Indentation on multiline single generic bound

src/formatting/types.rs

@@ -942,6 +942,24 @@ fn join_bounds_inner(
         ast::GenericBound::Trait(..) => last_line_extendable(s),
     };
 
+    // Whether a PathSegment segment includes internal array containing more than one item
+    let is_segment_with_multi_items_array = |seg: &ast::PathSegment| {
+        if let Some(args_in) = &seg.args {
+            match &**args_in {
+                ast::AngleBracketed(args) => {
+                    if args.args.len() > 1 {
+                        true
+                    } else {
+                        false
+                    }
+                }
+                _ => false,
+            }
+        } else {
+            false
+        }
+    };
+
     let result = items.iter().enumerate().try_fold(
         (String::new(), None, false),
         |(strs, prev_trailing_span, prev_extendable), (i, item)| {
@@ -1036,10 +1054,33 @@ fn join_bounds_inner(
         },
     )?;
 
-    if !force_newline
-        && items.len() > 1
-        && (result.0.contains('\n') || result.0.len() > shape.width)
-    {
+    // Whether retry the function with forced newline is needed:
+    //   Only if result is not already multiline and did not exceed line width,
+    //   and either there is more than one item;
+    //       or the single item is of type `Trait`,
+    //          and any of the internal arrays contains more than one item;
+    let retry_with_force_newline =
+        if force_newline || (!result.0.contains('\n') && result.0.len() <= shape.width) {
+            false
+        } else {
+            if items.len() > 1 {
+                true
+            } else {
+                match items[0] {
+                    ast::GenericBound::Trait(ref poly_trait_ref, ..) => {
+                        let segments = &poly_trait_ref.trait_ref.path.segments;
+                        if segments.len() > 1 {
+                            true
+                        } else {
+                            is_segment_with_multi_items_array(&segments[0])
+                        }
+                    }
+                    _ => false,
+                }
+            }
+        };
+
+    if retry_with_force_newline {
         join_bounds_inner(context, shape, items, need_indent, true)
     } else {
         Some(result.0)

tests/source/issue-4689.rs

@@ -0,0 +1,147 @@
+// Based on the issue description
+pub trait PrettyPrinter<'tcx>:
+Printer<
+'tcx,
+Error = fmt::Error,
+Path = Self,
+Region = Self,
+Type = Self,
+DynExistential = Self,
+Const = Self,
+>
+{
+//
+}
+pub trait PrettyPrinter<'tcx>:
+Printer<
+'tcx,
+Error = fmt::Error,
+Path = Self,
+Region = Self,
+Type = Self,
+DynExistential = Self,
+Const = Self,
+> + fmt::Write
+{
+//
+}
+pub trait PrettyPrinter<'tcx>:
+Printer<
+'tcx,
+Error = fmt::Error,
+Path = Self,
+Region = Self,
+Type = Self,
+DynExistential = Self,
+Const = Self,
+> + fmt::Write1 + fmt::Write2
+{
+//
+}
+pub trait PrettyPrinter<'tcx>:
+fmt::Write + Printer<
+'tcx,
+Error = fmt::Error,
+Path = Self,
+Region = Self,
+Type = Self,
+DynExistential = Self,
+Const = Self,
+>
+{
+//
+}
+pub trait PrettyPrinter<'tcx>:
+fmt::Write + Printer1<
+'tcx,
+Error = fmt::Error,
+Path = Self,
+Region = Self,
+Type = Self,
+DynExistential = Self,
+Const = Self,
+> + Printer2<
+'tcx,
+Error = fmt::Error,
+Path = Self,
+Region = Self,
+Type = Self,
+DynExistential = Self,
+Const = Self,
+>
+{
+//
+}
+
+// Some test cases to ensure other cases formatting were not changed
+fn f() -> Box<
+FnMut() -> Thing<
+WithType = LongItemName,
+Error = LONGLONGLONGLONGLONGONGEvenLongerErrorNameLongerLonger,
+>,
+> {
+}
+fn f() -> Box<
+FnMut() -> Thing<
+WithType = LongItemName,
+Error = LONGLONGLONGLONGLONGONGEvenLongerErrorNameLongerLonger,
+> + fmt::Write1
++ fmt::Write2,
+> {
+}
+
+fn foo<F>(foo2: F)
+where
+F: Fn(
+// this comment is deleted
+)
+{
+}
+fn foo<F>(foo2: F)
+where
+F: Fn(
+// this comment is deleted
+) + fmt::Write
+{
+}
+
+fn elaborate_bounds<F>(mut mk_cand: F)
+where
+F: for<> FnMut(
+&mut ProbeContext<>,
+ty::PolyTraitRefffffffffffffffffffffffffffffffff<>,
+tyyyyyyyyyyyyyyyyyyyyy::AssociatedItem,
+),
+{
+}
+fn elaborate_bounds<F>(mut mk_cand: F)
+where
+F: for<> FnMut(
+&mut ProbeContext<>,
+ty::PolyTraitRefffffffffffffffffffffffffffffffff<>,
+tyyyyyyyyyyyyyyyyyyyyy::AssociatedItem,
+) + fmt::Write,
+{
+}
+
+fn build_sorted_static_get_entry_names(
+mut entries: entryyyyyyyy,
+) -> (
+impl Fn(
+AlphabeticalTraversal,
+Seconddddddddddddddddddddddddddddddddddd
+) -> Parammmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
++ Sendddddddddddddddddddddddddddddddddddddddddddd
+) {
+}
+
+pub trait SomeTrait:
+Cloneeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
++ Eqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq
+{
+}
+
+trait B = where
+for<'b> &'b Self: Send
++ Cloneeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
++ Copyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy;

tests/target/issue-4689.rs

@@ -0,0 +1,150 @@
+// Based on the issue description
+pub trait PrettyPrinter<'tcx>:
+    Printer<
+        'tcx,
+        Error = fmt::Error,
+        Path = Self,
+        Region = Self,
+        Type = Self,
+        DynExistential = Self,
+        Const = Self,
+    >
+{
+    //
+}
+pub trait PrettyPrinter<'tcx>:
+    Printer<
+        'tcx,
+        Error = fmt::Error,
+        Path = Self,
+        Region = Self,
+        Type = Self,
+        DynExistential = Self,
+        Const = Self,
+    > + fmt::Write
+{
+    //
+}
+pub trait PrettyPrinter<'tcx>:
+    Printer<
+        'tcx,
+        Error = fmt::Error,
+        Path = Self,
+        Region = Self,
+        Type = Self,
+        DynExistential = Self,
+        Const = Self,
+    > + fmt::Write1
+    + fmt::Write2
+{
+    //
+}
+pub trait PrettyPrinter<'tcx>:
+    fmt::Write
+    + Printer<
+        'tcx,
+        Error = fmt::Error,
+        Path = Self,
+        Region = Self,
+        Type = Self,
+        DynExistential = Self,
+        Const = Self,
+    >
+{
+    //
+}
+pub trait PrettyPrinter<'tcx>:
+    fmt::Write
+    + Printer1<
+        'tcx,
+        Error = fmt::Error,
+        Path = Self,
+        Region = Self,
+        Type = Self,
+        DynExistential = Self,
+        Const = Self,
+    > + Printer2<
+        'tcx,
+        Error = fmt::Error,
+        Path = Self,
+        Region = Self,
+        Type = Self,
+        DynExistential = Self,
+        Const = Self,
+    >
+{
+    //
+}
+
+// Some test cases to ensure other cases formatting were not changed
+fn f() -> Box<
+    FnMut() -> Thing<
+        WithType = LongItemName,
+        Error = LONGLONGLONGLONGLONGONGEvenLongerErrorNameLongerLonger,
+    >,
+> {
+}
+fn f() -> Box<
+    FnMut() -> Thing<
+            WithType = LongItemName,
+            Error = LONGLONGLONGLONGLONGONGEvenLongerErrorNameLongerLonger,
+        > + fmt::Write1
+        + fmt::Write2,
+> {
+}
+
+fn foo<F>(foo2: F)
+where
+    F: Fn(
+        // this comment is deleted
+    ),
+{
+}
+fn foo<F>(foo2: F)
+where
+    F: Fn(
+            // this comment is deleted
+        ) + fmt::Write,
+{
+}
+
+fn elaborate_bounds<F>(mut mk_cand: F)
+where
+    F: FnMut(
+        &mut ProbeContext,
+        ty::PolyTraitRefffffffffffffffffffffffffffffffff,
+        tyyyyyyyyyyyyyyyyyyyyy::AssociatedItem,
+    ),
+{
+}
+fn elaborate_bounds<F>(mut mk_cand: F)
+where
+    F: FnMut(
+            &mut ProbeContext,
+            ty::PolyTraitRefffffffffffffffffffffffffffffffff,
+            tyyyyyyyyyyyyyyyyyyyyy::AssociatedItem,
+        ) + fmt::Write,
+{
+}
+
+fn build_sorted_static_get_entry_names(
+    mut entries: entryyyyyyyy,
+) -> (
+    impl Fn(
+        AlphabeticalTraversal,
+        Seconddddddddddddddddddddddddddddddddddd,
+    ) -> Parammmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
+    + Sendddddddddddddddddddddddddddddddddddddddddddd
+) {
+}
+
+pub trait SomeTrait:
+    Cloneeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
+    + Eqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq
+{
+}
+
+trait B = where
+    for<'b> &'b Self: Send
+        + Cloneeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
+        + Copyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy;