clang-tidy: use constexpr for unmodified structs

[neheb]

Found with cppcoreguidelines-interfaces-global-init

Signed-off-by: Rosen Penev rosenp@gmail.com

Went overboard and converted all extern const to constexpr.

[piponazo]

Just for the sake of keeping track about important changes, I would move the 2nd commit to a separate PR. We discussed in the past to do such radical formatting on the whole project and we hesitated about it ... mainly because of the following reasons:

• It would make more difficult to merge things from 0.27-maintenance to master.
• It would make more difficult to track the history of changes in files.

It has been almost 2 years since we decided to move on to c++11 in master, and probably we will have the last 0.27 release this year. For me it would be fine to do the clang-format change in master, but let's give the change for other contributors to share their thoughts on this.

[piponazo]

Honestly, I do not understand the benefits of these changes. Could you please give some details about it? 😉

[neheb]

Hrm maybe another time.

[clanmills]

We discussed in the past to do such radical formatting on the whole project and we hesitated about it ... mainly because of the following reasons:

• It would make more difficult to merge things from 0.27-maintenance to master.
• It would make more difficult to track the history of changes in files.

It has been almost 2 years since we decided to move on to c++11 in master, and probably we will have the last 0.27 release this year.

Let's not do this to the code at the moment. We have to decide:

1. Is 'master' ready to be released as 0.28?
   There are quite a lot of PRs in 0.27-maintenance that should be ported to 'master'.
   I would like to see 0.28 released.
2. Will we have a 0.27.4 release?

Making a release is always more work that expected. It's discussed in Chapter 13 of my book https://clanmills.com/exiv2/book/#13-9

My priority in 2020 is to get the book finished. I'm willing to one more release of Exiv2 - either 0.27.4 or 0.28. I am willing to do 0.28 in 2021 and that would include merging the PRs from 0.27.3. After that's done, we can reformat all the code.

Realistically 0.28 RC1 could be 2021-03-01, RC2 2021-04-01, and GM 2021-05-01. Ready for the LGM conference in Rennes in May.

I don't know of any security issues in 0.27-maintenance. It's possible that 0.27.4 will never be needed, or it will be 0.27.3+security fixes.