Merge #19071: doc: Separate repository for the gui

66666d5 doc: Mention repo split in the READMEs (MarcoFalke)
faceed7 doc: Add redirect for GUI issues and pull requests (MarcoFalke)

Pull request description:

  ## 🥅 Goals

  Splitting up the GUI (and splitting out modules in general) has been brought up often in recent years. Now that the GUI is primarily connected through (internal) interfaces with the node, it seems an appropriate time to revive this discussion.

  Before looking for solutions, we should define a set of goals that we want to achieve. I will start with some ideas to get started and I hope that others will chime in to share and prioritize their goals.

  ### Separate issue and patch management

  It is currently not possible to subscribe to only a subset of modules in Bitcoin Core, or exclude modules from issue and patch notifications. While it is possible to reactively mute conversations in the stream of all ongoing discussions, there is no way to proactively achieve this. Moreover, the list of open issues and pull request will always include GUI related ones by default. Only with [filters](https://github.com/bitcoin/bitcoin/pulls?q=is%3Aopen+is%3Apr+-label%3AGUI) it is possible to hide them.

  ### More focused review and interests

  Long term goals of the GUI are partially unclear #17395 . Bitcoin Core developers are generally fluent on the command line. Thus, they might not be interested or motivated to review improvements to the GUI, which might not affect their workflow on the command line at all.  Splitting up the GUI will hopefully attract similar minded people to a project whose primary goal is to build and improve the GUI.

  ### Maintain high quality assurance

  The quality of the GUI (and even more importantly Bitcoin Core in general) must not degrade. This means that code review itself is not negatively affected by splitting the GUI, but also the integration of the GUI into the rest of Bitcoin Core. One issue could arise when arbitrary version-combinations are allowed. We are struggling hard to test against all supported versions of Boost. Making the GUI version another dimension is going to make testing impossible.

  ### The GUI *is* Bitcoin Core

  When a user downloads Bitcoin Core from our website (or another package manager) they expect the GUI to be included. This should not change (at least not as a result of splitting up the GUI into another project).

  Similarly, when building Bitcoin Core, the gui should still be built when `--with-gui` is specified.

  ## 🌳 Proposed solution: Monotree

  TLDR. Everything stays the same, the development process for the GUI changes slightly.

  Long version:
  * An exact mirror of the master development branch is hosted at `bitcoin-core/gui`. The new repository is used to track gui-only issues and pull requests. Global changes that happen to touch gui code still go to the *main* repo.
  * All pull requests will be merged into `bitcoin/bitcoin`.
  * Decision making process and maintainers will be identical for both repos.

  ### Disadvantages

  * Review activity might decrease?

  * It doesn't go far enough. bitcoin/bitcoin#3440 is proposing a modularized Bitcoin Core. The GUI could be an "add-on", connected over RPC or capnproto (bitcoin/bitcoin#10102). Thus, the gui could even be hosted as a subtree or completely separate project.

  ### Advantages

  * Review activity might increase? It is impossible to predict the future, but for example the `libsecp256k1` subtree has a lot of domain specific experts, maintainers and reviewers. I think longer term it makes sense to at least try this route for the gui as well.

  * A smaller step is easier to undo when it turns out to come with any unforeseen downsides.

  * No substantial changes to the decision making progress.

  * Nothing changes in how developers set up their dev environment or how users build from the source. Also, the release binaries and process will stay exactly the same. No version drift. Finally, code sharing between the GUI and Bitcoin Core is not made any harder.

  * The organizational side. There are 72 open issues (~14%) and 61 open PRs (~16%) with the GUI label. If moved to its own repo, non-GUI developers wouldn't have to be distracted with GUI-only issues and PRs and GUI enhancements. GUI developers have their own repo to focus on GUI development exclusively.

  ### Implementation (outstanding TODOs)

  * Adjust maintainer merge script bitcoin-core/bitcoin-maintainer-tools#57
  * Create bitcoin-core/gui repository (empty or with master branch only)
  * Assign all existing bitcoin core maintainers to the new repo
  * Celebrate? 🥳

  * Long-term: Think how long the grace period is for existing GUI related issues and pull requests. Issues can be transferred with a script after a grace period of some months?

ACKs for top commit:
  fjahr:
    ACK 66666d5
  Sjors:
    ACK 66666d5
  troygiorshev:
    re-ACK 66666d5
  practicalswift:
    re-ACK 66666d5
  hebasto:
    re-ACK 66666d5

Tree-SHA512: 2e1a8de945fa6995583059a2e322621763fccce74a869f9aa750f73546b26350487c4acc4222c03cb3ac1f88e80f0b9d9a3a80a200432fee0d785f52c5cb6174

Author: MarcoFalke

.github/ISSUE_TEMPLATE.md

@@ -4,7 +4,11 @@ General bitcoin questions and/or support requests are best directed to the Bitco
 
 For reporting security issues, please read instructions at https://bitcoincore.org/en/contact/.
 
-If the node is "stuck" during sync or giving "block checksum mismatch" errors, please ensure your hardware is stable by running memtest and observe CPU temperature with a load-test tool such as linpack before creating an issue! -->
+If the node is "stuck" during sync or giving "block checksum mismatch" errors, please ensure your hardware is stable by running memtest and observe CPU temperature with a load-test tool such as linpack before creating an issue!
+
+Any report, issue or feature request related to the GUI should be reported at
+https://github.com/bitcoin-core/gui/issues/
+-->
 
 <!-- Describe the issue -->
 <!--- What behavior did you expect? -->

.github/ISSUE_TEMPLATE/gui_issue.md

@@ -0,0 +1,11 @@
+---
+name: An issue or feature request related to the GUI
+about: Any report, issue or feature request related to the GUI should be reported at https://github.com/bitcoin-core/gui/issues/
+title: Any report, issue or feature request related to the GUI should be reported at https://github.com/bitcoin-core/gui/issues/
+labels: GUI
+assignees: ''
+
+---
+
+Any report, issue or feature request related to the GUI should be reported at
+https://github.com/bitcoin-core/gui/issues/

.github/PULL_REQUEST_TEMPLATE.md

@@ -3,6 +3,10 @@
 
 Pull requests without a rationale and clear improvement may be closed
 immediately.
+
+GUI-related pull requests should be opened against
+https://github.com/bitcoin-core/gui
+first. See CONTRIBUTING.md
 -->
 
 <!--

CONTRIBUTING.md

@@ -84,6 +84,26 @@ To contribute a patch, the workflow is as follows:
   1. Create topic branch
   1. Commit patches
 
+For GUI-related issues or pull requests, the https://github.com/bitcoin-core/gui repository should be used.
+For all other issues and pull requests, the https://github.com/bitcoin/bitcoin node repository should be used.
+
+The master branch for all monotree repositories is identical.
+
+As a rule of thumb, everything that only modifies `src/qt` is a GUI-only pull
+request. However:
+
+* For global refactoring or other transversal changes the node repository
+  should be used.
+* For GUI-related build system changes, the node repository should be used
+  because the change needs review by the build systems reviewers.
+* Changes in `src/interfaces` need to go to the node repository because they
+  might affect other components like the wallet.
+
+For large GUI changes that include build system and interface changes, it is
+recommended to first open a pull request against the GUI repository. When there
+is agreement to proceed with the changes, a pull request with the build system
+and interfaces changes can be submitted to the node repository.
+
 The project coding conventions in the [developer notes](doc/developer-notes.md)
 must be followed.
 

README.md

@@ -25,9 +25,14 @@ information or see https://opensource.org/licenses/MIT.
 Development Process
 -------------------
 
-The `master` branch is regularly built (see doc/build-*.md for instructions) and tested, but is not guaranteed to be
+The `master` branch is regularly built (see `doc/build-*.md` for instructions) and tested, but it is not guaranteed to be
 completely stable. [Tags](https://github.com/bitcoin/bitcoin/tags) are created
-regularly to indicate new official, stable release versions of Bitcoin Core.
+regularly from release branches to indicate new official, stable release versions of Bitcoin Core.
+
+The https://github.com/bitcoin-core/gui repository is used exclusively for the
+development of the GUI. Its master branch is identical in all monotree
+repositories. Release branches and tags do not exist, so please do not fork
+that repository unless it is for development reasons.
 
 The contribution workflow is described in [CONTRIBUTING.md](CONTRIBUTING.md)
 and useful hints for developers can be found in [doc/developer-notes.md](doc/developer-notes.md).