Auto merge of #12227 - y21:issue12225, r=Manishearth

[`redundant_locals`]: take by-value closure captures into account

Fixes #12225

The same problem in the linked issue can happen to regular closures too, and conveniently async blocks are closures in the HIR so fixing closures will fix async blocks as well.

changelog: [`redundant_locals`]: avoid linting when redefined variable is captured by-value

Author: bors

clippy_lints/src/redundant_locals.rs

@@ -4,8 +4,10 @@ use clippy_utils::ty::needs_ordered_drop;
 use rustc_ast::Mutability;
 use rustc_hir::def::Res;
 use rustc_hir::{BindingAnnotation, ByRef, ExprKind, HirId, Local, Node, Pat, PatKind, QPath};
+use rustc_hir_typeck::expr_use_visitor::PlaceBase;
 use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_middle::lint::in_external_macro;
+use rustc_middle::ty::UpvarCapture;
 use rustc_session::declare_lint_pass;
 use rustc_span::symbol::Ident;
 use rustc_span::DesugaringKind;
@@ -69,6 +71,7 @@ impl<'tcx> LateLintPass<'tcx> for RedundantLocals {
             // the local is user-controlled
             && !in_external_macro(cx.sess(), local.span)
             && !is_from_proc_macro(cx, expr)
+            && !is_by_value_closure_capture(cx, local.hir_id, binding_id)
         {
             span_lint_and_help(
                 cx,
@@ -82,6 +85,29 @@ impl<'tcx> LateLintPass<'tcx> for RedundantLocals {
     }
 }
 
+/// Checks if the enclosing body is a closure and if the given local is captured by value.
+///
+/// In those cases, the redefinition may be necessary to force a move:
+/// ```
+/// fn assert_static<T: 'static>(_: T) {}
+///
+/// let v = String::new();
+/// let closure = || {
+///   let v = v; // <- removing this redefinition makes `closure` no longer `'static`
+///   dbg!(&v);
+/// };
+/// assert_static(closure);
+/// ```
+fn is_by_value_closure_capture(cx: &LateContext<'_>, redefinition: HirId, root_variable: HirId) -> bool {
+    let closure_def_id = cx.tcx.hir().enclosing_body_owner(redefinition);
+
+    cx.tcx.is_closure_or_coroutine(closure_def_id.to_def_id())
+        && cx.tcx.closure_captures(closure_def_id).iter().any(|c| {
+            matches!(c.info.capture_kind, UpvarCapture::ByValue)
+                && matches!(c.place.base, PlaceBase::Upvar(upvar) if upvar.var_path.hir_id == root_variable)
+        })
+}
+
 /// Find the annotation of a binding introduced by a pattern, or `None` if it's not introduced.
 fn find_binding(pat: &Pat<'_>, name: Ident) -> Option<BindingAnnotation> {
     let mut ret = None;

tests/ui/redundant_locals.rs

@@ -1,6 +1,7 @@
 //@aux-build:proc_macros.rs
 #![allow(unused, clippy::no_effect, clippy::needless_pass_by_ref_mut)]
 #![warn(clippy::redundant_locals)]
+#![feature(async_closure, coroutines)]
 
 extern crate proc_macros;
 use proc_macros::{external, with_span};
@@ -163,3 +164,48 @@ fn drop_compose() {
     let b = ComposeDrop { d: WithDrop(1) };
     let a = a;
 }
+
+fn issue12225() {
+    fn assert_static<T: 'static>(_: T) {}
+
+    let v1 = String::new();
+    let v2 = String::new();
+    let v3 = String::new();
+    let v4 = String::new();
+    let v5 = String::new();
+    let v6 = String::new();
+
+    assert_static(|| {
+        let v1 = v1;
+        dbg!(&v1);
+    });
+    assert_static(async {
+        let v2 = v2;
+        dbg!(&v2);
+    });
+    assert_static(|| async {
+        let v3 = v3;
+        dbg!(&v3);
+    });
+    assert_static(async || {
+        let v4 = v4;
+        dbg!(&v4);
+    });
+    assert_static(static || {
+        let v5 = v5;
+        yield;
+    });
+    assert_static(|| {
+        let v6 = v6;
+        yield;
+    });
+
+    fn foo(a: &str, b: &str) {}
+
+    let do_not_move = String::new();
+    let things_to_move = vec!["a".to_string(), "b".to_string()];
+    let futures = things_to_move.into_iter().map(|move_me| async {
+        let move_me = move_me;
+        foo(&do_not_move, &move_me)
+    });
+}

tests/ui/redundant_locals.stderr

@@ -1,169 +1,169 @@
 error: redundant redefinition of a binding `x`
-  --> $DIR/redundant_locals.rs:12:5
+  --> $DIR/redundant_locals.rs:13:5
    |
 LL |     let x = x;
    |     ^^^^^^^^^^
    |
 help: `x` is initially defined here
-  --> $DIR/redundant_locals.rs:11:9
+  --> $DIR/redundant_locals.rs:12:9
    |
 LL |     let x = 1;
    |         ^
    = note: `-D clippy::redundant-locals` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::redundant_locals)]`
 
 error: redundant redefinition of a binding `x`
-  --> $DIR/redundant_locals.rs:17:5
+  --> $DIR/redundant_locals.rs:18:5
    |
 LL |     let mut x = x;
    |     ^^^^^^^^^^^^^^
    |
 help: `x` is initially defined here
-  --> $DIR/redundant_locals.rs:16:9
+  --> $DIR/redundant_locals.rs:17:9
    |
 LL |     let mut x = 1;
    |         ^^^^^
 
 error: redundant redefinition of a binding `x`
-  --> $DIR/redundant_locals.rs:47:5
+  --> $DIR/redundant_locals.rs:48:5
    |
 LL |     let x = x;
    |     ^^^^^^^^^^
    |
 help: `x` is initially defined here
-  --> $DIR/redundant_locals.rs:46:14
+  --> $DIR/redundant_locals.rs:47:14
    |
 LL | fn parameter(x: i32) {
    |              ^
 
 error: redundant redefinition of a binding `x`
-  --> $DIR/redundant_locals.rs:52:5
+  --> $DIR/redundant_locals.rs:53:5
    |
 LL |     let x = x;
    |     ^^^^^^^^^^
    |
 help: `x` is initially defined here
-  --> $DIR/redundant_locals.rs:51:9
+  --> $DIR/redundant_locals.rs:52:9
    |
 LL |     let x = 1;
    |         ^
 
 error: redundant redefinition of a binding `x`
-  --> $DIR/redundant_locals.rs:53:5
+  --> $DIR/redundant_locals.rs:54:5
    |
 LL |     let x = x;
    |     ^^^^^^^^^^
    |
 help: `x` is initially defined here
-  --> $DIR/redundant_locals.rs:52:9
+  --> $DIR/redundant_locals.rs:53:9
    |
 LL |     let x = x;
    |         ^
 
 error: redundant redefinition of a binding `x`
-  --> $DIR/redundant_locals.rs:54:5
+  --> $DIR/redundant_locals.rs:55:5
    |
 LL |     let x = x;
    |     ^^^^^^^^^^
    |
 help: `x` is initially defined here
-  --> $DIR/redundant_locals.rs:53:9
+  --> $DIR/redundant_locals.rs:54:9
    |
 LL |     let x = x;
    |         ^
 
 error: redundant redefinition of a binding `x`
-  --> $DIR/redundant_locals.rs:55:5
+  --> $DIR/redundant_locals.rs:56:5
    |
 LL |     let x = x;
    |     ^^^^^^^^^^
    |
 help: `x` is initially defined here
-  --> $DIR/redundant_locals.rs:54:9
+  --> $DIR/redundant_locals.rs:55:9
    |
 LL |     let x = x;
    |         ^
 
 error: redundant redefinition of a binding `a`
-  --> $DIR/redundant_locals.rs:61:5
+  --> $DIR/redundant_locals.rs:62:5
    |
 LL |     let a = a;
    |     ^^^^^^^^^^
    |
 help: `a` is initially defined here
-  --> $DIR/redundant_locals.rs:59:9
+  --> $DIR/redundant_locals.rs:60:9
    |
 LL |     let a = 1;
    |         ^
 
 error: redundant redefinition of a binding `b`
-  --> $DIR/redundant_locals.rs:62:5
+  --> $DIR/redundant_locals.rs:63:5
    |
 LL |     let b = b;
    |     ^^^^^^^^^^
    |
 help: `b` is initially defined here
-  --> $DIR/redundant_locals.rs:60:9
+  --> $DIR/redundant_locals.rs:61:9
    |
 LL |     let b = 2;
    |         ^
 
 error: redundant redefinition of a binding `x`
-  --> $DIR/redundant_locals.rs:68:9
+  --> $DIR/redundant_locals.rs:69:9
    |
 LL |         let x = x;
    |         ^^^^^^^^^^
    |
 help: `x` is initially defined here
-  --> $DIR/redundant_locals.rs:67:13
+  --> $DIR/redundant_locals.rs:68:13
    |
 LL |         let x = 1;
    |             ^
 
 error: redundant redefinition of a binding `x`
-  --> $DIR/redundant_locals.rs:75:9
+  --> $DIR/redundant_locals.rs:76:9
    |
 LL |         let x = x;
    |         ^^^^^^^^^^
    |
 help: `x` is initially defined here
-  --> $DIR/redundant_locals.rs:74:13
+  --> $DIR/redundant_locals.rs:75:13
    |
 LL |         let x = 1;
    |             ^
 
 error: redundant redefinition of a binding `x`
-  --> $DIR/redundant_locals.rs:78:9
+  --> $DIR/redundant_locals.rs:79:9
    |
 LL |         let x = x;
    |         ^^^^^^^^^^
    |
 help: `x` is initially defined here
-  --> $DIR/redundant_locals.rs:77:6
+  --> $DIR/redundant_locals.rs:78:6
    |
 LL |     |x: i32| {
    |      ^
 
 error: redundant redefinition of a binding `x`
-  --> $DIR/redundant_locals.rs:97:9
+  --> $DIR/redundant_locals.rs:98:9
    |
 LL |         let x = x;
    |         ^^^^^^^^^^
    |
 help: `x` is initially defined here
-  --> $DIR/redundant_locals.rs:94:9
+  --> $DIR/redundant_locals.rs:95:9
    |
 LL |     let x = 1;
    |         ^
 
 error: redundant redefinition of a binding `a`
-  --> $DIR/redundant_locals.rs:152:5
+  --> $DIR/redundant_locals.rs:153:5
    |
 LL |     let a = a;
    |     ^^^^^^^^^^
    |
 help: `a` is initially defined here
-  --> $DIR/redundant_locals.rs:150:9
+  --> $DIR/redundant_locals.rs:151:9
    |
 LL |     let a = WithoutDrop(1);
    |         ^