clippy_lints/src/block_in_if_condition.rs

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