Handle comments between Trait Generics and Bounds

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 ",
@@ -1138,23 +1144,23 @@ pub(crate) fn format_trait(
             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 between trait bounds.
         if !generic_bounds.is_empty() {
+            // 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 bound_hi = generic_bounds.last().unwrap().span().hi();
-            let snippet = context.snippet(mk_sp(ident_hi, bound_hi));
-            if contains_comment(snippet) {
-                return None;
-            }
-
-            result = rewrite_assign_rhs_with(
+            let ident_hi = context
+                .snippet_provider
+                .span_after(mk_sp(ident_hi, item.span.hi()), ":");
+            result = rewrite_trait_rhs_with_comments(
                 context,
                 result + ":",
                 generic_bounds,
                 shape,
                 RhsTactics::ForceNextLineWithoutIndent,
+                mk_sp(ident_hi, bound_lo),
+                true,
             )?;
         }
 
@@ -1192,11 +1198,9 @@ pub(crate) fn format_trait(
             }
             result.push_str(&where_clause_str);
         }
-        let pre_block_span = if !generics.where_clause.predicates.is_empty() {
-            mk_sp(generics.where_clause.span.hi(), item.span.hi())
-        } else {
-            item.span
-        };
+
+        /* 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('/') {
             // 1 = `{`

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

@@ -0,0 +1,111 @@
+// Based on issue #2055:
+pub trait A {}
+pub trait B {}
+pub trait C {}
+pub trait Foo1:
+A + C
++ B
+{}
+pub trait Foo2:
+// A and C
+A + C
++ B
+{}
+pub trait Foo3:
+/* A and C */
+A + C
++ B
+{}
+pub trait Foo4:// A and C
+A + C
++ B
+{}
+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{
+fn name(&self) -> String;
+}
+/*comment1*/trait Person{
+fn name(&self) -> String;
+}
+trait Student:/* comment1 */Person/* comment2 */{
+fn university(&self) -> String;
+}
+trait Programmer/* comment1 */{
+fn fav_language(&self) -> String;
+}
+trait CompSciStudent1:/* comment1 */Programmer + Student/* comment2 */{
+fn git_username(&self) -> String;
+}
+trait CompSciStudent2:/* comment1 Longggggggggggggggggggggggggggggggggggggggggggggggggg */Programmer + Student/* comment2 */{
+fn git_username(&self) -> String;
+}
+trait CompSciStudent3:// comment1
+Programmer + Student/* comment2 */{
+fn git_username(&self) -> String;
+}
+trait CompSciStudent4:// comment1 Longgggggggggggggggggggggggggggggggggggggggggggggggggg
+Programmer + Student/* comment2 */{
+fn git_username(&self) -> String;
+}
+
+// Comment before Ident
+trait /* comment1 */ Person {
+    fn fav_language(&self) -> String;
+}
+trait // comment1
+Person {
+    fn fav_language(&self) -> String;
+}
+trait /* comment 1 */ Programmer /* comment2 */ {
+    fn fav_language(&self) -> String;
+}
+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>;
+}