[tor-bugs] #32921 [Core Tor/Tor]: Code and script changes to run clang-format without breaking checkSpaces or coccinelle

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#32921: Code and script changes to run clang-format without breaking checkSpaces or
coccinelle
----------------------------+------------------------------------
 Reporter:  nickm           |          Owner:  nickm
     Type:  enhancement     |         Status:  needs_review
 Priority:  Medium          |      Milestone:  Tor: 0.4.3.x-final
Component:  Core Tor/Tor    |        Version:
 Severity:  Normal          |     Resolution:
 Keywords:  style, 043-can  |  Actual Points:  1.5
Parent ID:  #29226          |         Points:
 Reviewer:  catalyst        |        Sponsor:
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Comment (by catalyst):

 Doing a little digging through documentation, it seems like
 `StatementMacros` is new in clang-format-8.0, and `SpaceAfterLogicalNot`
 is new in clang-format-9.0.  The latest branch removes
 `SpaceAfterLogicalNot`, which helps with the latter.  (If we want to go as
 far back as clang-format-3.8 for Debian stretch, we might have to do a lot
 more digging.)

 Once I comment out those directives, clang-format-6.0 on Ubuntu Xenial
 seems to accept the .clang-format file.  (We'll have to parameterize the
 clang-format executable name in the helper script if we want this to run
 easily on Xenial, though, because 3.8 is the default there.)

 We can remove `StatementMacros` by changing the ht.h macros to use the
 "redeclare incomplete struct" trick for eating semicolons, and adjusting
 uses of those macros.  (The examples in the comments in ht.h use
 semicolons after those macros anyway, even though it might cause compiler
 errors/warnings.)  We might want to do that as a child ticket of this
 ticket.

 (Note that we seem to have two readily findable instances of this
 technique with different struct tags: `struct dummy_semicolon_eater__` in
 src/lib/cc/compat_compiler.h and `struct tor_semicolon_eater` in
 src/lib/conf/conftesting.h.  We might want to consolidate them.  I prefer
 the `tor_` prefix for future library-friendliness.)

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/32921#comment:16>
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