Avoid using the cell_leak feature

Author: topecongiro

rustfmt-core/rustfmt-lib/src/formatting/report.rs

@@ -1,4 +1,4 @@
-use std::cell::{Ref, RefCell};
+use std::cell::RefCell;
 use std::collections::{BTreeMap, BTreeSet, HashSet};
 use std::rc::Rc;
 
@@ -92,8 +92,9 @@ impl FormatReport {
     /// various warnings and errors encountered during formatting.
     //
     // NOTE: Avoid using this method internally: use `format_result_as_rc` instead.
-    pub fn format_result(&self) -> impl Iterator<Item = (&FileName, &FormatResult)> {
-        Ref::leak(RefCell::borrow(&self.format_result)).iter()
+    // FIXME(topecongiro): Avoid requiring a mutable reference.
+    pub fn format_result(&mut self) -> impl Iterator<Item = (&FileName, &FormatResult)> {
+        Rc::make_mut(&mut self.format_result).get_mut().iter()
     }
 
     pub(crate) fn format_result_as_rc(&self) -> Rc<RefCell<BTreeMap<FileName, FormatResult>>> {

rustfmt-core/rustfmt-lib/src/lib.rs

@@ -1,6 +1,5 @@
 #![deny(rust_2018_idioms)]
 #![warn(unreachable_pub)]
-#![feature(cell_leak)]
 
 #[macro_use]
 extern crate lazy_static;

rustfmt-core/rustfmt-lib/src/test/configuration_snippet.rs

@@ -186,7 +186,7 @@ impl ConfigCodeBlock {
             return false;
         }
 
-        let report = report.unwrap();
+        let mut report = report.unwrap();
         let result = report.format_result().next().unwrap();
         let text = result.1.formatted_text();
         !self.formatted_has_diff(text)

rustfmt-core/rustfmt-lib/src/test/mod.rs

@@ -651,7 +651,7 @@ fn idempotent_check(
     } else {
         read_config(filename)
     };
-    let format_report = match format_file(filename, builder, config) {
+    let mut format_report = match format_file(filename, builder, config) {
         Ok(report) => report,
         Err(_) => return Err(IdempotentCheckError::Parse),
     };