2 files changed, 330 insertions, 2 deletions

diff --git a/crates/ra_ide_api/src/folding_ranges.rs b/crates/ra_ide_api/src/folding_ranges.rs
new file mode 100644
index 000000000..b96145f05
--- /dev/null
+++ b/crates/ra_ide_api/src/folding_ranges.rs
@@ -0,0 +1,326 @@
+use rustc_hash::FxHashSet;
+
+use ra_syntax::{
+    AstNode, Direction, SourceFile, SyntaxNode, TextRange,
+    SyntaxKind::{self, *},
+    ast::{self, VisibilityOwner},
+};
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum FoldKind {
+    Comment,
+    Imports,
+    Mods,
+    Block,
+}
+
+#[derive(Debug)]
+pub struct Fold {
+    pub range: TextRange,
+    pub kind: FoldKind,
+}
+
+pub(crate) fn folding_ranges(file: &SourceFile) -> Vec<Fold> {
+    let mut res = vec![];
+    let mut visited_comments = FxHashSet::default();
+    let mut visited_imports = FxHashSet::default();
+    let mut visited_mods = FxHashSet::default();
+
+    for node in file.syntax().descendants() {
+        // Fold items that span multiple lines
+        if let Some(kind) = fold_kind(node.kind()) {
+            if node.text().contains('\n') {
+                res.push(Fold { range: node.range(), kind });
+            }
+        }
+
+        // Fold groups of comments
+        if node.kind() == COMMENT && !visited_comments.contains(&node) {
+            if let Some(range) = contiguous_range_for_comment(node, &mut visited_comments) {
+                res.push(Fold { range, kind: FoldKind::Comment })
+            }
+        }
+
+        // Fold groups of imports
+        if node.kind() == USE_ITEM && !visited_imports.contains(&node) {
+            if let Some(range) = contiguous_range_for_group(node, &mut visited_imports) {
+                res.push(Fold { range, kind: FoldKind::Imports })
+            }
+        }
+
+        // Fold groups of mods
+        if node.kind() == MODULE && !has_visibility(&node) && !visited_mods.contains(&node) {
+            if let Some(range) =
+                contiguous_range_for_group_unless(node, has_visibility, &mut visited_mods)
+            {
+                res.push(Fold { range, kind: FoldKind::Mods })
+            }
+        }
+    }
+
+    res
+}
+
+fn fold_kind(kind: SyntaxKind) -> Option<FoldKind> {
+    match kind {
+        COMMENT => Some(FoldKind::Comment),
+        USE_ITEM => Some(FoldKind::Imports),
+        NAMED_FIELD_DEF_LIST | FIELD_PAT_LIST | ITEM_LIST | EXTERN_ITEM_LIST | USE_TREE_LIST
+        | BLOCK | ENUM_VARIANT_LIST | TOKEN_TREE => Some(FoldKind::Block),
+        _ => None,
+    }
+}
+
+fn has_visibility(node: &SyntaxNode) -> bool {
+    ast::Module::cast(node).and_then(|m| m.visibility()).is_some()
+}
+
+fn contiguous_range_for_group<'a>(
+    first: &'a SyntaxNode,
+    visited: &mut FxHashSet<&'a SyntaxNode>,
+) -> Option<TextRange> {
+    contiguous_range_for_group_unless(first, |_| false, visited)
+}
+
+fn contiguous_range_for_group_unless<'a>(
+    first: &'a SyntaxNode,
+    unless: impl Fn(&'a SyntaxNode) -> bool,
+    visited: &mut FxHashSet<&'a SyntaxNode>,
+) -> Option<TextRange> {
+    visited.insert(first);
+
+    let mut last = first;
+    for node in first.siblings(Direction::Next) {
+        if let Some(ws) = ast::Whitespace::cast(node) {
+            // There is a blank line, which means that the group ends here
+            if ws.count_newlines_lazy().take(2).count() == 2 {
+                break;
+            }
+
+            // Ignore whitespace without blank lines
+            continue;
+        }
+
+        // Stop if we find a node that doesn't belong to the group
+        if node.kind() != first.kind() || unless(node) {
+            break;
+        }
+
+        visited.insert(node);
+        last = node;
+    }
+
+    if first != last {
+        Some(TextRange::from_to(first.range().start(), last.range().end()))
+    } else {
+        // The group consists of only one element, therefore it cannot be folded
+        None
+    }
+}
+
+fn contiguous_range_for_comment<'a>(
+    first: &'a SyntaxNode,
+    visited: &mut FxHashSet<&'a SyntaxNode>,
+) -> Option<TextRange> {
+    visited.insert(first);
+
+    // Only fold comments of the same flavor
+    let group_flavor = ast::Comment::cast(first)?.flavor();
+
+    let mut last = first;
+    for node in first.siblings(Direction::Next) {
+        if let Some(ws) = ast::Whitespace::cast(node) {
+            // There is a blank line, which means the group ends here
+            if ws.count_newlines_lazy().take(2).count() == 2 {
+                break;
+            }
+
+            // Ignore whitespace without blank lines
+            continue;
+        }
+
+        match ast::Comment::cast(node) {
+            Some(next_comment) if next_comment.flavor() == group_flavor => {
+                visited.insert(node);
+                last = node;
+            }
+            // The comment group ends because either:
+            // * An element of a different kind was reached
+            // * A comment of a different flavor was reached
+            _ => break,
+        }
+    }
+
+    if first != last {
+        Some(TextRange::from_to(first.range().start(), last.range().end()))
+    } else {
+        // The group consists of only one element, therefore it cannot be folded
+        None
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use test_utils::extract_ranges;
+
+    fn do_check(text: &str, fold_kinds: &[FoldKind]) {
+        let (ranges, text) = extract_ranges(text, "fold");
+        let file = SourceFile::parse(&text);
+        let folds = folding_ranges(&file);
+
+        assert_eq!(
+            folds.len(),
+            ranges.len(),
+            "The amount of folds is different than the expected amount"
+        );
+        assert_eq!(
+            folds.len(),
+            fold_kinds.len(),
+            "The amount of fold kinds is different than the expected amount"
+        );
+        for ((fold, range), fold_kind) in
+            folds.into_iter().zip(ranges.into_iter()).zip(fold_kinds.into_iter())
+        {
+            assert_eq!(fold.range.start(), range.start());
+            assert_eq!(fold.range.end(), range.end());
+            assert_eq!(&fold.kind, fold_kind);
+        }
+    }
+
+    #[test]
+    fn test_fold_comments() {
+        let text = r#"
+<fold>// Hello
+// this is a multiline
+// comment
+//</fold>
+
+// But this is not
+
+fn main() <fold>{
+    <fold>// We should
+    // also
+    // fold
+    // this one.</fold>
+    <fold>//! But this one is different
+    //! because it has another flavor</fold>
+    <fold>/* As does this
+    multiline comment */</fold>
+}</fold>"#;
+
+        let fold_kinds = &[
+            FoldKind::Comment,
+            FoldKind::Block,
+            FoldKind::Comment,
+            FoldKind::Comment,
+            FoldKind::Comment,
+        ];
+        do_check(text, fold_kinds);
+    }
+
+    #[test]
+    fn test_fold_imports() {
+        let text = r#"
+<fold>use std::<fold>{
+    str,
+    vec,
+    io as iop
+}</fold>;</fold>
+
+fn main() <fold>{
+}</fold>"#;
+
+        let folds = &[FoldKind::Imports, FoldKind::Block, FoldKind::Block];
+        do_check(text, folds);
+    }
+
+    #[test]
+    fn test_fold_mods() {
+        let text = r#"
+
+pub mod foo;
+<fold>mod after_pub;
+mod after_pub_next;</fold>
+
+<fold>mod before_pub;
+mod before_pub_next;</fold>
+pub mod bar;
+
+mod not_folding_single;
+pub mod foobar;
+pub not_folding_single_next;
+
+<fold>#[cfg(test)]
+mod with_attribute;
+mod with_attribute_next;</fold>
+
+fn main() <fold>{
+}</fold>"#;
+
+        let folds = &[FoldKind::Mods, FoldKind::Mods, FoldKind::Mods, FoldKind::Block];
+        do_check(text, folds);
+    }
+
+    #[test]
+    fn test_fold_import_groups() {
+        let text = r#"
+<fold>use std::str;
+use std::vec;
+use std::io as iop;</fold>
+
+<fold>use std::mem;
+use std::f64;</fold>
+
+use std::collections::HashMap;
+// Some random comment
+use std::collections::VecDeque;
+
+fn main() <fold>{
+}</fold>"#;
+
+        let folds = &[FoldKind::Imports, FoldKind::Imports, FoldKind::Block];
+        do_check(text, folds);
+    }
+
+    #[test]
+    fn test_fold_import_and_groups() {
+        let text = r#"
+<fold>use std::str;
+use std::vec;
+use std::io as iop;</fold>
+
+<fold>use std::mem;
+use std::f64;</fold>
+
+<fold>use std::collections::<fold>{
+    HashMap,
+    VecDeque,
+}</fold>;</fold>
+// Some random comment
+
+fn main() <fold>{
+}</fold>"#;
+
+        let folds = &[
+            FoldKind::Imports,
+            FoldKind::Imports,
+            FoldKind::Imports,
+            FoldKind::Block,
+            FoldKind::Block,
+        ];
+        do_check(text, folds);
+    }
+
+    #[test]
+    fn test_folds_macros() {
+        let text = r#"
+macro_rules! foo <fold>{
+    ($($tt:tt)*) => { $($tt)* }
+}</fold>
+"#;
+
+        let folds = &[FoldKind::Block];
+        do_check(text, folds);
+    }
+}
diff --git a/crates/ra_ide_api/src/lib.rs b/crates/ra_ide_api/src/lib.rs
index 35f38fbb7..d6f63490d 100644
--- a/crates/ra_ide_api/src/lib.rs
+++ b/crates/ra_ide_api/src/lib.rs
@@ -34,6 +34,7 @@ mod assists;
 mod diagnostics;
 mod syntax_tree;
 mod line_index;
+mod folding_ranges;
 mod line_index_utils;
 
 #[cfg(test)]
@@ -64,9 +65,10 @@ pub use crate::{
     hover::{HoverResult},
     line_index::{LineIndex, LineCol},
     line_index_utils::translate_offset_with_edit,
+    folding_ranges::{Fold, FoldKind},
 };
 pub use ra_ide_api_light::{
-    Fold, FoldKind, HighlightedRange, Severity, StructureNode, LocalEdit,
+    HighlightedRange, Severity, StructureNode, LocalEdit,
 };
 pub use ra_db::{
     Canceled, CrateGraph, CrateId, FileId, FilePosition, FileRange, SourceRootId,
@@ -314,7 +316,7 @@ impl Analysis {
     /// Returns the set of folding ranges.
     pub fn folding_ranges(&self, file_id: FileId) -> Vec<Fold> {
         let file = self.db.parse(file_id);
-        ra_ide_api_light::folding_ranges(&file)
+        folding_ranges::folding_ranges(&file)
     }
 
     /// Fuzzy searches for a symbol.