3 files changed, 85 insertions, 1 deletions

diff --git a/crates/libeditor/src/code_actions.rs b/crates/libeditor/src/code_actions.rs
index 6c41923dd..c25ee973c 100644
--- a/crates/libeditor/src/code_actions.rs
+++ b/crates/libeditor/src/code_actions.rs
@@ -14,6 +14,7 @@ use libsyntax2::{
 
 use {TextUnit, EditBuilder, Edit};
 
+#[derive(Debug)]
 pub struct ActionResult {
     pub edit: Edit,
     pub cursor_position: Option<TextUnit>,
diff --git a/crates/libeditor/src/lib.rs b/crates/libeditor/src/lib.rs
index 6bae7a3fa..f8bc73ae9 100644
--- a/crates/libeditor/src/lib.rs
+++ b/crates/libeditor/src/lib.rs
@@ -7,11 +7,12 @@ mod symbols;
 mod line_index;
 mod edit;
 mod code_actions;
+mod typing;
 
 use libsyntax2::{
     ast::{self, NameOwner},
     AstNode,
-    algo::{walk, find_leaf_at_offset},
+    algo::{walk, find_leaf_at_offset, find_covering_node},
     SyntaxKind::{self, *},
 };
 pub use libsyntax2::{ParsedFile, TextRange, TextUnit};
@@ -24,6 +25,7 @@ pub use self::{
         ActionResult, find_node,
         flip_comma, add_derive, add_impl,
     },
+    typing::join_lines,
 };
 
 #[derive(Debug)]
diff --git a/crates/libeditor/src/typing.rs b/crates/libeditor/src/typing.rs
new file mode 100644
index 000000000..f49dd0fdc
--- /dev/null
+++ b/crates/libeditor/src/typing.rs
@@ -0,0 +1,81 @@
+use libsyntax2::{
+    TextUnit, TextRange, SyntaxNodeRef,
+    ast,
+    algo::{
+        walk::preorder,
+        find_covering_node,
+    },
+};
+
+use {ActionResult, EditBuilder};
+
+pub fn join_lines(file: &ast::ParsedFile, range: TextRange) -> ActionResult {
+    let range = if range.is_empty() {
+        let text = file.syntax().text();
+        let text = &text[TextRange::from_to(range.start(), TextUnit::of_str(&text))];
+        let pos = text.bytes().take_while(|&b| b != b'\n').count();
+        if pos == text.len() {
+            return ActionResult {
+                edit: EditBuilder::new().finish(),
+                cursor_position: None
+            };
+        }
+        let pos: TextUnit = (pos as u32).into();
+        TextRange::offset_len(
+            range.start() + pos,
+            TextUnit::of_char('\n'),
+        )
+    } else {
+        range
+    };
+    let node = find_covering_node(file.syntax(), range);
+    let mut edit = EditBuilder::new();
+    for node in preorder(node) {
+        let text = match node.leaf_text() {
+            Some(text) => text,
+            None => continue,
+        };
+        let range = match intersect(range, node.range()) {
+            Some(range) => range,
+            None => continue,
+        } - node.range().start();
+        for (pos, _) in text[range].bytes().enumerate().filter(|&(_, b)| b == b'\n') {
+            let pos: TextUnit = (pos as u32).into();
+            let off = node.range().start() + range.start() + pos;
+            remove_newline(&mut edit, node, text.as_str(), off);
+        }
+    }
+
+    ActionResult {
+        edit: edit.finish(),
+        cursor_position: None,
+    }
+}
+
+fn intersect(r1: TextRange, r2: TextRange) -> Option<TextRange> {
+    let start = r1.start().max(r2.start());
+    let end = r1.end().min(r2.end());
+    if start <= end {
+        Some(TextRange::from_to(start, end))
+    } else {
+        None
+    }
+}
+
+fn remove_newline(
+    edit: &mut EditBuilder,
+    node: SyntaxNodeRef,
+    node_text: &str,
+    offset: TextUnit,
+) {
+    let suff = &node_text[TextRange::from_to(
+        offset - node.range().start() + TextUnit::of_char('\n'),
+        TextUnit::of_str(node_text),
+    )];
+    let spaces = suff.bytes().take_while(|&b| b == b' ').count();
+
+    edit.replace(
+        TextRange::offset_len(offset, ((spaces + 1) as u32).into()),
+        " ".to_string(),
+    );
+}