[DEV-1658] Support projection v2 engine

[w1am]

Adds support for selecting the V2 projection engine when creating a projection via a new engine version option. V1 remains the default.

Closes DEV-1658.

[linear]

DEV-1658 Rust | Support projection v2 engine

[qodo-code-review]

Review Summary by Qodo

Add projection engine version selection support

✨ Enhancement

Walkthroughs

Description

• Adds ProjectionEngineVersion enum supporting V1 and V2 engines
• Introduces engine_version field to projection creation options
• Implements builder method for setting engine version preference
• Updates protobuf schema to include engine version parameter

Diagram

flowchart LR
  A["ProjectionEngineVersion enum<br/>V1 default, V2 option"] --> B["CreateProjectionOptions<br/>engine_version field"]
  B --> C["ProjectionClient<br/>passes to protobuf"]
  C --> D["projections.proto<br/>engine_version parameter"]

Loading

File Changes

1. kurrentdb/src/options/projections.rs ✨ Enhancement +27/-0

Add projection engine version enum and options

• Adds ProjectionEngineVersion enum with V1 (default) and V2 variants
• Implements as_i32() conversion method for protobuf serialization
• Adds engine_version field to CreateProjectionOptions struct
• Implements builder method engine_version() for fluent configuration

kurrentdb/src/options/projections.rs

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2. kurrentdb/src/event_store/generated/projections.rs Dependencies +2/-0

Add engine version field to protobuf message

• Adds engine_version: i32 field to protobuf Options message
• Field uses tag 5 in protobuf schema

kurrentdb/src/event_store/generated/projections.rs

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3. kurrentdb/src/projection_client.rs ✨ Enhancement +1/-0

Pass engine version to projection creation request

• Passes engine_version from options to protobuf request
• Converts enum value using as_i32() method

kurrentdb/src/projection_client.rs

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View more (1)

4. kurrentdb/protos/projections.proto ⚙️ Configuration changes +1/-0

Add engine version field to protobuf schema

• Adds int32 engine_version = 5 field to Options message
• Positioned after query field in schema

kurrentdb/protos/projections.proto

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[qodo-code-review]

Code Review by Qodo

🐞 Bugs (1) 📘 Rule violations (0)

1. V1 sent as non-zero 🐞 Bug ≡ Correctness

Description

ProjectionClient::create always sets engine_version from options, and the default V1 maps to 1, so
requests will always carry a non-zero engine_version even when the user didn’t opt into V2. This
removes the ability to send the protobuf-default value (0 / omitted-on-wire) for the default path,
which can break or change behavior on servers that treat 0/unspecified specially.

Code

kurrentdb/src/projection_client.rs[R75-80]

            projections::create_req::Options {
                query: query.clone(),
+                engine_version: options.engine_version.as_i32(),
                mode: Some(projections::create_req::options::Mode::Continuous(
                    projections::create_req::options::Continuous {
                        name: name.as_ref().to_string(),

Evidence

The protobuf schema introduces engine_version as a plain int32 (defaulting to 0 in proto3), but the
Rust API’s default (V1) is converted to 1 and is always assigned into the request, meaning the field
is never left at its default value for the default engine selection path.

kurrentdb/protos/projections.proto[28-32]
kurrentdb/src/options/projections.rs[6-19]
kurrentdb/src/projection_client.rs[74-84]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

### Issue description
`ProjectionClient::create` unconditionally sets `engine_version`, and the default `ProjectionEngineVersion::V1` is mapped to `1`. In proto3, an `int32` defaults to `0` (and is typically omitted on the wire when 0), so the client can no longer send the default/unspecified value for the default engine.

### Issue Context
This change alters on-wire behavior for the default code path (previously “no engine version field existed / was absent”, now “engine_version is explicitly set to 1”). If servers differentiate between 0/unspecified and explicit values, this can change behavior.

### Fix Focus Areas
- kurrentdb/src/options/projections.rs[13-19]
- kurrentdb/src/projection_client.rs[74-84]
- kurrentdb/protos/projections.proto[21-40]

### Suggested direction
- Map `V1` to `0` (so it stays protobuf-default) and `V2` to `1` (or whatever the server expects), OR
- Make `engine_version` `optional int32` (or better, a proto `enum`) and only populate it when the user selects `V2`.

ⓘ Copy this prompt and use it to remediate the issue with your preferred AI generation tools

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[github-actions]

@w1am 👉 Created pull request targeting release/v1.2: #230