Wasm rust_library produces bad magic number

[KaiserKarel]

Attempting to use rust_wasm_bindgen to cause a transition results in a wasm file with a bad magic number:

error: failed to parse input file as wasm
    caused by: Bad magic number (at offset 0)

My BUILD:

load("@io_bazel_rules_rust//rust:rust.bzl", "rust_binary")
load("@io_bazel_rules_rust//rust:rust.bzl", "rust_library")
load("@io_bazel_rules_rust//wasm_bindgen:wasm_bindgen.bzl", "rust_wasm_bindgen")

rust_binary(
    name = "example",
    edition = "2018",
    srcs = [
        "src/main.rs",
    ],
    deps = [
        "//cargo:wasmer_runtime",
    ],
    data = [":wasm_bindgen_bg.wasm"]
)


rust_wasm_bindgen(
    name = "wasm_bindgen",
    wasm_file = ":wasm"
)

rust_library(
    name = "wasm",
    srcs = [
        "wasm/src/lib.rs",
    ],
    edition = "2018",
)

I invoke bazel using bazel build //app:example