2 files changed, 144 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..817da28d1
--- /dev/null
+++ b/crates/ra_editor/src/folding_ranges.rs
@@ -0,0 +1,142 @@
+use std::collections::HashSet;
+
+use ra_syntax::{
+    File, TextRange, SyntaxNodeRef,
+    SyntaxKind,
+    algo::{walk, Direction, siblings},
+};
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum FoldKind {
+    Comment,
+    Imports,
+}
+
+#[derive(Debug)]
+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
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_fold_comments() {
+        let text = r#"
+// Hello
+// this is a multiline
+// comment
+//
+
+// But this is not
+
+fn main() {
+    // We should
+    // also
+    // fold
+    // this one.
+}"#;
+
+        let file = File::parse(&text);
+        let folds = folding_ranges(&file);
+        assert_eq!(folds.len(), 2);
+        assert_eq!(folds[0].range.start(), 1.into());
+        assert_eq!(folds[0].range.end(), 46.into());
+        assert_eq!(folds[0].kind, FoldKind::Comment);
+
+        assert_eq!(folds[1].range.start(), 84.into());
+        assert_eq!(folds[1].range.end(), 137.into());
+        assert_eq!(folds[1].kind, FoldKind::Comment);
+    }
+
+    #[test]
+    fn test_fold_imports() {
+        let text = r#"
+use std::str;
+use std::vec;
+use std::io as iop;
+
+fn main() {
+}"#;
+
+        let file = File::parse(&text);
+        let folds = folding_ranges(&file);
+        assert_eq!(folds.len(), 1);
+        assert_eq!(folds[0].range.start(), 1.into());
+        assert_eq!(folds[0].range.end(), 48.into());
+        assert_eq!(folds[0].kind, FoldKind::Imports);
+    }
+
+
+}
\ No newline at end of file
diff --git a/crates/ra_editor/src/lib.rs b/crates/ra_editor/src/lib.rs
index 78ed34c7c..de929d73a 100644
--- a/crates/ra_editor/src/lib.rs
+++ b/crates/ra_editor/src/lib.rs
@@ -10,6 +10,7 @@ mod extend_selection;
 mod symbols;
 mod line_index;
 mod edit;
+mod folding_ranges;
 mod code_actions;
 mod typing;
 mod completion;
@@ -36,6 +37,7 @@ pub use self::{
     },
     typing::{join_lines, on_eq_typed},
     completion::{scope_completion, CompletionItem},
+    folding_ranges::{Fold, FoldKind, folding_ranges}
 };
 
 #[derive(Debug)]