add config inline_attribute_width

If the line width is width within config width, attribute is inline.
I don't want to change default rustfmt behavior, so config default value is 0.

Author: rchaser53

src/config/mod.rs

@@ -145,6 +145,8 @@ create_config! {
     emit_mode: EmitMode, EmitMode::Files, false,
         "What emit Mode to use when none is supplied";
     make_backup: bool, false, false, "Backup changed files";
+    inline_attribute_width: usize, 0, false,
+        "Attributes is in line when line width is within inline_attribute_width";
 }
 
 /// Loads a config by checking the client-supplied options and if appropriate, the

src/imports.rs

@@ -7,7 +7,7 @@ use syntax::source_map::{self, BytePos, Span, DUMMY_SP};
 
 use crate::comment::combine_strs_with_missing_comments;
 use crate::config::lists::*;
-use crate::config::{Edition, IndentStyle};
+use crate::config::{Edition, IndentStyle, Version};
 use crate::lists::{
     definitive_tactic, itemize_list, write_list, ListFormatting, ListItem, Separator,
 };
@@ -249,7 +249,23 @@ impl UseTree {
             let lo = attrs.last().as_ref()?.span().hi();
             let hi = self.span.lo();
             let span = mk_sp(lo, hi);
-            combine_strs_with_missing_comments(context, &attr_str, &use_str, span, shape, false)
+
+            let allow_extend = if context.config.version() == Version::Two {
+                let line_len = attr_str.len() + 1 + use_str.len();
+                !attrs.clone().first().unwrap().is_sugared_doc
+                    && context.config.inline_attribute_width() >= line_len
+            } else {
+                false
+            };
+
+            combine_strs_with_missing_comments(
+                context,
+                &attr_str,
+                &use_str,
+                span,
+                shape,
+                allow_extend,
+            )
         } else {
             Some(use_str)
         }

tests/config/inline_attribute_width.toml

@@ -0,0 +1 @@
+inline_attribute_width = 50

tests/source/issue-3343/one.rs

@@ -0,0 +1,14 @@
+// rustfmt-version: One
+// rustfmt-config: inline_attribute_width.toml
+
+#[cfg(feature = "alloc")]
+use core::slice;
+
+#[cfg(feature = "alloc")]
+use total_len_is::_50__;
+
+#[cfg(feature = "alloc")]
+use total_len_is::_51___;
+
+/// comment
+use core::convert;

tests/source/issue-3343/two.rs

@@ -0,0 +1,14 @@
+// rustfmt-version: Two
+// rustfmt-config: inline_attribute_width.toml
+
+#[cfg(feature = "alloc")]
+use core::slice;
+
+#[cfg(feature = "alloc")]
+use total_len_is::_50__;
+
+#[cfg(feature = "alloc")]
+use total_len_is::_51___;
+
+/// comment
+use core::convert;

tests/target/issue-3343/one.rs

@@ -0,0 +1,14 @@
+// rustfmt-version: One
+// rustfmt-config: inline_attribute_width.toml
+
+#[cfg(feature = "alloc")]
+use core::slice;
+
+#[cfg(feature = "alloc")]
+use total_len_is::_50__;
+
+#[cfg(feature = "alloc")]
+use total_len_is::_51___;
+
+/// comment
+use core::convert;

tests/target/issue-3343/two.rs

@@ -0,0 +1,12 @@
+// rustfmt-version: Two
+// rustfmt-config: inline_attribute_width.toml
+
+#[cfg(feature = "alloc")] use core::slice;
+
+#[cfg(feature = "alloc")] use total_len_is::_50__;
+
+#[cfg(feature = "alloc")]
+use total_len_is::_51___;
+
+/// comment
+use core::convert;