The only acceptable versions of clang-format are 8 and 9 for now
(until another round of big-churn-from-formatting, at which point
we'll update the required version).
clang-format-9 says:
SpacesInSquareBrackets (bool)
If true, spaces will be inserted after [ and before ]. Lambdas
or unspecified size array declarations will not be affected.
clang-format-10 changes part of that to:
Lambdas without arguments or unspecified size array
declarations will not be affected.
This means that 9 will only allow `[name]` for captures, and 10
will only allow `[ name ]` for captures, so they ping-pong all
the lambda's in the codebase back and forth. Just don't.
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