Foreign Function Interface on ErrorVault — Developer Error Code Dictionary

Fix E0805: Extern Types Cannot Have Lifetimes

Wed, 12 Aug 2026 19:56:04 +0800

1. Symptoms

When attempting to declare an extern type with a lifetime annotation, the Rust compiler immediately halts compilation and produces error E0805. The error message clearly indicates that lifetime parameters are prohibited on extern type declarations.

The compiler output typically appears as follows:

error[E0805]: extern types cannot have lifetimes
 --> src/main.rs:3:17
  |
3 | extern "C" { type Foo<'a>; }
  |                      ^^-- lifetime used in type

In more complex scenarios involving multiple lifetime parameters or where the extern type is nested within generic structures, the error message may expand to show the full context of where the invalid lifetime annotation appears:

Fix E0667: Async Not Allowed in Extern Declarations

Mon, 10 Aug 2026 22:20:04 +0800

1. Symptoms

The Rust compiler emits error E0667 when attempting to declare an async function within an extern block or alongside the #[no_mangle] attribute for foreign function interface definitions. This error manifests during compilation and prevents the binary from being built.

When triggered, the compiler produces output similar to the following:

error[E0667]: `async` is not allowed in extern declarations
 --> src/main.rs:3:1
  |
3 | extern "C" {
  | ^^^^^^^^^^^^^^ invalid decoration
4 |     pub async fn foreign_async_function();
  |              ^^^^^ invalid here

The error message specifically highlights the async keyword as invalid, pointing to its location within the extern block. In some variations of the error, the compiler may also indicate that this restriction applies to both extern blocks and FFI function declarations with #[no_mangle].

Fix E0583: Linkage Name Is Not Unique

Mon, 03 Aug 2026 12:44:04 +0800

1. Symptoms

When the Rust compiler encounters error E0583, you will see a diagnostic message similar to the following in your build output:

error[E0583]: linkage name is not unique
  --> src/main.rs:10:1
   |
10 | extern "C" {
11 |     #[link_name = "my_function"]
12 |     fn my_function();
13 |     #[link_name = "my_function"]
14 |     fn my_function();
15 | }
   |
   = linkage name `my_function` used in multiple `extern` blocks for the same ABI

The compiler identifies that the same linkage name appears multiple times within an extern block, which violates the uniqueness requirement for foreign function symbols. The error points to the specific lines where the duplicate declarations occur and includes a note explaining that the linkage name must be unique for each ABI.