clippy_lints/src/manual_ok_or.rs

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