clippy_lints/src/block_in_if_condition.rs

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