clippy_lints/src/misc_early.rs

   1 use crate::utils::{constants, snippet, snippet_opt, span_help_and_lint, span_lint, span_lint_and_then};
   2 use if_chain::if_chain;
   3 use rustc::lint::{in_external_macro, EarlyContext, EarlyLintPass, LintArray, LintContext, LintPass};
   4 use rustc::{declare_tool_lint, lint_array};
   5 use rustc_data_structures::fx::FxHashMap;
   6 use rustc_errors::Applicability;
   7 use std::char;
   8 use syntax::ast::*;
   9 use syntax::source_map::Span;
  10 use syntax::visit::{walk_expr, FnKind, Visitor};
  11
  12 declare_clippy_lint! {
  13     /// **What it does:** Checks for structure field patterns bound to wildcards.
  14     ///
  15     /// **Why is this bad?** Using `..` instead is shorter and leaves the focus on
  16     /// the fields that are actually bound.
  17     ///
  18     /// **Known problems:** None.
  19     ///
  20     /// **Example:**
  21     /// ```ignore
  22     /// let { a: _, b: ref b, c: _ } = ..
  23     /// ```
  24     pub UNNEEDED_FIELD_PATTERN,
  25     style,
  26     "struct fields bound to a wildcard instead of using `..`"
  27 }
  28
  29 declare_clippy_lint! {
  30     /// **What it does:** Checks for function arguments having the similar names
  31     /// differing by an underscore.
  32     ///
  33     /// **Why is this bad?** It affects code readability.
  34     ///
  35     /// **Known problems:** None.
  36     ///
  37     /// **Example:**
  38     /// ```rust
  39     /// fn foo(a: i32, _a: i32) {}
  40     /// ```
  41     pub DUPLICATE_UNDERSCORE_ARGUMENT,
  42     style,
  43     "function arguments having names which only differ by an underscore"
  44 }
  45
  46 declare_clippy_lint! {
  47     /// **What it does:** Detects closures called in the same expression where they
  48     /// are defined.
  49     ///
  50     /// **Why is this bad?** It is unnecessarily adding to the expression's
  51     /// complexity.
  52     ///
  53     /// **Known problems:** None.
  54     ///
  55     /// **Example:**
  56     /// ```rust
  57     /// (|| 42)()
  58     /// ```
  59     pub REDUNDANT_CLOSURE_CALL,
  60     complexity,
  61     "throwaway closures called in the expression they are defined"
  62 }
  63
  64 declare_clippy_lint! {
  65     /// **What it does:** Detects expressions of the form `--x`.
  66     ///
  67     /// **Why is this bad?** It can mislead C/C++ programmers to think `x` was
  68     /// decremented.
  69     ///
  70     /// **Known problems:** None.
  71     ///
  72     /// **Example:**
  73     /// ```rust
  74     /// let mut x = 3;
  75     /// --x;
  76     /// ```
  77     pub DOUBLE_NEG,
  78     style,
  79     "`--x`, which is a double negation of `x` and not a pre-decrement as in C/C++"
  80 }
  81
  82 declare_clippy_lint! {
  83     /// **What it does:** Warns on hexadecimal literals with mixed-case letter
  84     /// digits.
  85     ///
  86     /// **Why is this bad?** It looks confusing.
  87     ///
  88     /// **Known problems:** None.
  89     ///
  90     /// **Example:**
  91     /// ```rust
  92     /// let y = 0x1a9BAcD;
  93     /// ```
  94     pub MIXED_CASE_HEX_LITERALS,
  95     style,
  96     "hex literals whose letter digits are not consistently upper- or lowercased"
  97 }
  98
  99 declare_clippy_lint! {
 100     /// **What it does:** Warns if literal suffixes are not separated by an
 101     /// underscore.
 102     ///
 103     /// **Why is this bad?** It is much less readable.
 104     ///
 105     /// **Known problems:** None.
 106     ///
 107     /// **Example:**
 108     /// ```rust
 109     /// let y = 123832i32;
 110     /// ```
 111     pub UNSEPARATED_LITERAL_SUFFIX,
 112     pedantic,
 113     "literals whose suffix is not separated by an underscore"
 114 }
 115
 116 declare_clippy_lint! {
 117     /// **What it does:** Warns if an integral constant literal starts with `0`.
 118     ///
 119     /// **Why is this bad?** In some languages (including the infamous C language
 120     /// and most of its
 121     /// family), this marks an octal constant. In Rust however, this is a decimal
 122     /// constant. This could
 123     /// be confusing for both the writer and a reader of the constant.
 124     ///
 125     /// **Known problems:** None.
 126     ///
 127     /// **Example:**
 128     ///
 129     /// In Rust:
 130     /// ```rust
 131     /// fn main() {
 132     ///     let a = 0123;
 133     ///     println!("{}", a);
 134     /// }
 135     /// ```
 136     ///
 137     /// prints `123`, while in C:
 138     ///
 139     /// ```c
 140     /// #include <stdio.h>
 141     ///
 142     /// int main() {
 143     ///     int a = 0123;
 144     ///     printf("%d\n", a);
 145     /// }
 146     /// ```
 147     ///
 148     /// prints `83` (as `83 == 0o123` while `123 == 0o173`).
 149     pub ZERO_PREFIXED_LITERAL,
 150     complexity,
 151     "integer literals starting with `0`"
 152 }
 153
 154 declare_clippy_lint! {
 155     /// **What it does:** Warns if a generic shadows a built-in type.
 156     ///
 157     /// **Why is this bad?** This gives surprising type errors.
 158     ///
 159     /// **Known problems:** None.
 160     ///
 161     /// **Example:**
 162     ///
 163     /// ```ignore
 164     /// impl<u32> Foo<u32> {
 165     ///     fn impl_func(&self) -> u32 {
 166     ///         42
 167     ///     }
 168     /// }
 169     /// ```
 170     pub BUILTIN_TYPE_SHADOW,
 171     style,
 172     "shadowing a builtin type"
 173 }
 174
 175 #[derive(Copy, Clone)]
 176 pub struct MiscEarly;
 177
 178 impl LintPass for MiscEarly {
 179     fn get_lints(&self) -> LintArray {
 180         lint_array!(
 181             UNNEEDED_FIELD_PATTERN,
 182             DUPLICATE_UNDERSCORE_ARGUMENT,
 183             REDUNDANT_CLOSURE_CALL,
 184             DOUBLE_NEG,
 185             MIXED_CASE_HEX_LITERALS,
 186             UNSEPARATED_LITERAL_SUFFIX,
 187             ZERO_PREFIXED_LITERAL,
 188             BUILTIN_TYPE_SHADOW
 189         )
 190     }
 191
 192     fn name(&self) -> &'static str {
 193         "MiscEarlyLints"
 194     }
 195 }
 196
 197 // Used to find `return` statements or equivalents e.g. `?`
 198 struct ReturnVisitor {
 199     found_return: bool,
 200 }
 201
 202 impl ReturnVisitor {
 203     fn new() -> Self {
 204         Self { found_return: false }
 205     }
 206 }
 207
 208 impl<'ast> Visitor<'ast> for ReturnVisitor {
 209     fn visit_expr(&mut self, ex: &'ast Expr) {
 210         if let ExprKind::Ret(_) = ex.node {
 211             self.found_return = true;
 212         } else if let ExprKind::Try(_) = ex.node {
 213             self.found_return = true;
 214         }
 215
 216         walk_expr(self, ex)
 217     }
 218 }
 219
 220 impl EarlyLintPass for MiscEarly {
 221     fn check_generics(&mut self, cx: &EarlyContext<'_>, gen: &Generics) {
 222         for param in &gen.params {
 223             if let GenericParamKind::Type { .. } = param.kind {
 224                 let name = param.ident.as_str();
 225                 if constants::BUILTIN_TYPES.contains(&&*name) {
 226                     span_lint(
 227                         cx,
 228                         BUILTIN_TYPE_SHADOW,
 229                         param.ident.span,
 230                         &format!("This generic shadows the built-in type `{}`", name),
 231                     );
 232                 }
 233             }
 234         }
 235     }
 236
 237     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &Pat, _: &mut bool) {
 238         if let PatKind::Struct(ref npat, ref pfields, _) = pat.node {
 239             let mut wilds = 0;
 240             let type_name = npat
 241                 .segments
 242                 .last()
 243                 .expect("A path must have at least one segment")
 244                 .ident
 245                 .name;
 246
 247             for field in pfields {
 248                 if let PatKind::Wild = field.node.pat.node {
 249                     wilds += 1;
 250                 }
 251             }
 252             if !pfields.is_empty() && wilds == pfields.len() {
 253                 span_help_and_lint(
 254                     cx,
 255                     UNNEEDED_FIELD_PATTERN,
 256                     pat.span,
 257                     "All the struct fields are matched to a wildcard pattern, consider using `..`.",
 258                     &format!("Try with `{} {{ .. }}` instead", type_name),
 259                 );
 260                 return;
 261             }
 262             if wilds > 0 {
 263                 let mut normal = vec![];
 264
 265                 for field in pfields {
 266                     match field.node.pat.node {
 267                         PatKind::Wild => {},
 268                         _ => {
 269                             if let Ok(n) = cx.sess().source_map().span_to_snippet(field.span) {
 270                                 normal.push(n);
 271                             }
 272                         },
 273                     }
 274                 }
 275                 for field in pfields {
 276                     if let PatKind::Wild = field.node.pat.node {
 277                         wilds -= 1;
 278                         if wilds > 0 {
 279                             span_lint(
 280                                 cx,
 281                                 UNNEEDED_FIELD_PATTERN,
 282                                 field.span,
 283                                 "You matched a field with a wildcard pattern. Consider using `..` instead",
 284                             );
 285                         } else {
 286                             span_help_and_lint(
 287                                 cx,
 288                                 UNNEEDED_FIELD_PATTERN,
 289                                 field.span,
 290                                 "You matched a field with a wildcard pattern. Consider using `..` \
 291                                  instead",
 292                                 &format!("Try with `{} {{ {}, .. }}`", type_name, normal[..].join(", ")),
 293                             );
 294                         }
 295                     }
 296                 }
 297             }
 298         }
 299     }
 300
 301     fn check_fn(&mut self, cx: &EarlyContext<'_>, _: FnKind<'_>, decl: &FnDecl, _: Span, _: NodeId) {
 302         let mut registered_names: FxHashMap<String, Span> = FxHashMap::default();
 303
 304         for arg in &decl.inputs {
 305             if let PatKind::Ident(_, ident, None) = arg.pat.node {
 306                 let arg_name = ident.to_string();
 307
 308                 if arg_name.starts_with('_') {
 309                     if let Some(correspondence) = registered_names.get(&arg_name[1..]) {
 310                         span_lint(
 311                             cx,
 312                             DUPLICATE_UNDERSCORE_ARGUMENT,
 313                             *correspondence,
 314                             &format!(
 315                                 "`{}` already exists, having another argument having almost the same \
 316                                  name makes code comprehension and documentation more difficult",
 317                                 arg_name[1..].to_owned()
 318                             ),
 319                         );;
 320                     }
 321                 } else {
 322                     registered_names.insert(arg_name, arg.pat.span);
 323                 }
 324             }
 325         }
 326     }
 327
 328     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
 329         if in_external_macro(cx.sess(), expr.span) {
 330             return;
 331         }
 332         match expr.node {
 333             ExprKind::Call(ref paren, _) => {
 334                 if let ExprKind::Paren(ref closure) = paren.node {
 335                     if let ExprKind::Closure(_, _, _, ref decl, ref block, _) = closure.node {
 336                         let mut visitor = ReturnVisitor::new();
 337                         visitor.visit_expr(block);
 338                         if !visitor.found_return {
 339                             span_lint_and_then(
 340                                 cx,
 341                                 REDUNDANT_CLOSURE_CALL,
 342                                 expr.span,
 343                                 "Try not to call a closure in the expression where it is declared.",
 344                                 |db| {
 345                                     if decl.inputs.is_empty() {
 346                                         let hint = snippet(cx, block.span, "..").into_owned();
 347                                         db.span_suggestion(
 348                                             expr.span,
 349                                             "Try doing something like: ",
 350                                             hint,
 351                                             Applicability::MachineApplicable, // snippet
 352                                         );
 353                                     }
 354                                 },
 355                             );
 356                         }
 357                     }
 358                 }
 359             },
 360             ExprKind::Unary(UnOp::Neg, ref inner) => {
 361                 if let ExprKind::Unary(UnOp::Neg, _) = inner.node {
 362                     span_lint(
 363                         cx,
 364                         DOUBLE_NEG,
 365                         expr.span,
 366                         "`--x` could be misinterpreted as pre-decrement by C programmers, is usually a no-op",
 367                     );
 368                 }
 369             },
 370             ExprKind::Lit(ref lit) => self.check_lit(cx, lit),
 371             _ => (),
 372         }
 373     }
 374
 375     fn check_block(&mut self, cx: &EarlyContext<'_>, block: &Block) {
 376         for w in block.stmts.windows(2) {
 377             if_chain! {
 378                 if let StmtKind::Local(ref local) = w[0].node;
 379                 if let Option::Some(ref t) = local.init;
 380                 if let ExprKind::Closure(..) = t.node;
 381                 if let PatKind::Ident(_, ident, _) = local.pat.node;
 382                 if let StmtKind::Semi(ref second) = w[1].node;
 383                 if let ExprKind::Assign(_, ref call) = second.node;
 384                 if let ExprKind::Call(ref closure, _) = call.node;
 385                 if let ExprKind::Path(_, ref path) = closure.node;
 386                 then {
 387                     if ident == path.segments[0].ident {
 388                         span_lint(
 389                             cx,
 390                             REDUNDANT_CLOSURE_CALL,
 391                             second.span,
 392                             "Closure called just once immediately after it was declared",
 393                         );
 394                     }
 395                 }
 396             }
 397         }
 398     }
 399 }
 400
 401 impl MiscEarly {
 402     fn check_lit(self, cx: &EarlyContext<'_>, lit: &Lit) {
 403         if_chain! {
 404             if let LitKind::Int(value, ..) = lit.node;
 405             if let Some(src) = snippet_opt(cx, lit.span);
 406             if let Some(firstch) = src.chars().next();
 407             if char::to_digit(firstch, 10).is_some();
 408             then {
 409                 let mut prev = '\0';
 410                 for ch in src.chars() {
 411                     if ch == 'i' || ch == 'u' {
 412                         if prev != '_' {
 413                             span_lint(cx, UNSEPARATED_LITERAL_SUFFIX, lit.span,
 414                                         "integer type suffix should be separated by an underscore");
 415                         }
 416                         break;
 417                     }
 418                     prev = ch;
 419                 }
 420                 if src.starts_with("0x") {
 421                     let mut seen = (false, false);
 422                     for ch in src.chars() {
 423                         match ch {
 424                             'a' ..= 'f' => seen.0 = true,
 425                             'A' ..= 'F' => seen.1 = true,
 426                             'i' | 'u'   => break,   // start of suffix already
 427                             _ => ()
 428                         }
 429                     }
 430                     if seen.0 && seen.1 {
 431                         span_lint(cx, MIXED_CASE_HEX_LITERALS, lit.span,
 432                                     "inconsistent casing in hexadecimal literal");
 433                     }
 434                 } else if src.starts_with("0b") || src.starts_with("0o") {
 435                     /* nothing to do */
 436                 } else if value != 0 && src.starts_with('0') {
 437                     span_lint_and_then(cx,
 438                                         ZERO_PREFIXED_LITERAL,
 439                                         lit.span,
 440                                         "this is a decimal constant",
 441                                         |db| {
 442                         db.span_suggestion(
 443                             lit.span,
 444                             "if you mean to use a decimal constant, remove the `0` to remove confusion",
 445                             src.trim_start_matches(|c| c == '_' || c == '0').to_string(),
 446                             Applicability::MaybeIncorrect,
 447                         );
 448                         db.span_suggestion(
 449                             lit.span,
 450                             "if you mean to use an octal constant, use `0o`",
 451                             format!("0o{}", src.trim_start_matches(|c| c == '_' || c == '0')),
 452                             Applicability::MaybeIncorrect,
 453                         );
 454                     });
 455                 }
 456             }
 457         }
 458         if_chain! {
 459             if let LitKind::Float(..) = lit.node;
 460             if let Some(src) = snippet_opt(cx, lit.span);
 461             if let Some(firstch) = src.chars().next();
 462             if char::to_digit(firstch, 10).is_some();
 463             then {
 464                 let mut prev = '\0';
 465                 for ch in src.chars() {
 466                     if ch == 'f' {
 467                         if prev != '_' {
 468                             span_lint(cx, UNSEPARATED_LITERAL_SUFFIX, lit.span,
 469                                         "float type suffix should be separated by an underscore");
 470                         }
 471                         break;
 472                     }
 473                     prev = ch;
 474                 }
 475             }
 476         }
 477     }
 478 }