Use default field values in a few more cases

Makes the use expressions significantly shorter.

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -2312,12 +2312,12 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
             tcx: TyCtxt<'hir>,
             issue_span: Span,
             expr_span: Span,
-            body_expr: Option<&'hir hir::Expr<'hir>>,
-            loop_bind: Option<&'hir Ident>,
-            loop_span: Option<Span>,
-            head_span: Option<Span>,
-            pat_span: Option<Span>,
-            head: Option<&'hir hir::Expr<'hir>>,
+            body_expr: Option<&'hir hir::Expr<'hir>> = None,
+            loop_bind: Option<&'hir Ident> = None,
+            loop_span: Option<Span> = None,
+            head_span: Option<Span> = None,
+            pat_span: Option<Span> = None,
+            head: Option<&'hir hir::Expr<'hir>> = None,
         }
         impl<'hir> Visitor<'hir> for ExprFinder<'hir> {
             fn visit_expr(&mut self, ex: &'hir hir::Expr<'hir>) {
@@ -2383,17 +2383,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                 hir::intravisit::walk_expr(self, ex);
             }
         }
-        let mut finder = ExprFinder {
-            tcx,
-            expr_span: span,
-            issue_span,
-            loop_bind: None,
-            body_expr: None,
-            head_span: None,
-            loop_span: None,
-            pat_span: None,
-            head: None,
-        };
+        let mut finder = ExprFinder { tcx, expr_span: span, issue_span, .. };
         finder.visit_expr(tcx.hir_body(body_id).value);
 
         if let Some(body_expr) = finder.body_expr
@@ -2628,13 +2618,13 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
 
         struct ExpressionFinder<'tcx> {
             capture_span: Span,
-            closure_change_spans: Vec<Span>,
-            closure_arg_span: Option<Span>,
-            in_closure: bool,
-            suggest_arg: String,
+            closure_change_spans: Vec<Span> = vec![],
+            closure_arg_span: Option<Span> = None,
+            in_closure: bool = false,
+            suggest_arg: String = String::new(),
             tcx: TyCtxt<'tcx>,
-            closure_local_id: Option<hir::HirId>,
-            closure_call_changes: Vec<(Span, String)>,
+            closure_local_id: Option<hir::HirId> = None,
+            closure_call_changes: Vec<(Span, String)> = vec![],
         }
         impl<'hir> Visitor<'hir> for ExpressionFinder<'hir> {
             fn visit_expr(&mut self, e: &'hir hir::Expr<'hir>) {
@@ -2715,16 +2705,8 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         }) = self.infcx.tcx.hir_node(self.mir_hir_id())
             && let hir::Node::Expr(expr) = self.infcx.tcx.hir_node(body_id.hir_id)
         {
-            let mut finder = ExpressionFinder {
-                capture_span: *capture_kind_span,
-                closure_change_spans: vec![],
-                closure_arg_span: None,
-                in_closure: false,
-                suggest_arg: String::new(),
-                closure_local_id: None,
-                closure_call_changes: vec![],
-                tcx: self.infcx.tcx,
-            };
+            let mut finder =
+                ExpressionFinder { capture_span: *capture_kind_span, tcx: self.infcx.tcx, .. };
             finder.visit_expr(expr);
 
             if finder.closure_change_spans.is_empty() || finder.closure_call_changes.is_empty() {

compiler/rustc_borrowck/src/lib.rs

@@ -4,6 +4,7 @@
 #![allow(internal_features)]
 #![feature(assert_matches)]
 #![feature(box_patterns)]
+#![feature(default_field_values)]
 #![feature(file_buffered)]
 #![feature(if_let_guard)]
 #![feature(negative_impls)]

compiler/rustc_hir_analysis/src/hir_wf_check.rs

@@ -51,12 +51,12 @@ pub(super) fn diagnostic_hir_wf_check<'tcx>(
     struct HirWfCheck<'tcx> {
         tcx: TyCtxt<'tcx>,
         predicate: ty::Predicate<'tcx>,
-        cause: Option<ObligationCause<'tcx>>,
-        cause_depth: usize,
+        cause: Option<ObligationCause<'tcx>> = None,
+        cause_depth: usize = 0,
         icx: ItemCtxt<'tcx>,
         def_id: LocalDefId,
         param_env: ty::ParamEnv<'tcx>,
-        depth: usize,
+        depth: usize = 0,
     }
 
     impl<'tcx> Visitor<'tcx> for HirWfCheck<'tcx> {
@@ -124,16 +124,8 @@ pub(super) fn diagnostic_hir_wf_check<'tcx>(
         }
     }
 
-    let mut visitor = HirWfCheck {
-        tcx,
-        predicate,
-        cause: None,
-        cause_depth: 0,
-        icx,
-        def_id,
-        param_env: tcx.param_env(def_id.to_def_id()),
-        depth: 0,
-    };
+    let param_env = tcx.param_env(def_id.to_def_id());
+    let mut visitor = HirWfCheck { tcx, predicate, icx, def_id, param_env, .. };
 
     // Get the starting `hir::Ty` using our `WellFormedLoc`.
     // We will walk 'into' this type to try to find

compiler/rustc_hir_analysis/src/lib.rs

@@ -59,6 +59,7 @@ This API is completely unstable and subject to change.
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(rustc::untranslatable_diagnostic)]
 #![feature(assert_matches)]
+#![feature(default_field_values)]
 #![feature(gen_blocks)]
 #![feature(if_let_guard)]
 #![feature(iter_intersperse)]