clippy_lints/src/block_in_if_condition.rs

   1 use crate::utils::*;
   2 use matches::matches;
   3 use rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
   4 use rustc::hir::*;
   5 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   6 use rustc::{declare_tool_lint, lint_array};
   7
   8 declare_clippy_lint! {
   9     /// **What it does:** Checks for `if` conditions that use blocks to contain an
  10     /// expression.
  11     ///
  12     /// **Why is this bad?** It isn't really Rust style, same as using parentheses
  13     /// to contain expressions.
  14     ///
  15     /// **Known problems:** None.
  16     ///
  17     /// **Example:**
  18     /// ```rust
  19     /// if { true } { /* ... */ }
  20     /// ```
  21     pub BLOCK_IN_IF_CONDITION_EXPR,
  22     style,
  23     "braces that can be eliminated in conditions, e.g., `if { true } ...`"
  24 }
  25
  26 declare_clippy_lint! {
  27     /// **What it does:** Checks for `if` conditions that use blocks containing
  28     /// statements, or conditions that use closures with blocks.
  29     ///
  30     /// **Why is this bad?** Using blocks in the condition makes it hard to read.
  31     ///
  32     /// **Known problems:** None.
  33     ///
  34     /// **Example:**
  35     /// ```ignore
  36     /// if { let x = somefunc(); x } {}
  37     /// // or
  38     /// if somefunc(|x| { x == 47 }) {}
  39     /// ```
  40     pub BLOCK_IN_IF_CONDITION_STMT,
  41     style,
  42     "complex blocks in conditions, e.g., `if { let x = true; x } ...`"
  43 }
  44
  45 #[derive(Copy, Clone)]
  46 pub struct BlockInIfCondition;
  47
  48 impl LintPass for BlockInIfCondition {
  49     fn get_lints(&self) -> LintArray {
  50         lint_array!(BLOCK_IN_IF_CONDITION_EXPR, BLOCK_IN_IF_CONDITION_STMT)
  51     }
  52
  53     fn name(&self) -> &'static str {
  54         "BlockInIfCondition"
  55     }
  56 }
  57
  58 struct ExVisitor<'a, 'tcx: 'a> {
  59     found_block: Option<&'tcx Expr>,
  60     cx: &'a LateContext<'a, 'tcx>,
  61 }
  62
  63 impl<'a, 'tcx: 'a> Visitor<'tcx> for ExVisitor<'a, 'tcx> {
  64     fn visit_expr(&mut self, expr: &'tcx Expr) {
  65         if let ExprKind::Closure(_, _, eid, _, _) = expr.node {
  66             let body = self.cx.tcx.hir().body(eid);
  67             let ex = &body.value;
  68             if matches!(ex.node, ExprKind::Block(_, _)) && !in_macro(body.value.span) {
  69                 self.found_block = Some(ex);
  70                 return;
  71             }
  72         }
  73         walk_expr(self, expr);
  74     }
  75     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
  76         NestedVisitorMap::None
  77     }
  78 }
  79
  80 const BRACED_EXPR_MESSAGE: &str = "omit braces around single expression condition";
  81 const COMPLEX_BLOCK_MESSAGE: &str = "in an 'if' condition, avoid complex blocks or closures with blocks; \
  82                                      instead, move the block or closure higher and bind it with a 'let'";
  83
  84 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BlockInIfCondition {
  85     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  86         if let ExprKind::If(check, then, _) = &expr.node {
  87             if let ExprKind::Block(block, _) = &check.node {
  88                 if block.rules == DefaultBlock {
  89                     if block.stmts.is_empty() {
  90                         if let Some(ex) = &block.expr {
  91                             // don't dig into the expression here, just suggest that they remove
  92                             // the block
  93                             if in_macro(expr.span) || differing_macro_contexts(expr.span, ex.span) {
  94                                 return;
  95                             }
  96                             span_help_and_lint(
  97                                 cx,
  98                                 BLOCK_IN_IF_CONDITION_EXPR,
  99                                 check.span,
 100                                 BRACED_EXPR_MESSAGE,
 101                                 &format!(
 102                                     "try\nif {} {} ... ",
 103                                     snippet_block(cx, ex.span, ".."),
 104                                     snippet_block(cx, then.span, "..")
 105                                 ),
 106                             );
 107                         }
 108                     } else {
 109                         let span = block.expr.as_ref().map_or_else(|| block.stmts[0].span, |e| e.span);
 110                         if in_macro(span) || differing_macro_contexts(expr.span, span) {
 111                             return;
 112                         }
 113                         // move block higher
 114                         span_help_and_lint(
 115                             cx,
 116                             BLOCK_IN_IF_CONDITION_STMT,
 117                             check.span,
 118                             COMPLEX_BLOCK_MESSAGE,
 119                             &format!(
 120                                 "try\nlet res = {};\nif res {} ... ",
 121                                 snippet_block(cx, block.span, ".."),
 122                                 snippet_block(cx, then.span, "..")
 123                             ),
 124                         );
 125                     }
 126                 }
 127             } else {
 128                 let mut visitor = ExVisitor { found_block: None, cx };
 129                 walk_expr(&mut visitor, check);
 130                 if let Some(block) = visitor.found_block {
 131                     span_lint(cx, BLOCK_IN_IF_CONDITION_STMT, block.span, COMPLEX_BLOCK_MESSAGE);
 132                 }
 133             }
 134         }
 135     }
 136 }