Remove Drop-caused migration-added captures

All of these were added due to insignificant Drop types being present.

Author: Mark-Simulacrum

compiler/rustc_infer/src/infer/at.rs

@@ -195,10 +195,10 @@ impl<'a, 'tcx> Trace<'a, 'tcx> {
         let Trace { at, trace, a_is_expected } = self;
         at.infcx.commit_if_ok(|_| {
             let mut fields = at.infcx.combine_fields(trace, at.param_env);
-            fields.sub(a_is_expected).relate(a, b).map(move |_| {
-                let _ = &fields;
-                InferOk { value: (), obligations: fields.obligations }
-            })
+            fields
+                .sub(a_is_expected)
+                .relate(a, b)
+                .map(move |_| InferOk { value: (), obligations: fields.obligations })
         })
     }
 
@@ -212,10 +212,10 @@ impl<'a, 'tcx> Trace<'a, 'tcx> {
         let Trace { at, trace, a_is_expected } = self;
         at.infcx.commit_if_ok(|_| {
             let mut fields = at.infcx.combine_fields(trace, at.param_env);
-            fields.equate(a_is_expected).relate(a, b).map(move |_| {
-                let _ = &fields;
-                InferOk { value: (), obligations: fields.obligations }
-            })
+            fields
+                .equate(a_is_expected)
+                .relate(a, b)
+                .map(move |_| InferOk { value: (), obligations: fields.obligations })
         })
     }
 
@@ -227,10 +227,10 @@ impl<'a, 'tcx> Trace<'a, 'tcx> {
         let Trace { at, trace, a_is_expected } = self;
         at.infcx.commit_if_ok(|_| {
             let mut fields = at.infcx.combine_fields(trace, at.param_env);
-            fields.lub(a_is_expected).relate(a, b).map(move |t| {
-                let _ = &fields;
-                InferOk { value: t, obligations: fields.obligations }
-            })
+            fields
+                .lub(a_is_expected)
+                .relate(a, b)
+                .map(move |t| InferOk { value: t, obligations: fields.obligations })
         })
     }
 
@@ -242,10 +242,10 @@ impl<'a, 'tcx> Trace<'a, 'tcx> {
         let Trace { at, trace, a_is_expected } = self;
         at.infcx.commit_if_ok(|_| {
             let mut fields = at.infcx.combine_fields(trace, at.param_env);
-            fields.glb(a_is_expected).relate(a, b).map(move |t| {
-                let _ = &fields;
-                InferOk { value: t, obligations: fields.obligations }
-            })
+            fields
+                .glb(a_is_expected)
+                .relate(a, b)
+                .map(move |t| InferOk { value: t, obligations: fields.obligations })
         })
     }
 }

compiler/rustc_mir_build/src/lints.rs

@@ -41,7 +41,6 @@ crate fn check<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
         let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
         let sp = tcx.sess.source_map().guess_head_span(tcx.hir().span_with_body(hir_id));
         tcx.struct_span_lint_hir(UNCONDITIONAL_RECURSION, hir_id, sp, |lint| {
-            let _ = &vis;
             let mut db = lint.build("function cannot return without recursing");
             db.span_label(sp, "cannot return without recursing");
             // offer some help to the programmer.

compiler/rustc_trait_selection/src/traits/query/type_op/custom.rs

@@ -40,10 +40,7 @@ where
             info!("fully_perform({:?})", self);
         }
 
-        scrape_region_constraints(infcx, || {
-            let _ = &self;
-            (self.closure)(infcx)
-        })
+        scrape_region_constraints(infcx, || (self.closure)(infcx))
     }
 }
 

compiler/rustc_trait_selection/src/traits/specialize/mod.rs

@@ -394,7 +394,6 @@ fn report_conflicting_impls(
     // now because the struct_lint methods don't return back the DiagnosticBuilder
     // that's passed in.
     let decorate = |err: LintDiagnosticBuilder<'_>| {
-        let _ = &overlap;
         let msg = format!(
             "conflicting implementations of trait `{}`{}{}",
             overlap.trait_desc,

compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs

@@ -105,7 +105,6 @@ impl ChildrenExt for Children {
 
                 // FIXME: should postpone string formatting until we decide to actually emit.
                 with_no_trimmed_paths(|| {
-                    let _ = &overlap;
                     OverlapError {
                         with_impl: possible_sibling,
                         trait_desc: trait_ref.print_only_trait_path().to_string(),

compiler/rustc_typeck/src/check/compare_method.rs

@@ -1192,7 +1192,6 @@ fn compare_type_predicate_entailment<'tcx>(
         normalize_cause.clone(),
     );
     tcx.infer_ctxt().enter(|infcx| {
-        let _ = &impl_ty_own_bounds;
         let inh = Inherited::new(infcx, impl_ty.def_id.expect_local());
         let infcx = &inh.infcx;
 

compiler/rustc_typeck/src/check/method/probe.rs

@@ -441,7 +441,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // this creates one big transaction so that all type variables etc
         // that we create during the probe process are removed later
         self.probe(|_| {
-            let _ = &steps;
             let mut probe_cx = ProbeContext::new(
                 self,
                 span,

src/librustdoc/doctest.rs

@@ -964,7 +964,6 @@ impl Tester for Collector {
                 test_type: test::TestType::DocTest,
             },
             testfn: test::DynTestFn(Box::new(move || {
-                let _ = &config;
                 let report_unused_externs = |uext| {
                     unused_externs.lock().unwrap().push(uext);
                 };

src/tools/clippy/clippy_utils/src/lib.rs

@@ -990,10 +990,7 @@ pub fn can_move_expr_to_closure(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) ->
         captures: HirIdMap::default(),
     };
     v.visit_expr(expr);
-    v.allow_closure.then(|| {
-        let _ = &v;
-        v.captures
-    })
+    v.allow_closure.then(|| v.captures)
 }
 
 /// Returns the method names and argument list of nested method call expressions that make up