clippy_lints/src/blocks_in_if_conditions.rs

   1 use crate::utils::{differing_macro_contexts, higher, snippet_block_with_applicability, span_lint, span_lint_and_sugg};
   2 use rustc_errors::Applicability;
   3 use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
   4 use rustc_hir::{BlockCheckMode, Expr, ExprKind};
   5 use rustc_lint::{LateContext, LateLintPass, LintContext};
   6 use rustc_middle::hir::map::Map;
   7 use rustc_middle::lint::in_external_macro;
   8 use rustc_session::{declare_lint_pass, declare_tool_lint};
   9
  10 declare_clippy_lint! {
  11     /// **What it does:** Checks for `if` conditions that use blocks containing an
  12     /// expression, statements or conditions that use closures with blocks.
  13     ///
  14     /// **Why is this bad?** Style, using blocks in the condition makes it hard to read.
  15     ///
  16     /// **Known problems:** None.
  17     ///
  18     /// **Examples:**
  19     /// ```rust
  20     /// // Bad
  21     /// if { true } { /* ... */ }
  22     ///
  23     /// // Good
  24     /// if true { /* ... */ }
  25     /// ```
  26     ///
  27     /// // or
  28     ///
  29     /// ```rust
  30     /// # fn somefunc() -> bool { true };
  31     /// // Bad
  32     /// if { let x = somefunc(); x } { /* ... */ }
  33     ///
  34     /// // Good
  35     /// let res = { let x = somefunc(); x };
  36     /// if res { /* ... */ }
  37     /// ```
  38     pub BLOCKS_IN_IF_CONDITIONS,
  39     style,
  40     "useless or complex blocks that can be eliminated in conditions"
  41 }
  42
  43 declare_lint_pass!(BlocksInIfConditions => [BLOCKS_IN_IF_CONDITIONS]);
  44
  45 struct ExVisitor<'a, 'tcx> {
  46     found_block: Option<&'tcx Expr<'tcx>>,
  47     cx: &'a LateContext<'tcx>,
  48 }
  49
  50 impl<'a, 'tcx> Visitor<'tcx> for ExVisitor<'a, 'tcx> {
  51     type Map = Map<'tcx>;
  52
  53     fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
  54         if let ExprKind::Closure(_, _, eid, _, _) = expr.kind {
  55             let body = self.cx.tcx.hir().body(eid);
  56             let ex = &body.value;
  57             if matches!(ex.kind, ExprKind::Block(_, _)) && !body.value.span.from_expansion() {
  58                 self.found_block = Some(ex);
  59                 return;
  60             }
  61         }
  62         walk_expr(self, expr);
  63     }
  64     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
  65         NestedVisitorMap::None
  66     }
  67 }
  68
  69 const BRACED_EXPR_MESSAGE: &str = "omit braces around single expression condition";
  70 const COMPLEX_BLOCK_MESSAGE: &str = "in an `if` condition, avoid complex blocks or closures with blocks; \
  71                                     instead, move the block or closure higher and bind it with a `let`";
  72
  73 impl<'tcx> LateLintPass<'tcx> for BlocksInIfConditions {
  74     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  75         if in_external_macro(cx.sess(), expr.span) {
  76             return;
  77         }
  78         if let Some((cond, _, _)) = higher::if_block(&expr) {
  79             if let ExprKind::Block(block, _) = &cond.kind {
  80                 if block.rules == BlockCheckMode::DefaultBlock {
  81                     if block.stmts.is_empty() {
  82                         if let Some(ex) = &block.expr {
  83                             // don't dig into the expression here, just suggest that they remove
  84                             // the block
  85                             if expr.span.from_expansion() || differing_macro_contexts(expr.span, ex.span) {
  86                                 return;
  87                             }
  88                             let mut applicability = Applicability::MachineApplicable;
  89                             span_lint_and_sugg(
  90                                 cx,
  91                                 BLOCKS_IN_IF_CONDITIONS,
  92                                 cond.span,
  93                                 BRACED_EXPR_MESSAGE,
  94                                 "try",
  95                                 format!(
  96                                     "{}",
  97                                     snippet_block_with_applicability(
  98                                         cx,
  99                                         ex.span,
 100                                         "..",
 101                                         Some(expr.span),
 102                                         &mut applicability
 103                                     )
 104                                 ),
 105                                 applicability,
 106                             );
 107                         }
 108                     } else {
 109                         let span = block.expr.as_ref().map_or_else(|| block.stmts[0].span, |e| e.span);
 110                         if span.from_expansion() || differing_macro_contexts(expr.span, span) {
 111                             return;
 112                         }
 113                         // move block higher
 114                         let mut applicability = Applicability::MachineApplicable;
 115                         span_lint_and_sugg(
 116                             cx,
 117                             BLOCKS_IN_IF_CONDITIONS,
 118                             expr.span.with_hi(cond.span.hi()),
 119                             COMPLEX_BLOCK_MESSAGE,
 120                             "try",
 121                             format!(
 122                                 "let res = {}; if res",
 123                                 snippet_block_with_applicability(
 124                                     cx,
 125                                     block.span,
 126                                     "..",
 127                                     Some(expr.span),
 128                                     &mut applicability
 129                                 ),
 130                             ),
 131                             applicability,
 132                         );
 133                     }
 134                 }
 135             } else {
 136                 let mut visitor = ExVisitor { found_block: None, cx };
 137                 walk_expr(&mut visitor, cond);
 138                 if let Some(block) = visitor.found_block {
 139                     span_lint(cx, BLOCKS_IN_IF_CONDITIONS, block.span, COMPLEX_BLOCK_MESSAGE);
 140                 }
 141             }
 142         }
 143     }
 144 }