clippy_lints/src/manual_ok_or.rs

   1 use crate::utils::{
   2     indent_of, is_type_diagnostic_item, match_qpath, paths, reindent_multiline, snippet_opt, span_lint_and_sugg,
   3 };
   4 use if_chain::if_chain;
   5 use rustc_errors::Applicability;
   6 use rustc_hir::{def, Expr, ExprKind, PatKind, QPath};
   7 use rustc_lint::LintContext;
   8 use rustc_lint::{LateContext, LateLintPass};
   9 use rustc_middle::lint::in_external_macro;
  10 use rustc_session::{declare_lint_pass, declare_tool_lint};
  11 use rustc_span::symbol::sym;
  12
  13 declare_clippy_lint! {
  14     /// **What it does:**
  15     /// Finds patterns that reimplement `Option::ok_or`.
  16     ///
  17     /// **Why is this bad?**
  18     /// Concise code helps focusing on behavior instead of boilerplate.
  19     ///
  20     /// **Known problems:** None.
  21     ///
  22     /// **Examples:**
  23     /// ```rust
  24     /// let foo: Option<i32> = None;
  25     /// foo.map_or(Err("error"), |v| Ok(v));
  26     ///
  27     /// let foo: Option<i32> = None;
  28     /// foo.map_or(Err("error"), |v| Ok(v));
  29     /// ```
  30     ///
  31     /// Use instead:
  32     /// ```rust
  33     /// let foo: Option<i32> = None;
  34     /// foo.ok_or("error");
  35     /// ```
  36     pub MANUAL_OK_OR,
  37     pedantic,
  38     "finds patterns that can be encoded more concisely with `Option::ok_or`"
  39 }
  40
  41 declare_lint_pass!(ManualOkOr => [MANUAL_OK_OR]);
  42
  43 impl LateLintPass<'_> for ManualOkOr {
  44     fn check_expr(&mut self, cx: &LateContext<'tcx>, scrutinee: &'tcx Expr<'tcx>) {
  45         if in_external_macro(cx.sess(), scrutinee.span) {
  46             return;
  47         }
  48
  49         if_chain! {
  50             if let ExprKind::MethodCall(method_segment, _, args, _) = scrutinee.kind;
  51             if method_segment.ident.name == sym!(map_or);
  52             if args.len() == 3;
  53             let method_receiver = &args[0];
  54             let ty = cx.typeck_results().expr_ty(method_receiver);
  55             if is_type_diagnostic_item(cx, ty, sym::option_type);
  56             let or_expr = &args[1];
  57             if is_ok_wrapping(cx, &args[2]);
  58             if let ExprKind::Call(Expr { kind: ExprKind::Path(err_path), .. }, &[ref err_arg]) = or_expr.kind;
  59             if match_qpath(err_path, &paths::RESULT_ERR);
  60             if let Some(method_receiver_snippet) = snippet_opt(cx, method_receiver.span);
  61             if let Some(err_arg_snippet) = snippet_opt(cx, err_arg.span);
  62             if let Some(indent) = indent_of(cx, scrutinee.span);
  63             then {
  64                 let reindented_err_arg_snippet =
  65                     reindent_multiline(err_arg_snippet.into(), true, Some(indent + 4));
  66                 span_lint_and_sugg(
  67                     cx,
  68                     MANUAL_OK_OR,
  69                     scrutinee.span,
  70                     "this pattern reimplements `Option::ok_or`",
  71                     "replace with",
  72                     format!(
  73                         "{}.ok_or({})",
  74                         method_receiver_snippet,
  75                         reindented_err_arg_snippet
  76                     ),
  77                     Applicability::MachineApplicable,
  78                 );
  79             }
  80         }
  81     }
  82 }
  83
  84 fn is_ok_wrapping(cx: &LateContext<'_>, map_expr: &Expr<'_>) -> bool {
  85     if let ExprKind::Path(ref qpath) = map_expr.kind {
  86         if match_qpath(qpath, &paths::RESULT_OK) {
  87             return true;
  88         }
  89     }
  90     if_chain! {
  91         if let ExprKind::Closure(_, _, body_id, ..) = map_expr.kind;
  92         let body = cx.tcx.hir().body(body_id);
  93         if let PatKind::Binding(_, param_id, ..) = body.params[0].pat.kind;
  94         if let ExprKind::Call(Expr { kind: ExprKind::Path(ok_path), .. }, &[ref ok_arg]) = body.value.kind;
  95         if match_qpath(ok_path, &paths::RESULT_OK);
  96         if let ExprKind::Path(QPath::Resolved(_, ok_arg_path)) = ok_arg.kind;
  97         if let def::Res::Local(ok_arg_path_id) = ok_arg_path.res;
  98         then { param_id == ok_arg_path_id } else { false }
  99     }
 100 }