Rust Errors on ErrorVault — Developer Error Code Dictionary

Fix E0524: Rust Compiler Error - Variable Previously Captured

Wed, 29 Apr 2026 03:08:04 +0800

1. Symptoms

The Rust compiler emits error E0524 when attempting to use a variable that has already been captured by a closure. This error manifests in several distinct patterns that Rust developers commonly encounter.

Primary Error Message:

error[E0524]: `x` was previously captured by this closure
 --> src/main.rs:6:5
 |
3 | let c2 = || {
 | -- first capture is here
4 | println!("{:?}", x);
 | - ^ first borrow is here
5 | };
6 | drop(x);
 | ^ second move into this closure
 |
 = note: closure cannot be invoked once a variable from the outer scope has been moved out of
 = note: this error originates in the macro `$crate:: println :: macro :: _____ $`
---

**Additional Error Manifestations:**

```rust
// Example 1: Double move error
let x = vec![1, 2, 3];
let closure1 = || {
 let _y = x; // x is moved here
};
let closure2 = || {
 let _z = x; // E0524: x was already moved
};

// Example 2: Move after borrow
let mut data = String::from("hello");
let print_fn = || println!("{}", data); // borrowed here
let modify_fn = || {
 data.push_str(" world"); // E0524: cannot move after borrow
};

// Example 3: Complex closure scenario
fn main() {
 let value = 42;
 let closure_a = || {
 let _captured = value;
 println!("closure_a took ownership");
 };
 let closure_b = || {
 println!("value is still needed here: {}", value); // E0524
 };
 closure_a();
 closure_b();
}

The compiler error always indicates which closure performed the first capture and which line attempted the second capture, making it relatively straightforward to identify the conflict point.

Fix E0067: illegal erase coercion

Sun, 26 Apr 2026 05:32:04 +0800

Fix E0067: illegal erase coercion

Error E0067 is a Rust compiler error that signals an attempt to perform an illegal “erase” coercion. In Rust’s type system, certain type conversions are allowed implicitly (coercions), but others are not. This error occurs when you try to erase a lifetime or otherwise remove type information in a way that Rust’s coercion system does not permit.

1. Symptoms

When `E0067` occurs, you will see output similar to this:

error[E0067]: illegal erase coercion –> src/main.rs:10:12 | 10 | let g: fn() = f; | ^^^^ | = note: this error was previously described as “illegal erase coercion”

Fix E0519: Private Type in Function Return Type

Sun, 26 Apr 2026 03:08:04 +0800

1. Symptoms

Error E0519 is a Rust compiler error that appears when you define a public function but the function’s return type references a type that is not accessible outside its defining module. The compiler prevents this because it would create an unusable API—callers would have no way to use the return value if they cannot see its type.

The error message in Rust looks like this:

error[E0519]: private type `InnerStruct` in return type of this function
 --> src/lib.rs:9:5
 |
9 | pub fn get_inner() -> InnerStruct {
 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ private type in return type
 |
note: `InnerStruct` is private to this module
 --> src/lib.rs:1:1
 |
1 | struct InnerStruct {
 | ^^^^^^^^^^^^^^^^^^ private struct

The compiler explicitly tells you which type is private and where it is defined. In this example, InnerStruct is marked struct (implicitly private) at line 1, but get_inner() is marked pub fn at line 9. This combination is invalid because external code cannot construct or interact with the return value.

Fix E0772: Function pointer called with wrong number of arguments

Sat, 25 Apr 2026 17:32:04 +0800

1. Symptoms

The Rust compiler emits error E0772 when attempting to invoke a function pointer with a mismatched argument count. This error occurs during the type-checking phase of compilation.


The compiler clearly indicates the discrepancy between the expected argument count and the actual number provided. In this case, the function pointer expects 2 arguments, but 3 were supplied.

**Additional symptom patterns:**

```rust
// Example 1: Too few arguments
error[E0772]: this function takes 3 argument(s) but 1 argument(s) were supplied
 --> src/main.rs:10:20
 |
10 | let result = func_ptr(arg1);
 | ^^^^^^^^^ -- expected 2 more argument(s)

// Example 2: Calling with zero arguments when one is expected
error[E0772]: this function takes 1 argument(s) but 0 argument(s) were supplied
 --> src/main.rs:15:5
 |
15 | func_ptr();
 | ^^^^^^^^

// Example 3: With closures and function pointers
error[E0772]: this function takes 2 argument(s) but 3 argument(s) were supplied
 --> src/main.rs:20:14
 |
20 | (func_ptr)(1, 2, 3);
 | ^^^^^^^^ ---------

The error message always follows the pattern: this function takes N argument(s) but M argument(s) were supplied, where N is the expected count and M is the actual count.

Fix E0137: More Than One Trait Bound for Type

Fri, 24 Apr 2026 00:44:04 +0800

1. Symptoms

When you attempt to compile Rust code that specifies multiple trait bounds incorrectly for a single type parameter, the compiler halts with error E0137. This error manifests with a clear diagnostic message that identifies the problematic type and indicates that only one trait bound is allowed.

error[E0137]: more than one trait bound for `TypeName`
 --> src/main.rs:5:20
 |
5 | fn process<T: Clone + Display>(value: T) {}
 | ^^^^^^^ help: consider joining the trait bounds with a `+`: `Clone + Display`
 |
 = note: this error is being displayed to you because of user-facing `.into_iter()` calls
 = note: rustc 1.75.0 (firm version 3)

The compiler output explicitly points to the offending type parameter and shows the duplicate trait bounds. In most cases, the compiler helpfully suggests using the + operator to combine multiple trait bounds properly.

Fix E0730: Type Parameter Defaults Only Allowed in Function Items

Tue, 21 Apr 2026 17:32:04 +0800

1. Symptoms

When compiling Rust code with default type parameters in invalid contexts, you will encounter the E0730 error. The compiler produces a clear message indicating the restriction.

error[E0730]: default type parameters are only allowed in function items
 --> src/main.rs:5:1
 |
5 | impl<T = i32> Trait for Foo<T> {}
 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to 1 previous error

The error specifically states that default type parameters are only allowed in function items. This means you cannot use the = DefaultValue syntax for type parameters in impl blocks, type aliases, or other non-function contexts.

Rust Errors on ErrorVault — Developer Error Code Dictionary

Fix E0524: Rust Compiler Error - Variable Previously Captured

1. Symptoms

Fix E0067: illegal erase coercion

Fix E0067: illegal erase coercion

1. Symptoms

When E0067 occurs, you will see output similar to this:

Fix E0519: Private Type in Function Return Type

1. Symptoms

Fix E0772: Function pointer called with wrong number of arguments

1. Symptoms

The Rust compiler emits error E0772 when attempting to invoke a function pointer with a mismatched argument count. This error occurs during the type-checking phase of compilation.

Fix E0137: More Than One Trait Bound for Type

1. Symptoms

Fix E0730: Type Parameter Defaults Only Allowed in Function Items

1. Symptoms

When `E0067` occurs, you will see output similar to this: