Wrong error for string literal suffix when stuck together

[GuillaumeGomez]

Code

let s = r#" \ "#r"\ ";

Current output

error: unknown character escape: ` `
 --> src/main.rs:2:20
  |
2 | let s = r#" \ "#r"\ ";
  |                    ^ unknown character escape
  |
  = help: for more information, visit <https://doc.rust-lang.org/reference/tokens.html#literals>
help: if you meant to write a literal backslash (perhaps escaping in a regular expression), consider a raw string literal
  |
2 | let s = r#" \ "#rr"\ ";
  |                  +

error: expected one of `.`, `;`, `?`, `else`, or an operator, found `"\ "`
 --> src/main.rs:2:18
  |
2 | let s = r#" \ "#r"\ ";
  |                  ^^^^ expected one of `.`, `;`, `?`, `else`, or an operator

Desired output

error: suffixes on string literals are invalid
 --> src/main.rs:2:9
  |
2 | let s = r#" \ "#r"\ ";
  |         ^^^^^^^^^ invalid suffix `r`

Rationale and extra context

It seems like #r is not considered as a suffix whereas it should

Other cases

Rust Version

1.90.0-nightly (2025-07-17 e4662966273ed58b51f9)

Anything else?

No response

[Kijewski]

This is an odd case. r#" \ "#r"\ " are two tokens:

• r#" \ "#r ← the raw string " \\ " with a suffix r and
• an invalid string "\ ". Invalid because backslash + space is not a valid escape sequence.

So it is indeed parsed as two tokens, but the hint should mention that a space is needed.

-2 | let s = r#" \ "#rr"\ ";
+2 | let s = r#" \ "#r r"\ ";