add config inline_attribute_width

Configurations.md

@@ -2408,6 +2408,27 @@ pub enum Foo {}
 pub enum Foo {}
 ```
 
+## `inline_attribute_width`
+
+Write an item and its attribute on the same line if their combined width is below a threshold
+
+- **Default value**: 0
+- **Possible values**: any positive integer
+- **Stable**: No (tracking issue: #3343)
+
+### Example
+
+#### `0` (default):
+```rust
+#[cfg(feature = "alloc")]
+use core::slice;
+```
+
+#### `50`:
+```rust
+#[cfg(feature = "alloc")] use core::slice;
+```
+
 ## `emit_mode`
 
 Internal option

src/config/mod.rs

@@ -105,6 +105,9 @@ create_config! {
         "Minimum number of blank lines which must be put between items";
     edition: Edition, Edition::Edition2015, true, "The edition of the parser (RFC 2052)";
     version: Version, Version::One, false, "Version of formatting rules";
+    inline_attribute_width: usize, 0, false,
+        "Write an item and its attribute on the same line \
+        if their combined width is below a threshold";
 
     // Options that can change the source code beyond whitespace/blocks (somewhat linty things)
     merge_derives: bool, true, true, "Merge multiple `#[derive(...)]` into a single one";

src/imports.rs

@@ -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 attrs.len() == 1 {
+                let line_len = attr_str.len() + 1 + use_str.len();
+                !attrs.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)
         }

src/reorder.rs

@@ -83,7 +83,22 @@ fn rewrite_reorderable_item(
         _ => return None,
     };
 
-    combine_strs_with_missing_comments(context, &attrs_str, &item_str, missed_span, shape, false)
+    let allow_extend = if attrs.len() == 1 {
+        let line_len = attrs_str.len() + 1 + item_str.len();
+        !attrs.first().unwrap().is_sugared_doc
+            && context.config.inline_attribute_width() >= line_len
+    } else {
+        false
+    };
+
+    combine_strs_with_missing_comments(
+        context,
+        &attrs_str,
+        &item_str,
+        missed_span,
+        shape,
+        allow_extend,
+    )
 }
 
 /// Rewrite a list of items with reordering. Every item in `items` must have

tests/source/issue-3343.rs

@@ -0,0 +1,48 @@
+// rustfmt-inline_attribute_width: 50
+
+#[cfg(feature = "alloc")]
+use core::slice;
+
+#[cfg(feature = "alloc")]
+use total_len_is::_50__;
+
+#[cfg(feature = "alloc")]
+use total_len_is::_51___;
+
+#[cfg(feature = "alloc")]
+extern crate len_is_50_;
+
+#[cfg(feature = "alloc")]
+extern crate len_is_51__;
+
+/// this is a comment to test is_sugared_doc property
+use core::convert;
+
+#[fooooo]
+#[barrrrr]
+use total_len_is_::_51______;
+
+#[cfg(not(all(
+    feature = "std",
+    any(
+        target_os = "linux",
+        target_os = "android",
+        target_os = "netbsd",
+        target_os = "dragonfly",
+        target_os = "haiku",
+        target_os = "emscripten",
+        target_os = "solaris",
+        target_os = "cloudabi",
+        target_os = "macos",
+        target_os = "ios",
+        target_os = "freebsd",
+        target_os = "openbsd",
+        target_os = "bitrig",
+        target_os = "redox",
+        target_os = "fuchsia",
+        windows,
+        all(target_arch = "wasm32", feature = "stdweb"),
+        all(target_arch = "wasm32", feature = "wasm-bindgen"),
+    )
+)))]
+use core::slice;

tests/target/issue-3343.rs

@@ -0,0 +1,45 @@
+// rustfmt-inline_attribute_width: 50
+
+#[cfg(feature = "alloc")] use core::slice;
+
+#[cfg(feature = "alloc")] use total_len_is::_50__;
+
+#[cfg(feature = "alloc")]
+use total_len_is::_51___;
+
+#[cfg(feature = "alloc")] extern crate len_is_50_;
+
+#[cfg(feature = "alloc")]
+extern crate len_is_51__;
+
+/// this is a comment to test is_sugared_doc property
+use core::convert;
+
+#[fooooo]
+#[barrrrr]
+use total_len_is_::_51______;
+
+#[cfg(not(all(
+    feature = "std",
+    any(
+        target_os = "linux",
+        target_os = "android",
+        target_os = "netbsd",
+        target_os = "dragonfly",
+        target_os = "haiku",
+        target_os = "emscripten",
+        target_os = "solaris",
+        target_os = "cloudabi",
+        target_os = "macos",
+        target_os = "ios",
+        target_os = "freebsd",
+        target_os = "openbsd",
+        target_os = "bitrig",
+        target_os = "redox",
+        target_os = "fuchsia",
+        windows,
+        all(target_arch = "wasm32", feature = "stdweb"),
+        all(target_arch = "wasm32", feature = "wasm-bindgen"),
+    )
+)))]
+use core::slice;