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;
   5 use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
   6 use rustc_hir::*;
   7 use rustc_lint::{LateContext, LateLintPass, LintContext};
   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     /// ```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((check, then, _)) = higher::if_block(&expr) {
  83             if let ExprKind::Block(block, _) = &check.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                             span_help_and_lint(
  93                                 cx,
  94                                 BLOCK_IN_IF_CONDITION_EXPR,
  95                                 check.span,
  96                                 BRACED_EXPR_MESSAGE,
  97                                 &format!(
  98                                     "try\nif {} {} ... ",
  99                                     snippet_block(cx, ex.span, ".."),
 100                                     snippet_block(cx, then.span, "..")
 101                                 ),
 102                             );
 103                         }
 104                     } else {
 105                         let span = block.expr.as_ref().map_or_else(|| block.stmts[0].span, |e| e.span);
 106                         if span.from_expansion() || differing_macro_contexts(expr.span, span) {
 107                             return;
 108                         }
 109                         // move block higher
 110                         span_help_and_lint(
 111                             cx,
 112                             BLOCK_IN_IF_CONDITION_STMT,
 113                             check.span,
 114                             COMPLEX_BLOCK_MESSAGE,
 115                             &format!(
 116                                 "try\nlet res = {};\nif res {} ... ",
 117                                 snippet_block(cx, block.span, ".."),
 118                                 snippet_block(cx, then.span, "..")
 119                             ),
 120                         );
 121                     }
 122                 }
 123             } else {
 124                 let mut visitor = ExVisitor { found_block: None, cx };
 125                 walk_expr(&mut visitor, check);
 126                 if let Some(block) = visitor.found_block {
 127                     span_lint(cx, BLOCK_IN_IF_CONDITION_STMT, block.span, COMPLEX_BLOCK_MESSAGE);
 128                 }
 129             }
 130         }
 131     }
 132 }