Add new lint hashset_insert_after_contains

CHANGELOG.md

@@ -5798,6 +5798,7 @@ Released 2018-09-13
 [`semicolon_outside_block`]: https://rust-lang.github.io/rust-clippy/master/index.html#semicolon_outside_block
 [`separated_literal_suffix`]: https://rust-lang.github.io/rust-clippy/master/index.html#separated_literal_suffix
 [`serde_api_misuse`]: https://rust-lang.github.io/rust-clippy/master/index.html#serde_api_misuse
+[`set_contains_or_insert`]: https://rust-lang.github.io/rust-clippy/master/index.html#set_contains_or_insert
 [`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
 [`shadow_unrelated`]: https://rust-lang.github.io/rust-clippy/master/index.html#shadow_unrelated

clippy_lints/src/declared_lints.rs

@@ -645,6 +645,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::semicolon_block::SEMICOLON_OUTSIDE_BLOCK_INFO,
     crate::semicolon_if_nothing_returned::SEMICOLON_IF_NOTHING_RETURNED_INFO,
     crate::serde_api::SERDE_API_MISUSE_INFO,
+    crate::set_contains_or_insert::SET_CONTAINS_OR_INSERT_INFO,
     crate::shadow::SHADOW_REUSE_INFO,
     crate::shadow::SHADOW_SAME_INFO,
     crate::shadow::SHADOW_UNRELATED_INFO,

clippy_lints/src/lib.rs

@@ -318,6 +318,7 @@ mod self_named_constructors;
 mod semicolon_block;
 mod semicolon_if_nothing_returned;
 mod serde_api;
+mod set_contains_or_insert;
 mod shadow;
 mod significant_drop_tightening;
 mod single_call_fn;
@@ -1172,6 +1173,7 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
     });
     store.register_late_pass(move |_| Box::new(string_patterns::StringPatterns::new(msrv())));
     store.register_early_pass(|| Box::new(field_scoped_visibility_modifiers::FieldScopedVisibilityModifiers));
+    store.register_late_pass(|_| Box::new(set_contains_or_insert::HashsetInsertAfterContains));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }
 

clippy_lints/src/set_contains_or_insert.rs

@@ -0,0 +1,125 @@
+use std::ops::ControlFlow;
+
+use clippy_utils::diagnostics::span_lint;
+use clippy_utils::ty::is_type_diagnostic_item;
+use clippy_utils::visitors::for_each_expr;
+use clippy_utils::{higher, peel_hir_expr_while, SpanlessEq};
+use rustc_hir::{Expr, ExprKind, UnOp};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::declare_lint_pass;
+use rustc_span::symbol::Symbol;
+use rustc_span::{sym, Span};
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for usage of `contains` to see if a value is not
+    /// present on `HashSet` followed by a `insert`.
+    ///
+    /// ### Why is this bad?
+    /// Using just `insert` and checking the returned `bool` is more efficient.
+    ///
+    /// ### Known problems
+    /// In case the value that wants to be inserted is borrowed and also expensive or impossible
+    /// to clone. In such a scenario, the developer might want to check with `contains` before inserting,
+    /// to avoid the clone. In this case, it will report a false positive.
+    ///
+    /// ### Example
+    /// ```rust
+    /// use std::collections::HashSet;
+    /// let mut set = HashSet::new();
+    /// let value = 5;
+    /// if !set.contains(&value) {
+    ///     set.insert(value);
+    ///     println!("inserted {value:?}");
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// use std::collections::HashSet;
+    /// let mut set = HashSet::new();
+    /// let value = 5;
+    /// if set.insert(&value) {
+    ///     println!("inserted {value:?}");
+    /// }
+    /// ```
+    #[clippy::version = "1.80.0"]
+    pub SET_CONTAINS_OR_INSERT,
+    nursery,
+    "call to `HashSet::contains` followed by `HashSet::insert`"
+}
+
+declare_lint_pass!(HashsetInsertAfterContains => [SET_CONTAINS_OR_INSERT]);
+
+impl<'tcx> LateLintPass<'tcx> for HashsetInsertAfterContains {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+        if !expr.span.from_expansion()
+            && let Some(higher::If {
+                cond: cond_expr,
+                then: then_expr,
+                ..
+            }) = higher::If::hir(expr)
+            && let Some(contains_expr) = try_parse_op_call(cx, cond_expr, sym!(contains))//try_parse_contains(cx, cond_expr)
+            && let Some(insert_expr) = find_insert_calls(cx, &contains_expr, then_expr)
+        {
+            span_lint(
+                cx,
+                SET_CONTAINS_OR_INSERT,
+                vec![contains_expr.span, insert_expr.span],
+                "usage of `HashSet::insert` after `HashSet::contains`",
+            );
+        }
+    }
+}
+
+struct OpExpr<'tcx> {
+    receiver: &'tcx Expr<'tcx>,
+    value: &'tcx Expr<'tcx>,
+    span: Span,
+}
+
+fn try_parse_op_call<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, symbol: Symbol) -> Option<OpExpr<'tcx>> {
+    let expr = peel_hir_expr_while(expr, |e| {
+        if let ExprKind::Unary(UnOp::Not, e) = e.kind {
+            Some(e)
+        } else {
+            None
+        }
+    });
+
+    if let ExprKind::MethodCall(path, receiver, [value], span) = expr.kind {
+        let value = value.peel_borrows();
+        let value = peel_hir_expr_while(value, |e| {
+            if let ExprKind::Unary(UnOp::Deref, e) = e.kind {
+                Some(e)
+            } else {
+                None
+            }
+        });
+        let receiver = receiver.peel_borrows();
+        let receiver_ty = cx.typeck_results().expr_ty(receiver).peel_refs();
+        if value.span.eq_ctxt(expr.span)
+            && is_type_diagnostic_item(cx, receiver_ty, sym::HashSet)
+            && path.ident.name == symbol
+        {
+            return Some(OpExpr { receiver, value, span });
+        }
+    }
+    None
+}
+
+fn find_insert_calls<'tcx>(
+    cx: &LateContext<'tcx>,
+    contains_expr: &OpExpr<'tcx>,
+    expr: &'tcx Expr<'_>,
+) -> Option<OpExpr<'tcx>> {
+    for_each_expr(cx, expr, |e| {
+        if let Some(insert_expr) = try_parse_op_call(cx, e, sym!(insert))
+            && SpanlessEq::new(cx).eq_expr(contains_expr.receiver, insert_expr.receiver)
+            && SpanlessEq::new(cx).eq_expr(contains_expr.value, insert_expr.value)
+        {
+            ControlFlow::Break(insert_expr)
+        } else {
+            ControlFlow::Continue(())
+        }
+    })
+}

tests/ui/set_contains_or_insert.rs

@@ -0,0 +1,83 @@
+#![allow(unused)]
+#![allow(clippy::nonminimal_bool)]
+#![allow(clippy::needless_borrow)]
+#![warn(clippy::set_contains_or_insert)]
+
+use std::collections::HashSet;
+
+fn main() {
+    should_warn_cases();
+
+    should_not_warn_cases();
+}
+
+fn should_warn_cases() {
+    let mut set = HashSet::new();
+    let value = 5;
+
+    if !set.contains(&value) {
+        set.insert(value);
+        println!("Just a comment");
+    }
+
+    if set.contains(&value) {
+        set.insert(value);
+        println!("Just a comment");
+    }
+
+    if !set.contains(&value) {
+        set.insert(value);
+    }
+
+    if !!set.contains(&value) {
+        set.insert(value);
+        println!("Just a comment");
+    }
+
+    if (&set).contains(&value) {
+        set.insert(value);
+    }
+
+    let borrow_value = &6;
+    if !set.contains(borrow_value) {
+        set.insert(*borrow_value);
+    }
+
+    let borrow_set = &mut set;
+    if !borrow_set.contains(&value) {
+        borrow_set.insert(value);
+    }
+}
+
+fn should_not_warn_cases() {
+    let mut set = HashSet::new();
+    let value = 5;
+    let another_value = 6;
+
+    if !set.contains(&value) {
+        set.insert(another_value);
+    }
+
+    if !set.contains(&value) {
+        println!("Just a comment");
+    }
+
+    if simply_true() {
+        set.insert(value);
+    }
+
+    if !set.contains(&value) {
+        set.replace(value); //it is not insert
+        println!("Just a comment");
+    }
+
+    if set.contains(&value) {
+        println!("value is already in set");
+    } else {
+        set.insert(value);
+    }
+}
+
+fn simply_true() -> bool {
+    true
+}

tests/ui/set_contains_or_insert.stderr

@@ -0,0 +1,61 @@
+error: usage of `HashSet::insert` after `HashSet::contains`
+  --> tests/ui/set_contains_or_insert.rs:18:13
+   |
+LL |     if !set.contains(&value) {
+   |             ^^^^^^^^^^^^^^^^
+LL |         set.insert(value);
+   |             ^^^^^^^^^^^^^
+   |
+   = note: `-D clippy::set-contains-or-insert` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::set_contains_or_insert)]`
+
+error: usage of `HashSet::insert` after `HashSet::contains`
+  --> tests/ui/set_contains_or_insert.rs:23:12
+   |
+LL |     if set.contains(&value) {
+   |            ^^^^^^^^^^^^^^^^
+LL |         set.insert(value);
+   |             ^^^^^^^^^^^^^
+
+error: usage of `HashSet::insert` after `HashSet::contains`
+  --> tests/ui/set_contains_or_insert.rs:28:13
+   |
+LL |     if !set.contains(&value) {
+   |             ^^^^^^^^^^^^^^^^
+LL |         set.insert(value);
+   |             ^^^^^^^^^^^^^
+
+error: usage of `HashSet::insert` after `HashSet::contains`
+  --> tests/ui/set_contains_or_insert.rs:32:14
+   |
+LL |     if !!set.contains(&value) {
+   |              ^^^^^^^^^^^^^^^^
+LL |         set.insert(value);
+   |             ^^^^^^^^^^^^^
+
+error: usage of `HashSet::insert` after `HashSet::contains`
+  --> tests/ui/set_contains_or_insert.rs:37:15
+   |
+LL |     if (&set).contains(&value) {
+   |               ^^^^^^^^^^^^^^^^
+LL |         set.insert(value);
+   |             ^^^^^^^^^^^^^
+
+error: usage of `HashSet::insert` after `HashSet::contains`
+  --> tests/ui/set_contains_or_insert.rs:42:13
+   |
+LL |     if !set.contains(borrow_value) {
+   |             ^^^^^^^^^^^^^^^^^^^^^^
+LL |         set.insert(*borrow_value);
+   |             ^^^^^^^^^^^^^^^^^^^^^
+
+error: usage of `HashSet::insert` after `HashSet::contains`
+  --> tests/ui/set_contains_or_insert.rs:47:20
+   |
+LL |     if !borrow_set.contains(&value) {
+   |                    ^^^^^^^^^^^^^^^^
+LL |         borrow_set.insert(value);
+   |                    ^^^^^^^^^^^^^
+
+error: aborting due to 7 previous errors
+