Function check_catch_frame

src/diagnostics/unused_variables.rs:347–418

Check a catch frame for unused catch variables only. Catch frames inherit the parent scope, so we only flag variables that are in the catch frame's own `parameters` list (the catch variable itself, e.g. `$e` in `catch (Exception $e)`).

(
    frame: &crate::scope_collector::Frame,
    scope: &ScopeMap,
    ctx: &mut DiagnosticCtx<'_>,
    always_skip: &HashSet<&str>,
)

/// that are in the catch frame's own `parameters` list (the catch
/// variable itself, e.g. `$e` in `catch (Exception $e)`).
fn check_catch_frame(
    frame: &crate::scope_collector::Frame,
    scope: &ScopeMap,
    ctx: &mut DiagnosticCtx<'_>,
    always_skip: &HashSet<&str>,
) {
    for param in &frame.parameters {
        let var_name = param.as_str();

        if always_skip.contains(var_name) {
            continue;
        }
        if var_name == "$_" || var_name.starts_with("$_") {
            continue;
        }

        // Check for reads inside the catch block body.
        let has_read = scope.accesses.iter().any(|a| {
            a.name == var_name
                && matches!(a.kind, AccessKind::Read | AccessKind::ReadWrite)
                && a.offset >= frame.start
                && a.offset <= frame.end
        });

        if has_read {
            continue;
        }

        // Find the catch variable's write offset — the closest write
        // *before* this frame's start.  Using `.find()` would return the
        // first write in the file, which for nested catches with the same
        // variable name points at the wrong catch clause.
        let diag_offset = scope
            .accesses
            .iter()
            .filter(|a| {
                a.name == var_name && matches!(a.kind, AccessKind::Write) && a.offset <= frame.start
            })
            .max_by_key(|a| a.offset)
            .or_else(|| {
                scope
                    .accesses
                    .iter()
                    .find(|a| a.name == var_name && matches!(a.kind, AccessKind::Write))
            })
            .map(|a| a.offset)
            .unwrap_or(frame.start);

        let var_len = var_name.len();
        let range = match ctx.backend.offset_range_to_lsp_range(
            ctx.uri,
            ctx.content,
            diag_offset as usize,
            diag_offset as usize + var_len,
        ) {
            Some(r) => r,
            None => continue,
        };