Atlas now manages ClickHouse WASM modules and WASM User Defined Functions (UDFs) as first-class resources. Define a wasm_module once in HCL, reference it from one or more function blocks with lang = WASM, and Atlas plans and applies the required SQL.

ClickHouse WASM modules ship a compiled WASM binary into the server, and WASM UDFs expose one of a module's exported functions as a callable SQL function. Atlas models these as two connected resources: a wasm_module that holds the binary and its hash, and a function with lang = WASM that points at a module and names the export to call.

Enabling WASM Support

WASM support is opt-in. Set wasm_modules = true on the ClickHouse schema mode in your env:

atlas.hcl

env "local" {
  url = "clickhouse://your_username:your_password@localhost:9000"
  dev = "clickhouse://your_username:your_password@localhost:9004"

  migration {
    dir = "file://migrations"
  }

  schema {
    src = "file://schema/main.hcl"

    mode "clickhouse" {
      wasm_modules = true
    }
  }
}

WASM Modules

The new wasm_module resource manages ClickHouse WASM modules. ClickHouse stores modules as binary WASM, so the binary is supplied as base64 or hexadecimal through expressions such as base64Decode(...) or unhex(...).

code: Expression returning the raw WASM binary from base64 or hexadecimal input. Write-only; never emitted during inspection.
hash: Expression evaluating to the expected UInt256 SHA-256 hash of the module binary.

schema/main.hcl

wasm_module "math_module" {
  code = sql("unhex('0061736d0100000001070160027f7f017f030201000707010373756200000a09010700200020016b0b')")
  hash = sql("reinterpretAsUInt256(unhex('a957fcb890da31e0e4a72bbdb0e04c50ba7ff5cb6946b21d674f9dcb6e7cd488'))")
}

Atlas generates:

atlas migrate diff

-- Create wasm module "math_module"
INSERT INTO system.webassembly_modules (name, code, hash) SELECT 'math_module', unhex('0061736d0100000001070160027f7f017f030201000707010373756200000a09010700200020016b0b'), reinterpretAsUInt256(unhex('a957fcb890da31e0e4a72bbdb0e04c50ba7ff5cb6946b21d674f9dcb6e7cd488'));

WASM User Defined Functions

Functions can now be declared in yoru schema with lang = WASM and reference a previously declared wasm_module.