rust-clippy/clippy_lints/src/transmute/transmute_int_to_char.rs

use super::TRANSMUTE_INT_TO_CHAR;
use crate::utils::{span_lint_and_then, sugg};
use rustc_ast as ast;
use rustc_errors::Applicability;
use rustc_hir::Expr;
use rustc_lint::LateContext;
use rustc_middle::ty;
use rustc_middle::ty::Ty;

/// Checks for `transmute_int_to_char` lint.
/// Returns `true` if it's triggered, otherwise returns `false`.
pub(super) fn check<'tcx>(
    cx: &LateContext<'tcx>,
    e: &'tcx Expr<'_>,
    from_ty: Ty<'tcx>,
    to_ty: Ty<'tcx>,
    args: &'tcx [Expr<'_>],
) -> bool {
    match (&from_ty.kind(), &to_ty.kind()) {
        (ty::Int(ty::IntTy::I32) | ty::Uint(ty::UintTy::U32), &ty::Char) => {
            {
                span_lint_and_then(
                    cx,
                    TRANSMUTE_INT_TO_CHAR,
                    e.span,
                    &format!("transmute from a `{}` to a `char`", from_ty),
                    |diag| {
                        let arg = sugg::Sugg::hir(cx, &args[0], "..");
                        let arg = if let ty::Int(_) = from_ty.kind() {
                            arg.as_ty(ast::UintTy::U32.name_str())
                        } else {
                            arg
                        };
                        diag.span_suggestion(
                            e.span,
                            "consider using",
                            format!("std::char::from_u32({}).unwrap()", arg.to_string()),
                            Applicability::Unspecified,
                        );
                    },
                )
            };
            true
        },
        _ => false,
    }
}