1 files changed, 284 insertions, 0 deletions

diff --git a/crates/ra_ide_db/src/line_index.rs b/crates/ra_ide_db/src/line_index.rs
new file mode 100644
index 000000000..452c87ac5
--- /dev/null
+++ b/crates/ra_ide_db/src/line_index.rs
@@ -0,0 +1,284 @@
+//! `LineIndex` maps flat `TextUnit` offsets into `(Line, Column)`
+//! representation.
+
+use ra_syntax::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 {
+    /// Zero-based
+    pub line: u32,
+    /// Zero-based
+    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.is_empty() {
+                    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.is_empty() {
+            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 {
+        //FIXME: 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_offset, arb_text};
+
+    #[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));
+    }
+}