clippy_lints/src/question_mark.rs

   1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution.
   3 //
   4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   7 // option. This file may not be copied, modified, or distributed
   8 // except according to those terms.
   9
  10 use crate::rustc::hir::def::Def;
  11 use crate::rustc::hir::*;
  12 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  13 use crate::rustc::{declare_tool_lint, lint_array};
  14 use crate::syntax::ptr::P;
  15 use crate::utils::sugg::Sugg;
  16 use if_chain::if_chain;
  17
  18 use crate::rustc_errors::Applicability;
  19 use crate::utils::paths::*;
  20 use crate::utils::{match_def_path, match_type, span_lint_and_then, SpanlessEq};
  21
  22 /// **What it does:** Checks for expressions that could be replaced by the question mark operator
  23 ///
  24 /// **Why is this bad?** Question mark usage is more idiomatic
  25 ///
  26 /// **Known problems:** None
  27 ///
  28 /// **Example:**
  29 /// ```rust
  30 /// if option.is_none() {
  31 ///     return None;
  32 /// }
  33 /// ```
  34 ///
  35 /// Could be written:
  36 ///
  37 /// ```rust
  38 /// option?;
  39 /// ```
  40 declare_clippy_lint! {
  41     pub QUESTION_MARK,
  42     style,
  43     "checks for expressions that could be replaced by the question mark operator"
  44 }
  45
  46 #[derive(Copy, Clone)]
  47 pub struct Pass;
  48
  49 impl LintPass for Pass {
  50     fn get_lints(&self) -> LintArray {
  51         lint_array!(QUESTION_MARK)
  52     }
  53 }
  54
  55 impl Pass {
  56     /// Check if the given expression on the given context matches the following structure:
  57     ///
  58     /// ```ignore
  59     /// if option.is_none() {
  60     ///    return None;
  61     /// }
  62     /// ```
  63     ///
  64     /// If it matches, it will suggest to use the question mark operator instead
  65     fn check_is_none_and_early_return_none(cx: &LateContext<'_, '_>, expr: &Expr) {
  66         if_chain! {
  67             if let ExprKind::If(if_expr, body, else_) = &expr.node;
  68             if let ExprKind::MethodCall(segment, _, args) = &if_expr.node;
  69             if segment.ident.name == "is_none";
  70             if Self::expression_returns_none(cx, body);
  71             if let Some(subject) = args.get(0);
  72             if Self::is_option(cx, subject);
  73
  74             then {
  75                 if let Some(else_) = else_ {
  76                     if_chain! {
  77                         if let ExprKind::Block(block, None) = &else_.node;
  78                         if block.stmts.len() == 0;
  79                         if let Some(block_expr) = &block.expr;
  80                         if SpanlessEq::new(cx).ignore_fn().eq_expr(subject, block_expr);
  81                         then {
  82                             span_lint_and_then(
  83                                 cx,
  84                                 QUESTION_MARK,
  85                                 expr.span,
  86                                 "this block may be rewritten with the `?` operator",
  87                                 |db| {
  88                                     db.span_suggestion_with_applicability(
  89                                         expr.span,
  90                                         "replace_it_with",
  91                                         format!("Some({}?)", Sugg::hir(cx, subject, "..")),
  92                                         Applicability::MaybeIncorrect, // snippet
  93                                     );
  94                                 }
  95                             )
  96                         }
  97                     }
  98                     return;
  99                 }
 100
 101                 span_lint_and_then(
 102                     cx,
 103                     QUESTION_MARK,
 104                     expr.span,
 105                     "this block may be rewritten with the `?` operator",
 106                     |db| {
 107                         let receiver_str = &Sugg::hir(cx, subject, "..");
 108
 109                         db.span_suggestion_with_applicability(
 110                             expr.span,
 111                             "replace_it_with",
 112                             format!("{}?;", receiver_str),
 113                             Applicability::MaybeIncorrect, // snippet
 114                         );
 115                     }
 116                 )
 117             }
 118         }
 119     }
 120
 121     fn is_option(cx: &LateContext<'_, '_>, expression: &Expr) -> bool {
 122         let expr_ty = cx.tables.expr_ty(expression);
 123
 124         match_type(cx, expr_ty, &OPTION)
 125     }
 126
 127     fn expression_returns_none(cx: &LateContext<'_, '_>, expression: &Expr) -> bool {
 128         match expression.node {
 129             ExprKind::Block(ref block, _) => {
 130                 if let Some(return_expression) = Self::return_expression(block) {
 131                     return Self::expression_returns_none(cx, &return_expression);
 132                 }
 133
 134                 false
 135             },
 136             ExprKind::Ret(Some(ref expr)) => Self::expression_returns_none(cx, expr),
 137             ExprKind::Path(ref qp) => {
 138                 if let Def::VariantCtor(def_id, _) = cx.tables.qpath_def(qp, expression.hir_id) {
 139                     return match_def_path(cx.tcx, def_id, &OPTION_NONE);
 140                 }
 141
 142                 false
 143             },
 144             _ => false,
 145         }
 146     }
 147
 148     fn return_expression(block: &Block) -> Option<P<Expr>> {
 149         // Check if last expression is a return statement. Then, return the expression
 150         if_chain! {
 151             if block.stmts.len() == 1;
 152             if let Some(expr) = block.stmts.iter().last();
 153             if let StmtKind::Semi(ref expr, _) = expr.node;
 154             if let ExprKind::Ret(ref ret_expr) = expr.node;
 155             if let &Some(ref ret_expr) = ret_expr;
 156
 157             then {
 158                 return Some(ret_expr.clone());
 159             }
 160         }
 161
 162         // Check for `return` without a semicolon.
 163         if_chain! {
 164             if block.stmts.len() == 0;
 165             if let Some(ExprKind::Ret(Some(ret_expr))) = block.expr.as_ref().map(|e| &e.node);
 166             then {
 167                 return Some(ret_expr.clone());
 168             }
 169         }
 170
 171         None
 172     }
 173 }
 174
 175 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
 176     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
 177         Self::check_is_none_and_early_return_none(cx, expr);
 178     }
 179 }