use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::snippet_with_applicability;
use rustc_errors::Applicability;
use rustc_hir::{Item, ItemKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_target::spec::abi::Abi;

declare_clippy_lint! {
    /// ### What it does
    /// Checks for Rust ABI functions with the `#[no_mangle]` attribute.
    ///
    /// ### Why is this bad?
    /// The Rust ABI is not stable, but in many simple cases matches
    /// enough with the C ABI that it is possible to forget to add
    /// `extern "C"` to a function called from C. Changes to the
    /// Rust ABI can break this at any point.
    ///
    /// ### Example
    /// ```rust
    ///  #[no_mangle]
    ///  fn example(arg_one: u32, arg_two: usize) {}
    /// ```
    ///
    /// Use instead:
    /// ```rust
    ///  #[no_mangle]
    ///  extern "C" fn example(arg_one: u32, arg_two: usize) {}
    /// ```
    #[clippy::version = "1.69.0"]
    pub NO_MANGLE_WITH_RUST_ABI,
    pedantic,
    "convert Rust ABI functions to C ABI"
}
declare_lint_pass!(NoMangleWithRustAbi => [NO_MANGLE_WITH_RUST_ABI]);

impl<'tcx> LateLintPass<'tcx> for NoMangleWithRustAbi {
    fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
        if let ItemKind::Fn(fn_sig, _, _) = &item.kind {
            let attrs = cx.tcx.hir().attrs(item.hir_id());
            let mut applicability = Applicability::MachineApplicable;
            let snippet = snippet_with_applicability(cx, fn_sig.span, "..", &mut applicability);
            for attr in attrs {
                if let Some(ident) = attr.ident()
                    && ident.name == rustc_span::sym::no_mangle
                    && fn_sig.header.abi == Abi::Rust
                    && !snippet.contains("extern") {

                    let suggestion = snippet.split_once("fn")
                        .map_or(String::new(), |(first, second)| format!(r#"{first}extern "C" fn{second}"#));

                    span_lint_and_sugg(
                        cx,
                        NO_MANGLE_WITH_RUST_ABI,
                        fn_sig.span,
                        "attribute #[no_mangle] set on a Rust ABI function",
                        "try",
                        suggestion,
                        applicability
                    );
                }
            }
        }
    }
}