implement Drop from FmtVisitor in order to simplify failures passing

src/expr.rs

@@ -522,9 +522,6 @@ pub fn rewrite_block_with_visitor(
     let inner_attrs = attrs.map(inner_attributes);
     let label_str = rewrite_label(label);
     visitor.visit_block(block, inner_attrs.as_ref().map(|a| &**a), has_braces);
-    if visitor.macro_rewrite_failure {
-        context.macro_rewrite_failure.replace(true);
-    }
     Some(format!("{}{}{}", prefix, label_str, visitor.buffer))
 }
 

src/formatting.rs

@@ -175,7 +175,7 @@ impl<'a, T: FormatHandler + 'a> FormatContext<'a, T> {
         }
 
         self.handler
-            .handle_formatted_file(path, visitor.buffer, &mut self.report)
+            .handle_formatted_file(path, visitor.buffer.to_owned(), &mut self.report)
     }
 }
 

src/items.rs

@@ -747,10 +747,6 @@ pub fn format_impl(
 
             visitor.format_missing(item.span.hi() - BytePos(1));
 
-            if visitor.macro_rewrite_failure {
-                context.macro_rewrite_failure.replace(true);
-            }
-
             let inner_indent_str = visitor.block_indent.to_string_with_newline(context.config);
             let outer_indent_str = offset.block_only().to_string_with_newline(context.config);
 
@@ -1110,10 +1106,6 @@ pub fn format_trait(context: &RewriteContext, item: &ast::Item, offset: Indent)
 
             visitor.format_missing(item.span.hi() - BytePos(1));
 
-            if visitor.macro_rewrite_failure {
-                context.macro_rewrite_failure.replace(true);
-            }
-
             let inner_indent_str = visitor.block_indent.to_string_with_newline(context.config);
             let outer_indent_str = offset.block_only().to_string_with_newline(context.config);
 

src/macros.rs

@@ -69,10 +69,7 @@ impl Rewrite for ast::Item {
         visitor.block_indent = shape.indent;
         visitor.last_pos = self.span().lo();
         visitor.visit_item(self);
-        if visitor.macro_rewrite_failure {
-            context.macro_rewrite_failure.replace(true);
-        }
-        Some(visitor.buffer)
+        Some(visitor.buffer.to_owned())
     }
 }
 

src/visitor.rs

@@ -60,6 +60,7 @@ impl<'a> SnippetProvider<'a> {
 }
 
 pub struct FmtVisitor<'a> {
+    parent_context: Option<&'a RewriteContext<'a>>,
     pub parse_session: &'a ParseSess,
     pub source_map: &'a SourceMap,
     pub buffer: String,
@@ -75,7 +76,21 @@ pub struct FmtVisitor<'a> {
     pub(crate) report: FormatReport,
 }
 
+impl<'a> Drop for FmtVisitor<'a> {
+    fn drop(&mut self) {
+        if let Some(ctx) = self.parent_context {
+            if self.macro_rewrite_failure {
+                ctx.macro_rewrite_failure.replace(true);
+            }
+        }
+    }
+}
+
 impl<'b, 'a: 'b> FmtVisitor<'a> {
+    fn set_parent_context(&mut self, context: &'a RewriteContext) {
+        self.parent_context = Some(context);
+    }
+
     pub fn shape(&self) -> Shape {
         Shape::indented(self.block_indent, self.config)
     }
@@ -579,12 +594,14 @@ impl<'b, 'a: 'b> FmtVisitor<'a> {
     }
 
     pub fn from_context(ctx: &'a RewriteContext) -> FmtVisitor<'a> {
-        FmtVisitor::from_source_map(
+        let mut visitor = FmtVisitor::from_source_map(
             ctx.parse_session,
             ctx.config,
             ctx.snippet_provider,
             ctx.report.clone(),
-        )
+        );
+        visitor.set_parent_context(ctx);
+        visitor
     }
 
     pub(crate) fn from_source_map(
@@ -594,6 +611,7 @@ impl<'b, 'a: 'b> FmtVisitor<'a> {
         report: FormatReport,
     ) -> FmtVisitor<'a> {
         FmtVisitor {
+            parent_context: None,
             parse_session,
             source_map: parse_session.source_map(),
             buffer: String::with_capacity(snippet_provider.big_snippet.len() * 2),