Unsafe on ErrorVault — Developer Error Code Dictionary

Fix E0378: GlobalAlloc Implementation Error in Rust

Thu, 30 Jul 2026 22:20:04 +0800

Fix E0378: GlobalAlloc Implementation Error in Rust

1. Symptoms

When you encounter error E0378 in Rust, the compiler produces error messages that vary slightly depending on the specific issue with your GlobalAlloc implementation. The most common manifestations appear in your terminal as follows:

error[E0378]: implementation of `GlobalAlloc` trait is not general enough
  --> src/main.rs:17:1
   |
17 | impl GlobalAlloc for MyAllocator {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: implementation requires `_: FnOnce() -> *mut (dyn Core + 'static)`
   = note:    and `_: FnOnce(NonNull<u8>, Layout) -> ()` is not a subtype of `_: FnOnce() -> *mut (dyn Core + 'static)`

Another common variant appears when method signatures don’t match the trait definition:

Fix E0739: #[target_feature] Attribute Not Allowed on Safe Functions

Thu, 23 Jul 2026 07:56:04 +0800

1. Symptoms

When attempting to compile Rust code that uses the #[target_feature] attribute on a safe function, the compiler produces error E0739 with a clear diagnostic message. The error indicates that the attribute cannot be applied to non-unsafe functions because using CPU-specific features requires unsafe guarantees.

The typical compiler output looks like this:

error[E0739]: the `#[target_feature(...)]` attribute is not yet allowed on safe functions
  --> src/main.rs:10:1
   |
10 | #[target_feature(sse, sse2)]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^ attribute was applied to safe function
   |
   = note: require the function to be marked `unsafe` because using the target_feature attribute is unsafe

In this example, the compiler is telling you that the function at line 10 in src/main.rs uses the #[target_feature] attribute but is not marked as unsafe. The error also appears when using multiple features like #[target_feature(avx, avx2)] or #[target_feature(simd128)] on WebAssembly targets.

Fix E0794: Invalid discriminant value for enum in Rust

Tue, 21 Jul 2026 22:20:04 +0800

1. Symptoms

When the Rust compiler encounters error E0794, you will see output similar to the following in your terminal:

error[E0794]: invalid discriminant value for enum `EnumName`, valid values are 0..2
  --> src/main.rs:10:17
   |
10 |     let _ = unsafe { transmute::<u8, EnumName>(3u8) };
   |                      ^^^^^^^^^^^^^^^^^^^^^^^^ invalid discriminant value
   |
   = note: values are validated based on the enum discriminant type and defined variants

The error message specifies which discriminant values are considered valid for your enum, helping you understand the range of acceptable values. The compiler indicates the exact location in your source code where the invalid discriminant is being used, and it clarifies the bounds of valid discriminants based on the number of variants defined in your enum.

Fix E0310: The Lifetime of the Destination Pointer Must Be Specified

Fri, 17 Jul 2026 19:56:04 +0800

Fix E0310: The Lifetime of the Destination Pointer Must Be Specified

Rust’s ownership and borrowing system is one of its defining features, providing memory safety guarantees at compile time without requiring garbage collection. However, when working with raw pointers in unsafe code, the compiler sometimes cannot infer the necessary lifetime relationships on its own. Error E0310 surfaces in exactly this scenario—when you invoke pointer-manipulation functions like std::ptr::read or std::ptr::write and the compiler cannot determine the validity window of the resulting reference.

Fix E0795: Mismatched Function Pointer Alignment in Rust

Fri, 17 Jul 2026 12:44:04 +0800

1. Symptoms

When the Rust compiler encounters error E0795, you will see output similar to the following:

error[E0795]: function pointer types that differ only in their alignment
  --> src/main.rs:10:5
   |
10 |     let fp: fn() = extern_func;
   |              ^^^^^^^^^^^^^^^^ expected function pointer with alignment 1, found one with alignment 8
   |
   = note: `extern_func` points to a function with stricter alignment requirements than what the target type accepts
   = note: this commonly occurs when passing function pointers across FFI boundaries with mismatched ABIs

In more severe cases involving extern blocks, the error may manifest as:

Fix E0640: Self-referential struct definition

Wed, 15 Jul 2026 05:32:04 +0800

1. Symptoms

When you attempt to compile a Rust program containing a struct definition where one field directly references the struct type itself (outside of pointer wrappers), the compiler emits error E0640. The error message clearly indicates that the struct definition contains an unsupported self-referential pattern.

Shell output demonstrating the error looks like the following:

error[E0640]: self-referential struct
  --> src/main.rs:5:5
   |
5  |     name: String,
6  |     // ERROR: next points back to the containing struct
7  |     next: Option<Node>,
   |           ^^^^^^^^^^^^^^ self-referential struct
   |
   = note: this error indicates that the struct is self-referential
   = help: consider using `Box<Self>`, `Arc<Self>`, `Rc<Self>`, or a reference type
   = help: for more information, see https://doc.rust-lang.org/reference/structures.html

A slightly different manifestation occurs when attempting to embed the struct directly within itself as a field rather than behind a smart pointer wrapper:

Fix E0376: Cannot Use Unsafe Trait as Trait Object

Mon, 08 Jun 2026 10:20:04 +0800

Fix E0376: Cannot Use Unsafe Trait as Trait Object

The Rust compiler error E0376 occurs when attempting to create a trait object (dyn Trait) from the Unsafe trait. The Unsafe trait is fundamentally incompatible with dynamic dispatch because it represents a marker trait with special semantic meaning that cannot be safely abstracted at runtime.

1. Symptoms

When you attempt to use the Unsafe trait with dynamic dispatch syntax, the compiler produces a clear error message: