Do not overflow a long item

Take the first line's width of a single item into account when
trying to overflow something.

Closes #2676.

src/overflow.rs

@@ -422,7 +422,7 @@ impl<'a, T: 'a + Rewrite + ToExpr + Spanned> Context<'a, T> {
         let extend_width = if items_str.is_empty() {
             paren_overhead
         } else {
-            paren_overhead / 2
+            first_line_width(items_str) + (paren_overhead / 2)
         };
         let nested_indent_str = self.nested_shape
             .indent

tests/source/expr.rs

@@ -391,3 +391,10 @@ fn dots() {
     ..= ..= ..;
     (..) .. ..; // ((..) .. (..))
 }
+
+// #2676
+// A function call with a large single argument.
+fn foo() {
+    let my_var =
+        Mutex::new(RpcClientType::connect(server_iddd).chain_err(|| "Unable to create RPC client")?);
+}

tests/target/expr.rs

@@ -416,3 +416,11 @@ fn dots() {
     ..= ..= ..;
     (..).. ..; // ((..) .. (..))
 }
+
+// #2676
+// A function call with a large single argument.
+fn foo() {
+    let my_var = Mutex::new(
+        RpcClientType::connect(server_iddd).chain_err(|| "Unable to create RPC client")?
+    );
+}