--- /dev/null
+use crate::utils::{
+ differing_macro_contexts, in_macro, is_type_diagnostic_item, match_def_path, match_qpath, paths, snippet,
+ snippet_with_macro_callsite, span_lint_and_sugg,
+};
+use if_chain::if_chain;
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind, LangItem, MatchSource, QPath};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::lint::in_external_macro;
+use rustc_middle::ty::{self, Ty};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::sym;
+
+declare_clippy_lint! {
+ /// **What it does:** Checks for usages of `Err(x)?`.
+ ///
+ /// **Why is this bad?** The `?` operator is designed to allow calls that
+ /// can fail to be easily chained. For example, `foo()?.bar()` or
+ /// `foo(bar()?)`. Because `Err(x)?` can't be used that way (it will
+ /// always return), it is more clear to write `return Err(x)`.
+ ///
+ /// **Known problems:** None.
+ ///
+ /// **Example:**
+ /// ```rust
+ /// fn foo(fail: bool) -> Result<i32, String> {
+ /// if fail {
+ /// Err("failed")?;
+ /// }
+ /// Ok(0)
+ /// }
+ /// ```
+ /// Could be written:
+ ///
+ /// ```rust
+ /// fn foo(fail: bool) -> Result<i32, String> {
+ /// if fail {
+ /// return Err("failed".into());
+ /// }
+ /// Ok(0)
+ /// }
+ /// ```
+ pub TRY_ERR,
+ style,
+ "return errors explicitly rather than hiding them behind a `?`"
+}
+
+declare_lint_pass!(TryErr => [TRY_ERR]);
+
+impl<'tcx> LateLintPass<'tcx> for TryErr {
+ fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+ // Looks for a structure like this:
+ // match ::std::ops::Try::into_result(Err(5)) {
+ // ::std::result::Result::Err(err) =>
+ // #[allow(unreachable_code)]
+ // return ::std::ops::Try::from_error(::std::convert::From::from(err)),
+ // ::std::result::Result::Ok(val) =>
+ // #[allow(unreachable_code)]
+ // val,
+ // };
+ if_chain! {
+ if !in_external_macro(cx.tcx.sess, expr.span);
+ if let ExprKind::Match(ref match_arg, _, MatchSource::TryDesugar) = expr.kind;
+ if let ExprKind::Call(ref match_fun, ref try_args) = match_arg.kind;
+ if let ExprKind::Path(ref match_fun_path) = match_fun.kind;
+ if matches!(match_fun_path, QPath::LangItem(LangItem::TryIntoResult, _));
+ if let Some(ref try_arg) = try_args.get(0);
+ if let ExprKind::Call(ref err_fun, ref err_args) = try_arg.kind;
+ if let Some(ref err_arg) = err_args.get(0);
+ if let ExprKind::Path(ref err_fun_path) = err_fun.kind;
+ if match_qpath(err_fun_path, &paths::RESULT_ERR);
+ if let Some(return_ty) = find_return_type(cx, &expr.kind);
+ then {
+ let prefix;
+ let suffix;
+ let err_ty;
+
+ if let Some(ty) = result_error_type(cx, return_ty) {
+ prefix = "Err(";
+ suffix = ")";
+ err_ty = ty;
+ } else if let Some(ty) = poll_result_error_type(cx, return_ty) {
+ prefix = "Poll::Ready(Err(";
+ suffix = "))";
+ err_ty = ty;
+ } else if let Some(ty) = poll_option_result_error_type(cx, return_ty) {
+ prefix = "Poll::Ready(Some(Err(";
+ suffix = ")))";
+ err_ty = ty;
+ } else {
+ return;
+ };
+
+ let expr_err_ty = cx.typeck_results().expr_ty(err_arg);
+ let differing_contexts = differing_macro_contexts(expr.span, err_arg.span);
+
+ let origin_snippet = if in_macro(expr.span) && in_macro(err_arg.span) && differing_contexts {
+ snippet(cx, err_arg.span.ctxt().outer_expn_data().call_site, "_")
+ } else if err_arg.span.from_expansion() && !in_macro(expr.span) {
+ snippet_with_macro_callsite(cx, err_arg.span, "_")
+ } else {
+ snippet(cx, err_arg.span, "_")
+ };
+ let suggestion = if err_ty == expr_err_ty {
+ format!("return {}{}{}", prefix, origin_snippet, suffix)
+ } else {
+ format!("return {}{}.into(){}", prefix, origin_snippet, suffix)
+ };
+
+ span_lint_and_sugg(
+ cx,
+ TRY_ERR,
+ expr.span,
+ "returning an `Err(_)` with the `?` operator",
+ "try this",
+ suggestion,
+ Applicability::MachineApplicable
+ );
+ }
+ }
+ }
+}
+
+/// Finds function return type by examining return expressions in match arms.
+fn find_return_type<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx ExprKind<'_>) -> Option<Ty<'tcx>> {
+ if let ExprKind::Match(_, ref arms, MatchSource::TryDesugar) = expr {
+ for arm in arms.iter() {
+ if let ExprKind::Ret(Some(ref ret)) = arm.body.kind {
+ return Some(cx.typeck_results().expr_ty(ret));
+ }
+ }
+ }
+ None
+}
+
+/// Extracts the error type from Result<T, E>.
+fn result_error_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
+ if_chain! {
+ if let ty::Adt(_, subst) = ty.kind();
+ if is_type_diagnostic_item(cx, ty, sym::result_type);
+ let err_ty = subst.type_at(1);
+ then {
+ Some(err_ty)
+ } else {
+ None
+ }
+ }
+}
+
+/// Extracts the error type from Poll<Result<T, E>>.
+fn poll_result_error_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
+ if_chain! {
+ if let ty::Adt(def, subst) = ty.kind();
+ if match_def_path(cx, def.did, &paths::POLL);
+ let ready_ty = subst.type_at(0);
+
+ if let ty::Adt(ready_def, ready_subst) = ready_ty.kind();
+ if cx.tcx.is_diagnostic_item(sym::result_type, ready_def.did);
+ let err_ty = ready_subst.type_at(1);
+
+ then {
+ Some(err_ty)
+ } else {
+ None
+ }
+ }
+}
+
+/// Extracts the error type from Poll<Option<Result<T, E>>>.
+fn poll_option_result_error_type<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
+ if_chain! {
+ if let ty::Adt(def, subst) = ty.kind();
+ if match_def_path(cx, def.did, &paths::POLL);
+ let ready_ty = subst.type_at(0);
+
+ if let ty::Adt(ready_def, ready_subst) = ready_ty.kind();
+ if cx.tcx.is_diagnostic_item(sym::option_type, ready_def.did);
+ let some_ty = ready_subst.type_at(0);
+
+ if let ty::Adt(some_def, some_subst) = some_ty.kind();
+ if cx.tcx.is_diagnostic_item(sym::result_type, some_def.did);
+ let err_ty = some_subst.type_at(1);
+
+ then {
+ Some(err_ty)
+ } else {
+ None
+ }
+ }
+}
projects / rustc.git / blobdiff