Go "go:embed cannot apply to var of type" - Fix Embed Targets in CI

By Kaveh Alemi·Latchkey

//go:embed may only target a string, a []byte, or an embed.FS. Pointing it at any other type - or embedding multiple files into a scalar string/[]byte - is a compile error, because the directive and the variable type must agree.

What this error means

A build fails with go:embed cannot apply to var of type <T> or invalid go:embed: multiple files for type string. The pattern matches files, but the variable it binds to is the wrong type for what was embedded.

go build output

./assets.go:9:5: go:embed cannot apply to var of type int
# or, many files into a scalar:
./assets.go:9:5: invalid go:embed: multiple files matched but type is string

Common causes

The target var is not an embeddable type

//go:embed requires string, []byte, or embed.FS. Any other type (an int, a struct, a map) is rejected.

Multiple files embedded into a scalar

A string or []byte can hold exactly one file. A pattern that matches several files (or a directory) must target an embed.FS.

How to fix it

Use embed.FS for multiple files

Bind a directory or multi-file pattern to an embed.FS.

import "embed"

//go:embed templates/*.html
var templates embed.FS

Use string or []byte for a single file

//go:embed version.txt
var version string

How to prevent it

Match the embed target type to what you embed: scalar for one file, embed.FS for many.
Import embed whenever you use embed.FS.
Use embed.FS for any directory or glob that can match multiple files.

Frequently asked questions

What causes ""cannot apply to var of type""?

//go:embed requires string, []byte, or embed.FS. Any other type (an int, a struct, a map) is rejected.

How do I fix "cannot apply to var of type"?

Bind a directory or multi-file pattern to an embed.FS.