Changes per comments and with added test cases

src/formatting/expr.rs

@@ -1938,12 +1938,13 @@ pub(crate) fn rewrite_assign_rhs<S: Into<String>, R: Rewrite>(
     rewrite_assign_rhs_with(context, lhs, ex, shape, RhsTactics::Default)
 }
 
-pub(crate) fn rewrite_assign_rhs_expr<R: Rewrite>(
+pub(crate) fn rewrite_rhs_expr<R: Rewrite>(
     context: &RewriteContext<'_>,
     lhs: &str,
     ex: &R,
     shape: Shape,
     rhs_tactics: RhsTactics,
+    lhs_separator: &str,
 ) -> Option<String> {
     let last_line_width = last_line_width(&lhs).saturating_sub(if lhs.contains('\n') {
         shape.indent.width()
@@ -1956,7 +1957,7 @@ pub(crate) fn rewrite_assign_rhs_expr<R: Rewrite>(
         offset: shape.offset + last_line_width + 1,
         ..shape
     });
-    let has_rhs_comment = if let Some(offset) = lhs.find_last_uncommented("=") {
+    let has_rhs_comment = if let Some(offset) = lhs.find_last_uncommented(lhs_separator) {
         lhs.trim_end().len() > offset + 1
     } else {
         false
@@ -1980,7 +1981,7 @@ pub(crate) fn rewrite_assign_rhs_with<S: Into<String>, R: Rewrite>(
     rhs_tactics: RhsTactics,
 ) -> Option<String> {
     let lhs = lhs.into();
-    let rhs = rewrite_assign_rhs_expr(context, &lhs, ex, shape, rhs_tactics)?;
+    let rhs = rewrite_rhs_expr(context, &lhs, ex, shape, rhs_tactics, "=")?;
     Some(lhs + &rhs)
 }
 
@@ -2000,7 +2001,7 @@ pub(crate) fn rewrite_assign_rhs_with_comments<S: Into<String>, R: Rewrite>(
     } else {
         shape
     };
-    let rhs = rewrite_assign_rhs_expr(context, &lhs, ex, shape, rhs_tactics)?;
+    let rhs = rewrite_rhs_expr(context, &lhs, ex, shape, rhs_tactics, "=")?;
 
     if contains_comment {
         let rhs = rhs.trim_start();
@@ -2010,6 +2011,35 @@ pub(crate) fn rewrite_assign_rhs_with_comments<S: Into<String>, R: Rewrite>(
     }
 }
 
+pub(crate) fn rewrite_trait_rhs_with_comments<S: Into<String>, R: Rewrite>(
+    context: &RewriteContext<'_>,
+    lhs: S,
+    ex: &R,
+    shape: Shape,
+    rhs_tactics: RhsTactics,
+    between_span: Span,
+    allow_extend: bool,
+) -> Option<String> {
+    let lhs = lhs.into();
+    let contains_comment = contains_comment(context.snippet(between_span));
+
+    let rhs = rewrite_rhs_expr(context, &lhs, ex, shape, rhs_tactics, ":")?;
+
+    if contains_comment {
+        let rhs = rhs.trim_start();
+        combine_strs_with_missing_comments(
+            context,
+            &lhs,
+            &rhs,
+            between_span,
+            shape.block_left(context.config.tab_spaces())?,
+            allow_extend,
+        )
+    } else {
+        Some(lhs + &rhs)
+    }
+}
+
 fn choose_rhs<R: Rewrite>(
     context: &RewriteContext<'_>,
     expr: &R,

src/formatting/items.rs

@@ -19,7 +19,7 @@ use crate::formatting::{
     },
     expr::{
         is_empty_block, is_simple_block_stmt, rewrite_assign_rhs, rewrite_assign_rhs_with,
-        rewrite_assign_rhs_with_comments, RhsTactics,
+        rewrite_assign_rhs_with_comments, rewrite_trait_rhs_with_comments, RhsTactics,
     },
     lists::{definitive_tactic, itemize_list, write_list, ListFormatting, Separator},
     macros::{rewrite_macro, MacroPosition},
@@ -1122,6 +1122,12 @@ pub(crate) fn format_trait(
     if let ast::ItemKind::Trait(trait_kind) = &item.kind {
         let ast::TraitKind(is_auto, unsafety, ref generics, ref generic_bounds, ref trait_items) =
             **trait_kind;
+
+        // FIXME: rustfmt fails to format when there are comments before the ident.
+        if contains_comment(context.snippet(mk_sp(item.span.lo(), item.ident.span.lo()))) {
+            return None;
+        }
+
         let mut result = String::with_capacity(128);
         let header = format!(
             "{}{}{}trait ",
@@ -1131,35 +1137,23 @@ pub(crate) fn format_trait(
         );
         result.push_str(&header);
 
-        // FIXME: rustfmt fails to format when there are comments before the ident.
-        if contains_comment(context.snippet(mk_sp(item.span.lo(), generics.span.lo()))) {
-            return None;
-        }
-
         let body_lo = context.snippet_provider.span_after(item.span, "{");
 
         let shape = Shape::indented(offset, context.config).offset_left(result.len())?;
         let generics_str =
             rewrite_generics(context, rewrite_ident(context, item.ident), generics, shape)?;
         result.push_str(&generics_str);
 
-        // FIXME(#2055): rustfmt fails to format when there are comments within trait bounds.
         if !generic_bounds.is_empty() {
-            let bound_lo = generic_bounds.first().unwrap().span().lo();
-            let bound_hi = generic_bounds.last().unwrap().span().hi();
-            let snippet = context.snippet(mk_sp(bound_lo, bound_hi));
-            if contains_comment(snippet) {
-                return None;
-            }
-
             // Rewrite rhs and combine lhs with pre-bound comment
+            let bound_lo = generic_bounds.first().unwrap().span().lo();
             let ident_hi = context
                 .snippet_provider
                 .span_after(item.span, &item.ident.as_str());
             let ident_hi = context
                 .snippet_provider
                 .span_after(mk_sp(ident_hi, item.span.hi()), ":");
-            result = rewrite_assign_rhs_with_comments(
+            result = rewrite_trait_rhs_with_comments(
                 context,
                 result + ":",
                 generic_bounds,
@@ -1205,7 +1199,7 @@ pub(crate) fn format_trait(
             result.push_str(&where_clause_str);
         }
 
-        /* Note: `where_clause` always exists; Span is empty when no where clause in the code */
+        /* Note: `where_clause` always exists; Span is empty when no `where` clause in the code */
         let pre_block_span = mk_sp(generics.where_clause.span.hi(), item.span.hi());
         let pre_block_snippet = context.snippet(pre_block_span);
         if let Some(lo) = pre_block_snippet.find('/') {

src/formatting/macros.rs

@@ -1356,6 +1356,9 @@ impl MacroBranch {
             result += " =>";
         }
 
+        // Note (from issue #4759): comments between the end of `whole_body` and
+        // the end of `span` are currently ignored.
+
         if !context.config.format_macro_bodies() {
             result += " ";
             result += context.snippet(self.whole_body);

tests/source/lhs-to-rhs-between-comments/trait.rs

@@ -25,6 +25,15 @@ A + C
 + B
 {}
 pub trait Foo6:/* A and C */A + C    + B{}
+pub trait Foo7:
+A+C
+// and B
++B{}
+pub trait Foo8:
+// A and C
+A+C
+// and B
++B{}
 
 // Other cases
 trait Person{
@@ -68,3 +77,35 @@ trait /* comment 1 */ Programmer /* comment2 */ {
 trait /* comment1 */ CompSciStudent1: /* comment2 */ Programmer + Student /* comment3 */ {
     fn git_username(&self) -> String;
 }
+
+// Traits with where and comments
+trait Bar where Self: Sized, Option<Self>: Foo
+{}
+/*comment0*/trait Bar/*comment1*/where Self: Sized/*comment2*/,/*comment3*/Option<Self>: Foo/*comment4*/
+{}
+trait Bar//comment1 Longgggggggggggggggggggggggggggggggggggggggggggggggggg
+where Self: Sized/*comment2*/,/*comment3*/Option<Self>: Foo/*comment4*/
+{}
+trait Bar/*comment1*/where Self: Sized/*comment2*/,/*comment3*/Option<Self>: Foo//comment4 Longgggggggggggggggggggggggggggggggggggggggggggggggggg
+{}
+trait Bar/*comment1 Longgggggggggggggggggggggggggggggggggggggggggggggggggg*/where Self: Sized/*comment2 Longgggggggggggggggggggggggggggggggggggggggggggggggggg*/,/*comment3 Longgggggggggggggggggggggggggggggggggggggggggggggggggg*/Option<Self>: Foo/*comment4 Longgggggggggggggggggggggggggggggggggggggggggggggggggg*/
+{}
+trait ConstCheck<T>:/*comment1*/Foo where T: Baz/*comment2*/{ 
+    const   J:   i32;
+}
+
+// Some other trait cases with comments
+/*comment0*/auto trait Example/*comment1*/{}
+pub unsafe auto trait PubUnsafeExample/*comment1*/{}
+pub unsafe auto trait PubUnsafeExample// comment1
+{}
+trait Foo/*comment1*/{ type Bar: Baz; type Inner: Foo   = Box< Foo >; }
+pub trait Iterator/*comment1*/{
+    type Item;
+    fn next(&mut self) -> Option<Self::Item>;
+}
+pub trait Iterator//comment1
+{
+    type Item;
+    fn next(&mut self) -> Option<Self::Item>;
+}

tests/target/lhs-to-rhs-between-comments/trait.rs

@@ -19,6 +19,21 @@ pub trait Foo4: // A and C
 }
 pub trait Foo5: /* A and C */ A + C + B {}
 pub trait Foo6: /* A and C */ A + C + B {}
+pub trait Foo7:
+    A
+    + C
+    // and B
+    + B
+{
+}
+pub trait Foo8:
+    // A and C
+    A
+    + C
+    // and B
+    + B
+{
+}
 
 // Other cases
 trait Person {
@@ -68,3 +83,69 @@ trait /* comment 1 */ Programmer /* comment2 */ {
 trait /* comment1 */ CompSciStudent1: /* comment2 */ Programmer + Student /* comment3 */ {
     fn git_username(&self) -> String;
 }
+
+// Traits with where and comments
+trait Bar
+where
+    Self: Sized,
+    Option<Self>: Foo,
+{
+}
+/*comment0*/
+trait Bar
+/*comment1*/
+where
+    Self: Sized, /*comment2*/
+    /*comment3*/ Option<Self>: Foo, /*comment4*/
+{
+}
+trait Bar
+//comment1 Longgggggggggggggggggggggggggggggggggggggggggggggggggg
+where
+    Self: Sized, /*comment2*/
+    /*comment3*/ Option<Self>: Foo, /*comment4*/
+{
+}
+trait Bar
+/*comment1*/
+where
+    Self: Sized, /*comment2*/
+    /*comment3*/ Option<Self>: Foo,
+//comment4 Longgggggggggggggggggggggggggggggggggggggggggggggggggg
+{
+}
+trait Bar
+/*comment1 Longgggggggggggggggggggggggggggggggggggggggggggggggggg*/
+where
+    Self: Sized, /*comment2 Longgggggggggggggggggggggggggggggggggggggggggggggggggg*/
+    /*comment3 Longgggggggggggggggggggggggggggggggggggggggggggggggggg*/ Option<Self>: Foo,
+/*comment4 Longgggggggggggggggggggggggggggggggggggggggggggggggggg*/
+{
+}
+trait ConstCheck<T>: /*comment1*/ Foo
+where
+    T: Baz, /*comment2*/
+{
+    const J: i32;
+}
+
+// Some other trait cases with comments
+/*comment0*/
+auto trait Example /*comment1*/ {}
+pub unsafe auto trait PubUnsafeExample /*comment1*/ {}
+pub unsafe auto trait PubUnsafeExample // comment1
+{
+}
+trait Foo /*comment1*/ {
+    type Bar: Baz;
+    type Inner: Foo = Box<Foo>;
+}
+pub trait Iterator /*comment1*/ {
+    type Item;
+    fn next(&mut self) -> Option<Self::Item>;
+}
+pub trait Iterator //comment1
+{
+    type Item;
+    fn next(&mut self) -> Option<Self::Item>;
+}

tests/target/trait.rs

@@ -86,11 +86,13 @@ trait Y // comment
 
 // #2055
 pub trait Foo:
-// A and C
-A + C
-// and B
+    // A and C
+    A
+    + C
+    // and B
     + B
-{}
+{
+}
 
 // #2158
 trait Foo {

tests/target/trait_2015_edition.rs

@@ -89,11 +89,13 @@ trait Y // comment
 
 // #2055
 pub trait Foo:
-// A and C
-A + C
-// and B
+    // A and C
+    A
+    + C
+    // and B
     + B
-{}
+{
+}
 
 // #2158
 trait Foo {