Rust support in Shopify Functions

You can write your functions in Rust. This guide describes the shopify_function Rust crate that Shopify provides to help developers build with Shopify Functions.

Requirements

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You need to have graphql_client installed as a dependency in your project:

How it works

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The shopify_function Rust crate bundles graphql_client-based type generation, reduces boilerplate code, and makes it easier to test various function inputs. It includes the following components:

Component	Description
`shopify_function_target`	An attribute macro that transforms the following function to: Generate structs and output types for the Function API target from the specified input query and GraphQL schema. Export a WebAssembly function with the specified name, which must match the target export in the function extension configuration. Automatically handle input parsing from `STDIN` and output serialization to `STDOUT`.
`run_function_with_input`	A utility for unit testing that enables you to add new tests based on a given JSON input string.

Viewing the generated types

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To preview the types generated by the shopify_function Rust crate, use the cargo doc command.

You can also use the cargo-expand crate to view the generated source, or use the rust-analyzer VSCode extension to get IntelliSense for Rust and the generated types.

Example implementations

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Explore example implementations using the shopify_function Rust crate.

For API versions 2023-07 and earlier, the generate_types and shopify_function macros can be used directly to conform to previous WebAssembly requirements.

Rust Shopify Function example

Explore an example of how to use the shopify_function crate to implement a Shopify Function in Rust.

Rust Shopify Function example for earlier versions

Explore an example of how to use the shopify_function crate to implement a Shopify Function in Rust compatible with API versions 2023-07 and earlier.

Binary size tips

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Shopify Functions compiled Wasm file must be under 256 kB. Here are a few tips to keep binary size small when using Rust:

Update the shopify_function crate to the latest version.
For regular expressions, use the regex_lite crate.
Follow tips & documentation on the johnthagen/min-sized-rust GitHub repository.

The Functions templates already use many of those tips. Using Rust nightly can help further reduce size with:
Use wasm-snip to remove the panicking code, then wasm-opt to strip debug information. For example:
Bring your own types and deserializers.

Instead of using the generated structs from the shopify_function_macro crate, write the appropropriate struct definitions and derive the deserializsers using mini_serde.

The structs from shopify_function_macro can be used as a starting point, see them with cargo expand.

Alternative serializers are generally less efficient than serde, make sure to benchmark the instruction count when going down this path.

Next steps

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Explore the reference documentation for the shopify_function Rust crate.