Windmill Rust Patterns

Apply these Windmill-specific patterns when writing Rust code in backend/ .

Error Handling

Use Error from windmill_common::error . Return Result<T, Error> or JsonResult<T> :

use windmill_common::error::{Error, Result};

pub async fn get_job(db: &DB, id: Uuid) -> Result<Job> { sqlx::query_as!(Job, "SELECT id, workspace_id FROM v2_job WHERE id = $1", id) .fetch_optional(db) .await? .ok_or_else(|| Error::NotFound("job not found".to_string()))?; }

Never panic in library code. Reserve .unwrap() for compile-time guarantees.

SQLx Patterns

Never use SELECT * — always list columns explicitly. Critical for backwards compatibility when workers lag behind API version:

// Correct sqlx::query_as!(Job, "SELECT id, workspace_id, path FROM v2_job WHERE id = $1", id)

// Wrong — breaks when columns are added sqlx::query_as!(Job, "SELECT * FROM v2_job WHERE id = $1", id)

Use batch operations to avoid N+1:

// Preferred — single query with IN clause sqlx::query!("SELECT ... WHERE id = ANY($1)", &ids[..]).fetch_all(db).await?

Use transactions for multi-step operations. Parameterize all queries.

JSON Handling

Prefer Box<serde_json::value::RawValue> over serde_json::Value when storing/passing JSON without inspection:

pub struct Job { pub args: Option<Box<serde_json::value::RawValue>>, }

Only use serde_json::Value when you need to inspect or modify the JSON.

Serde Optimizations

#[derive(Serialize, Deserialize)] pub struct Job { #[serde(skip_serializing_if = "Option::is_none")] pub parent_job: Option<Uuid>, #[serde(skip_serializing_if = "Vec::is_empty")] pub tags: Vec<String>, #[serde(default)] pub priority: i32, }

Async & Concurrency

Never block the async runtime. Use spawn_blocking for CPU-intensive work:

let result = tokio::task::spawn_blocking(move || expensive_computation(&data)).await?;

Mutex selection: Prefer std::sync::Mutex (or parking_lot::Mutex ) for data protection. Only use tokio::sync::Mutex when holding locks across .await points.

Use tokio::sync::mpsc (bounded) for channels. Avoid std::thread::sleep in async contexts.

Module Structure & Visibility

• Use pub(crate) instead of pub when possible

• Place new code in the appropriate crate based on functionality

• API endpoints go in windmill-api/src/ organized by domain

• Shared functionality goes in windmill-common/src/

Code Navigation

Always use rust-analyzer LSP for go-to-definition, find-references, and type info. Do not guess at module paths.

Axum Handlers

Destructure extractors directly in function signatures:

async fn process_job( Extension(db): Extension<DB>, Path((workspace, job_id)): Path<(String, Uuid)>, Query(pagination): Query<Pagination>, ) -> Result<Json<Job>> { ... }