map_identity: simplify lint emission (rust-lang#15797)

Instead of calling `span_lint_and_*` in multiple places, call
`span_lint_and_then` once and then use the `Diag` methods.

Diff best viewed with whitespace ignored

changelog: none

Author: blyxyas

clippy_lints/src/methods/map_identity.rs

@@ -1,4 +1,4 @@
-use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
+use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::source::snippet_with_applicability;
 use clippy_utils::ty::{is_copy, is_type_diagnostic_item};
 use clippy_utils::{is_expr_untyped_identity_function, is_mutable, is_trait_method, path_to_local_with_projections};
@@ -27,48 +27,46 @@ pub(super) fn check(
         && is_expr_untyped_identity_function(cx, map_arg)
         && let Some(call_span) = expr.span.trim_start(caller.span)
     {
-        let main_sugg = (call_span, String::new());
-        let mut app = if is_copy(cx, caller_ty) {
-            // there is technically a behavioral change here for `Copy` iterators, where
-            // `iter.map(|x| x).next()` would mutate a temporary copy of the iterator and
-            // changing it to `iter.next()` mutates iter directly
-            Applicability::Unspecified
-        } else {
-            Applicability::MachineApplicable
-        };
+        span_lint_and_then(cx, MAP_IDENTITY, call_span, MSG, |diag| {
+            let main_sugg = (call_span, String::new());
+            let mut app = if is_copy(cx, caller_ty) {
+                // there is technically a behavioral change here for `Copy` iterators, where
+                // `iter.map(|x| x).next()` would mutate a temporary copy of the iterator and
+                // changing it to `iter.next()` mutates iter directly
+                Applicability::Unspecified
+            } else {
+                Applicability::MachineApplicable
+            };
 
-        let needs_to_be_mutable = cx.typeck_results().expr_ty_adjusted(expr).is_mutable_ptr();
-        if needs_to_be_mutable && !is_mutable(cx, caller) {
-            if let Some(hir_id) = path_to_local_with_projections(caller)
-                && let Node::Pat(pat) = cx.tcx.hir_node(hir_id)
-                && let PatKind::Binding(_, _, ident, _) = pat.kind
-            {
-                // We can reach the binding -- suggest making it mutable
-                let suggs = vec![main_sugg, (ident.span.shrink_to_lo(), String::from("mut "))];
+            let needs_to_be_mutable = cx.typeck_results().expr_ty_adjusted(expr).is_mutable_ptr();
+            if needs_to_be_mutable && !is_mutable(cx, caller) {
+                if let Some(hir_id) = path_to_local_with_projections(caller)
+                    && let Node::Pat(pat) = cx.tcx.hir_node(hir_id)
+                    && let PatKind::Binding(_, _, ident, _) = pat.kind
+                {
+                    // We can reach the binding -- suggest making it mutable
+                    let suggs = vec![main_sugg, (ident.span.shrink_to_lo(), String::from("mut "))];
 
-                let ident = snippet_with_applicability(cx.sess(), ident.span, "_", &mut app);
+                    let ident = snippet_with_applicability(cx.sess(), ident.span, "_", &mut app);
 
-                span_lint_and_then(cx, MAP_IDENTITY, call_span, MSG, |diag| {
                     diag.multipart_suggestion(
                         format!("remove the call to `{name}`, and make `{ident}` mutable"),
                         suggs,
                         app,
                     );
-                });
-            } else {
-                // If we can't make the binding mutable, prevent the suggestion from being automatically applied,
-                // and add a complementary help message.
-                app = Applicability::Unspecified;
-
-                let method_requiring_mut = if let Node::Expr(expr) = cx.tcx.parent_hir_node(expr.hir_id)
-                    && let ExprKind::MethodCall(method, ..) = expr.kind
-                {
-                    Some(method.ident)
                 } else {
-                    None
-                };
+                    // If we can't make the binding mutable, prevent the suggestion from being automatically applied,
+                    // and add a complementary help message.
+                    app = Applicability::Unspecified;
+
+                    let method_requiring_mut = if let Node::Expr(expr) = cx.tcx.parent_hir_node(expr.hir_id)
+                        && let ExprKind::MethodCall(method, ..) = expr.kind
+                    {
+                        Some(method.ident)
+                    } else {
+                        None
+                    };
 
-                span_lint_and_then(cx, MAP_IDENTITY, call_span, MSG, |diag| {
                     diag.span_suggestion(main_sugg.0, format!("remove the call to `{name}`"), main_sugg.1, app);
 
                     let note = if let Some(method_requiring_mut) = method_requiring_mut {
@@ -77,18 +75,10 @@ pub(super) fn check(
                         "this must be made mutable".to_string()
                     };
                     diag.span_note(caller.span, note);
-                });
+                }
+            } else {
+                diag.span_suggestion(main_sugg.0, format!("remove the call to `{name}`"), main_sugg.1, app);
             }
-        } else {
-            span_lint_and_sugg(
-                cx,
-                MAP_IDENTITY,
-                main_sugg.0,
-                MSG,
-                format!("remove the call to `{name}`"),
-                main_sugg.1,
-                app,
-            );
-        }
+        });
     }
 }