Use the correct BytePos for the opening brace position (rust-lang#3742)

Author: topecongiro

src/items.rs

@@ -1,7 +1,7 @@
 // Formatting top-level items - functions, structs, enums, traits, impls.
 
 use std::borrow::Cow;
-use std::cmp::{min, Ordering};
+use std::cmp::{max, min, Ordering};
 
 use regex::Regex;
 use rustc_target::spec::abi;
@@ -733,15 +733,16 @@ pub(crate) fn format_impl(
         }
 
         result.push('{');
-        // this is an impl body snippet(impl SampleImple { /* here */ })
-        let snippet = context.snippet(mk_sp(item.span.hi(), self_ty.span.hi()));
+        // this is an impl body snippet(impl SampleImpl { /* here */ })
+        let lo = max(self_ty.span.hi(), generics.where_clause.span.hi());
+        let snippet = context.snippet(mk_sp(lo, item.span.hi()));
         let open_pos = snippet.find_uncommented("{")? + 1;
 
         if !items.is_empty() || contains_comment(&snippet[open_pos..]) {
             let mut visitor = FmtVisitor::from_context(context);
             let item_indent = offset.block_only().block_indent(context.config);
             visitor.block_indent = item_indent;
-            visitor.last_pos = self_ty.span.hi() + BytePos(open_pos as u32);
+            visitor.last_pos = lo + BytePos(open_pos as u32);
 
             visitor.visit_attrs(&item.attrs, ast::AttrStyle::Inner);
             visitor.visit_impl_items(items);

tests/source/issue-3740.rs

@@ -0,0 +1,10 @@
+impl<T, const SIZE: usize> IntoNormalized for Vector<T, { SIZE }>
+    where
+        Vector<T, { SIZE }>: Div<Vector<T, { SIZE }>>,
+        for<'a> &'a Vector<T, { SIZE }>: IntoLength<Output = T>,
+{
+    type Output = Vector<T, { SIZE }>;
+    fn into_normalized(self) -> Self::Output {
+
+    }
+}

tests/target/issue-3740.rs

@@ -0,0 +1,8 @@
+impl<T, const SIZE: usize> IntoNormalized for Vector<T, { SIZE }>
+where
+    Vector<T, { SIZE }>: Div<Vector<T, { SIZE }>>,
+    for<'a> &'a Vector<T, { SIZE }>: IntoLength<Output = T>,
+{
+    type Output = Vector<T, { SIZE }>;
+    fn into_normalized(self) -> Self::Output {}
+}