From bdf105245bc5d548c21f3626ed576a808eac57ba Mon Sep 17 00:00:00 2001
From: rchaser53 <tayoshizawa29@gmail.com>
Date: Thu, 16 May 2019 13:22:25 +0900
Subject: [PATCH 1/2] fix `Const generics are handled incorrectly`

---
 src/comment.rs             | 6 ++++++
 tests/target/issue-3554.rs | 4 ++++
 2 files changed, 10 insertions(+)
 create mode 100644 tests/target/issue-3554.rs

diff --git a/src/comment.rs b/src/comment.rs
index 232d3745e59..be94e2db2c9 100644
--- a/src/comment.rs
+++ b/src/comment.rs
@@ -880,6 +880,12 @@ pub(crate) fn recover_missing_comment_in_span(
         Some(String::new())
     } else {
         let missing_snippet = context.snippet(span);
+        let trimmed_missing_snippet = missing_snippet.trim();
+        if !trimmed_missing_snippet.starts_with("//") && !trimmed_missing_snippet.starts_with("/*")
+        {
+            return None;
+        };
+
         let pos = missing_snippet.find('/').unwrap_or(0);
         // 1 = ` `
         let total_width = missing_comment.len() + used_width + 1;
diff --git a/tests/target/issue-3554.rs b/tests/target/issue-3554.rs
new file mode 100644
index 00000000000..4ece90403e1
--- /dev/null
+++ b/tests/target/issue-3554.rs
@@ -0,0 +1,4 @@
+#![feature(const_generics)]
+
+pub struct S<const N: usize>;
+impl S<{ 0 }> {}

From 53142b486d847e2bf846fd82b02ad602bab85d41 Mon Sep 17 00:00:00 2001
From: rchaser53 <tayoshizawa29@gmail.com>
Date: Thu, 16 May 2019 21:27:34 +0900
Subject: [PATCH 2/2] use the span between the self_ty and left brace

---
 src/comment.rs | 6 ------
 src/items.rs   | 3 ++-
 src/visitor.rs | 9 ++-------
 3 files changed, 4 insertions(+), 14 deletions(-)

diff --git a/src/comment.rs b/src/comment.rs
index be94e2db2c9..232d3745e59 100644
--- a/src/comment.rs
+++ b/src/comment.rs
@@ -880,12 +880,6 @@ pub(crate) fn recover_missing_comment_in_span(
         Some(String::new())
     } else {
         let missing_snippet = context.snippet(span);
-        let trimmed_missing_snippet = missing_snippet.trim();
-        if !trimmed_missing_snippet.starts_with("//") && !trimmed_missing_snippet.starts_with("/*")
-        {
-            return None;
-        };
-
         let pos = missing_snippet.find('/').unwrap_or(0);
         // 1 = ` `
         let total_width = missing_comment.len() + used_width + 1;
diff --git a/src/items.rs b/src/items.rs
index 17e67b3f79f..202eb2cf117 100644
--- a/src/items.rs
+++ b/src/items.rs
@@ -664,7 +664,6 @@ pub(crate) fn format_impl(
     context: &RewriteContext<'_>,
     item: &ast::Item,
     offset: Indent,
-    where_span_end: Option<BytePos>,
 ) -> Option<String> {
     if let ast::ItemKind::Impl(_, _, _, ref generics, _, ref self_ty, ref items) = item.node {
         let mut result = String::with_capacity(128);
@@ -691,6 +690,8 @@ pub(crate) fn format_impl(
             option.compress_where();
         }
 
+        let misssing_span = mk_sp(self_ty.span.hi(), item.span.hi());
+        let where_span_end = context.snippet_provider.opt_span_before(misssing_span, "{");
         let where_clause_str = rewrite_where_clause(
             context,
             &generics.where_clause,
diff --git a/src/visitor.rs b/src/visitor.rs
index f317e015423..5fdd0625dff 100644
--- a/src/visitor.rs
+++ b/src/visitor.rs
@@ -5,7 +5,7 @@ use syntax::source_map::{self, BytePos, Pos, SourceMap, Span};
 use syntax::{ast, visit};
 
 use crate::attr::*;
-use crate::comment::{CodeCharKind, CommentCodeSlices, FindUncommented};
+use crate::comment::{CodeCharKind, CommentCodeSlices};
 use crate::config::file_lines::FileName;
 use crate::config::{BraceStyle, Config, Version};
 use crate::expr::{format_expr, ExprType};
@@ -359,13 +359,8 @@ impl<'b, 'a: 'b> FmtVisitor<'a> {
             match item.node {
                 ast::ItemKind::Use(ref tree) => self.format_import(item, tree),
                 ast::ItemKind::Impl(..) => {
-                    let snippet = self.snippet(item.span);
-                    let where_span_end = snippet
-                        .find_uncommented("{")
-                        .map(|x| BytePos(x as u32) + source!(self, item.span).lo());
                     let block_indent = self.block_indent;
-                    let rw = self
-                        .with_context(|ctx| format_impl(&ctx, item, block_indent, where_span_end));
+                    let rw = self.with_context(|ctx| format_impl(&ctx, item, block_indent));
                     self.push_rewrite(item.span, rw);
                 }
                 ast::ItemKind::Trait(..) => {