feat: introduce proposal design process

proposals/0000-template.md

@@ -0,0 +1,62 @@
+- Start Date: (fill me in with today's date, YYYY-MM-DD)
+- Proposal PR: (fill in after opening the PR)
+- Github Issue: (if available, link the issue containing the original request for this change)
+
+# Summary
+
+Explain the feature briefly.
+
+# Basic example
+
+When applicable, write a snippet of code showing how the new feature would
+be used.
+
+# Motivation
+
+Give us more background and explanation: Why do we need this feature? What use cases does it support? What's the expected
+outcome?
+
+Focus on explaining the motivation for this feature. We'd like to understand it, so that even if we don't accept this
+proposal, others can use the motivation to develop alternative solutions.
+
+# Detailed design
+
+This is the bulk of the proposal. Explain the design in enough detail for somebody
+familiar with Haystack to understand, and for somebody familiar with the
+implementation to implement. Get into specifics and corner-cases,
+and include examples of how the feature is used. Also, if there's any new terminology involved,
+define it here.
+
+# Drawbacks
+
+Look at the feature from the other side: what are the reasons why we should _not_ work on it? Consider the following:
+
+- What's the implementation cost, both in terms of code size and complexity?
+- Can the solution you're proposing be implemented as a separate package, outside of Haystack?
+- Does it teach people more about Haystack?
+- How does this feature integrate with other existing and planned features?
+- What's the cost of migrating existing Haystack pipelines (is it a breaking change?)?
+
+There are tradeoffs to choosing any path. Attempt to identify them here.
+
+# Alternatives
+
+What other designs have you considered? What's the impact of not adding this feature?
+
+# Adoption strategy
+
+If we implement this proposal, how will the existing Haystack users adopt it? Is
+this a breaking change? Can we write a migration script?
+
+# How we teach this
+
+Would implementing this feature mean the documentation must be re-organized
+or updated? Does it change how Haystack is taught to new developers at any level?
+
+How should this feature be taught to the existing Haystack users (for example with a page in the docs,
+a tutorial, ...).
+
+# Unresolved questions
+
+Optional, but suggested for first drafts. What parts of the design are still
+TBD?

proposals/README.md

@@ -0,0 +1,97 @@
+# Haystack proposals design process
+
+Most of the changes to Haystack, including bug fixes and small improvements,
+are implemented through the normal Pull Request workflow, according to our
+[contribution guidelines](../CONTRIBUTING.md).
+
+Some changes, though, are "substantial", and these are the ones we want to put through a bit
+of a design process to make sure we're all on the same page before we invest the time
+into the actual implementation of a new feature or a deep refactoring.
+
+We've introduced the "Proposals design process" to provide a
+consistent and controlled path for such changes to Haystack.
+
+We will apply the same level of rigor to both core developers and
+Community proposals. The primary difference between them is in the design phase:
+core developers proposals tend to be submitted at the end of the design process
+whereas the Community ones tend to be submitted at the beginning, as a way
+to kickstart it.
+
+## When do I follow the process?
+
+Follow the process if you intend to make "substantial" changes to
+Haystack, `rest_api` or `ui`, or the process itself. What we define as a
+"substantial" change is evolving based on community norms and
+on what part of the project you are proposing to change, but it may include the following:
+
+- A new feature that creates new API surface areas.
+- A new component (Nodes, Pipelines, Document Stores).
+- Removing features that already shipped in the current minor version.
+- A deep refactoring that would require new tests or introduce new dependencies.
+- A change that's complex enough to require multiple steps to be delivered.
+
+Some changes don't require a proposal, for example:
+
+- Minor bug fixes.
+- Rephrasing, reorganizing, or otherwise "changing shape does not change meaning".
+- Addition and removal of warnings or other error messages.
+- Additions only likely to be noticed by other contributors, invisible to Haystack users.
+
+In any case, the core developers might politely ask you to submit a proposal before merging
+a new feature when they see fit.
+
+## Before creating a proposal
+
+Laying some groundwork ahead of the proposal can make the process smoother.
+
+Although there is no single way to prepare for submitting a proposal, it is generally a good idea
+to collect feedback from other project developers first, to make sure that the change is
+is actually needed. As we're an open source community where everyone can impact the project, we all
+need to make an effort to build consensus.
+
+When you're preparing for writing and submitting a proposal, talk the idea over on our official
+[Discord server](https://haystack.deepset.ai/community/join) and in a Github
+issue or discussion in the [Haystack repository](https://github.com/deepset-ai/haystack).
+
+## The process
+
+In short, to get a major feature added to Haystack, you usually first merge the proposal into
+the Haystack repo as a Markdown file. At that point, the proposal is 'active' and may be
+implemented with the goal of eventually including it into the Haystack codebase.
+
+To create a proposal:
+
+1. Copy `0000-template.md` to `text/0000-my-feature.md`, where 'my-feature' is a descriptive name of the feature you're proposing. Don't assign an identification number yet.
+2. Fill in the proposal. Pay attention to details. Proposals that present convincing motivation, demonstrate an understanding of the feature impact, and honestly present the drawbacks and alternatives tend to be received well.
+3. Submit a pull request. This ensures the document receives design feedback from a larger community. As the author, you should be prepared to revise it in response.
+4. Rename the file using the PR number, for example from `text/0000-my-feature.md` to `text/4242-my-feature.md`.
+5. Reach an agreement with the reviewers and integrate the feedback you got. Proposals that have broad support are much more likely to make progress than those that don't receive any comments.
+6. Now it's time for the core developers to take over and decide whether the proposal is a candidate for inclusion in Haystack. Note that a team review may take a long time, and we suggest that you ask members of the community to review it first.
+7. Proposals that are candidates for inclusion in Haystack enter a "final comment period" lasting 3 calendar days. To let you know that your proposal is entering the final comment period, we add a comment and a label to your PR.
+8. A proposal can be modified based on feedback from the core developers and community. Big changes may trigger a new final comment period.
+9. Core developers may reject a proposal once the public discussion and adding comments are over, adding the reason for rejection. A core developer then closes the related PR.
+10. Core developers may accept a proposal at the close of its final comment period. A core developer then merges the related PR. At this point, the proposal becomes 'active'.
+
+## The proposal lifecycle
+
+Once a proposal becomes active, the authors are free to implement it and submit the feature as one or more pull
+requests to the Haystack repo. Becoming 'active' is not a rubber stamp, and in particular still doesn't
+mean the feature will ultimately be merged; it does mean that the core team has agreed to it in
+principle and is open to merging it if the implementation reflects the contents of the proposal.
+
+The fact that a given proposal has been accepted and is 'active' doesn't imply it has a priority assigned or somebody's
+currently working on it.
+
+To change an active proposal, open follow-up PRs. Our goal is to write each proposal so that
+it reflects the final design of the feature, but the nature of the process means that we cannot
+expect every merged proposal to actually reflect what the end result will be at the time of the next release.
+That's why we try to keep each proposal document somewhat in sync with the feature as planned, tracking such
+changes through follow-up pull requests to the document.
+
+As the author of a proposal, you're not obligated to implement it. Of course, the author (like any other developer)
+is welcome to post an implementation for review after the proposal has been accepted.
+
+## Inspiration
+
+Haystack's proposals design process process owes its inspiration to the [React](https://github.com/reactjs/rfcs) and
+[Rust](https://github.com/rust-lang/rfcs) RFC processes. We're open to changing it if needed.

docs/decisions/pydantic-dataclasses.md → proposals/text/2170-pydantic-dataclasses.md

@@ -1,16 +1,18 @@
-# Dataclasses
+<!--
+NOTE: this document was imported from a different process and is not compliant with the proposal template. Do not
+use it as a reference for new proposals.
+-->
+- Start Date: 2021-10-14
+- Proposal PR: n/a
+- Github Issue: https://github.com/deepset-ai/haystack/pull/1598
+- Deciders: @tholor
 
-* Status: accepted
-* Deciders: @tholor
-* Date: 2021-10-14
-
-Technical Story: https://github.com/deepset-ai/haystack/pull/1598
 
 ## Context and Problem Statement
 
 Originally we implemented Haystack's primitive based on Python's vanilla `dataclasses`. However, shortly after we realized this causes issues with FastAPI, which uses Pydantic's implementation. We need to decide which version (vanilla Python's or Pydantic's) to use in our codebase.
 
-## Decision Drivers 
+## Decision Drivers
 
 * The Swagger autogenerated documentation for REST API in FastAPI was broken where the dataclasses include non-standard fields (`pd.dataframe` + `np.ndarray`)
 
@@ -72,7 +74,7 @@ else:
 * https://github.com/deepset-ai/haystack/pull/1598
 * https://github.com/deepset-ai/haystack/issues/1593
 * https://github.com/deepset-ai/haystack/issues/1582
-* https://github.com/deepset-ai/haystack/pull/1398 
+* https://github.com/deepset-ai/haystack/pull/1398
 * https://github.com/deepset-ai/haystack/issues/1232
 
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