1 files changed, 171 insertions, 0 deletions

diff --git a/crates/ra_ide/src/typing/on_enter.rs b/crates/ra_ide/src/typing/on_enter.rs
new file mode 100644
index 000000000..359794f67
--- /dev/null
+++ b/crates/ra_ide/src/typing/on_enter.rs
@@ -0,0 +1,171 @@
+//! Handles the `Enter` key press. At the momently, this only continues
+//! comments, but should handle indent some time in the future as well.
+
+use ra_db::{FilePosition, SourceDatabase};
+use ra_ide_db::RootDatabase;
+use ra_syntax::{
+    ast::{self, AstToken},
+    AstNode, SmolStr, SourceFile,
+    SyntaxKind::*,
+    SyntaxToken, TextUnit, TokenAtOffset,
+};
+use ra_text_edit::TextEdit;
+
+use crate::{SourceChange, SourceFileEdit};
+
+pub(crate) fn on_enter(db: &RootDatabase, position: FilePosition) -> Option<SourceChange> {
+    let parse = db.parse(position.file_id);
+    let file = parse.tree();
+    let comment = file
+        .syntax()
+        .token_at_offset(position.offset)
+        .left_biased()
+        .and_then(ast::Comment::cast)?;
+
+    if comment.kind().shape.is_block() {
+        return None;
+    }
+
+    let prefix = comment.prefix();
+    let comment_range = comment.syntax().text_range();
+    if position.offset < comment_range.start() + TextUnit::of_str(prefix) {
+        return None;
+    }
+
+    // Continuing non-doc line comments (like this one :) ) is annoying
+    if prefix == "//" && comment_range.end() == position.offset {
+        return None;
+    }
+
+    let indent = node_indent(&file, comment.syntax())?;
+    let inserted = format!("\n{}{} ", indent, prefix);
+    let cursor_position = position.offset + TextUnit::of_str(&inserted);
+    let edit = TextEdit::insert(position.offset, inserted);
+
+    Some(
+        SourceChange::source_file_edit(
+            "on enter",
+            SourceFileEdit { edit, file_id: position.file_id },
+        )
+        .with_cursor(FilePosition { offset: cursor_position, file_id: position.file_id }),
+    )
+}
+
+fn node_indent(file: &SourceFile, token: &SyntaxToken) -> Option<SmolStr> {
+    let ws = match file.syntax().token_at_offset(token.text_range().start()) {
+        TokenAtOffset::Between(l, r) => {
+            assert!(r == *token);
+            l
+        }
+        TokenAtOffset::Single(n) => {
+            assert!(n == *token);
+            return Some("".into());
+        }
+        TokenAtOffset::None => unreachable!(),
+    };
+    if ws.kind() != WHITESPACE {
+        return None;
+    }
+    let text = ws.text();
+    let pos = text.rfind('\n').map(|it| it + 1).unwrap_or(0);
+    Some(text[pos..].into())
+}
+
+#[cfg(test)]
+mod tests {
+    use test_utils::{add_cursor, assert_eq_text, extract_offset};
+
+    use crate::mock_analysis::single_file;
+
+    use super::*;
+
+    fn apply_on_enter(before: &str) -> Option<String> {
+        let (offset, before) = extract_offset(before);
+        let (analysis, file_id) = single_file(&before);
+        let result = analysis.on_enter(FilePosition { offset, file_id }).unwrap()?;
+
+        assert_eq!(result.source_file_edits.len(), 1);
+        let actual = result.source_file_edits[0].edit.apply(&before);
+        let actual = add_cursor(&actual, result.cursor_position.unwrap().offset);
+        Some(actual)
+    }
+
+    fn do_check(ra_fixture_before: &str, ra_fixture_after: &str) {
+        let actual = apply_on_enter(ra_fixture_before).unwrap();
+        assert_eq_text!(ra_fixture_after, &actual);
+    }
+
+    fn do_check_noop(ra_fixture_text: &str) {
+        assert!(apply_on_enter(ra_fixture_text).is_none())
+    }
+
+    #[test]
+    fn test_on_enter() {
+        do_check(
+            r"
+/// Some docs<|>
+fn foo() {
+}
+",
+            r"
+/// Some docs
+/// <|>
+fn foo() {
+}
+",
+        );
+        do_check(
+            r"
+impl S {
+    /// Some<|> docs.
+    fn foo() {}
+}
+",
+            r"
+impl S {
+    /// Some
+    /// <|> docs.
+    fn foo() {}
+}
+",
+        );
+        do_check(
+            r"
+fn main() {
+    // Fix<|> me
+    let x = 1 + 1;
+}
+",
+            r"
+fn main() {
+    // Fix
+    // <|> me
+    let x = 1 + 1;
+}
+",
+        );
+        do_check(
+            r"
+///<|> Some docs
+fn foo() {
+}
+",
+            r"
+///
+/// <|> Some docs
+fn foo() {
+}
+",
+        );
+        do_check_noop(
+            r"
+fn main() {
+    // Fix me<|>
+    let x = 1 + 1;
+}
+",
+        );
+
+        do_check_noop(r"<|>//! docz");
+    }
+}