Clang tidy auto refactor (braces, nullptr, and using)

[SteveBronder]

Summary

Running clang-tidy with the checks below. This refactor is only aesthetic and does not change how any of the code is executed.

readability-braces-around-statements:

• Adds braces around conditionals and ifs

modernize-use-using:
everywhere clang-tidy can replace a typedef with a using it will aka
typedef double A; becomes using A = double;

modernize-use-nullptr:
using nullptr instead of NULL

The original PR also had a cleanup to return a braced init list but after looking at the I didn't like it

Tests

refactor is only aesthetic so no new tests

Checklist

• Math issue Update internals to use more modern c++ #1308

• Copyright holder: Steve Bronder

  The copyright holder is typically you or your assignee, such as a university or company. By submitting this pull request, the copyright holder is agreeing to the license the submitted work under the following licenses:
  - Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
  - Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

• the basic tests are passing

  • unit tests pass (to run, use: ./runTests.py test/unit)
  • header checks pass, (make test-headers)
  • docs build, (make doxygen)
  • code passes the built in C++ standards checks (make cpplint)

• the code is written in idiomatic C++ and changes are documented in the doxygen

• the new changes are tested

[rok-cesnovar]

I dont understand this error.

git push https://****:****@github.com/bstatcomp/math.git clang-tidy-auto-refactor

remote: Permission to bstatcomp/math.git denied to ****.

fatal: unable to access 'https://****:****@github.com/bstatcomp/math.git/': The requested URL returned error: 403

This was never an issue before. Do we need to set something up on the fork or is Github acting up?

[SteveBronder]

I think we need to add the jenkinsbot user as a contributor to the bstat fork. I checked the 'allow edits from maintainers' thing was on but github must be goofing it for some reason

[rok-cesnovar]

I gave stan-buidlbot write access but that invite needs to be confirmed. But yeah the maintainers thing should suffice. Weird.

[SteveBronder]

@serban-nicusor-toptal we just sent the stan buildbot an email for permissions so it can make pushes to branches on the bstatcomp fork, I think that would fix the error below?

++ clang-format --version
+ git commit -m '[Jenkins] auto-formatting by clang-format version 5.0.0-3~16.04.1 (tags/RELEASE_500/final)'
[clang-tidy-auto-refactor d68c93a] [Jenkins] auto-formatting by clang-format version 5.0.0-3~16.04.1 (tags/RELEASE_500/final)
 81 files changed, 105 insertions(+), 105 deletions(-)
+ git push https://****:****@github.com/bstatcomp/math.git clang-tidy-auto-refactor
remote: Permission to bstatcomp/math.git denied to ****.
fatal: unable to access 'https://****:****@github.com/bstatcomp/math.git/': The requested URL returned error: 403
+ echo 'Exiting build because clang-format found changes.'
Exiting build because clang-format found changes.
+ echo 'Those changes are now found on stan-dev/math under branch clang-tidy-auto-refactor'
Those changes are now found on stan-dev/math under branch clang-tidy-auto-refactor
+ echo 'Please '\''git pull'\'' before continuing to develop.'
Please 'git pull' before continuing to develop.
+ exit 1
script returned exit code 1

[serban-nicusor-toptal]

@SteveBronder Hey, I don't have access to that email :(

[seantalts]

I think doing this for the PR should solve it: https://help.github.com/en/articles/allowing-changes-to-a-pull-request-branch-created-from-a-fork

Just a NB for all devs: the hope is that you all have clang-format and the githook (sh ./hooks/install_hooks.sh) installed locally so that commits are atomic and well-formatted as well as the resulting code.