Function diagnose 

pub fn diagnose(
    text: &str,
    rope: &Rope,
    variables: &BTreeMap<String, String>,
    profile_name: Option<&str>,
) -> Vec<Diagnostic>

Parse text as SQL and return diagnostics for any parse errors and variable issues.

Resolves psql-style variables before parsing. Unresolved variables produce diagnostics at their position in the original text. Parse errors from the resolved SQL are mapped back to original-text positions via the substitution log.

Arguments

• text — The original SQL source text (as the editor shows it).
• rope — A Rope built from the same text, used for byte-offset to line/column conversion.
• variables — Variable definitions from the project config.
• profile_name — Active profile name (if any), shown in undefined-variable messages. When None, the diagnostic suggests setting a profile.

Returns

A (possibly empty) vec of LSP diagnostics. Variable diagnostics are WARNING if the file has the warn pragma, ERROR otherwise. Parse errors are always ERROR.