Change references from "master" branch to "main" branch

[willschlitzer]

As discussed in #1356, PyGMT is changing its default branch from "master" to "main". This pull request changes the references to "master" in the CI job files, maintenance.md, and the README.

Fixes #1356

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If adding new functionality, add an example to docstrings or tutorials.

Slash Commands

You can write slash commands (/command) in the first line of a comment to perform
specific operations. Supported slash commands are:

• /format: automatically format and lint the code
• /test-gmt-dev: run full tests on the latest GMT development version

[weiji14]

This reminds me, we'll need to rename the 'master' branch on https://dagshub.com/GenericMappingTools/pygmt to 'main' too.

[maxrjones]

While GitHub will redirect links, I think we should update the links in these files to reflect the new main name as part of this process:

./doc/install.rst
./doc/conf.py
./pygmt/src/x2sys_cross.py
./doc/contributing.md
./doc/external_resources.md
./.github/config.yml

[willschlitzer]

While GitHub will redirect links, I think we should update the links in these files to reflect the new main name as part of this process:

./doc/install.rst
./doc/conf.py
./pygmt/src/x2sys_cross.py
./doc/contributing.md
./doc/external_resources.md
./.github/config.yml

./doc/install.rst and ./pygmt/src/x2sys_cross.py
It looks like the only instance of master is in reference to the GMT branch

[maxrjones]

While GitHub will redirect links, I think we should update the links in these files to reflect the new main name as part of this process:

./doc/install.rst
./doc/conf.py
./pygmt/src/x2sys_cross.py
./doc/contributing.md
./doc/external_resources.md
./.github/config.yml

./doc/install.rst and ./pygmt/src/x2sys_cross.py
It looks like the only instance of master is in reference to the GMT branch

sounds good, I did a quick search but didn't spend much time checking the references.

[seisman]

Maybe we should give this PR a final review and merge it several days before the v0.4.1 release, so that we can have more time to check if there are any related issues in the upcoming v0.4.1 release.

[core-man]

contributing.md still have sentences using master:

• Line 98:

  our tests. This way, the *master* branch is always stable.
  

• Line 173:

  See the [`environment.yml`](https://github.com/GenericMappingTools/pygmt/blob/master/environment.yml)
  

[core-man]

I think all "master" are changed to "main" except in some places indicated above. Great~

[weiji14]

Besides those mentioned at #1360 (comment), here's a few more:

• pygmt/doc/conf.py

  Line 117 in 6a4b871

  master_doc = "index"

• pygmt/doc/_templates/layout.html

  Line 35 in 6a4b871

  <a href="{{ pathto(master_doc) }}"><h2 class="sidebar-title">{{ project }}</h2></a>

• https://github.com/GenericMappingTools/pygmt/blame/v0.4.0/doc/install.rst#L72

[willschlitzer]

@weiji14 @core-man I made the changes you requested

[seisman]

Besides those mentioned at #1360 (comment), here's a few more:

• pygmt/doc/conf.py

  Line 117 in 6a4b871

  master_doc = "index"

• pygmt/doc/_templates/layout.html

  Line 35 in 6a4b871

  <a href="{{ pathto(master_doc) }}"><h2 class="sidebar-title">{{ project }}</h2></a>

I don't think we can change master_doc to main_doc. It's a sphinx configuration and is used internally by sphinx (see https://github.com/sphinx-doc/sphinx/search?q=master_doc).

EDIT: Sphinx has renamed master_doc to root_doc in sphinx v4.0. We can change master_doc to root_doc here, but it means PyGMT will require sphinx >= 4.0, which was release in May, 2021.

[weiji14]

Besides those mentioned at #1360 (comment), here's a few more:

• pygmt/doc/conf.py

  Line 117 in 6a4b871

  master_doc = "index"

• pygmt/doc/_templates/layout.html

  Line 35 in 6a4b871

  <a href="{{ pathto(master_doc) }}"><h2 class="sidebar-title">{{ project }}</h2></a>

I don't think we can change master_doc to main_doc. It's a sphinx configuration and is used internally by sphinx (see https://github.com/sphinx-doc/sphinx/search?q=master_doc).

EDIT: Sphinx has renamed master_doc to root_doc in sphinx v4.0. We can change master_doc to root_doc here, but it means PyGMT will require sphinx >= 4.0, which was release in May, 2021.

Was just about to say that root_doc should be used instead. We have sphinx 4.1.2 in CI (https://github.com/GenericMappingTools/pygmt/runs/3235302620?check_suite_focus=true#step:6:187) so it should be fine.

[maxrjones]

Does this get merged before or after the actual renaming of the branch?

[seisman]

Does this get merged before or after the actual renaming of the branch?

Either should work. I prefer to merge this PR after renaming the branch, so that we can immediately know how renaming the main branch affects PRs.

[maxrjones]

Does this get merged before or after the actual renaming of the branch?

Either should work. I prefer to merge this PR after renaming the branch, so that we can immediately know how renaming the main branch affects PRs.

OK, I can rename the branch after the current workflows finish and then ping here to merge in the PR.

[maxrjones]

Looks good to merge after checks pass, thanks @willschlitzer!

[weiji14]

Looks good to merge after checks pass, thanks @willschlitzer!

Thanks heaps @willschlitzer! I'll squash and merge this in directly since the "master" -> "main" rename has been done (otherwise the links on https://www.pygmt.org/dev/index.html won't work).