Function lower_expr 

pub fn lower_expr(
    expr: &Expr,
    ctx: ExprLoweringContext<'_>,
) -> Result<Expr, ExprLowerError>

Lower a syntax expression into HIR, rejecting unresolved references.

This is the batch-pipeline boundary: the lowered tree is guaranteed to contain no ExprKind::Error node.

Errors

Returns the first ExprLowerError if any expression-level reference cannot be resolved to a canonical module identity or lexical local binding.