diff --git a/CHANGELOG.md b/CHANGELOG.md index f662de122f9..5ce63c0a157 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -1690,6 +1690,7 @@ Released 2018-09-13 [`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 [`search_is_some`]: https://rust-lang.github.io/rust-clippy/master/index.html#search_is_some +[`self_assignment`]: https://rust-lang.github.io/rust-clippy/master/index.html#self_assignment [`serde_api_misuse`]: https://rust-lang.github.io/rust-clippy/master/index.html#serde_api_misuse [`shadow_reuse`]: https://rust-lang.github.io/rust-clippy/master/index.html#shadow_reuse [`shadow_same`]: https://rust-lang.github.io/rust-clippy/master/index.html#shadow_same diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs index 17501e8e6da..87c297e72eb 100644 --- a/clippy_lints/src/lib.rs +++ b/clippy_lints/src/lib.rs @@ -284,6 +284,7 @@ mod reference; mod regex; mod repeat_once; mod returns; +mod self_assignment; mod serde_api; mod shadow; mod single_component_path_imports; @@ -773,6 +774,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: &repeat_once::REPEAT_ONCE, &returns::LET_AND_RETURN, &returns::NEEDLESS_RETURN, + &self_assignment::SELF_ASSIGNMENT, &serde_api::SERDE_API_MISUSE, &shadow::SHADOW_REUSE, &shadow::SHADOW_SAME, @@ -1090,6 +1092,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: store.register_late_pass(|| box pattern_type_mismatch::PatternTypeMismatch); store.register_late_pass(|| box stable_sort_primitive::StableSortPrimitive); store.register_late_pass(|| box repeat_once::RepeatOnce); + store.register_late_pass(|| box self_assignment::SelfAssignment); store.register_group(true, "clippy::restriction", Some("clippy_restriction"), vec![ LintId::of(&arithmetic::FLOAT_ARITHMETIC), @@ -1421,6 +1424,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: LintId::of(&repeat_once::REPEAT_ONCE), LintId::of(&returns::LET_AND_RETURN), LintId::of(&returns::NEEDLESS_RETURN), + LintId::of(&self_assignment::SELF_ASSIGNMENT), LintId::of(&serde_api::SERDE_API_MISUSE), LintId::of(&single_component_path_imports::SINGLE_COMPONENT_PATH_IMPORTS), LintId::of(&slow_vector_initialization::SLOW_VECTOR_INITIALIZATION), @@ -1714,6 +1718,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf: LintId::of(&ptr::MUT_FROM_REF), LintId::of(&ranges::REVERSED_EMPTY_RANGES), LintId::of(®ex::INVALID_REGEX), + LintId::of(&self_assignment::SELF_ASSIGNMENT), LintId::of(&serde_api::SERDE_API_MISUSE), LintId::of(&suspicious_trait_impl::SUSPICIOUS_ARITHMETIC_IMPL), LintId::of(&suspicious_trait_impl::SUSPICIOUS_OP_ASSIGN_IMPL), diff --git a/clippy_lints/src/self_assignment.rs b/clippy_lints/src/self_assignment.rs new file mode 100644 index 00000000000..e096c9aebc1 --- /dev/null +++ b/clippy_lints/src/self_assignment.rs @@ -0,0 +1,51 @@ +use crate::utils::{eq_expr_value, snippet, span_lint}; +use rustc_hir::{Expr, ExprKind}; +use rustc_lint::{LateContext, LateLintPass}; +use rustc_session::{declare_lint_pass, declare_tool_lint}; + +declare_clippy_lint! { + /// **What it does:** Checks for explicit self-assignments. + /// + /// **Why is this bad?** Self-assignments are redundant and unlikely to be + /// intentional. + /// + /// **Known problems:** If expression contains any deref coercions or + /// indexing operations they are assumed not to have any side effects. + /// + /// **Example:** + /// + /// ```rust + /// struct Event { + /// id: usize, + /// x: i32, + /// y: i32, + /// } + /// + /// fn copy_position(a: &mut Event, b: &Event) { + /// a.x = b.x; + /// a.y = a.y; + /// } + /// ``` + pub SELF_ASSIGNMENT, + correctness, + "explicit self-assignment" +} + +declare_lint_pass!(SelfAssignment => [SELF_ASSIGNMENT]); + +impl<'tcx> LateLintPass<'tcx> for SelfAssignment { + fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { + if let ExprKind::Assign(lhs, rhs, _) = &expr.kind { + if eq_expr_value(cx, lhs, rhs) { + let lhs = snippet(cx, lhs.span, ""); + let rhs = snippet(cx, rhs.span, ""); + span_lint( + cx, + SELF_ASSIGNMENT, + expr.span, + &format!("self-assignment of `{}` to `{}`", rhs, lhs), + ); + } + } + } +} diff --git a/src/lintlist/mod.rs b/src/lintlist/mod.rs index 3229c8da507..bf58c117aaa 100644 --- a/src/lintlist/mod.rs +++ b/src/lintlist/mod.rs @@ -1956,6 +1956,13 @@ pub static ref ALL_LINTS: Vec = vec![ deprecation: None, module: "methods", }, + Lint { + name: "self_assignment", + group: "correctness", + desc: "explicit self-assignment", + deprecation: None, + module: "self_assignment", + }, Lint { name: "serde_api_misuse", group: "correctness", diff --git a/tests/ui/self_assignment.rs b/tests/ui/self_assignment.rs new file mode 100644 index 00000000000..a7cbb9cd78b --- /dev/null +++ b/tests/ui/self_assignment.rs @@ -0,0 +1,67 @@ +#![warn(clippy::self_assignment)] + +pub struct S<'a> { + a: i32, + b: [i32; 10], + c: Vec>, + e: &'a mut i32, + f: &'a mut i32, +} + +pub fn positives(mut a: usize, b: &mut u32, mut s: S) { + a = a; + *b = *b; + s = s; + s.a = s.a; + s.b[10] = s.b[5 + 5]; + s.c[0][1] = s.c[0][1]; + s.b[a] = s.b[a]; + *s.e = *s.e; + s.b[a + 10] = s.b[10 + a]; + + let mut t = (0, 1); + t.1 = t.1; + t.0 = (t.0); +} + +pub fn negatives_not_equal(mut a: usize, b: &mut usize, mut s: S) { + dbg!(&a); + a = *b; + dbg!(&a); + s.b[1] += s.b[1]; + s.b[1] = s.b[2]; + s.c[1][0] = s.c[0][1]; + s.b[a] = s.b[*b]; + s.b[a + 10] = s.b[a + 11]; + *s.e = *s.f; + + let mut t = (0, 1); + t.0 = t.1; +} + +#[allow(clippy::eval_order_dependence)] +pub fn negatives_side_effects() { + let mut v = vec![1, 2, 3, 4, 5]; + let mut i = 0; + v[{ + i += 1; + i + }] = v[{ + i += 1; + i + }]; + + fn next(n: &mut usize) -> usize { + let v = *n; + *n += 1; + v + } + + let mut w = vec![1, 2, 3, 4, 5]; + let mut i = 0; + let i = &mut i; + w[next(i)] = w[next(i)]; + w[next(i)] = w[next(i)]; +} + +fn main() {} diff --git a/tests/ui/self_assignment.stderr b/tests/ui/self_assignment.stderr new file mode 100644 index 00000000000..826e0d0ba88 --- /dev/null +++ b/tests/ui/self_assignment.stderr @@ -0,0 +1,70 @@ +error: self-assignment of `a` to `a` + --> $DIR/self_assignment.rs:12:5 + | +LL | a = a; + | ^^^^^ + | + = note: `-D clippy::self-assignment` implied by `-D warnings` + +error: self-assignment of `*b` to `*b` + --> $DIR/self_assignment.rs:13:5 + | +LL | *b = *b; + | ^^^^^^^ + +error: self-assignment of `s` to `s` + --> $DIR/self_assignment.rs:14:5 + | +LL | s = s; + | ^^^^^ + +error: self-assignment of `s.a` to `s.a` + --> $DIR/self_assignment.rs:15:5 + | +LL | s.a = s.a; + | ^^^^^^^^^ + +error: self-assignment of `s.b[5 + 5]` to `s.b[10]` + --> $DIR/self_assignment.rs:16:5 + | +LL | s.b[10] = s.b[5 + 5]; + | ^^^^^^^^^^^^^^^^^^^^ + +error: self-assignment of `s.c[0][1]` to `s.c[0][1]` + --> $DIR/self_assignment.rs:17:5 + | +LL | s.c[0][1] = s.c[0][1]; + | ^^^^^^^^^^^^^^^^^^^^^ + +error: self-assignment of `s.b[a]` to `s.b[a]` + --> $DIR/self_assignment.rs:18:5 + | +LL | s.b[a] = s.b[a]; + | ^^^^^^^^^^^^^^^ + +error: self-assignment of `*s.e` to `*s.e` + --> $DIR/self_assignment.rs:19:5 + | +LL | *s.e = *s.e; + | ^^^^^^^^^^^ + +error: self-assignment of `s.b[10 + a]` to `s.b[a + 10]` + --> $DIR/self_assignment.rs:20:5 + | +LL | s.b[a + 10] = s.b[10 + a]; + | ^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: self-assignment of `t.1` to `t.1` + --> $DIR/self_assignment.rs:23:5 + | +LL | t.1 = t.1; + | ^^^^^^^^^ + +error: self-assignment of `(t.0)` to `t.0` + --> $DIR/self_assignment.rs:24:5 + | +LL | t.0 = (t.0); + | ^^^^^^^^^^^ + +error: aborting due to 11 previous errors +