Remove unconditional-send-future config

Author: y21

CHANGELOG.md

@@ -6220,7 +6220,6 @@ Released 2018-09-13
 [`too-many-lines-threshold`]: https://doc.rust-lang.org/clippy/lint_configuration.html#too-many-lines-threshold
 [`trivial-copy-size-limit`]: https://doc.rust-lang.org/clippy/lint_configuration.html#trivial-copy-size-limit
 [`type-complexity-threshold`]: https://doc.rust-lang.org/clippy/lint_configuration.html#type-complexity-threshold
-[`unconditional-send-futures`]: https://doc.rust-lang.org/clippy/lint_configuration.html#unconditional-send-futures
 [`unnecessary-box-size`]: https://doc.rust-lang.org/clippy/lint_configuration.html#unnecessary-box-size
 [`unreadable-literal-lint-fractions`]: https://doc.rust-lang.org/clippy/lint_configuration.html#unreadable-literal-lint-fractions
 [`upper-case-acronyms-aggressive`]: https://doc.rust-lang.org/clippy/lint_configuration.html#upper-case-acronyms-aggressive

book/src/lint_configuration.md

@@ -883,33 +883,6 @@ The maximum complexity a type can have
 * [`type_complexity`](https://rust-lang.github.io/rust-clippy/master/index.html#type_complexity)
 
 
-## `unconditional-send-futures`
-Whether `future_not_send` should require futures to implement `Send` unconditionally.
-Enabling this makes the lint more strict and requires generic functions have `Send` bounds
-on type parameters.
-
-### Example
-```
-async fn foo<R>(r: R) {
-    std::future::ready(()).await;
-    r;
-}
-```
-The returned future by this async function may or may not be `Send` - it depends on the particular type
-that `R` is instantiated with at call site, so it is **not** unconditionally `Send`.
-Adding an `R: Send` bound to the function definition satisfies it, but is more restrictive for callers.
-
-For library crate authors that want to make sure that their async functions are compatible
-with both single-threaded and multi-threaded executors, the default behavior of allowing `!Send` futures
-if type parameters are `!Send` makes sense.
-
-**Default Value:** `false`
-
----
-**Affected lints:**
-* [`future_not_send`](https://rust-lang.github.io/rust-clippy/master/index.html#future_not_send)
-
-
 ## `unnecessary-box-size`
 The byte size a `T` in `Box<T>` can have, below which it triggers the `clippy::unnecessary_box` lint
 

clippy_config/src/conf.rs

@@ -645,26 +645,6 @@ define_Conf! {
     /// The maximum complexity a type can have
     #[lints(type_complexity)]
     type_complexity_threshold: u64 = 250,
-    /// Whether `future_not_send` should require futures to implement `Send` unconditionally.
-    /// Enabling this makes the lint more strict and requires generic functions have `Send` bounds
-    /// on type parameters.
-    ///
-    /// ### Example
-    /// ```
-    /// async fn foo<R>(r: R) {
-    ///     std::future::ready(()).await;
-    ///     r;
-    /// }
-    /// ```
-    /// The returned future by this async function may or may not be `Send` - it depends on the particular type
-    /// that `R` is instantiated with at call site, so it is **not** unconditionally `Send`.
-    /// Adding an `R: Send` bound to the function definition satisfies it, but is more restrictive for callers.
-    ///
-    /// For library crate authors that want to make sure that their async functions are compatible
-    /// with both single-threaded and multi-threaded executors, the default behavior of allowing `!Send` futures
-    /// if type parameters are `!Send` makes sense.
-    #[lints(future_not_send)]
-    unconditional_send_futures: bool = false,
     /// The byte size a `T` in `Box<T>` can have, below which it triggers the `clippy::unnecessary_box` lint
     #[lints(unnecessary_box_returns)]
     unnecessary_box_size: u64 = 128,

clippy_lints/src/future_not_send.rs

@@ -1,6 +1,5 @@
 use std::ops::ControlFlow;
 
-use clippy_config::Conf;
 use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::return_ty;
 use rustc_hir::intravisit::FnKind;
@@ -11,7 +10,7 @@ use rustc_middle::ty::print::PrintTraitRefExt;
 use rustc_middle::ty::{
     self, AliasTy, Binder, ClauseKind, PredicateKind, Ty, TyCtxt, TypeVisitable, TypeVisitableExt, TypeVisitor,
 };
-use rustc_session::impl_lint_pass;
+use rustc_session::declare_lint_pass;
 use rustc_span::def_id::LocalDefId;
 use rustc_span::{Span, sym};
 use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
@@ -20,23 +19,17 @@ use rustc_trait_selection::traits::{self, FulfillmentError, ObligationCtxt};
 declare_clippy_lint! {
     /// ### What it does
     /// This lint requires Future implementations returned from
-    /// functions and methods to implement the `Send` marker trait.
+    /// functions and methods to implement the `Send` marker trait,
+    /// ignoring type parameters.
+    ///
+    /// If a function is generic and its Future conditionally implements `Send`
+    /// based on a generic parameter then it is considered `Send` and no warning is emitted.
     ///
-    /// The default configuration of this lint only emits warnings for futures
-    /// that are unconditionally `!Send`, ignoring generic parameters.
     /// This can be used by library authors (public and internal) to ensure
-    /// their functions are compatible with multi-threaded runtimes that require `Send` futures,
+    /// their functions are compatible with both multi-threaded runtimes that require `Send` futures,
     /// as well as single-threaded runtimes where callers may choose `!Send` types
     /// for generic parameters.
     ///
-    /// A more strict version can be enabled through the `unconditional_send_futures` configuration,
-    /// which requires that futures must always unconditionally implement `Send`,
-    /// even if whether the future is `Send` or not is determined at call site for generic functions.
-    /// This can be useful for binary crates that always use a multi-threaded runtime to find `!Send` futures
-    /// as early as possible and keep errors contained in the most relevant place,
-    /// instead of propagating `!Send` and be left with a hard-to-debug error in an
-    /// unrelated place (e.g. the final future passed to `tokio::spawn()`).
-    ///
     /// ### Why is this bad?
     /// A Future implementation captures some state that it
     /// needs to eventually produce its final value. When targeting a multithreaded
@@ -66,19 +59,7 @@ declare_clippy_lint! {
     "public Futures must be Send"
 }
 
-pub struct FutureNotSend {
-    unconditionally_not_send: bool,
-}
-
-impl FutureNotSend {
-    pub fn new(conf: &'static Conf) -> Self {
-        Self {
-            unconditionally_not_send: conf.unconditional_send_futures,
-        }
-    }
-}
-
-impl_lint_pass!(FutureNotSend => [FUTURE_NOT_SEND]);
+declare_lint_pass!(FutureNotSend => [FUTURE_NOT_SEND]);
 
 impl<'tcx> LateLintPass<'tcx> for FutureNotSend {
     fn check_fn(
@@ -111,43 +92,27 @@ impl<'tcx> LateLintPass<'tcx> for FutureNotSend {
                 ocx.register_bound(cause, cx.param_env, ret_ty, send_trait);
                 let send_errors = ocx.select_all_or_error();
 
-                let is_send = if self.unconditionally_not_send {
-                    send_errors.is_empty()
-                } else {
-                    // Allow errors that try to prove `Send` for types that "mention" a generic parameter at the "top
-                    // level".
-                    // For example, allow errors that `T: Send` can't be proven, but reject `Rc<T>: Send` errors,
-                    // which is always unconditionally `!Send` for any possible type `T`.
-                    //
-                    // We also allow associated type projections if the self type is either itself a projection or a
-                    // type parameter.
-                    // This is to prevent emitting warnings for e.g. holding a `<Fut as Future>::Output` across await
-                    // points, where `Fut` is a type parameter.
-
-                    struct TypeWalker;
-                    impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for TypeWalker {
-                        type Result = ControlFlow<bool>;
-                        fn visit_ty(&mut self, ty: Ty<'tcx>) -> Self::Result {
-                            match ty.kind() {
-                                ty::Param(_) => ControlFlow::Break(true),
-                                ty::Alias(ty::AliasTyKind::Projection, ty) => ty.visit_with(self),
-                                _ => ControlFlow::Break(false),
-                            }
-                        }
-                    }
+                // Allow errors that try to prove `Send` for types that "mention" a generic parameter at the "top
+                // level".
+                // For example, allow errors that `T: Send` can't be proven, but reject `Rc<T>: Send` errors,
+                // which is always unconditionally `!Send` for any possible type `T`.
+                //
+                // We also allow associated type projections if the self type is either itself a projection or a
+                // type parameter.
+                // This is to prevent emitting warnings for e.g. holding a `<Fut as Future>::Output` across await
+                // points, where `Fut` is a type parameter.
 
-                    send_errors.iter().all(|err| {
-                        err.obligation
-                            .predicate
-                            .as_trait_clause()
-                            .map(Binder::skip_binder)
-                            .is_some_and(|pred| {
-                                pred.def_id() == send_trait
-                                    && pred.self_ty().has_param()
-                                    && TypeWalker.visit_ty(pred.self_ty()) == ControlFlow::Break(true)
-                            })
-                    })
-                };
+                let is_send = send_errors.iter().all(|err| {
+                    err.obligation
+                        .predicate
+                        .as_trait_clause()
+                        .map(Binder::skip_binder)
+                        .is_some_and(|pred| {
+                            pred.def_id() == send_trait
+                                && pred.self_ty().has_param()
+                                && TyParamAtTopLevelVisitor.visit_ty(pred.self_ty()) == ControlFlow::Break(true)
+                        })
+                });
 
                 if !is_send {
                     span_lint_and_then(
@@ -177,3 +142,15 @@ impl<'tcx> LateLintPass<'tcx> for FutureNotSend {
         }
     }
 }
+
+struct TyParamAtTopLevelVisitor;
+impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for TyParamAtTopLevelVisitor {
+    type Result = ControlFlow<bool>;
+    fn visit_ty(&mut self, ty: Ty<'tcx>) -> Self::Result {
+        match ty.kind() {
+            ty::Param(_) => ControlFlow::Break(true),
+            ty::Alias(ty::AliasTyKind::Projection, ty) => ty.visit_with(self),
+            _ => ControlFlow::Break(false),
+        }
+    }
+}

clippy_lints/src/lib.rs

@@ -777,7 +777,7 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
     store.register_late_pass(|_| Box::new(unnamed_address::UnnamedAddress));
     store.register_late_pass(|_| Box::<dereference::Dereferencing<'_>>::default());
     store.register_late_pass(|_| Box::new(option_if_let_else::OptionIfLetElse));
-    store.register_late_pass(move |_| Box::new(future_not_send::FutureNotSend::new(conf)));
+    store.register_late_pass(|_| Box::new(future_not_send::FutureNotSend));
     store.register_late_pass(move |_| Box::new(large_futures::LargeFuture::new(conf)));
     store.register_late_pass(|_| Box::new(if_let_mutex::IfLetMutex));
     store.register_late_pass(|_| Box::new(if_not_else::IfNotElse));