id_effect_lints 0.12.0

use crate::diag::span_lint_and_help;
use crate::utils::*;
use rustc_hir::ItemKind;
use rustc_lint::LateContext;

use crate::{
  NO_NESTED_RESULT_IN_PUB_API, NO_STATIC_SERVICE_GLOBALS, NO_THREAD_LOCAL_FOR_REQUEST_CONTEXT,
};

// ─── E-02: No static service globals ─────────────────────────────────────────

/// Flags `static` items whose types look like service types.
pub fn check_no_static_service_globals(cx: &LateContext<'_>, item: &rustc_hir::Item<'_>) {
  // ItemKind::Static(mutbl, ident, ty, body) in nightly-2026+
  if let ItemKind::Static(_, _, ty, _) = &item.kind
    && !is_primitive_ty(ty)
  {
    span_lint_and_help(
      cx,
      NO_STATIC_SERVICE_GLOBALS,
      item.span,
      "`static` item found; services must not live in global statics",
      None,
      "list the service in `R` (`caps!(Key, …)`), provide it with a `Layer`, and read it with `~Key` in `effect!` or `need::<Key>()`",
    );
  }
}

// ─── E-03: No thread_local! for request context ───────────────────────────────

pub fn check_no_thread_local(cx: &LateContext<'_>, item: &rustc_hir::Item<'_>) {
  use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
  let def_id = item.owner_id.to_def_id();
  let span = match item.kind {
    // `#[thread_local] static` (the attribute is parsed, so ask codegen's view of it).
    ItemKind::Static(..)
      if cx
        .tcx
        .codegen_fn_attrs(def_id)
        .flags
        .contains(CodegenFnAttrFlags::THREAD_LOCAL) =>
    {
      item.span
    }
    // `thread_local! { static X: T = … }` expands to `const X: LocalKey<T>`; report the macro
    // call (the expansion itself is std's, so a lint there would be suppressed).
    ItemKind::Const(..)
      if ty_is_adt_named(cx, cx.tcx.type_of(def_id).skip_binder(), "LocalKey") =>
    {
      item.span.source_callsite()
    }
    _ => return,
  };
  span_lint_and_help(
    cx,
    NO_THREAD_LOCAL_FOR_REQUEST_CONTEXT,
    span,
    "`thread_local!` storage found in Effect code",
    None,
    "use `FiberRef::new(initial)` for fiber-scoped dynamic state",
  );
}

// ─── F-01: No Result<Result<…>> in public APIs ───────────────────────────────

pub fn check_no_nested_result_type(cx: &LateContext<'_>, item: &rustc_hir::Item<'_>) {
  let is_pub = cx.tcx.visibility(item.owner_id.def_id).is_public();
  if !is_pub {
    return;
  }
  // ItemKind::TyAlias(ident, generics, ty) in nightly-2026+
  if let ItemKind::TyAlias(_, _, ty) = &item.kind
    && is_nested_result(ty)
  {
    span_lint_and_help(
      cx,
      NO_NESTED_RESULT_IN_PUB_API,
      item.span,
      "public type alias is `Result<Result<_, _>, _>`",
      None,
      "use `Or<E1, E2>` or a flat `E: From<E1> + From<E2>` channel",
    );
  }
}

/// Also check function return types (called from check_fn in the pass).
pub fn check_no_nested_result_fn<'tcx>(
  cx: &LateContext<'tcx>,
  decl: &'tcx rustc_hir::FnDecl<'tcx>,
  is_pub: bool,
  span: rustc_span::Span,
) {
  if !is_pub {
    return;
  }
  if let rustc_hir::FnRetTy::Return(ty) = &decl.output
    && is_nested_result(ty)
  {
    span_lint_and_help(
      cx,
      NO_NESTED_RESULT_IN_PUB_API,
      span,
      "public function returns `Result<Result<_, _>, _>`",
      None,
      "use `Or<E1, E2>` or flatten errors via `E: From<E1> + From<E2>`",
    );
  }
}

// ─── Helpers ─────────────────────────────────────────────────────────────────

fn is_nested_result(ty: &rustc_hir::Ty<'_>) -> bool {
  if !ty_last_segment_is(ty, "Result") {
    return false;
  }
  if let rustc_hir::TyKind::Path(rustc_hir::QPath::Resolved(_, path)) = &ty.kind
    && let Some(last) = path.segments.last()
    && let Some(args) = last.args
    && let Some(rustc_hir::GenericArg::Type(ok_ty)) = args.args.first()
  {
    return ty_last_segment_is(ok_ty.as_unambig_ty(), "Result");
  }
  false
}

fn is_primitive_ty(ty: &rustc_hir::Ty<'_>) -> bool {
  // `static NAME: &str = "…"` is a constant, not a service.
  if let rustc_hir::TyKind::Ref(_, inner) = &ty.kind {
    return is_primitive_ty(inner.ty);
  }
  matches!(
      &ty.kind,
      rustc_hir::TyKind::Path(rustc_hir::QPath::Resolved(_, path))
          if path.segments.last().is_some_and(|s| matches!(
              s.ident.name.as_str(),
              "u8" | "u16" | "u32" | "u64" | "u128" | "usize"
              | "i8" | "i16" | "i32" | "i64" | "i128" | "isize"
              | "f32" | "f64" | "bool" | "char" | "str" | "String"
          ))
  ) || matches!(
    ty.kind,
    rustc_hir::TyKind::Tup(_) | rustc_hir::TyKind::Never
  )
}