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