3 files changed, 614 insertions, 1 deletions

diff --git a/crates/ra_ide_api/src/lib.rs b/crates/ra_ide_api/src/lib.rs
index 81ca57035..35f38fbb7 100644
--- a/crates/ra_ide_api/src/lib.rs
+++ b/crates/ra_ide_api/src/lib.rs
@@ -33,6 +33,8 @@ mod impls;
 mod assists;
 mod diagnostics;
 mod syntax_tree;
+mod line_index;
+mod line_index_utils;
 
 #[cfg(test)]
 mod marks;
@@ -60,10 +62,11 @@ pub use crate::{
     references::ReferenceSearchResult,
     assists::{Assist, AssistId},
     hover::{HoverResult},
+    line_index::{LineIndex, LineCol},
+    line_index_utils::translate_offset_with_edit,
 };
 pub use ra_ide_api_light::{
     Fold, FoldKind, HighlightedRange, Severity, StructureNode, LocalEdit,
-    LineIndex, LineCol, translate_offset_with_edit,
 };
 pub use ra_db::{
     Canceled, CrateGraph, CrateId, FileId, FilePosition, FileRange, SourceRootId,
diff --git a/crates/ra_ide_api/src/line_index.rs b/crates/ra_ide_api/src/line_index.rs
new file mode 100644
index 000000000..bf004c33a
--- /dev/null
+++ b/crates/ra_ide_api/src/line_index.rs
@@ -0,0 +1,280 @@
+use crate::TextUnit;
+use rustc_hash::FxHashMap;
+use superslice::Ext;
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct LineIndex {
+    pub(crate) newlines: Vec<TextUnit>,
+    pub(crate) utf16_lines: FxHashMap<u32, Vec<Utf16Char>>,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+pub struct LineCol {
+    pub line: u32,
+    pub col_utf16: u32,
+}
+
+#[derive(Clone, Debug, Hash, PartialEq, Eq)]
+pub(crate) struct Utf16Char {
+    pub(crate) start: TextUnit,
+    pub(crate) end: TextUnit,
+}
+
+impl Utf16Char {
+    fn len(&self) -> TextUnit {
+        self.end - self.start
+    }
+}
+
+impl LineIndex {
+    pub fn new(text: &str) -> LineIndex {
+        let mut utf16_lines = FxHashMap::default();
+        let mut utf16_chars = Vec::new();
+
+        let mut newlines = vec![0.into()];
+        let mut curr_row = 0.into();
+        let mut curr_col = 0.into();
+        let mut line = 0;
+        for c in text.chars() {
+            curr_row += TextUnit::of_char(c);
+            if c == '\n' {
+                newlines.push(curr_row);
+
+                // Save any utf-16 characters seen in the previous line
+                if utf16_chars.len() > 0 {
+                    utf16_lines.insert(line, utf16_chars);
+                    utf16_chars = Vec::new();
+                }
+
+                // Prepare for processing the next line
+                curr_col = 0.into();
+                line += 1;
+                continue;
+            }
+
+            let char_len = TextUnit::of_char(c);
+            if char_len.to_usize() > 1 {
+                utf16_chars.push(Utf16Char { start: curr_col, end: curr_col + char_len });
+            }
+
+            curr_col += char_len;
+        }
+
+        // Save any utf-16 characters seen in the last line
+        if utf16_chars.len() > 0 {
+            utf16_lines.insert(line, utf16_chars);
+        }
+
+        LineIndex { newlines, utf16_lines }
+    }
+
+    pub fn line_col(&self, offset: TextUnit) -> LineCol {
+        let line = self.newlines.upper_bound(&offset) - 1;
+        let line_start_offset = self.newlines[line];
+        let col = offset - line_start_offset;
+
+        LineCol { line: line as u32, col_utf16: self.utf8_to_utf16_col(line as u32, col) as u32 }
+    }
+
+    pub fn offset(&self, line_col: LineCol) -> TextUnit {
+        //TODO: return Result
+        let col = self.utf16_to_utf8_col(line_col.line, line_col.col_utf16);
+        self.newlines[line_col.line as usize] + col
+    }
+
+    fn utf8_to_utf16_col(&self, line: u32, mut col: TextUnit) -> usize {
+        if let Some(utf16_chars) = self.utf16_lines.get(&line) {
+            let mut correction = TextUnit::from_usize(0);
+            for c in utf16_chars {
+                if col >= c.end {
+                    correction += c.len() - TextUnit::from_usize(1);
+                } else {
+                    // From here on, all utf16 characters come *after* the character we are mapping,
+                    // so we don't need to take them into account
+                    break;
+                }
+            }
+
+            col -= correction;
+        }
+
+        col.to_usize()
+    }
+
+    fn utf16_to_utf8_col(&self, line: u32, col: u32) -> TextUnit {
+        let mut col: TextUnit = col.into();
+        if let Some(utf16_chars) = self.utf16_lines.get(&line) {
+            for c in utf16_chars {
+                if col >= c.start {
+                    col += c.len() - TextUnit::from_usize(1);
+                } else {
+                    // From here on, all utf16 characters come *after* the character we are mapping,
+                    // so we don't need to take them into account
+                    break;
+                }
+            }
+        }
+
+        col
+    }
+}
+
+#[cfg(test)]
+/// Simple reference implementation to use in proptests
+pub fn to_line_col(text: &str, offset: TextUnit) -> LineCol {
+    let mut res = LineCol { line: 0, col_utf16: 0 };
+    for (i, c) in text.char_indices() {
+        if i + c.len_utf8() > offset.to_usize() {
+            // if it's an invalid offset, inside a multibyte char
+            // return as if it was at the start of the char
+            break;
+        }
+        if c == '\n' {
+            res.line += 1;
+            res.col_utf16 = 0;
+        } else {
+            res.col_utf16 += 1;
+        }
+    }
+    res
+}
+
+#[cfg(test)]
+mod test_line_index {
+    use super::*;
+    use proptest::{prelude::*, proptest};
+    use ra_text_edit::test_utils::{arb_text, arb_offset};
+
+    #[test]
+    fn test_line_index() {
+        let text = "hello\nworld";
+        let index = LineIndex::new(text);
+        assert_eq!(index.line_col(0.into()), LineCol { line: 0, col_utf16: 0 });
+        assert_eq!(index.line_col(1.into()), LineCol { line: 0, col_utf16: 1 });
+        assert_eq!(index.line_col(5.into()), LineCol { line: 0, col_utf16: 5 });
+        assert_eq!(index.line_col(6.into()), LineCol { line: 1, col_utf16: 0 });
+        assert_eq!(index.line_col(7.into()), LineCol { line: 1, col_utf16: 1 });
+        assert_eq!(index.line_col(8.into()), LineCol { line: 1, col_utf16: 2 });
+        assert_eq!(index.line_col(10.into()), LineCol { line: 1, col_utf16: 4 });
+        assert_eq!(index.line_col(11.into()), LineCol { line: 1, col_utf16: 5 });
+        assert_eq!(index.line_col(12.into()), LineCol { line: 1, col_utf16: 6 });
+
+        let text = "\nhello\nworld";
+        let index = LineIndex::new(text);
+        assert_eq!(index.line_col(0.into()), LineCol { line: 0, col_utf16: 0 });
+        assert_eq!(index.line_col(1.into()), LineCol { line: 1, col_utf16: 0 });
+        assert_eq!(index.line_col(2.into()), LineCol { line: 1, col_utf16: 1 });
+        assert_eq!(index.line_col(6.into()), LineCol { line: 1, col_utf16: 5 });
+        assert_eq!(index.line_col(7.into()), LineCol { line: 2, col_utf16: 0 });
+    }
+
+    fn arb_text_with_offset() -> BoxedStrategy<(TextUnit, String)> {
+        arb_text().prop_flat_map(|text| (arb_offset(&text), Just(text))).boxed()
+    }
+
+    fn to_line_col(text: &str, offset: TextUnit) -> LineCol {
+        let mut res = LineCol { line: 0, col_utf16: 0 };
+        for (i, c) in text.char_indices() {
+            if i + c.len_utf8() > offset.to_usize() {
+                // if it's an invalid offset, inside a multibyte char
+                // return as if it was at the start of the char
+                break;
+            }
+            if c == '\n' {
+                res.line += 1;
+                res.col_utf16 = 0;
+            } else {
+                res.col_utf16 += 1;
+            }
+        }
+        res
+    }
+
+    proptest! {
+        #[test]
+        fn test_line_index_proptest((offset, text) in arb_text_with_offset()) {
+            let expected = to_line_col(&text, offset);
+            let line_index = LineIndex::new(&text);
+            let actual = line_index.line_col(offset);
+
+            assert_eq!(actual, expected);
+        }
+    }
+}
+
+#[cfg(test)]
+mod test_utf8_utf16_conv {
+    use super::*;
+
+    #[test]
+    fn test_char_len() {
+        assert_eq!('メ'.len_utf8(), 3);
+        assert_eq!('メ'.len_utf16(), 1);
+    }
+
+    #[test]
+    fn test_empty_index() {
+        let col_index = LineIndex::new(
+            "
+const C: char = 'x';
+",
+        );
+        assert_eq!(col_index.utf16_lines.len(), 0);
+    }
+
+    #[test]
+    fn test_single_char() {
+        let col_index = LineIndex::new(
+            "
+const C: char = 'メ';
+",
+        );
+
+        assert_eq!(col_index.utf16_lines.len(), 1);
+        assert_eq!(col_index.utf16_lines[&1].len(), 1);
+        assert_eq!(col_index.utf16_lines[&1][0], Utf16Char { start: 17.into(), end: 20.into() });
+
+        // UTF-8 to UTF-16, no changes
+        assert_eq!(col_index.utf8_to_utf16_col(1, 15.into()), 15);
+
+        // UTF-8 to UTF-16
+        assert_eq!(col_index.utf8_to_utf16_col(1, 22.into()), 20);
+
+        // UTF-16 to UTF-8, no changes
+        assert_eq!(col_index.utf16_to_utf8_col(1, 15), TextUnit::from(15));
+
+        // UTF-16 to UTF-8
+        assert_eq!(col_index.utf16_to_utf8_col(1, 19), TextUnit::from(21));
+    }
+
+    #[test]
+    fn test_string() {
+        let col_index = LineIndex::new(
+            "
+const C: char = \"メ メ\";
+",
+        );
+
+        assert_eq!(col_index.utf16_lines.len(), 1);
+        assert_eq!(col_index.utf16_lines[&1].len(), 2);
+        assert_eq!(col_index.utf16_lines[&1][0], Utf16Char { start: 17.into(), end: 20.into() });
+        assert_eq!(col_index.utf16_lines[&1][1], Utf16Char { start: 21.into(), end: 24.into() });
+
+        // UTF-8 to UTF-16
+        assert_eq!(col_index.utf8_to_utf16_col(1, 15.into()), 15);
+
+        assert_eq!(col_index.utf8_to_utf16_col(1, 21.into()), 19);
+        assert_eq!(col_index.utf8_to_utf16_col(1, 25.into()), 21);
+
+        assert!(col_index.utf8_to_utf16_col(2, 15.into()) == 15);
+
+        // UTF-16 to UTF-8
+        assert_eq!(col_index.utf16_to_utf8_col(1, 15), TextUnit::from_usize(15));
+
+        assert_eq!(col_index.utf16_to_utf8_col(1, 18), TextUnit::from_usize(20));
+        assert_eq!(col_index.utf16_to_utf8_col(1, 19), TextUnit::from_usize(23));
+
+        assert_eq!(col_index.utf16_to_utf8_col(2, 15), TextUnit::from_usize(15));
+    }
+
+}
diff --git a/crates/ra_ide_api/src/line_index_utils.rs b/crates/ra_ide_api/src/line_index_utils.rs
new file mode 100644
index 000000000..799a920ad
--- /dev/null
+++ b/crates/ra_ide_api/src/line_index_utils.rs
@@ -0,0 +1,330 @@
+use ra_text_edit::{AtomTextEdit, TextEdit};
+use ra_syntax::{TextUnit, TextRange};
+use crate::{LineIndex, LineCol, line_index::Utf16Char};
+
+#[derive(Debug, Clone)]
+enum Step {
+    Newline(TextUnit),
+    Utf16Char(TextRange),
+}
+
+#[derive(Debug)]
+struct LineIndexStepIter<'a> {
+    line_index: &'a LineIndex,
+    next_newline_idx: usize,
+    utf16_chars: Option<(TextUnit, std::slice::Iter<'a, Utf16Char>)>,
+}
+
+impl<'a> LineIndexStepIter<'a> {
+    fn from(line_index: &LineIndex) -> LineIndexStepIter {
+        let mut x = LineIndexStepIter { line_index, next_newline_idx: 0, utf16_chars: None };
+        // skip first newline since it's not real
+        x.next();
+        x
+    }
+}
+
+impl<'a> Iterator for LineIndexStepIter<'a> {
+    type Item = Step;
+    fn next(&mut self) -> Option<Step> {
+        self.utf16_chars
+            .as_mut()
+            .and_then(|(newline, x)| {
+                let x = x.next()?;
+                Some(Step::Utf16Char(TextRange::from_to(*newline + x.start, *newline + x.end)))
+            })
+            .or_else(|| {
+                let next_newline = *self.line_index.newlines.get(self.next_newline_idx)?;
+                self.utf16_chars = self
+                    .line_index
+                    .utf16_lines
+                    .get(&(self.next_newline_idx as u32))
+                    .map(|x| (next_newline, x.iter()));
+                self.next_newline_idx += 1;
+                Some(Step::Newline(next_newline))
+            })
+    }
+}
+
+#[derive(Debug)]
+struct OffsetStepIter<'a> {
+    text: &'a str,
+    offset: TextUnit,
+}
+
+impl<'a> Iterator for OffsetStepIter<'a> {
+    type Item = Step;
+    fn next(&mut self) -> Option<Step> {
+        let (next, next_offset) = self
+            .text
+            .char_indices()
+            .filter_map(|(i, c)| {
+                if c == '\n' {
+                    let next_offset = self.offset + TextUnit::from_usize(i + 1);
+                    let next = Step::Newline(next_offset);
+                    Some((next, next_offset))
+                } else {
+                    let char_len = TextUnit::of_char(c);
+                    if char_len.to_usize() > 1 {
+                        let start = self.offset + TextUnit::from_usize(i);
+                        let end = start + char_len;
+                        let next = Step::Utf16Char(TextRange::from_to(start, end));
+                        let next_offset = end;
+                        Some((next, next_offset))
+                    } else {
+                        None
+                    }
+                }
+            })
+            .next()?;
+        let next_idx = (next_offset - self.offset).to_usize();
+        self.text = &self.text[next_idx..];
+        self.offset = next_offset;
+        Some(next)
+    }
+}
+
+#[derive(Debug)]
+enum NextSteps<'a> {
+    Use,
+    ReplaceMany(OffsetStepIter<'a>),
+    AddMany(OffsetStepIter<'a>),
+}
+
+#[derive(Debug)]
+struct TranslatedEdit<'a> {
+    delete: TextRange,
+    insert: &'a str,
+    diff: i64,
+}
+
+struct Edits<'a> {
+    edits: &'a [AtomTextEdit],
+    current: Option<TranslatedEdit<'a>>,
+    acc_diff: i64,
+}
+
+impl<'a> Edits<'a> {
+    fn from_text_edit(text_edit: &'a TextEdit) -> Edits<'a> {
+        let mut x = Edits { edits: text_edit.as_atoms(), current: None, acc_diff: 0 };
+        x.advance_edit();
+        x
+    }
+    fn advance_edit(&mut self) {
+        self.acc_diff += self.current.as_ref().map_or(0, |x| x.diff);
+        match self.edits.split_first() {
+            Some((next, rest)) => {
+                let delete = self.translate_range(next.delete);
+                let diff = next.insert.len() as i64 - next.delete.len().to_usize() as i64;
+                self.current = Some(TranslatedEdit { delete, insert: &next.insert, diff });
+                self.edits = rest;
+            }
+            None => {
+                self.current = None;
+            }
+        }
+    }
+
+    fn next_inserted_steps(&mut self) -> Option<OffsetStepIter<'a>> {
+        let cur = self.current.as_ref()?;
+        let res = Some(OffsetStepIter { offset: cur.delete.start(), text: &cur.insert });
+        self.advance_edit();
+        res
+    }
+
+    fn next_steps(&mut self, step: &Step) -> NextSteps {
+        let step_pos = match step {
+            &Step::Newline(n) => n,
+            &Step::Utf16Char(r) => r.end(),
+        };
+        let res = match &mut self.current {
+            Some(edit) => {
+                if step_pos <= edit.delete.start() {
+                    NextSteps::Use
+                } else if step_pos <= edit.delete.end() {
+                    let iter = OffsetStepIter { offset: edit.delete.start(), text: &edit.insert };
+                    // empty slice to avoid returning steps again
+                    edit.insert = &edit.insert[edit.insert.len()..];
+                    NextSteps::ReplaceMany(iter)
+                } else {
+                    let iter = OffsetStepIter { offset: edit.delete.start(), text: &edit.insert };
+                    // empty slice to avoid returning steps again
+                    edit.insert = &edit.insert[edit.insert.len()..];
+                    self.advance_edit();
+                    NextSteps::AddMany(iter)
+                }
+            }
+            None => NextSteps::Use,
+        };
+        res
+    }
+
+    fn translate_range(&self, range: TextRange) -> TextRange {
+        if self.acc_diff == 0 {
+            range
+        } else {
+            let start = self.translate(range.start());
+            let end = self.translate(range.end());
+            TextRange::from_to(start, end)
+        }
+    }
+
+    fn translate(&self, x: TextUnit) -> TextUnit {
+        if self.acc_diff == 0 {
+            x
+        } else {
+            TextUnit::from((x.to_usize() as i64 + self.acc_diff) as u32)
+        }
+    }
+
+    fn translate_step(&self, x: &Step) -> Step {
+        if self.acc_diff == 0 {
+            x.clone()
+        } else {
+            match x {
+                &Step::Newline(n) => Step::Newline(self.translate(n)),
+                &Step::Utf16Char(r) => Step::Utf16Char(self.translate_range(r)),
+            }
+        }
+    }
+}
+
+#[derive(Debug)]
+struct RunningLineCol {
+    line: u32,
+    last_newline: TextUnit,
+    col_adjust: TextUnit,
+}
+
+impl RunningLineCol {
+    fn new() -> RunningLineCol {
+        RunningLineCol { line: 0, last_newline: TextUnit::from(0), col_adjust: TextUnit::from(0) }
+    }
+
+    fn to_line_col(&self, offset: TextUnit) -> LineCol {
+        LineCol {
+            line: self.line,
+            col_utf16: ((offset - self.last_newline) - self.col_adjust).into(),
+        }
+    }
+
+    fn add_line(&mut self, newline: TextUnit) {
+        self.line += 1;
+        self.last_newline = newline;
+        self.col_adjust = TextUnit::from(0);
+    }
+
+    fn adjust_col(&mut self, range: &TextRange) {
+        self.col_adjust += range.len() - TextUnit::from(1);
+    }
+}
+
+pub fn translate_offset_with_edit(
+    line_index: &LineIndex,
+    offset: TextUnit,
+    text_edit: &TextEdit,
+) -> LineCol {
+    let mut state = Edits::from_text_edit(&text_edit);
+
+    let mut res = RunningLineCol::new();
+
+    macro_rules! test_step {
+        ($x:ident) => {
+            match &$x {
+                Step::Newline(n) => {
+                    if offset < *n {
+                        return res.to_line_col(offset);
+                    } else {
+                        res.add_line(*n);
+                    }
+                }
+                Step::Utf16Char(x) => {
+                    if offset < x.end() {
+                        // if the offset is inside a multibyte char it's invalid
+                        // clamp it to the start of the char
+                        let clamp = offset.min(x.start());
+                        return res.to_line_col(clamp);
+                    } else {
+                        res.adjust_col(x);
+                    }
+                }
+            }
+        };
+    }
+
+    for orig_step in LineIndexStepIter::from(line_index) {
+        loop {
+            let translated_step = state.translate_step(&orig_step);
+            match state.next_steps(&translated_step) {
+                NextSteps::Use => {
+                    test_step!(translated_step);
+                    break;
+                }
+                NextSteps::ReplaceMany(ns) => {
+                    for n in ns {
+                        test_step!(n);
+                    }
+                    break;
+                }
+                NextSteps::AddMany(ns) => {
+                    for n in ns {
+                        test_step!(n);
+                    }
+                }
+            }
+        }
+    }
+
+    loop {
+        match state.next_inserted_steps() {
+            None => break,
+            Some(ns) => {
+                for n in ns {
+                    test_step!(n);
+                }
+            }
+        }
+    }
+
+    res.to_line_col(offset)
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use proptest::{prelude::*, proptest};
+    use crate::line_index;
+    use ra_text_edit::test_utils::{arb_offset, arb_text_with_edit};
+    use ra_text_edit::TextEdit;
+
+    #[derive(Debug)]
+    struct ArbTextWithEditAndOffset {
+        text: String,
+        edit: TextEdit,
+        edited_text: String,
+        offset: TextUnit,
+    }
+
+    fn arb_text_with_edit_and_offset() -> BoxedStrategy<ArbTextWithEditAndOffset> {
+        arb_text_with_edit()
+            .prop_flat_map(|x| {
+                let edited_text = x.edit.apply(&x.text);
+                let arb_offset = arb_offset(&edited_text);
+                (Just(x), Just(edited_text), arb_offset).prop_map(|(x, edited_text, offset)| {
+                    ArbTextWithEditAndOffset { text: x.text, edit: x.edit, edited_text, offset }
+                })
+            })
+            .boxed()
+    }
+
+    proptest! {
+        #[test]
+        fn test_translate_offset_with_edit(x in arb_text_with_edit_and_offset()) {
+            let expected = line_index::to_line_col(&x.edited_text, x.offset);
+            let line_index = LineIndex::new(&x.text);
+            let actual = translate_offset_with_edit(&line_index, x.offset, &x.edit);
+
+            assert_eq!(actual, expected);
+        }
+    }
+}