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Contributing to Nektar++

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## Contents
This is a reasonably complete guide to help if you're interested in contributing
to Nektar++, either in reporting bugs or, hopefully, trying to fix them! It's
split up into a number of sections:

- [Issues and bug reports](#issues-and-bug-reports)
- [How to contribute](#how-to-contribute)
- [Submission checklist](#submission-checklist)
- [Git cheatsheet](#git-cheatsheet)
- [Testing and GitLab CI](#testing-and-gitlab)
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- [Documentation](#documentation)
- [Formatting guidelines](#formatting-guidelines)

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## Issues and bug reports
Think you've found a bug or issue with Nektar++? We're very keen to hear about
- In the first instance, you should raise an issue on the
  **[issue tracker](** -- be
  sure to do a quick search and see if anyone has reported the same thing first.
- Alternatively you can
  **[join the mailing list](**
  for more advice.

It's *really helpful* if you can include a small session file that reproduces
the error, and can give a good description of the problem you're having.

## How to contribute
If you've got a patch or feature, please consider contributing it back to the
project. It's a pretty simple process:

1. Fork the Nektar++ repository in `nektar/nektar` into your username's space.
2. Create a branch with the naming convention:
   - `feature/myawesomebranch`: a new feature that wasn't in Nektar++ already.
   - `fix/mygreatfix`: fixes an issue that isn't tracked in the issue tracker.
   - `ticket/123-myfantasticpatch`: fixes an issue that is tracked in the issue
     tracker (please include the issue number somewhere!)
   - `tidy/mybrillianttidying`: cosmetic fixes to bring existing files up to the
     Nektar++ code guidelines.
3. Make sure you've gone through the checklist below.
4. Submit a merge request to merge into `master`. If you just want to see the
   diff and are not quite ready to merge, use the `[WIP]` tag in the title to
   prevent your code from being accidentally merged.
5. Put a comment in the MR saying that it's ready to be merged.
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6. If your branch is a minor fix that could appear in the next patch release,
   then add the `Proposed patch` label to the merge request.
7. Respond to any comments in the code review.
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## Submission checklist
- Did you add regression tests (for fixes) or unit tests and/or normal tests for
  new features?
- Have you run your branch through GitLab CI and do all the tests pass?
- Have you fixed any new compiler warnings your code has introduced into the
  compilation step for all of the Linux CI environments?
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  - **unused parameters**: if these are genuinely needed (e.g. virtual functions
    in a derived class, please use `boost::ignore_unused()` to mark as such.
  - **switch case may fall-through**: for switch statements which
    *intentionally* exploit fall-through between cases, mark the end of such
    cases with the comment `/* Falls through. */` to suppress the warning.
  - Avoid `ASSERTL0(false, msg)`; instead use `NEKERROR(ErrorUtil:efatal, msg)`.
  - Ensure variables are initialised with sensible default values.
- Is there documentation in the user guide and/or developer guide?
- Have you added a CHANGELOG entry, including the MR number?
- Are there any massive files you might have added in the commit history? We try
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  to keep test files as small as possible. If so you'll need to rebase or
  filter-branch to remove those from the commit history.
- Is the code formatted correctly?
  - **Note:** unfortunately, Nektar++ has pretty inconsistent code formatting at
    the moment. To help in reviewing your submission, new files should be
    formatted according to the guidelines (or use `clang-format` as described
    below) -- otherwise, try to keep formatting consistent with the file you're
    working on.

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## Git cheatsheet
Although Gitlab gives a nice interface to view the diff between a branch and
master, for large merges, it can be slow. The following `git` aliases can
provide a quicker alternative. You can use these by inserting them into the
`.gitconfig` file in your home directory, or inside the `nektar++/.git/config`

branch-name = "!git rev-parse --abbrev-ref HEAD"
diff-nows = diff --color -w
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log-branch = log --pretty='%C(green)%h %C(red)%an %C(reset)(%C(blue)%ad%C(reset))%n%s' master..
diff-branch = diff -U5 --minimal --color -w master...
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This gives you four commands:

- `git branch-name` displays the current branch name
- `git diff-nows` shows a diff of your current commit in colour, without
  whitespace changes.
- `git log-branch` shows a minimised log of all the commits on the current
  branch that are not in `master`.
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- `git diff-branch` shows a diff of the current branch against `master`, without
  showing changes from `master` that aren't present in the branch (i.e. `git
  diff master...branch`), without whitespace changes. (This should be roughly
  equivalent to Gitlab's diff).
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If you prefer a graphical interface to see the files that have changed in your
commit, you can additionally use the `git gui` command to bring up a simple
interface. `git difftool` can also be used in combination with a GUI diff
viewer, to graphically view the output of `git diff`.

## Testing and GitLab CI
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Your new features or fixes should include tests that cover the code you've
added. There are numerous examples within the various `Tests` directory lying
within the source trees, and there is an example of writing `.tst` files for our
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`Tester` executable in the `tests/Examples` directory. Once you've written your
tests, add them to the `CMakeLists.txt` file for the relevant solver, or to the
appropriate demos directory for library features in whatever directory you are
working in.

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You should also test your branch on the Nektar++ GitLab CI, which will compile
and test the code against a number of Linux, Mac and Windows operating
systems. If your tests don't pass, we can't merge the code into master.

When you submit a merge request testing on GitLab CI will happen automatically,
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unless you have marked the merge request as a work-in-progress (WIP: prefix).
Each time you push commits to a non-WIP merge request branch, it will also
trigger a build.

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## Documentation
Nektar++ has a fairly comprehensive user guide and a developer guide that is
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presently very incomplete. The following are rough guidelines for what you
should provide:

- If you are writing user-exposed features, you should add some documentation to
  the user guide on how to use them.
- Any functions/classes should include Doxygen documentation.
- Generally, code should be well-commented using regular C++ comments to explain
  its function to help in reviewing it.

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Nektar++ also has a growing number of tutorials to help introduce users and
developers to the use of the library and the range of application solvers. These
are stored in a separate repository, but are available from the main repository
through a git submodule. To populate the docs/tutorial directory run `git
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submodule init` followed by `git submodule update --remote`. The latter command
will ensure you have the latest master branch of the tutorials within your
source tree.

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## Code review and merging
All merge requests will be reviewed by one of the senior developers. We try to
stick to the following process:
- Senior developer will be assigned, MR will be assigned a milestone to target a
  - If the branch is deemed to be minor and passes the checklist above, senior
    developer will handle the request by themselves.
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  - Otherwise, senior developer will ask one or more other developers to review
    the code.
- Submission checklist will be checked by the reviewers.
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- Where appropriate, reviewers will comment on regions of code that need further
  development and/or improvement.
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- In addition to any coding comments/suggestions, reviewers are asked to check
  the branch passes the regression tests and appropriate documentation has been
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- Once feedback received from the branch author (if necessary) and reviewers are
  happy, the branch will be merged.

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## Release branches
Nektar++ releases are versioned in the standard form `x.y.z` where `x` is a
major release, `y` a minor release and `z` a patch release:

- major releases are extremely infrequent (on the order of every 2-3 years) and
  denote major changes in functionality and the API;
- minor releases occur around twice per year and contain new features with minor
  API changes;
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- patch releases are targeted on roughly a monthly basis and are intended to
  fix minor issues in the code.
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The repository contains a number of _release branches_ named `release/x.y` for
each minor release, which are intended to contain **fixes and very minor
changes** from `master` and which form the next patch release. This allows us to
use `master` for the next minor release, whilst still having key fixes in patch

### Cherry-picking process

Any branches that are marked with the `Proposed patch` label should follow the
following additional steps to cherry pick commits into the `release/x.y` branch.

1. If the branch is on a remote other than `nektar/nektar`, make sure that's
   added to your local repository.
2. On a local terminal, run `git fetch --all` to pull the latest changes. It's
   important for the commands below that you do this _before_ you merge the
   branch into `master`.
3. Merge the branch into master as usual using GitLab.
4. Switch to the appropriate branch with `git checkout release/x.y` and update
   with `git pull`.
5. Now check the list of commits to cherry-pick.

   git log --oneline --no-merges --reverse origin/master..REMOTE/fix/BRANCHNAME

   where `REMOTE` is the remote on which the branch lives and `BRANCHNAME` is
   the fix branch. If the list is empty, you probably did a `git fetch` after
   you merged the branch into `master`; in this case use `origin/master^`.
6. If you're happy with the list (compare to the MR list on the GitLab MR if
   necessary), cherry-pick the commits with the command:

   git cherry-pick -x $(git rev-list --no-merges --reverse origin/master..REMOTE/fix/BRANCHNAME)

7. It's likely you'll encounter some conflicts, particularly with the
   `CHANGELOG`. To fix these:
   - `git status` to see what's broken
   - Fix appropriately
   - `git commit -a` to commit your fix
   - `git cherry-pick --continue`
8. If everything becomes horribly broken, `git cherry-pick --abort`.
9. Once you're happy, `git push` to send your changes back to GitLab.

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Steps 5 and 6 can be simplified by creating a script

logopts="--oneline --no-merges --reverse"
commits=`git log $logopts master..$1 | cut -f 1 -d " " | xargs`

echo "Will cherry-pick the following commits: $commits"
echo "Press ENTER to continue..."

cherryopts="-x --allow-empty --allow-empty-message"
git cherry-pick $cherryopts $commits
which accepts the name of the source branch as the sole argument.

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## Formatting guidelines
Nektar++ uses C++, a language notorious for being easy to make obtuse and
difficult to follow code. To hopefully alleviate this problem, there are a
number of fairly simple formatting guidelines you should follow. We are
reasonably relaxed about code formatting, but if you can follow the guidelines
below this would be fantastic.

### Basic rules
- All code should be wrapped to 80 characters.
- Indentation should be 4 spaces with **no tabs**. Namespaces should not be
  indented to give more room in the 80 character width.
- Please comment your code with Doxygen and inline comments wherever possible --
  but don't use trailing inline comments to save the 80 character limit!
- All code blocks (even one-line blocks) should use braces, and braces should be
  on new lines; for instance
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  if (someCondition)
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- **Don't use preprocessor directives and macros unless there is no viable
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- However, please make sure you do have a header guard inside your `.h` files,
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  which you should be sure to include in any headers you contribute.
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- Use one `.cpp` and `.h` file per C++ class, and try to keep `inline` header
  code to a minimum (unless performance is a major factor).
- Put spaces around binary operators and constants.
- Put spaces after `if`, `while`, etc., but not after function names (see the
  example above).

### Variables and naming
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- Please use sensible names and use camelCase as a broad naming convention.
  - Variables should start with a lowercase letter, e.g. `myAwesomeVariable`.
  - Function, `class`, `struct` and `typedef` names should begin with capital
    letters, e.g. `MyAwesomeFunction`.
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- Inside classes, member variables should be prefixed with `m_`,
  e.g. `m_myAwesomeVariable`.
  - Global constants used throughout the library should be prefixed with `k`
    (e.g. `kGeometricTolerance`), and enumerations should be prefixed with `e`
    (e.g. `eGeometry`).
- Use all uppercase letters with underscores between words for pre-processor
  definitions and macros.

### Using `clang-format`
Code formatting is reasonably boring, so Nektar++ comes with a `.clang-format`
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file to allow for automatic code formatting. As noted above, you can use this
for new files, or cosmetic `tidy/*` branches, but try to stick to existing
formatting elsewhere.

Installing it is straightforward on most package managers. Nektar++ relies on
options that are used in version 3.7 or later.
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There are a number of instructions on how to use `clang-format` inside a number
of text editors on the
[CLang website]( However at a
minimum, you should consider downloading the
script into one of your `$PATH` locations. You can then run the command

    git clang-format

before you do a `git commit`, and `clang-format` will automatically format your
diff according to the guidelines.