with leading
 underscores for parameter names and local variables. The C standard allows
 these uses. I think there isn't much harm for leading underscores for
 parameters and locals.

 Nick suggests waiting until after we merge #30236 to update that patch to
 use `_ ## x _ ## _module_name_private_field`. I'll open a new ticket for
 that.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/29209#comment:20>
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