clippy_lints/src/block_in_if_condition.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::utils::*;
  11 use matches::matches;
  12 use rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
  13 use rustc::hir::*;
  14 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  15 use rustc::{declare_tool_lint, lint_array};
  16
  17 /// **What it does:** Checks for `if` conditions that use blocks to contain an
  18 /// expression.
  19 ///
  20 /// **Why is this bad?** It isn't really Rust style, same as using parentheses
  21 /// to contain expressions.
  22 ///
  23 /// **Known problems:** None.
  24 ///
  25 /// **Example:**
  26 /// ```rust
  27 /// if { true } ..
  28 /// ```
  29 declare_clippy_lint! {
  30     pub BLOCK_IN_IF_CONDITION_EXPR,
  31     style,
  32     "braces that can be eliminated in conditions, e.g. `if { true } ...`"
  33 }
  34
  35 /// **What it does:** Checks for `if` conditions that use blocks containing
  36 /// statements, or conditions that use closures with blocks.
  37 ///
  38 /// **Why is this bad?** Using blocks in the condition makes it hard to read.
  39 ///
  40 /// **Known problems:** None.
  41 ///
  42 /// **Example:**
  43 /// ```rust
  44 /// if { let x = somefunc(); x } ..
  45 /// // or
  46 /// if somefunc(|x| { x == 47 }) ..
  47 /// ```
  48 declare_clippy_lint! {
  49     pub BLOCK_IN_IF_CONDITION_STMT,
  50     style,
  51     "complex blocks in conditions, e.g. `if { let x = true; x } ...`"
  52 }
  53
  54 #[derive(Copy, Clone)]
  55 pub struct BlockInIfCondition;
  56
  57 impl LintPass for BlockInIfCondition {
  58     fn get_lints(&self) -> LintArray {
  59         lint_array!(BLOCK_IN_IF_CONDITION_EXPR, BLOCK_IN_IF_CONDITION_STMT)
  60     }
  61 }
  62
  63 struct ExVisitor<'a, 'tcx: 'a> {
  64     found_block: Option<&'tcx Expr>,
  65     cx: &'a LateContext<'a, 'tcx>,
  66 }
  67
  68 impl<'a, 'tcx: 'a> Visitor<'tcx> for ExVisitor<'a, 'tcx> {
  69     fn visit_expr(&mut self, expr: &'tcx Expr) {
  70         if let ExprKind::Closure(_, _, eid, _, _) = expr.node {
  71             let body = self.cx.tcx.hir().body(eid);
  72             let ex = &body.value;
  73             if matches!(ex.node, ExprKind::Block(_, _)) && !in_macro(body.value.span) {
  74                 self.found_block = Some(ex);
  75                 return;
  76             }
  77         }
  78         walk_expr(self, expr);
  79     }
  80     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
  81         NestedVisitorMap::None
  82     }
  83 }
  84
  85 const BRACED_EXPR_MESSAGE: &str = "omit braces around single expression condition";
  86 const COMPLEX_BLOCK_MESSAGE: &str = "in an 'if' condition, avoid complex blocks or closures with blocks; \
  87                                      instead, move the block or closure higher and bind it with a 'let'";
  88
  89 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BlockInIfCondition {
  90     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  91         if let ExprKind::If(check, then, _) = &expr.node {
  92             if let ExprKind::Block(block, _) = &check.node {
  93                 if block.rules == DefaultBlock {
  94                     if block.stmts.is_empty() {
  95                         if let Some(ex) = &block.expr {
  96                             // don't dig into the expression here, just suggest that they remove
  97                             // the block
  98                             if in_macro(expr.span) || differing_macro_contexts(expr.span, ex.span) {
  99                                 return;
 100                             }
 101                             span_help_and_lint(
 102                                 cx,
 103                                 BLOCK_IN_IF_CONDITION_EXPR,
 104                                 check.span,
 105                                 BRACED_EXPR_MESSAGE,
 106                                 &format!(
 107                                     "try\nif {} {} ... ",
 108                                     snippet_block(cx, ex.span, ".."),
 109                                     snippet_block(cx, then.span, "..")
 110                                 ),
 111                             );
 112                         }
 113                     } else {
 114                         let span = block.expr.as_ref().map_or_else(|| block.stmts[0].span, |e| e.span);
 115                         if in_macro(span) || differing_macro_contexts(expr.span, span) {
 116                             return;
 117                         }
 118                         // move block higher
 119                         span_help_and_lint(
 120                             cx,
 121                             BLOCK_IN_IF_CONDITION_STMT,
 122                             check.span,
 123                             COMPLEX_BLOCK_MESSAGE,
 124                             &format!(
 125                                 "try\nlet res = {};\nif res {} ... ",
 126                                 snippet_block(cx, block.span, ".."),
 127                                 snippet_block(cx, then.span, "..")
 128                             ),
 129                         );
 130                     }
 131                 }
 132             } else {
 133                 let mut visitor = ExVisitor { found_block: None, cx };
 134                 walk_expr(&mut visitor, check);
 135                 if let Some(block) = visitor.found_block {
 136                     span_lint(cx, BLOCK_IN_IF_CONDITION_STMT, block.span, COMPLEX_BLOCK_MESSAGE);
 137                 }
 138             }
 139         }
 140     }
 141 }