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| 1 | +use crate::utils::{match_qpath, paths, snippet, span_lint_and_then}; |
| 2 | +use if_chain::if_chain; |
| 3 | +use rustc::hir::*; |
| 4 | +use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass}; |
| 5 | +use rustc::ty::Ty; |
| 6 | +use rustc::{declare_lint_pass, declare_tool_lint}; |
| 7 | +use rustc_errors::Applicability; |
| 8 | + |
| 9 | +declare_clippy_lint! { |
| 10 | + /// **What it does:** Checks for usages of `Err(x)?`. |
| 11 | + /// |
| 12 | + /// **Why is this bad?** The `?` operator is designed to allow calls that |
| 13 | + /// can fail to be easily chained. For example, `foo()?.bar()` or |
| 14 | + /// `foo(bar()?)`. Because `Err(x)?` can't be used that way (it will |
| 15 | + /// always return), it is more clear to write `return Err(x)`. |
| 16 | + /// |
| 17 | + /// **Known problems:** None. |
| 18 | + /// |
| 19 | + /// **Example:** |
| 20 | + /// |
| 21 | + /// ```rust,ignore |
| 22 | + /// // Bad |
| 23 | + /// fn foo(fail: bool) -> Result<i32, String> { |
| 24 | + /// if fail { |
| 25 | + /// Err("failed")?; |
| 26 | + /// } |
| 27 | + /// Ok(0) |
| 28 | + /// } |
| 29 | + /// |
| 30 | + /// // Good |
| 31 | + /// fn foo(fail: bool) -> Result<i32, String> { |
| 32 | + /// if fail { |
| 33 | + /// return Err("failed".into()); |
| 34 | + /// } |
| 35 | + /// Ok(0) |
| 36 | + /// } |
| 37 | + /// ``` |
| 38 | + pub TRY_ERR, |
| 39 | + style, |
| 40 | + "return errors explicitly rather than hiding them behind a `?`" |
| 41 | +} |
| 42 | + |
| 43 | +declare_lint_pass!(TryErr => [TRY_ERR]); |
| 44 | + |
| 45 | +impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TryErr { |
| 46 | + fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) { |
| 47 | + // Looks for a structure like this: |
| 48 | + // match ::std::ops::Try::into_result(Err(5)) { |
| 49 | + // ::std::result::Result::Err(err) => |
| 50 | + // #[allow(unreachable_code)] |
| 51 | + // return ::std::ops::Try::from_error(::std::convert::From::from(err)), |
| 52 | + // ::std::result::Result::Ok(val) => |
| 53 | + // #[allow(unreachable_code)] |
| 54 | + // val, |
| 55 | + // }; |
| 56 | + if_chain! { |
| 57 | + if let ExprKind::Match(ref match_arg, _, MatchSource::TryDesugar) = expr.node; |
| 58 | + if let ExprKind::Call(ref match_fun, ref try_args) = match_arg.node; |
| 59 | + if let ExprKind::Path(ref match_fun_path) = match_fun.node; |
| 60 | + if match_qpath(match_fun_path, &["std", "ops", "Try", "into_result"]); |
| 61 | + if let Some(ref try_arg) = try_args.get(0); |
| 62 | + if let ExprKind::Call(ref err_fun, ref err_args) = try_arg.node; |
| 63 | + if let Some(ref err_arg) = err_args.get(0); |
| 64 | + if let ExprKind::Path(ref err_fun_path) = err_fun.node; |
| 65 | + if match_qpath(err_fun_path, &paths::RESULT_ERR); |
| 66 | + if let Some(return_type) = find_err_return_type(cx, &expr.node); |
| 67 | + |
| 68 | + then { |
| 69 | + let err_type = cx.tables.expr_ty(err_arg); |
| 70 | + let suggestion = if err_type == return_type { |
| 71 | + format!("return Err({})", snippet(cx, err_arg.span, "_")) |
| 72 | + } else { |
| 73 | + format!("return Err({}.into())", snippet(cx, err_arg.span, "_")) |
| 74 | + }; |
| 75 | + |
| 76 | + span_lint_and_then( |
| 77 | + cx, |
| 78 | + TRY_ERR, |
| 79 | + expr.span, |
| 80 | + &format!("confusing error return, consider using `{}`", suggestion), |
| 81 | + |db| { |
| 82 | + db.span_suggestion( |
| 83 | + expr.span, |
| 84 | + "try this", |
| 85 | + suggestion, |
| 86 | + Applicability::MaybeIncorrect |
| 87 | + ); |
| 88 | + }, |
| 89 | + ); |
| 90 | + } |
| 91 | + } |
| 92 | + } |
| 93 | +} |
| 94 | + |
| 95 | +// In order to determine whether to suggest `.into()` or not, we need to find the error type the |
| 96 | +// function returns. To do that, we look for the From::from call (see tree above), and capture |
| 97 | +// its output type. |
| 98 | +fn find_err_return_type<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx ExprKind) -> Option<Ty<'tcx>> { |
| 99 | + if let ExprKind::Match(_, ref arms, MatchSource::TryDesugar) = expr { |
| 100 | + arms.iter().filter_map(|ty| find_err_return_type_arm(cx, ty)).nth(0) |
| 101 | + } else { |
| 102 | + None |
| 103 | + } |
| 104 | +} |
| 105 | + |
| 106 | +// Check for From::from in one of the match arms. |
| 107 | +fn find_err_return_type_arm<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arm: &'tcx Arm) -> Option<Ty<'tcx>> { |
| 108 | + if_chain! { |
| 109 | + if let ExprKind::Ret(Some(ref err_ret)) = arm.body.node; |
| 110 | + if let ExprKind::Call(ref from_error_path, ref from_error_args) = err_ret.node; |
| 111 | + if let ExprKind::Path(ref from_error_fn) = from_error_path.node; |
| 112 | + if match_qpath(from_error_fn, &["std", "ops", "Try", "from_error"]); |
| 113 | + if let Some(from_error_arg) = from_error_args.get(0); |
| 114 | + then { |
| 115 | + Some(cx.tables.expr_ty(from_error_arg)) |
| 116 | + } else { |
| 117 | + None |
| 118 | + } |
| 119 | + } |
| 120 | +} |
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