return_and_then: only lint returning expressions

If an expression is not going to return from the current function of
closure, it should not get linted.

This also allows `return` expression to be linted, in addition to the
final expression. Those require blockification and proper indentation.

clippy_lints/src/methods/return_and_then.rs

@@ -9,7 +9,7 @@ use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::source::{indent_of, reindent_multiline, snippet_with_applicability};
 use clippy_utils::ty::get_type_diagnostic_name;
 use clippy_utils::visitors::for_each_unconsumed_temporary;
-use clippy_utils::{is_expr_final_block_expr, peel_blocks};
+use clippy_utils::{get_parent_expr, peel_blocks};
 
 use super::RETURN_AND_THEN;
 
@@ -21,7 +21,7 @@ pub(super) fn check<'tcx>(
     recv: &'tcx hir::Expr<'tcx>,
     arg: &'tcx hir::Expr<'_>,
 ) {
-    if !is_expr_final_block_expr(cx.tcx, expr) {
+    if cx.tcx.hir_get_fn_id_for_return_block(expr.hir_id).is_none() {
         return;
     }
 
@@ -55,12 +55,24 @@ pub(super) fn check<'tcx>(
         None => &body_snip,
     };
 
-    let sugg = format!(
-        "let {} = {}?;\n{}",
-        arg_snip,
-        recv_snip,
-        reindent_multiline(inner, false, indent_of(cx, expr.span))
-    );
+    // If suggestion is going to get inserted as part of a `return` expression, it must be blockified.
+    let sugg = if let Some(parent_expr) = get_parent_expr(cx, expr) {
+        let base_indent = indent_of(cx, parent_expr.span);
+        let inner_indent = base_indent.map(|i| i + 4);
+        format!(
+            "{}\n{}\n{}",
+            reindent_multiline(&format!("{{\nlet {arg_snip} = {recv_snip}?;"), true, inner_indent),
+            reindent_multiline(inner, false, inner_indent),
+            reindent_multiline("}", false, base_indent),
+        )
+    } else {
+        format!(
+            "let {} = {}?;\n{}",
+            arg_snip,
+            recv_snip,
+            reindent_multiline(inner, false, indent_of(cx, expr.span))
+        )
+    };
 
     span_lint_and_sugg(
         cx,