src/tools/clippy/clippy_lints/src/functions/mod.rs

   1 mod must_use;
   2 mod not_unsafe_ptr_arg_deref;
   3 mod result_unit_err;
   4 mod too_many_arguments;
   5 mod too_many_lines;
   6
   7 use rustc_hir as hir;
   8 use rustc_hir::intravisit;
   9 use rustc_lint::{LateContext, LateLintPass};
  10 use rustc_session::{declare_tool_lint, impl_lint_pass};
  11 use rustc_span::Span;
  12
  13 declare_clippy_lint! {
  14     /// ### What it does
  15     /// Checks for functions with too many parameters.
  16     ///
  17     /// ### Why is this bad?
  18     /// Functions with lots of parameters are considered bad
  19     /// style and reduce readability (“what does the 5th parameter mean?”). Consider
  20     /// grouping some parameters into a new type.
  21     ///
  22     /// ### Example
  23     /// ```rust
  24     /// # struct Color;
  25     /// fn foo(x: u32, y: u32, name: &str, c: Color, w: f32, h: f32, a: f32, b: f32) {
  26     ///     // ..
  27     /// }
  28     /// ```
  29     #[clippy::version = "pre 1.29.0"]
  30     pub TOO_MANY_ARGUMENTS,
  31     complexity,
  32     "functions with too many arguments"
  33 }
  34
  35 declare_clippy_lint! {
  36     /// ### What it does
  37     /// Checks for functions with a large amount of lines.
  38     ///
  39     /// ### Why is this bad?
  40     /// Functions with a lot of lines are harder to understand
  41     /// due to having to look at a larger amount of code to understand what the
  42     /// function is doing. Consider splitting the body of the function into
  43     /// multiple functions.
  44     ///
  45     /// ### Example
  46     /// ```rust
  47     /// fn im_too_long() {
  48     ///     println!("");
  49     ///     // ... 100 more LoC
  50     ///     println!("");
  51     /// }
  52     /// ```
  53     #[clippy::version = "1.34.0"]
  54     pub TOO_MANY_LINES,
  55     pedantic,
  56     "functions with too many lines"
  57 }
  58
  59 declare_clippy_lint! {
  60     /// ### What it does
  61     /// Checks for public functions that dereference raw pointer
  62     /// arguments but are not marked `unsafe`.
  63     ///
  64     /// ### Why is this bad?
  65     /// The function should probably be marked `unsafe`, since
  66     /// for an arbitrary raw pointer, there is no way of telling for sure if it is
  67     /// valid.
  68     ///
  69     /// ### Known problems
  70     /// * It does not check functions recursively so if the pointer is passed to a
  71     /// private non-`unsafe` function which does the dereferencing, the lint won't
  72     /// trigger.
  73     /// * It only checks for arguments whose type are raw pointers, not raw pointers
  74     /// got from an argument in some other way (`fn foo(bar: &[*const u8])` or
  75     /// `some_argument.get_raw_ptr()`).
  76     ///
  77     /// ### Example
  78     /// ```rust,ignore
  79     /// // Bad
  80     /// pub fn foo(x: *const u8) {
  81     ///     println!("{}", unsafe { *x });
  82     /// }
  83     ///
  84     /// // Good
  85     /// pub unsafe fn foo(x: *const u8) {
  86     ///     println!("{}", unsafe { *x });
  87     /// }
  88     /// ```
  89     #[clippy::version = "pre 1.29.0"]
  90     pub NOT_UNSAFE_PTR_ARG_DEREF,
  91     correctness,
  92     "public functions dereferencing raw pointer arguments but not marked `unsafe`"
  93 }
  94
  95 declare_clippy_lint! {
  96     /// ### What it does
  97     /// Checks for a `#[must_use]` attribute on
  98     /// unit-returning functions and methods.
  99     ///
 100     /// ### Why is this bad?
 101     /// Unit values are useless. The attribute is likely
 102     /// a remnant of a refactoring that removed the return type.
 103     ///
 104     /// ### Examples
 105     /// ```rust
 106     /// #[must_use]
 107     /// fn useless() { }
 108     /// ```
 109     #[clippy::version = "1.40.0"]
 110     pub MUST_USE_UNIT,
 111     style,
 112     "`#[must_use]` attribute on a unit-returning function / method"
 113 }
 114
 115 declare_clippy_lint! {
 116     /// ### What it does
 117     /// Checks for a `#[must_use]` attribute without
 118     /// further information on functions and methods that return a type already
 119     /// marked as `#[must_use]`.
 120     ///
 121     /// ### Why is this bad?
 122     /// The attribute isn't needed. Not using the result
 123     /// will already be reported. Alternatively, one can add some text to the
 124     /// attribute to improve the lint message.
 125     ///
 126     /// ### Examples
 127     /// ```rust
 128     /// #[must_use]
 129     /// fn double_must_use() -> Result<(), ()> {
 130     ///     unimplemented!();
 131     /// }
 132     /// ```
 133     #[clippy::version = "1.40.0"]
 134     pub DOUBLE_MUST_USE,
 135     style,
 136     "`#[must_use]` attribute on a `#[must_use]`-returning function / method"
 137 }
 138
 139 declare_clippy_lint! {
 140     /// ### What it does
 141     /// Checks for public functions that have no
 142     /// `#[must_use]` attribute, but return something not already marked
 143     /// must-use, have no mutable arg and mutate no statics.
 144     ///
 145     /// ### Why is this bad?
 146     /// Not bad at all, this lint just shows places where
 147     /// you could add the attribute.
 148     ///
 149     /// ### Known problems
 150     /// The lint only checks the arguments for mutable
 151     /// types without looking if they are actually changed. On the other hand,
 152     /// it also ignores a broad range of potentially interesting side effects,
 153     /// because we cannot decide whether the programmer intends the function to
 154     /// be called for the side effect or the result. Expect many false
 155     /// positives. At least we don't lint if the result type is unit or already
 156     /// `#[must_use]`.
 157     ///
 158     /// ### Examples
 159     /// ```rust
 160     /// // this could be annotated with `#[must_use]`.
 161     /// fn id<T>(t: T) -> T { t }
 162     /// ```
 163     #[clippy::version = "1.40.0"]
 164     pub MUST_USE_CANDIDATE,
 165     pedantic,
 166     "function or method that could take a `#[must_use]` attribute"
 167 }
 168
 169 declare_clippy_lint! {
 170     /// ### What it does
 171     /// Checks for public functions that return a `Result`
 172     /// with an `Err` type of `()`. It suggests using a custom type that
 173     /// implements `std::error::Error`.
 174     ///
 175     /// ### Why is this bad?
 176     /// Unit does not implement `Error` and carries no
 177     /// further information about what went wrong.
 178     ///
 179     /// ### Known problems
 180     /// Of course, this lint assumes that `Result` is used
 181     /// for a fallible operation (which is after all the intended use). However
 182     /// code may opt to (mis)use it as a basic two-variant-enum. In that case,
 183     /// the suggestion is misguided, and the code should use a custom enum
 184     /// instead.
 185     ///
 186     /// ### Examples
 187     /// ```rust
 188     /// pub fn read_u8() -> Result<u8, ()> { Err(()) }
 189     /// ```
 190     /// should become
 191     /// ```rust,should_panic
 192     /// use std::fmt;
 193     ///
 194     /// #[derive(Debug)]
 195     /// pub struct EndOfStream;
 196     ///
 197     /// impl fmt::Display for EndOfStream {
 198     ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 199     ///         write!(f, "End of Stream")
 200     ///     }
 201     /// }
 202     ///
 203     /// impl std::error::Error for EndOfStream { }
 204     ///
 205     /// pub fn read_u8() -> Result<u8, EndOfStream> { Err(EndOfStream) }
 206     ///# fn main() {
 207     ///#     read_u8().unwrap();
 208     ///# }
 209     /// ```
 210     ///
 211     /// Note that there are crates that simplify creating the error type, e.g.
 212     /// [`thiserror`](https://docs.rs/thiserror).
 213     #[clippy::version = "1.49.0"]
 214     pub RESULT_UNIT_ERR,
 215     style,
 216     "public function returning `Result` with an `Err` type of `()`"
 217 }
 218
 219 #[derive(Copy, Clone)]
 220 pub struct Functions {
 221     too_many_arguments_threshold: u64,
 222     too_many_lines_threshold: u64,
 223 }
 224
 225 impl Functions {
 226     pub fn new(too_many_arguments_threshold: u64, too_many_lines_threshold: u64) -> Self {
 227         Self {
 228             too_many_arguments_threshold,
 229             too_many_lines_threshold,
 230         }
 231     }
 232 }
 233
 234 impl_lint_pass!(Functions => [
 235     TOO_MANY_ARGUMENTS,
 236     TOO_MANY_LINES,
 237     NOT_UNSAFE_PTR_ARG_DEREF,
 238     MUST_USE_UNIT,
 239     DOUBLE_MUST_USE,
 240     MUST_USE_CANDIDATE,
 241     RESULT_UNIT_ERR,
 242 ]);
 243
 244 impl<'tcx> LateLintPass<'tcx> for Functions {
 245     fn check_fn(
 246         &mut self,
 247         cx: &LateContext<'tcx>,
 248         kind: intravisit::FnKind<'tcx>,
 249         decl: &'tcx hir::FnDecl<'_>,
 250         body: &'tcx hir::Body<'_>,
 251         span: Span,
 252         hir_id: hir::HirId,
 253     ) {
 254         too_many_arguments::check_fn(cx, kind, decl, span, hir_id, self.too_many_arguments_threshold);
 255         too_many_lines::check_fn(cx, kind, span, body, self.too_many_lines_threshold);
 256         not_unsafe_ptr_arg_deref::check_fn(cx, kind, decl, body, hir_id);
 257     }
 258
 259     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
 260         must_use::check_item(cx, item);
 261         result_unit_err::check_item(cx, item);
 262     }
 263
 264     fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::ImplItem<'_>) {
 265         must_use::check_impl_item(cx, item);
 266         result_unit_err::check_impl_item(cx, item);
 267     }
 268
 269     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::TraitItem<'_>) {
 270         too_many_arguments::check_trait_item(cx, item, self.too_many_arguments_threshold);
 271         not_unsafe_ptr_arg_deref::check_trait_item(cx, item);
 272         must_use::check_trait_item(cx, item);
 273         result_unit_err::check_trait_item(cx, item);
 274     }
 275 }