clippy_lints/src/misc_early.rs

   1 use rustc::lint::*;
   2 use std::collections::HashMap;
   3 use syntax::ast::*;
   4 use syntax::codemap::Span;
   5 use syntax::visit::FnKind;
   6 use utils::{span_lint, span_help_and_lint, snippet, span_lint_and_then};
   7 /// **What it does:** This lint checks for structure field patterns bound to wildcards.
   8 ///
   9 /// **Why is this bad?** Using `..` instead is shorter and leaves the focus on the fields that are actually bound.
  10 ///
  11 /// **Known problems:** None.
  12 ///
  13 /// **Example:** `let { a: _, b: ref b, c: _ } = ..`
  14 declare_lint! {
  15     pub UNNEEDED_FIELD_PATTERN, Warn,
  16     "Struct fields are bound to a wildcard instead of using `..`"
  17 }
  18
  19 /// **What it does:** This lint checks for function arguments having the similar names differing by an underscore
  20 ///
  21 /// **Why is this bad?** It affects code readability
  22 ///
  23 /// **Known problems:** None.
  24 ///
  25 /// **Example:** `fn foo(a: i32, _a: i32) {}`
  26 declare_lint! {
  27     pub DUPLICATE_UNDERSCORE_ARGUMENT, Warn,
  28     "Function arguments having names which only differ by an underscore"
  29 }
  30
  31 /// **What it does:** This lint detects closures called in the same expression where they are defined.
  32 ///
  33 /// **Why is this bad?** It is unnecessarily adding to the expression's complexity.
  34 ///
  35 /// **Known problems:** None.
  36 ///
  37 /// **Example:** `(|| 42)()`
  38 declare_lint! {
  39     pub REDUNDANT_CLOSURE_CALL, Warn,
  40     "Closures should not be called in the expression they are defined"
  41 }
  42
  43 /// **What it does:** This lint detects expressions of the form `--x`
  44 ///
  45 /// **Why is this bad?** It can mislead C/C++ programmers to think `x` was decremented.
  46 ///
  47 /// **Known problems:** None.
  48 ///
  49 /// **Example:** `--x;`
  50 declare_lint! {
  51     pub DOUBLE_NEG, Warn,
  52     "`--x` is a double negation of `x` and not a pre-decrement as in C or C++"
  53 }
  54
  55
  56 #[derive(Copy, Clone)]
  57 pub struct MiscEarly;
  58
  59 impl LintPass for MiscEarly {
  60     fn get_lints(&self) -> LintArray {
  61         lint_array!(UNNEEDED_FIELD_PATTERN, DUPLICATE_UNDERSCORE_ARGUMENT, REDUNDANT_CLOSURE_CALL, DOUBLE_NEG)
  62     }
  63 }
  64
  65 impl EarlyLintPass for MiscEarly {
  66     fn check_pat(&mut self, cx: &EarlyContext, pat: &Pat) {
  67         if let PatKind::Struct(ref npat, ref pfields, _) = pat.node {
  68             let mut wilds = 0;
  69             let type_name = npat.segments.last().expect("A path must have at least one segment").identifier.name;
  70
  71             for field in pfields {
  72                 if field.node.pat.node == PatKind::Wild {
  73                     wilds += 1;
  74                 }
  75             }
  76             if !pfields.is_empty() && wilds == pfields.len() {
  77                 span_help_and_lint(cx,
  78                                    UNNEEDED_FIELD_PATTERN,
  79                                    pat.span,
  80                                    "All the struct fields are matched to a wildcard pattern, consider using `..`.",
  81                                    &format!("Try with `{} {{ .. }}` instead", type_name));
  82                 return;
  83             }
  84             if wilds > 0 {
  85                 let mut normal = vec![];
  86
  87                 for field in pfields {
  88                     if field.node.pat.node != PatKind::Wild {
  89                         if let Ok(n) = cx.sess().codemap().span_to_snippet(field.span) {
  90                             normal.push(n);
  91                         }
  92                     }
  93                 }
  94                 for field in pfields {
  95                     if field.node.pat.node == PatKind::Wild {
  96                         wilds -= 1;
  97                         if wilds > 0 {
  98                             span_lint(cx,
  99                                       UNNEEDED_FIELD_PATTERN,
 100                                       field.span,
 101                                       "You matched a field with a wildcard pattern. Consider using `..` instead");
 102                         } else {
 103                             span_help_and_lint(cx,
 104                                                UNNEEDED_FIELD_PATTERN,
 105                                                field.span,
 106                                                "You matched a field with a wildcard pattern. Consider using `..` \
 107                                                 instead",
 108                                                &format!("Try with `{} {{ {}, .. }}`",
 109                                                         type_name,
 110                                                         normal[..].join(", ")));
 111                         }
 112                     }
 113                 }
 114             }
 115         }
 116     }
 117
 118     fn check_fn(&mut self, cx: &EarlyContext, _: FnKind, decl: &FnDecl, _: &Block, _: Span, _: NodeId) {
 119         let mut registered_names: HashMap<String, Span> = HashMap::new();
 120
 121         for ref arg in &decl.inputs {
 122             if let PatKind::Ident(_, sp_ident, None) = arg.pat.node {
 123                 let arg_name = sp_ident.node.to_string();
 124
 125                 if arg_name.starts_with('_') {
 126                     if let Some(correspondence) = registered_names.get(&arg_name[1..]) {
 127                         span_lint(cx,
 128                                   DUPLICATE_UNDERSCORE_ARGUMENT,
 129                                   *correspondence,
 130                                   &format!("`{}` already exists, having another argument having almost the same \
 131                                             name makes code comprehension and documentation more difficult",
 132                                            arg_name[1..].to_owned()));;
 133                     }
 134                 } else {
 135                     registered_names.insert(arg_name, arg.pat.span);
 136                 }
 137             }
 138         }
 139     }
 140
 141     fn check_expr(&mut self, cx: &EarlyContext, expr: &Expr) {
 142         match expr.node {
 143             ExprKind::Call(ref paren, _) => {
 144                 if let ExprKind::Paren(ref closure) = paren.node {
 145                     if let ExprKind::Closure(_, ref decl, ref block, _) = closure.node {
 146                         span_lint_and_then(cx,
 147                                            REDUNDANT_CLOSURE_CALL,
 148                                            expr.span,
 149                                            "Try not to call a closure in the expression where it is declared.",
 150                                            |db| {
 151                                                if decl.inputs.is_empty() {
 152                                                    let hint = format!("{}", snippet(cx, block.span, ".."));
 153                                                    db.span_suggestion(expr.span, "Try doing something like: ", hint);
 154                                                }
 155                                            });
 156                     }
 157                 }
 158             }
 159             ExprKind::Unary(UnOp::Neg, ref inner) => {
 160                 if let ExprKind::Unary(UnOp::Neg, _) = inner.node {
 161                     span_lint(cx,
 162                               DOUBLE_NEG,
 163                               expr.span,
 164                               "`--x` could be misinterpreted as pre-decrement by C programmers, is usually a no-op");
 165     }
 166             }
 167             _ => ()
 168         }
 169     }
 170
 171     fn check_block(&mut self, cx: &EarlyContext, block: &Block) {
 172         for w in block.stmts.windows(2) {
 173             if_let_chain! {[
 174                 let StmtKind::Local(ref local) = w[0].node,
 175                 let Option::Some(ref t) = local.init,
 176                 let ExprKind::Closure(_, _, _, _) = t.node,
 177                 let PatKind::Ident(_, sp_ident, _) = local.pat.node,
 178                 let StmtKind::Semi(ref second) = w[1].node,
 179                 let ExprKind::Assign(_, ref call) = second.node,
 180                 let ExprKind::Call(ref closure, _) = call.node,
 181                 let ExprKind::Path(_, ref path) = closure.node
 182             ], {
 183                 if sp_ident.node == (&path.segments[0]).identifier {
 184                     span_lint(cx, REDUNDANT_CLOSURE_CALL, second.span, "Closure called just once immediately after it was declared");
 185                 }
 186             }}
 187         }
 188     }
 189 }