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
  11 use matches::matches;
  12 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  13 use crate::rustc::{declare_tool_lint, lint_array};
  14 use crate::rustc::hir::*;
  15 use crate::rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
  16 use crate::utils::*;
  17
  18 /// **What it does:** Checks for `if` conditions that use blocks to contain an
  19 /// expression.
  20 ///
  21 /// **Why is this bad?** It isn't really Rust style, same as using parentheses
  22 /// to contain expressions.
  23 ///
  24 /// **Known problems:** None.
  25 ///
  26 /// **Example:**
  27 /// ```rust
  28 /// if { true } ..
  29 /// ```
  30 declare_clippy_lint! {
  31     pub BLOCK_IN_IF_CONDITION_EXPR,
  32     style,
  33     "braces that can be eliminated in conditions, e.g. `if { true } ...`"
  34 }
  35
  36 /// **What it does:** Checks for `if` conditions that use blocks containing
  37 /// statements, or conditions that use closures with blocks.
  38 ///
  39 /// **Why is this bad?** Using blocks in the condition makes it hard to read.
  40 ///
  41 /// **Known problems:** None.
  42 ///
  43 /// **Example:**
  44 /// ```rust
  45 /// if { let x = somefunc(); x } ..
  46 /// // or
  47 /// if somefunc(|x| { x == 47 }) ..
  48 /// ```
  49 declare_clippy_lint! {
  50     pub BLOCK_IN_IF_CONDITION_STMT,
  51     style,
  52     "complex blocks in conditions, e.g. `if { let x = true; x } ...`"
  53 }
  54
  55 #[derive(Copy, Clone)]
  56 pub struct BlockInIfCondition;
  57
  58 impl LintPass for BlockInIfCondition {
  59     fn get_lints(&self) -> LintArray {
  60         lint_array!(BLOCK_IN_IF_CONDITION_EXPR, BLOCK_IN_IF_CONDITION_STMT)
  61     }
  62 }
  63
  64 struct ExVisitor<'a, 'tcx: 'a> {
  65     found_block: Option<&'tcx Expr>,
  66     cx: &'a LateContext<'a, 'tcx>,
  67 }
  68
  69 impl<'a, 'tcx: 'a> Visitor<'tcx> for ExVisitor<'a, 'tcx> {
  70     fn visit_expr(&mut self, expr: &'tcx Expr) {
  71         if let ExprKind::Closure(_, _, eid, _, _) = expr.node {
  72             let body = self.cx.tcx.hir.body(eid);
  73             let ex = &body.value;
  74             if matches!(ex.node, ExprKind::Block(_, _)) {
  75                 self.found_block = Some(ex);
  76                 return;
  77             }
  78         }
  79         walk_expr(self, expr);
  80     }
  81     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
  82         NestedVisitorMap::None
  83     }
  84 }
  85
  86 const BRACED_EXPR_MESSAGE: &str = "omit braces around single expression condition";
  87 const COMPLEX_BLOCK_MESSAGE: &str = "in an 'if' condition, avoid complex blocks or closures with blocks; \
  88                                      instead, move the block or closure higher and bind it with a 'let'";
  89
  90 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BlockInIfCondition {
  91     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  92         if let ExprKind::If(ref check, ref then, _) = expr.node {
  93             if let ExprKind::Block(ref block, _) = check.node {
  94                 if block.rules == DefaultBlock {
  95                     if block.stmts.is_empty() {
  96                         if let Some(ref ex) = block.expr {
  97                             // don't dig into the expression here, just suggest that they remove
  98                             // the block
  99                             if in_macro(expr.span) || differing_macro_contexts(expr.span, ex.span) {
 100                                 return;
 101                             }
 102                             span_help_and_lint(
 103                                 cx,
 104                                 BLOCK_IN_IF_CONDITION_EXPR,
 105                                 check.span,
 106                                 BRACED_EXPR_MESSAGE,
 107                                 &format!(
 108                                     "try\nif {} {} ... ",
 109                                     snippet_block(cx, ex.span, ".."),
 110                                     snippet_block(cx, then.span, "..")
 111                                 ),
 112                             );
 113                         }
 114                     } else {
 115                         let span = block
 116                             .expr
 117                             .as_ref()
 118                             .map_or_else(|| block.stmts[0].span, |e| e.span);
 119                         if in_macro(span) || differing_macro_contexts(expr.span, span) {
 120                             return;
 121                         }
 122                         // move block higher
 123                         span_help_and_lint(
 124                             cx,
 125                             BLOCK_IN_IF_CONDITION_STMT,
 126                             check.span,
 127                             COMPLEX_BLOCK_MESSAGE,
 128                             &format!(
 129                                 "try\nlet res = {};\nif res {} ... ",
 130                                 snippet_block(cx, block.span, ".."),
 131                                 snippet_block(cx, then.span, "..")
 132                             ),
 133                         );
 134                     }
 135                 }
 136             } else {
 137                 let mut visitor = ExVisitor {
 138                     found_block: None,
 139                     cx,
 140                 };
 141                 walk_expr(&mut visitor, check);
 142                 if let Some(block) = visitor.found_block {
 143                     span_lint(cx, BLOCK_IN_IF_CONDITION_STMT, block.span, COMPLEX_BLOCK_MESSAGE);
 144                 }
 145             }
 146         }
 147     }
 148 }