clippy_lints/src/misc_early.rs

   1 use crate::utils::{
   2     constants, snippet, snippet_opt, span_help_and_lint, span_lint, span_lint_and_sugg, span_lint_and_then,
   3 };
   4 use if_chain::if_chain;
   5 use rustc::lint::{in_external_macro, EarlyContext, EarlyLintPass, LintArray, LintContext, LintPass};
   6 use rustc::{declare_lint_pass, declare_tool_lint};
   7 use rustc_data_structures::fx::FxHashMap;
   8 use rustc_errors::Applicability;
   9 use syntax::ast::*;
  10 use syntax::source_map::Span;
  11 use syntax::visit::{walk_expr, FnKind, Visitor};
  12
  13 declare_clippy_lint! {
  14     /// **What it does:** Checks for structure field patterns bound to wildcards.
  15     ///
  16     /// **Why is this bad?** Using `..` instead is shorter and leaves the focus on
  17     /// the fields that are actually bound.
  18     ///
  19     /// **Known problems:** None.
  20     ///
  21     /// **Example:**
  22     /// ```ignore
  23     /// let { a: _, b: ref b, c: _ } = ..
  24     /// ```
  25     pub UNNEEDED_FIELD_PATTERN,
  26     style,
  27     "struct fields bound to a wildcard instead of using `..`"
  28 }
  29
  30 declare_clippy_lint! {
  31     /// **What it does:** Checks for function arguments having the similar names
  32     /// differing by an underscore.
  33     ///
  34     /// **Why is this bad?** It affects code readability.
  35     ///
  36     /// **Known problems:** None.
  37     ///
  38     /// **Example:**
  39     /// ```rust
  40     /// fn foo(a: i32, _a: i32) {}
  41     /// ```
  42     pub DUPLICATE_UNDERSCORE_ARGUMENT,
  43     style,
  44     "function arguments having names which only differ by an underscore"
  45 }
  46
  47 declare_clippy_lint! {
  48     /// **What it does:** Detects closures called in the same expression where they
  49     /// are defined.
  50     ///
  51     /// **Why is this bad?** It is unnecessarily adding to the expression's
  52     /// complexity.
  53     ///
  54     /// **Known problems:** None.
  55     ///
  56     /// **Example:**
  57     /// ```rust,ignore
  58     /// (|| 42)()
  59     /// ```
  60     pub REDUNDANT_CLOSURE_CALL,
  61     complexity,
  62     "throwaway closures called in the expression they are defined"
  63 }
  64
  65 declare_clippy_lint! {
  66     /// **What it does:** Detects expressions of the form `--x`.
  67     ///
  68     /// **Why is this bad?** It can mislead C/C++ programmers to think `x` was
  69     /// decremented.
  70     ///
  71     /// **Known problems:** None.
  72     ///
  73     /// **Example:**
  74     /// ```rust
  75     /// let mut x = 3;
  76     /// --x;
  77     /// ```
  78     pub DOUBLE_NEG,
  79     style,
  80     "`--x`, which is a double negation of `x` and not a pre-decrement as in C/C++"
  81 }
  82
  83 declare_clippy_lint! {
  84     /// **What it does:** Warns on hexadecimal literals with mixed-case letter
  85     /// digits.
  86     ///
  87     /// **Why is this bad?** It looks confusing.
  88     ///
  89     /// **Known problems:** None.
  90     ///
  91     /// **Example:**
  92     /// ```rust
  93     /// let y = 0x1a9BAcD;
  94     /// ```
  95     pub MIXED_CASE_HEX_LITERALS,
  96     style,
  97     "hex literals whose letter digits are not consistently upper- or lowercased"
  98 }
  99
 100 declare_clippy_lint! {
 101     /// **What it does:** Warns if literal suffixes are not separated by an
 102     /// underscore.
 103     ///
 104     /// **Why is this bad?** It is much less readable.
 105     ///
 106     /// **Known problems:** None.
 107     ///
 108     /// **Example:**
 109     /// ```rust
 110     /// let y = 123832i32;
 111     /// ```
 112     pub UNSEPARATED_LITERAL_SUFFIX,
 113     pedantic,
 114     "literals whose suffix is not separated by an underscore"
 115 }
 116
 117 declare_clippy_lint! {
 118     /// **What it does:** Warns if an integral constant literal starts with `0`.
 119     ///
 120     /// **Why is this bad?** In some languages (including the infamous C language
 121     /// and most of its
 122     /// family), this marks an octal constant. In Rust however, this is a decimal
 123     /// constant. This could
 124     /// be confusing for both the writer and a reader of the constant.
 125     ///
 126     /// **Known problems:** None.
 127     ///
 128     /// **Example:**
 129     ///
 130     /// In Rust:
 131     /// ```rust
 132     /// fn main() {
 133     ///     let a = 0123;
 134     ///     println!("{}", a);
 135     /// }
 136     /// ```
 137     ///
 138     /// prints `123`, while in C:
 139     ///
 140     /// ```c
 141     /// #include <stdio.h>
 142     ///
 143     /// int main() {
 144     ///     int a = 0123;
 145     ///     printf("%d\n", a);
 146     /// }
 147     /// ```
 148     ///
 149     /// prints `83` (as `83 == 0o123` while `123 == 0o173`).
 150     pub ZERO_PREFIXED_LITERAL,
 151     complexity,
 152     "integer literals starting with `0`"
 153 }
 154
 155 declare_clippy_lint! {
 156     /// **What it does:** Warns if a generic shadows a built-in type.
 157     ///
 158     /// **Why is this bad?** This gives surprising type errors.
 159     ///
 160     /// **Known problems:** None.
 161     ///
 162     /// **Example:**
 163     ///
 164     /// ```ignore
 165     /// impl<u32> Foo<u32> {
 166     ///     fn impl_func(&self) -> u32 {
 167     ///         42
 168     ///     }
 169     /// }
 170     /// ```
 171     pub BUILTIN_TYPE_SHADOW,
 172     style,
 173     "shadowing a builtin type"
 174 }
 175
 176 declare_lint_pass!(MiscEarlyLints => [
 177     UNNEEDED_FIELD_PATTERN,
 178     DUPLICATE_UNDERSCORE_ARGUMENT,
 179     REDUNDANT_CLOSURE_CALL,
 180     DOUBLE_NEG,
 181     MIXED_CASE_HEX_LITERALS,
 182     UNSEPARATED_LITERAL_SUFFIX,
 183     ZERO_PREFIXED_LITERAL,
 184     BUILTIN_TYPE_SHADOW
 185 ]);
 186
 187 // Used to find `return` statements or equivalents e.g., `?`
 188 struct ReturnVisitor {
 189     found_return: bool,
 190 }
 191
 192 impl ReturnVisitor {
 193     fn new() -> Self {
 194         Self { found_return: false }
 195     }
 196 }
 197
 198 impl<'ast> Visitor<'ast> for ReturnVisitor {
 199     fn visit_expr(&mut self, ex: &'ast Expr) {
 200         if let ExprKind::Ret(_) = ex.node {
 201             self.found_return = true;
 202         } else if let ExprKind::Try(_) = ex.node {
 203             self.found_return = true;
 204         }
 205
 206         walk_expr(self, ex)
 207     }
 208 }
 209
 210 impl EarlyLintPass for MiscEarlyLints {
 211     fn check_generics(&mut self, cx: &EarlyContext<'_>, gen: &Generics) {
 212         for param in &gen.params {
 213             if let GenericParamKind::Type { .. } = param.kind {
 214                 let name = param.ident.as_str();
 215                 if constants::BUILTIN_TYPES.contains(&&*name) {
 216                     span_lint(
 217                         cx,
 218                         BUILTIN_TYPE_SHADOW,
 219                         param.ident.span,
 220                         &format!("This generic shadows the built-in type `{}`", name),
 221                     );
 222                 }
 223             }
 224         }
 225     }
 226
 227     fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &Pat) {
 228         if let PatKind::Struct(ref npat, ref pfields, _) = pat.node {
 229             let mut wilds = 0;
 230             let type_name = npat
 231                 .segments
 232                 .last()
 233                 .expect("A path must have at least one segment")
 234                 .ident
 235                 .name;
 236
 237             for field in pfields {
 238                 if let PatKind::Wild = field.pat.node {
 239                     wilds += 1;
 240                 }
 241             }
 242             if !pfields.is_empty() && wilds == pfields.len() {
 243                 span_help_and_lint(
 244                     cx,
 245                     UNNEEDED_FIELD_PATTERN,
 246                     pat.span,
 247                     "All the struct fields are matched to a wildcard pattern, consider using `..`.",
 248                     &format!("Try with `{} {{ .. }}` instead", type_name),
 249                 );
 250                 return;
 251             }
 252             if wilds > 0 {
 253                 let mut normal = vec![];
 254
 255                 for field in pfields {
 256                     match field.pat.node {
 257                         PatKind::Wild => {},
 258                         _ => {
 259                             if let Ok(n) = cx.sess().source_map().span_to_snippet(field.span) {
 260                                 normal.push(n);
 261                             }
 262                         },
 263                     }
 264                 }
 265                 for field in pfields {
 266                     if let PatKind::Wild = field.pat.node {
 267                         wilds -= 1;
 268                         if wilds > 0 {
 269                             span_lint(
 270                                 cx,
 271                                 UNNEEDED_FIELD_PATTERN,
 272                                 field.span,
 273                                 "You matched a field with a wildcard pattern. Consider using `..` instead",
 274                             );
 275                         } else {
 276                             span_help_and_lint(
 277                                 cx,
 278                                 UNNEEDED_FIELD_PATTERN,
 279                                 field.span,
 280                                 "You matched a field with a wildcard pattern. Consider using `..` \
 281                                  instead",
 282                                 &format!("Try with `{} {{ {}, .. }}`", type_name, normal[..].join(", ")),
 283                             );
 284                         }
 285                     }
 286                 }
 287             }
 288         }
 289     }
 290
 291     fn check_fn(&mut self, cx: &EarlyContext<'_>, _: FnKind<'_>, decl: &FnDecl, _: Span, _: NodeId) {
 292         let mut registered_names: FxHashMap<String, Span> = FxHashMap::default();
 293
 294         for arg in &decl.inputs {
 295             if let PatKind::Ident(_, ident, None) = arg.pat.node {
 296                 let arg_name = ident.to_string();
 297
 298                 if arg_name.starts_with('_') {
 299                     if let Some(correspondence) = registered_names.get(&arg_name[1..]) {
 300                         span_lint(
 301                             cx,
 302                             DUPLICATE_UNDERSCORE_ARGUMENT,
 303                             *correspondence,
 304                             &format!(
 305                                 "`{}` already exists, having another argument having almost the same \
 306                                  name makes code comprehension and documentation more difficult",
 307                                 arg_name[1..].to_owned()
 308                             ),
 309                         );
 310                     }
 311                 } else {
 312                     registered_names.insert(arg_name, arg.pat.span);
 313                 }
 314             }
 315         }
 316     }
 317
 318     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
 319         if in_external_macro(cx.sess(), expr.span) {
 320             return;
 321         }
 322         match expr.node {
 323             ExprKind::Call(ref paren, _) => {
 324                 if let ExprKind::Paren(ref closure) = paren.node {
 325                     if let ExprKind::Closure(_, _, _, ref decl, ref block, _) = closure.node {
 326                         let mut visitor = ReturnVisitor::new();
 327                         visitor.visit_expr(block);
 328                         if !visitor.found_return {
 329                             span_lint_and_then(
 330                                 cx,
 331                                 REDUNDANT_CLOSURE_CALL,
 332                                 expr.span,
 333                                 "Try not to call a closure in the expression where it is declared.",
 334                                 |db| {
 335                                     if decl.inputs.is_empty() {
 336                                         let hint = snippet(cx, block.span, "..").into_owned();
 337                                         db.span_suggestion(
 338                                             expr.span,
 339                                             "Try doing something like: ",
 340                                             hint,
 341                                             Applicability::MachineApplicable, // snippet
 342                                         );
 343                                     }
 344                                 },
 345                             );
 346                         }
 347                     }
 348                 }
 349             },
 350             ExprKind::Unary(UnOp::Neg, ref inner) => {
 351                 if let ExprKind::Unary(UnOp::Neg, _) = inner.node {
 352                     span_lint(
 353                         cx,
 354                         DOUBLE_NEG,
 355                         expr.span,
 356                         "`--x` could be misinterpreted as pre-decrement by C programmers, is usually a no-op",
 357                     );
 358                 }
 359             },
 360             ExprKind::Lit(ref lit) => self.check_lit(cx, lit),
 361             _ => (),
 362         }
 363     }
 364
 365     fn check_block(&mut self, cx: &EarlyContext<'_>, block: &Block) {
 366         for w in block.stmts.windows(2) {
 367             if_chain! {
 368                 if let StmtKind::Local(ref local) = w[0].node;
 369                 if let Option::Some(ref t) = local.init;
 370                 if let ExprKind::Closure(..) = t.node;
 371                 if let PatKind::Ident(_, ident, _) = local.pat.node;
 372                 if let StmtKind::Semi(ref second) = w[1].node;
 373                 if let ExprKind::Assign(_, ref call) = second.node;
 374                 if let ExprKind::Call(ref closure, _) = call.node;
 375                 if let ExprKind::Path(_, ref path) = closure.node;
 376                 then {
 377                     if ident == path.segments[0].ident {
 378                         span_lint(
 379                             cx,
 380                             REDUNDANT_CLOSURE_CALL,
 381                             second.span,
 382                             "Closure called just once immediately after it was declared",
 383                         );
 384                     }
 385                 }
 386             }
 387         }
 388     }
 389 }
 390
 391 impl MiscEarlyLints {
 392     fn check_lit(self, cx: &EarlyContext<'_>, lit: &Lit) {
 393         // The `line!()` macro is compiler built-in and a special case for these lints.
 394         let lit_snip = match snippet_opt(cx, lit.span) {
 395             Some(snip) => {
 396                 if snip.contains('!') {
 397                     return;
 398                 }
 399                 snip
 400             },
 401             _ => return,
 402         };
 403
 404         if let LitKind::Int(value, lit_int_type) = lit.node {
 405             let suffix = match lit_int_type {
 406                 LitIntType::Signed(ty) => ty.ty_to_string(),
 407                 LitIntType::Unsigned(ty) => ty.ty_to_string(),
 408                 LitIntType::Unsuffixed => "",
 409             };
 410
 411             let maybe_last_sep_idx = lit_snip.len() - suffix.len() - 1;
 412             // Do not lint when literal is unsuffixed.
 413             if !suffix.is_empty() && lit_snip.as_bytes()[maybe_last_sep_idx] != b'_' {
 414                 span_lint_and_sugg(
 415                     cx,
 416                     UNSEPARATED_LITERAL_SUFFIX,
 417                     lit.span,
 418                     "integer type suffix should be separated by an underscore",
 419                     "add an underscore",
 420                     format!("{}_{}", &lit_snip[..=maybe_last_sep_idx], suffix),
 421                     Applicability::MachineApplicable,
 422                 );
 423             }
 424
 425             if lit_snip.starts_with("0x") {
 426                 let mut seen = (false, false);
 427                 for ch in lit_snip.as_bytes()[2..=maybe_last_sep_idx].iter() {
 428                     match ch {
 429                         b'a'..=b'f' => seen.0 = true,
 430                         b'A'..=b'F' => seen.1 = true,
 431                         _ => {},
 432                     }
 433                     if seen.0 && seen.1 {
 434                         span_lint(
 435                             cx,
 436                             MIXED_CASE_HEX_LITERALS,
 437                             lit.span,
 438                             "inconsistent casing in hexadecimal literal",
 439                         );
 440                         break;
 441                     }
 442                 }
 443             } else if lit_snip.starts_with("0b") || lit_snip.starts_with("0o") {
 444                 /* nothing to do */
 445             } else if value != 0 && lit_snip.starts_with('0') {
 446                 span_lint_and_then(
 447                     cx,
 448                     ZERO_PREFIXED_LITERAL,
 449                     lit.span,
 450                     "this is a decimal constant",
 451                     |db| {
 452                         db.span_suggestion(
 453                             lit.span,
 454                             "if you mean to use a decimal constant, remove the `0` to avoid confusion",
 455                             lit_snip.trim_start_matches(|c| c == '_' || c == '0').to_string(),
 456                             Applicability::MaybeIncorrect,
 457                         );
 458                         db.span_suggestion(
 459                             lit.span,
 460                             "if you mean to use an octal constant, use `0o`",
 461                             format!("0o{}", lit_snip.trim_start_matches(|c| c == '_' || c == '0')),
 462                             Applicability::MaybeIncorrect,
 463                         );
 464                     },
 465                 );
 466             }
 467         } else if let LitKind::Float(_, float_ty) = lit.node {
 468             let suffix = float_ty.ty_to_string();
 469             let maybe_last_sep_idx = lit_snip.len() - suffix.len() - 1;
 470             if lit_snip.as_bytes()[maybe_last_sep_idx] != b'_' {
 471                 span_lint_and_sugg(
 472                     cx,
 473                     UNSEPARATED_LITERAL_SUFFIX,
 474                     lit.span,
 475                     "float type suffix should be separated by an underscore",
 476                     "add an underscore",
 477                     format!("{}_{}", &lit_snip[..=maybe_last_sep_idx], suffix),
 478                     Applicability::MachineApplicable,
 479                 );
 480             }
 481         }
 482     }
 483 }