src/tools/clippy/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     ///
  32     /// // Bad
  33     /// if { let x = somefunc(); x } { /* ... */ }
  34     ///
  35     /// // Good
  36     /// let res = { let x = somefunc(); x };
  37     /// if res { /* ... */ }
  38     /// ```
  39     pub BLOCKS_IN_IF_CONDITIONS,
  40     style,
  41     "useless or complex blocks that can be eliminated in conditions"
  42 }
  43
  44 declare_lint_pass!(BlocksInIfConditions => [BLOCKS_IN_IF_CONDITIONS]);
  45
  46 struct ExVisitor<'a, 'tcx> {
  47     found_block: Option<&'tcx Expr<'tcx>>,
  48     cx: &'a LateContext<'tcx>,
  49 }
  50
  51 impl<'a, 'tcx> Visitor<'tcx> for ExVisitor<'a, 'tcx> {
  52     type Map = Map<'tcx>;
  53
  54     fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
  55         if let ExprKind::Closure(_, _, eid, _, _) = expr.kind {
  56             let body = self.cx.tcx.hir().body(eid);
  57             let ex = &body.value;
  58             if matches!(ex.kind, ExprKind::Block(_, _)) && !body.value.span.from_expansion() {
  59                 self.found_block = Some(ex);
  60                 return;
  61             }
  62         }
  63         walk_expr(self, expr);
  64     }
  65     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
  66         NestedVisitorMap::None
  67     }
  68 }
  69
  70 const BRACED_EXPR_MESSAGE: &str = "omit braces around single expression condition";
  71 const COMPLEX_BLOCK_MESSAGE: &str = "in an `if` condition, avoid complex blocks or closures with blocks; \
  72                                     instead, move the block or closure higher and bind it with a `let`";
  73
  74 impl<'tcx> LateLintPass<'tcx> for BlocksInIfConditions {
  75     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  76         if in_external_macro(cx.sess(), expr.span) {
  77             return;
  78         }
  79         if let Some((cond, _, _)) = higher::if_block(&expr) {
  80             if let ExprKind::Block(block, _) = &cond.kind {
  81                 if block.rules == BlockCheckMode::DefaultBlock {
  82                     if block.stmts.is_empty() {
  83                         if let Some(ex) = &block.expr {
  84                             // don't dig into the expression here, just suggest that they remove
  85                             // the block
  86                             if expr.span.from_expansion() || differing_macro_contexts(expr.span, ex.span) {
  87                                 return;
  88                             }
  89                             let mut applicability = Applicability::MachineApplicable;
  90                             span_lint_and_sugg(
  91                                 cx,
  92                                 BLOCKS_IN_IF_CONDITIONS,
  93                                 cond.span,
  94                                 BRACED_EXPR_MESSAGE,
  95                                 "try",
  96                                 format!(
  97                                     "{}",
  98                                     snippet_block_with_applicability(
  99                                         cx,
 100                                         ex.span,
 101                                         "..",
 102                                         Some(expr.span),
 103                                         &mut applicability
 104                                     )
 105                                 ),
 106                                 applicability,
 107                             );
 108                         }
 109                     } else {
 110                         let span = block.expr.as_ref().map_or_else(|| block.stmts[0].span, |e| e.span);
 111                         if span.from_expansion() || differing_macro_contexts(expr.span, span) {
 112                             return;
 113                         }
 114                         // move block higher
 115                         let mut applicability = Applicability::MachineApplicable;
 116                         span_lint_and_sugg(
 117                             cx,
 118                             BLOCKS_IN_IF_CONDITIONS,
 119                             expr.span.with_hi(cond.span.hi()),
 120                             COMPLEX_BLOCK_MESSAGE,
 121                             "try",
 122                             format!(
 123                                 "let res = {}; if res",
 124                                 snippet_block_with_applicability(
 125                                     cx,
 126                                     block.span,
 127                                     "..",
 128                                     Some(expr.span),
 129                                     &mut applicability
 130                                 ),
 131                             ),
 132                             applicability,
 133                         );
 134                     }
 135                 }
 136             } else {
 137                 let mut visitor = ExVisitor { found_block: None, cx };
 138                 walk_expr(&mut visitor, cond);
 139                 if let Some(block) = visitor.found_block {
 140                     span_lint(cx, BLOCKS_IN_IF_CONDITIONS, block.span, COMPLEX_BLOCK_MESSAGE);
 141                 }
 142             }
 143         }
 144     }
 145 }