Let chain error message with `||` is confusing and verbose

[ehuss]

Code

fn main() {
    if let true = true || false {}
}

Current output

error: expected expression, found `let` statement
 --> src/main.rs:6:8
  |
6 |     if let true = true || false {}
  |        ^^^^^^^^^^^^^^^
  |
  = note: only supported directly in conditions of `if` and `while` expressions
note: `||` operators are not supported in let chain expressions
 --> src/main.rs:6:24
  |
6 |     if let true = true || false {}
  |                        ^^

Desired output

error: `||` in an `if` expression with `let` is not allowed
 --> src/main.rs:2:17
  |
2 |     if let true = true || false {}
  |                        ^^
  |

Rationale and extra context

The current error message has several confusing factors:

• The primary error message expected expression, found `let` statement which is confusing. I suppose this is technically correct (let is not allowed in an if with a ||), but muddles the problem. There's also the confusion of using the term `let` statement`, where the term "statement" is confusing here.
• The note only supported directly in conditions of `if` and `while` expressions is confusing, since we are in an if expression.
• The final note of note: `||` operators are not supported in let chain expressions shows the actual problem, but it is lost in a sea of other text.

Other cases

Rust Version

rustc 1.88.0-nightly (df35ff6c3 2025-04-23)
binary: rustc
commit-hash: df35ff6c354f1f1fbf430b84e7dea37dfe997f34
commit-date: 2025-04-23
host: aarch64-apple-darwin
release: 1.88.0-nightly
LLVM version: 20.1.2

Anything else?

No response

[traviscross]

cc @est31 @fee1-dead

[Kivooeo]

@rustbot claim

[est31]

Agree that it could be improved. As you say, it's technically correct (explained how || in && chains plays together with precedence in more detail here), but the error is too close to the "language level" instead of the level the user is at.

There's also the confusion of using the term let statement`, where the term "statement" is confusing here.

Fine with dropping "statement" but the error message should not call it an expression in any case because the let chains RFC didn't make let into an expression in the general sense.

It's definitely implemented that way in the compiler AST, but compiler behaviour should follow the language level, including error message, even if colloquial understanding sees let inside while or if as an "expression".

[est31]

|| in an if expression with let is not allowed

I'd change it to:

|| in an if condition with let is not allowed

otherwise the suggestion is fine.