Merge #8674

8674: fix for #8664: Emit folding ranges for multi-line where clauses r=matklad a=m5tfi

#8664 

I added a test that assert folding multi-line where clauses while leaving single lined one. Please, let me know if the code needs further improvements.

Co-authored-by: m5tfi <72708423+m5tfi@users.noreply.github.com>

crates/ide/src/folding_ranges.rs

@@ -20,6 +20,7 @@ pub enum FoldKind {
     Consts,
     Statics,
     Array,
+    WhereClause,
 }
 
 #[derive(Debug)]
@@ -109,6 +110,13 @@ pub(crate) fn folding_ranges(file: &SourceFile) -> Vec<Fold> {
                         res.push(Fold { range, kind: FoldKind::Statics })
                     }
                 }
+
+                // Fold where clause
+                if node.kind() == WHERE_CLAUSE {
+                    if let Some(range) = fold_range_for_where_clause(&node) {
+                        res.push(Fold { range, kind: FoldKind::WhereClause })
+                    }
+                }
             }
         }
     }
@@ -241,6 +249,23 @@ fn contiguous_range_for_comment(
     }
 }
 
+fn fold_range_for_where_clause(node: &SyntaxNode) -> Option<TextRange> {
+    let first_where_pred = node.first_child();
+    let last_where_pred = node.last_child();
+
+    if first_where_pred != last_where_pred {
+        let mut it = node.descendants_with_tokens();
+        if let (Some(_where_clause), Some(where_kw), Some(last_comma)) =
+            (it.next(), it.next(), it.last())
+        {
+            let start = where_kw.text_range().end();
+            let end = last_comma.text_range().end();
+            return Some(TextRange::new(start, end));
+        }
+    }
+    None
+}
+
 #[cfg(test)]
 mod tests {
     use test_utils::extract_tags;
@@ -272,6 +297,7 @@ mod tests {
                 FoldKind::Consts => "consts",
                 FoldKind::Statics => "statics",
                 FoldKind::Array => "array",
+                FoldKind::WhereClause => "whereclause",
             };
             assert_eq!(kind, &attr.unwrap());
         }
@@ -513,4 +539,23 @@ static SECOND_STATIC: &str = "second";</fold>
             "#,
         )
     }
+
+    #[test]
+    fn fold_where_clause() {
+        // fold multi-line and don't fold single line.
+        check(
+            r#"
+fn foo()
+where<fold whereclause>
+    A: Foo,
+    B: Foo,
+    C: Foo,
+    D: Foo,</fold> {}
+
+fn bar()
+where
+    A: Bar, {}
+"#,
+        )
+    }
 }

crates/rust-analyzer/src/to_proto.rs

@@ -524,6 +524,7 @@ pub(crate) fn folding_range(
         | FoldKind::ArgList
         | FoldKind::Consts
         | FoldKind::Statics
+        | FoldKind::WhereClause
         | FoldKind::Array => None,
     };