diff --git a/CHANGELOG.md b/CHANGELOG.md index 6fb6cf75d96fe..f21768c449880 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -1918,6 +1918,7 @@ Released 2018-09-13 [`rest_pat_in_fully_bound_structs`]: https://rust-lang.github.io/rust-clippy/master/index.html#rest_pat_in_fully_bound_structs [`result_map_or_into_option`]: https://rust-lang.github.io/rust-clippy/master/index.html#result_map_or_into_option [`result_map_unit_fn`]: https://rust-lang.github.io/rust-clippy/master/index.html#result_map_unit_fn +[`result_unit_err`]: https://rust-lang.github.io/rust-clippy/master/index.html#result_unit_err [`reversed_empty_ranges`]: https://rust-lang.github.io/rust-clippy/master/index.html#reversed_empty_ranges [`same_functions_in_if_condition`]: https://rust-lang.github.io/rust-clippy/master/index.html#same_functions_in_if_condition [`same_item_push`]: https://rust-lang.github.io/rust-clippy/master/index.html#same_item_push diff --git a/clippy_lints/src/functions.rs b/clippy_lints/src/functions.rs index 50b39cf4ea7c0..fd45a6da61ca6 100644 --- a/clippy_lints/src/functions.rs +++ b/clippy_lints/src/functions.rs @@ -1,8 +1,9 @@ use crate::utils::{ - attr_by_name, attrs::is_proc_macro, is_must_use_ty, is_trait_impl_item, iter_input_pats, match_def_path, - must_use_attr, qpath_res, return_ty, snippet, snippet_opt, span_lint, span_lint_and_help, span_lint_and_then, - trait_ref_of_method, type_is_unsafe_function, + attr_by_name, attrs::is_proc_macro, is_must_use_ty, is_trait_impl_item, is_type_diagnostic_item, iter_input_pats, + last_path_segment, match_def_path, must_use_attr, qpath_res, return_ty, snippet, snippet_opt, span_lint, + span_lint_and_help, span_lint_and_then, trait_ref_of_method, type_is_unsafe_function, }; +use if_chain::if_chain; use rustc_ast::ast::Attribute; use rustc_data_structures::fx::FxHashSet; use rustc_errors::Applicability; @@ -16,6 +17,7 @@ use rustc_middle::ty::{self, Ty}; use rustc_session::{declare_tool_lint, impl_lint_pass}; use rustc_span::source_map::Span; use rustc_target::spec::abi::Abi; +use rustc_typeck::hir_ty_to_ty; declare_clippy_lint! { /// **What it does:** Checks for functions with too many parameters. @@ -169,6 +171,52 @@ declare_clippy_lint! { "function or method that could take a `#[must_use]` attribute" } +declare_clippy_lint! { + /// **What it does:** Checks for public functions that return a `Result` + /// with an `Err` type of `()`. It suggests using a custom type that + /// implements [`std::error::Error`]. + /// + /// **Why is this bad?** Unit does not implement `Error` and carries no + /// further information about what went wrong. + /// + /// **Known problems:** Of course, this lint assumes that `Result` is used + /// for a fallible operation (which is after all the intended use). However + /// code may opt to (mis)use it as a basic two-variant-enum. In that case, + /// the suggestion is misguided, and the code should use a custom enum + /// instead. + /// + /// **Examples:** + /// ```rust + /// pub fn read_u8() -> Result { Err(()) } + /// ``` + /// should become + /// ```rust,should_panic + /// use std::fmt; + /// + /// #[derive(Debug)] + /// pub struct EndOfStream; + /// + /// impl fmt::Display for EndOfStream { + /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + /// write!(f, "End of Stream") + /// } + /// } + /// + /// impl std::error::Error for EndOfStream { } + /// + /// pub fn read_u8() -> Result { Err(EndOfStream) } + ///# fn main() { + ///# read_u8().unwrap(); + ///# } + /// ``` + /// + /// Note that there are crates that simplify creating the error type, e.g. + /// [`thiserror`](https://docs.rs/thiserror). + pub RESULT_UNIT_ERR, + style, + "public function returning `Result` with an `Err` type of `()`" +} + #[derive(Copy, Clone)] pub struct Functions { threshold: u64, @@ -188,6 +236,7 @@ impl_lint_pass!(Functions => [ MUST_USE_UNIT, DOUBLE_MUST_USE, MUST_USE_CANDIDATE, + RESULT_UNIT_ERR, ]); impl<'tcx> LateLintPass<'tcx> for Functions { @@ -233,15 +282,16 @@ impl<'tcx> LateLintPass<'tcx> for Functions { fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) { let attr = must_use_attr(&item.attrs); if let hir::ItemKind::Fn(ref sig, ref _generics, ref body_id) = item.kind { + let is_public = cx.access_levels.is_exported(item.hir_id); + let fn_header_span = item.span.with_hi(sig.decl.output.span().hi()); + if is_public { + check_result_unit_err(cx, &sig.decl, item.span, fn_header_span); + } if let Some(attr) = attr { - let fn_header_span = item.span.with_hi(sig.decl.output.span().hi()); check_needless_must_use(cx, &sig.decl, item.hir_id, item.span, fn_header_span, attr); return; } - if cx.access_levels.is_exported(item.hir_id) - && !is_proc_macro(cx.sess(), &item.attrs) - && attr_by_name(&item.attrs, "no_mangle").is_none() - { + if is_public && !is_proc_macro(cx.sess(), &item.attrs) && attr_by_name(&item.attrs, "no_mangle").is_none() { check_must_use_candidate( cx, &sig.decl, @@ -257,11 +307,15 @@ impl<'tcx> LateLintPass<'tcx> for Functions { fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::ImplItem<'_>) { if let hir::ImplItemKind::Fn(ref sig, ref body_id) = item.kind { + let is_public = cx.access_levels.is_exported(item.hir_id); + let fn_header_span = item.span.with_hi(sig.decl.output.span().hi()); + if is_public && trait_ref_of_method(cx, item.hir_id).is_none() { + check_result_unit_err(cx, &sig.decl, item.span, fn_header_span); + } let attr = must_use_attr(&item.attrs); if let Some(attr) = attr { - let fn_header_span = item.span.with_hi(sig.decl.output.span().hi()); check_needless_must_use(cx, &sig.decl, item.hir_id, item.span, fn_header_span, attr); - } else if cx.access_levels.is_exported(item.hir_id) + } else if is_public && !is_proc_macro(cx.sess(), &item.attrs) && trait_ref_of_method(cx, item.hir_id).is_none() { @@ -284,18 +338,21 @@ impl<'tcx> LateLintPass<'tcx> for Functions { if sig.header.abi == Abi::Rust { self.check_arg_number(cx, &sig.decl, item.span.with_hi(sig.decl.output.span().hi())); } + let is_public = cx.access_levels.is_exported(item.hir_id); + let fn_header_span = item.span.with_hi(sig.decl.output.span().hi()); + if is_public { + check_result_unit_err(cx, &sig.decl, item.span, fn_header_span); + } let attr = must_use_attr(&item.attrs); if let Some(attr) = attr { - let fn_header_span = item.span.with_hi(sig.decl.output.span().hi()); check_needless_must_use(cx, &sig.decl, item.hir_id, item.span, fn_header_span, attr); } if let hir::TraitFn::Provided(eid) = *eid { let body = cx.tcx.hir().body(eid); Self::check_raw_ptr(cx, sig.header.unsafety, &sig.decl, body, item.hir_id); - if attr.is_none() && cx.access_levels.is_exported(item.hir_id) && !is_proc_macro(cx.sess(), &item.attrs) - { + if attr.is_none() && is_public && !is_proc_macro(cx.sess(), &item.attrs) { check_must_use_candidate( cx, &sig.decl, @@ -411,6 +468,29 @@ impl<'tcx> Functions { } } +fn check_result_unit_err(cx: &LateContext<'_>, decl: &hir::FnDecl<'_>, item_span: Span, fn_header_span: Span) { + if_chain! { + if !in_external_macro(cx.sess(), item_span); + if let hir::FnRetTy::Return(ref ty) = decl.output; + if let hir::TyKind::Path(ref qpath) = ty.kind; + if is_type_diagnostic_item(cx, hir_ty_to_ty(cx.tcx, ty), sym!(result_type)); + if let Some(ref args) = last_path_segment(qpath).args; + if let [_, hir::GenericArg::Type(ref err_ty)] = args.args; + if let hir::TyKind::Tup(t) = err_ty.kind; + if t.is_empty(); + then { + span_lint_and_help( + cx, + RESULT_UNIT_ERR, + fn_header_span, + "this returns a `Result<_, ()>", + None, + "use a custom Error type instead", + ); + } + } +} + fn check_needless_must_use( cx: &LateContext<'_>, decl: &hir::FnDecl<'_>, diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs index 097eca0af578c..26a727687b1d1 100644 --- a/clippy_lints/src/lib.rs +++ b/clippy_lints/src/lib.rs @@ -582,6 +582,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: &functions::MUST_USE_CANDIDATE, &functions::MUST_USE_UNIT, &functions::NOT_UNSAFE_PTR_ARG_DEREF, + &functions::RESULT_UNIT_ERR, &functions::TOO_MANY_ARGUMENTS, &functions::TOO_MANY_LINES, &future_not_send::FUTURE_NOT_SEND, @@ -1327,6 +1328,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: LintId::of(&functions::DOUBLE_MUST_USE), LintId::of(&functions::MUST_USE_UNIT), LintId::of(&functions::NOT_UNSAFE_PTR_ARG_DEREF), + LintId::of(&functions::RESULT_UNIT_ERR), LintId::of(&functions::TOO_MANY_ARGUMENTS), LintId::of(&get_last_with_len::GET_LAST_WITH_LEN), LintId::of(&identity_op::IDENTITY_OP), @@ -1558,6 +1560,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: LintId::of(&formatting::SUSPICIOUS_UNARY_OP_FORMATTING), LintId::of(&functions::DOUBLE_MUST_USE), LintId::of(&functions::MUST_USE_UNIT), + LintId::of(&functions::RESULT_UNIT_ERR), LintId::of(&if_let_some_result::IF_LET_SOME_RESULT), LintId::of(&inherent_to_string::INHERENT_TO_STRING), LintId::of(&len_zero::LEN_WITHOUT_IS_EMPTY), diff --git a/src/lintlist/mod.rs b/src/lintlist/mod.rs index 96c9d12d75fbb..d0fc8f0c8a907 100644 --- a/src/lintlist/mod.rs +++ b/src/lintlist/mod.rs @@ -2005,6 +2005,13 @@ pub static ref ALL_LINTS: Vec = vec![ deprecation: None, module: "map_unit_fn", }, + Lint { + name: "result_unit_err", + group: "style", + desc: "public function returning `Result` with an `Err` type of `()`", + deprecation: None, + module: "functions", + }, Lint { name: "reversed_empty_ranges", group: "correctness", diff --git a/tests/ui/doc_errors.rs b/tests/ui/doc_errors.rs index 445fc8d31d77a..f47b81a450ea9 100644 --- a/tests/ui/doc_errors.rs +++ b/tests/ui/doc_errors.rs @@ -1,5 +1,6 @@ // edition:2018 #![warn(clippy::missing_errors_doc)] +#![allow(clippy::result_unit_err)] use std::io; diff --git a/tests/ui/doc_errors.stderr b/tests/ui/doc_errors.stderr index f44d6693d303b..c7b616e289708 100644 --- a/tests/ui/doc_errors.stderr +++ b/tests/ui/doc_errors.stderr @@ -1,5 +1,5 @@ error: docs for function returning `Result` missing `# Errors` section - --> $DIR/doc_errors.rs:6:1 + --> $DIR/doc_errors.rs:7:1 | LL | / pub fn pub_fn_missing_errors_header() -> Result<(), ()> { LL | | unimplemented!(); @@ -9,7 +9,7 @@ LL | | } = note: `-D clippy::missing-errors-doc` implied by `-D warnings` error: docs for function returning `Result` missing `# Errors` section - --> $DIR/doc_errors.rs:10:1 + --> $DIR/doc_errors.rs:11:1 | LL | / pub async fn async_pub_fn_missing_errors_header() -> Result<(), ()> { LL | | unimplemented!(); @@ -17,7 +17,7 @@ LL | | } | |_^ error: docs for function returning `Result` missing `# Errors` section - --> $DIR/doc_errors.rs:15:1 + --> $DIR/doc_errors.rs:16:1 | LL | / pub fn pub_fn_returning_io_result() -> io::Result<()> { LL | | unimplemented!(); @@ -25,7 +25,7 @@ LL | | } | |_^ error: docs for function returning `Result` missing `# Errors` section - --> $DIR/doc_errors.rs:20:1 + --> $DIR/doc_errors.rs:21:1 | LL | / pub async fn async_pub_fn_returning_io_result() -> io::Result<()> { LL | | unimplemented!(); @@ -33,7 +33,7 @@ LL | | } | |_^ error: docs for function returning `Result` missing `# Errors` section - --> $DIR/doc_errors.rs:50:5 + --> $DIR/doc_errors.rs:51:5 | LL | / pub fn pub_method_missing_errors_header() -> Result<(), ()> { LL | | unimplemented!(); @@ -41,7 +41,7 @@ LL | | } | |_____^ error: docs for function returning `Result` missing `# Errors` section - --> $DIR/doc_errors.rs:55:5 + --> $DIR/doc_errors.rs:56:5 | LL | / pub async fn async_pub_method_missing_errors_header() -> Result<(), ()> { LL | | unimplemented!(); @@ -49,7 +49,7 @@ LL | | } | |_____^ error: docs for function returning `Result` missing `# Errors` section - --> $DIR/doc_errors.rs:84:5 + --> $DIR/doc_errors.rs:85:5 | LL | fn trait_method_missing_errors_header() -> Result<(), ()>; | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ diff --git a/tests/ui/double_must_use.rs b/tests/ui/double_must_use.rs index a48e675e4ea23..05e087b08bc14 100644 --- a/tests/ui/double_must_use.rs +++ b/tests/ui/double_must_use.rs @@ -1,4 +1,5 @@ #![warn(clippy::double_must_use)] +#![allow(clippy::result_unit_err)] #[must_use] pub fn must_use_result() -> Result<(), ()> { diff --git a/tests/ui/double_must_use.stderr b/tests/ui/double_must_use.stderr index bc37785294fca..8290ece1cad18 100644 --- a/tests/ui/double_must_use.stderr +++ b/tests/ui/double_must_use.stderr @@ -1,5 +1,5 @@ error: this function has an empty `#[must_use]` attribute, but returns a type already marked as `#[must_use]` - --> $DIR/double_must_use.rs:4:1 + --> $DIR/double_must_use.rs:5:1 | LL | pub fn must_use_result() -> Result<(), ()> { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ @@ -8,7 +8,7 @@ LL | pub fn must_use_result() -> Result<(), ()> { = help: either add some descriptive text or remove the attribute error: this function has an empty `#[must_use]` attribute, but returns a type already marked as `#[must_use]` - --> $DIR/double_must_use.rs:9:1 + --> $DIR/double_must_use.rs:10:1 | LL | pub fn must_use_tuple() -> (Result<(), ()>, u8) { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ @@ -16,7 +16,7 @@ LL | pub fn must_use_tuple() -> (Result<(), ()>, u8) { = help: either add some descriptive text or remove the attribute error: this function has an empty `#[must_use]` attribute, but returns a type already marked as `#[must_use]` - --> $DIR/double_must_use.rs:14:1 + --> $DIR/double_must_use.rs:15:1 | LL | pub fn must_use_array() -> [Result<(), ()>; 1] { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ diff --git a/tests/ui/result_unit_error.rs b/tests/ui/result_unit_error.rs new file mode 100644 index 0000000000000..a66f581b2159f --- /dev/null +++ b/tests/ui/result_unit_error.rs @@ -0,0 +1,38 @@ +#[warn(clippy::result_unit_err)] +#[allow(unused)] + +pub fn returns_unit_error() -> Result { + Err(()) +} + +fn private_unit_errors() -> Result { + Err(()) +} + +pub trait HasUnitError { + fn get_that_error(&self) -> Result; + + fn get_this_one_too(&self) -> Result { + Err(()) + } +} + +impl HasUnitError for () { + fn get_that_error(&self) -> Result { + Ok(true) + } +} + +trait PrivateUnitError { + fn no_problem(&self) -> Result; +} + +pub struct UnitErrorHolder; + +impl UnitErrorHolder { + pub fn unit_error(&self) -> Result { + Ok(0) + } +} + +fn main() {} diff --git a/tests/ui/result_unit_error.stderr b/tests/ui/result_unit_error.stderr new file mode 100644 index 0000000000000..b8230032491b6 --- /dev/null +++ b/tests/ui/result_unit_error.stderr @@ -0,0 +1,35 @@ +error: this returns a `Result<_, ()> + --> $DIR/result_unit_error.rs:4:1 + | +LL | pub fn returns_unit_error() -> Result { + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | + = note: `-D clippy::result-unit-err` implied by `-D warnings` + = help: use a custom Error type instead + +error: this returns a `Result<_, ()> + --> $DIR/result_unit_error.rs:13:5 + | +LL | fn get_that_error(&self) -> Result; + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | + = help: use a custom Error type instead + +error: this returns a `Result<_, ()> + --> $DIR/result_unit_error.rs:15:5 + | +LL | fn get_this_one_too(&self) -> Result { + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | + = help: use a custom Error type instead + +error: this returns a `Result<_, ()> + --> $DIR/result_unit_error.rs:33:5 + | +LL | pub fn unit_error(&self) -> Result { + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | + = help: use a custom Error type instead + +error: aborting due to 4 previous errors +