Compiler misinterprets cast and comparison as generic syntax

[reddevilmidzy]

I tried this code:

fn main() {
    let i = 1;
    if i as usize < 1 {}
}

I expected to compile successfully, just like the following code:

// this code compile successfully
fn main() {
    let i = 1;
    if i as usize > 1 {} // Change `<` to `>`
}

Instead, this happened: compile fail

error: `<` is interpreted as a start of generic arguments for `usize`, not a comparison
 --> src\main.rs:3:19
  |
3 |     if i as usize < 1 {}
  |                   ^ --- interpreted as generic arguments
  |                   |
  |                   not interpreted as comparison
  |
help: try comparing the cast value
  |
3 |     if (i as usize) < 1 {}
  |        +          +

I suspect that the compiler is interpreting the code as if I had written something like usize::<1>.

Meta

rustc --version --verbose:

<version>
rustc 1.88.0-nightly (0fe8f3454 2025-04-10)
binary: rustc
commit-hash: 0fe8f3454dbe9dda52a254991347e96bec579a6f
commit-date: 2025-04-10
host: x86_64-pc-windows-msvc
release: 1.88.0-nightly
LLVM version: 20.1.2

[y21]

I don't think that's a bug in the compiler. The syntax for as casts is <Expression> as <Type>. Turbofish (::<) is only required for expression paths, not type paths, so as usize< in this context indeed means that it's the start of a generic arguments list rather than the less than operator as the error message points out, and the fix to wrap the left hand side in parentheses seems correct