1 files changed, 86 insertions, 0 deletions

diff --git a/crates/ra_editor/src/folding_ranges.rs b/crates/ra_editor/src/folding_ranges.rs
new file mode 100644
index 000000000..4518e8d24
--- /dev/null
+++ b/crates/ra_editor/src/folding_ranges.rs
@@ -0,0 +1,86 @@
+use std::collections::HashSet;
+
+use ra_syntax::{
+    File, TextRange, SyntaxNodeRef,
+    SyntaxKind,
+    algo::{walk, Direction, siblings},
+};
+
+pub enum FoldKind {
+    Comment,
+    Imports,
+}
+
+pub struct Fold {
+    pub range: TextRange,
+    pub kind: FoldKind,
+}
+
+pub fn folding_ranges(file: &File) -> Vec<Fold> {
+    let syntax = file.syntax();
+
+    let mut res = vec![];
+    let mut visited = HashSet::new();
+
+    for node in walk::preorder(syntax) {
+        if visited.contains(&node) {
+            continue;
+        }
+
+        let range_and_kind = match node.kind() {
+            SyntaxKind::COMMENT => (
+                contiguous_range_for(SyntaxKind::COMMENT, node, &mut visited),
+                Some(FoldKind::Comment),
+            ),
+            SyntaxKind::USE_ITEM => (
+                contiguous_range_for(SyntaxKind::USE_ITEM, node, &mut visited),
+                Some(FoldKind::Imports),
+            ),
+            _ => (None, None),
+        };
+
+        match range_and_kind {
+            (Some(range), Some(kind)) => {
+                res.push(Fold {
+                    range: range,
+                    kind: kind
+                });
+            }
+            _ => {}
+        }
+    }
+
+    res
+}
+
+fn contiguous_range_for<'a>(
+    kind: SyntaxKind,
+    node: SyntaxNodeRef<'a>,
+    visited: &mut HashSet<SyntaxNodeRef<'a>>,
+) -> Option<TextRange> {
+    visited.insert(node);
+
+    let left = node;
+    let mut right = node;
+    for node in siblings(node, Direction::Forward) {
+        visited.insert(node);
+        match node.kind() {
+            SyntaxKind::WHITESPACE if !node.leaf_text().unwrap().as_str().contains("\n\n") => (),
+            k => {
+                if k == kind {
+                    right = node
+                } else {
+                    break;
+                }
+            }
+        }
+    }
+    if left != right {
+        Some(TextRange::from_to(
+            left.range().start(),
+            right.range().end(),
+        ))
+    } else {
+        None
+    }
+}
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