remove code duplication

Author: matthri

Diff for: clippy_lints/src/methods/get_first.rs

@@ -20,30 +20,23 @@ pub(super) fn check<'tcx>(
     if_chain! {
         if let Some(method_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
         if let Some(impl_id) = cx.tcx.impl_of_method(method_id);
-        if cx.tcx.type_of(impl_id).instantiate_identity().is_slice();
+        let identity = cx.tcx.type_of(impl_id).instantiate_identity();
         if let hir::ExprKind::Lit(Spanned { node: LitKind::Int(0, _), .. }) = arg.kind;
         then {
-            let mut app = Applicability::MachineApplicable;
-            let slice_name = snippet_with_applicability(cx, recv.span, "..", &mut app);
-            span_lint_and_sugg(
-                cx,
-                GET_FIRST,
-                expr.span,
-                &format!("accessing first element with `{slice_name}.get(0)`"),
-                "try",
-                format!("{slice_name}.first()"),
-                app,
-            );
-        }
-    }
-
-    if_chain! {
-        if let Some(method_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
-        if let Some(impl_id) = cx.tcx.impl_of_method(method_id);
-        if is_type_diagnostic_item(cx, cx.tcx.type_of(impl_id).instantiate_identity(), sym::VecDeque);
-        if let hir::ExprKind::Lit(Spanned { node: LitKind::Int(0, _), .. }) = arg.kind;
-        then {
-            let mut app = Applicability::MachineApplicable;
+            if identity.is_slice() {
+                let mut app = Applicability::MachineApplicable;
+                let slice_name = snippet_with_applicability(cx, recv.span, "..", &mut app);
+                span_lint_and_sugg(
+                    cx,
+                    GET_FIRST,
+                    expr.span,
+                    &format!("accessing first element with `{slice_name}.get(0)`"),
+                    "try",
+                    format!("{slice_name}.first()"),
+                    app,
+                );
+            } else if is_type_diagnostic_item(cx, identity, sym::VecDeque){
+                    let mut app = Applicability::MachineApplicable;
                     let slice_name = snippet_with_applicability(cx, recv.span, "..", &mut app);
                     span_lint_and_sugg(
                         cx,
@@ -54,6 +47,7 @@ pub(super) fn check<'tcx>(
                         format!("{slice_name}.front()"),
                         app,
                     );
+            }
         }
     }
 }