wip: importing to github

1 files changed, 213 insertions, 0 deletions

diff --git a/helix-core/src/graphemes.rs b/helix-core/src/graphemes.rs
new file mode 100644
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+++ b/helix-core/src/graphemes.rs
@@ -0,0 +1,213 @@
+// Based on https://github.com/cessen/led/blob/c4fa72405f510b7fd16052f90a598c429b3104a6/src/graphemes.rs
+use ropey::{iter::Chunks, str_utils::byte_to_char_idx, RopeSlice};
+use unicode_segmentation::{GraphemeCursor, GraphemeIncomplete};
+use unicode_width::UnicodeWidthStr;
+
+pub fn grapheme_width(g: &str) -> usize {
+    if g.as_bytes()[0] <= 127 {
+        // Fast-path ascii.
+        // Point 1: theoretically, ascii control characters should have zero
+        // width, but in our case we actually want them to have width: if they
+        // show up in text, we want to treat them as textual elements that can
+        // be editied.  So we can get away with making all ascii single width
+        // here.
+        // Point 2: we're only examining the first codepoint here, which means
+        // we're ignoring graphemes formed with combining characters.  However,
+        // if it starts with ascii, it's going to be a single-width grapeheme
+        // regardless, so, again, we can get away with that here.
+        // Point 3: we're only examining the first _byte_.  But for utf8, when
+        // checking for ascii range values only, that works.
+        1
+    } else {
+        // We use max(1) here because all grapeheme clusters--even illformed
+        // ones--should have at least some width so they can be edited
+        // properly.
+        UnicodeWidthStr::width(g).max(1)
+    }
+}
+
+pub fn nth_prev_grapheme_boundary(slice: &RopeSlice, char_idx: usize, n: usize) -> usize {
+    // TODO: implement this more efficiently.  This has to do a lot of
+    // re-scanning of rope chunks.  Probably move the main implementation here,
+    // and have prev_grapheme_boundary call this instead.
+    let mut char_idx = char_idx;
+    for _ in 0..n {
+        char_idx = prev_grapheme_boundary(slice, char_idx);
+    }
+    char_idx
+}
+
+/// Finds the previous grapheme boundary before the given char position.
+pub fn prev_grapheme_boundary(slice: &RopeSlice, char_idx: usize) -> usize {
+    // Bounds check
+    debug_assert!(char_idx <= slice.len_chars());
+
+    // We work with bytes for this, so convert.
+    let byte_idx = slice.char_to_byte(char_idx);
+
+    // Get the chunk with our byte index in it.
+    let (mut chunk, mut chunk_byte_idx, mut chunk_char_idx, _) = slice.chunk_at_byte(byte_idx);
+
+    // Set up the grapheme cursor.
+    let mut gc = GraphemeCursor::new(byte_idx, slice.len_bytes(), true);
+
+    // Find the previous grapheme cluster boundary.
+    loop {
+        match gc.prev_boundary(chunk, chunk_byte_idx) {
+            Ok(None) => return 0,
+            Ok(Some(n)) => {
+                let tmp = byte_to_char_idx(chunk, n - chunk_byte_idx);
+                return chunk_char_idx + tmp;
+            }
+            Err(GraphemeIncomplete::PrevChunk) => {
+                let (a, b, c, _) = slice.chunk_at_byte(chunk_byte_idx - 1);
+                chunk = a;
+                chunk_byte_idx = b;
+                chunk_char_idx = c;
+            }
+            Err(GraphemeIncomplete::PreContext(n)) => {
+                let ctx_chunk = slice.chunk_at_byte(n - 1).0;
+                gc.provide_context(ctx_chunk, n - ctx_chunk.len());
+            }
+            _ => unreachable!(),
+        }
+    }
+}
+
+pub fn nth_next_grapheme_boundary(slice: &RopeSlice, char_idx: usize, n: usize) -> usize {
+    // TODO: implement this more efficiently.  This has to do a lot of
+    // re-scanning of rope chunks.  Probably move the main implementation here,
+    // and have next_grapheme_boundary call this instead.
+    let mut char_idx = char_idx;
+    for _ in 0..n {
+        char_idx = next_grapheme_boundary(slice, char_idx);
+    }
+    char_idx
+}
+
+/// Finds the next grapheme boundary after the given char position.
+pub fn next_grapheme_boundary(slice: &RopeSlice, char_idx: usize) -> usize {
+    // Bounds check
+    debug_assert!(char_idx <= slice.len_chars());
+
+    // We work with bytes for this, so convert.
+    let byte_idx = slice.char_to_byte(char_idx);
+
+    // Get the chunk with our byte index in it.
+    let (mut chunk, mut chunk_byte_idx, mut chunk_char_idx, _) = slice.chunk_at_byte(byte_idx);
+
+    // Set up the grapheme cursor.
+    let mut gc = GraphemeCursor::new(byte_idx, slice.len_bytes(), true);
+
+    // Find the next grapheme cluster boundary.
+    loop {
+        match gc.next_boundary(chunk, chunk_byte_idx) {
+            Ok(None) => return slice.len_chars(),
+            Ok(Some(n)) => {
+                let tmp = byte_to_char_idx(chunk, n - chunk_byte_idx);
+                return chunk_char_idx + tmp;
+            }
+            Err(GraphemeIncomplete::NextChunk) => {
+                chunk_byte_idx += chunk.len();
+                let (a, _, c, _) = slice.chunk_at_byte(chunk_byte_idx);
+                chunk = a;
+                chunk_char_idx = c;
+            }
+            Err(GraphemeIncomplete::PreContext(n)) => {
+                let ctx_chunk = slice.chunk_at_byte(n - 1).0;
+                gc.provide_context(ctx_chunk, n - ctx_chunk.len());
+            }
+            _ => unreachable!(),
+        }
+    }
+}
+
+/// Returns whether the given char position is a grapheme boundary.
+pub fn is_grapheme_boundary(slice: &RopeSlice, char_idx: usize) -> bool {
+    // Bounds check
+    debug_assert!(char_idx <= slice.len_chars());
+
+    // We work with bytes for this, so convert.
+    let byte_idx = slice.char_to_byte(char_idx);
+
+    // Get the chunk with our byte index in it.
+    let (chunk, chunk_byte_idx, _, _) = slice.chunk_at_byte(byte_idx);
+
+    // Set up the grapheme cursor.
+    let mut gc = GraphemeCursor::new(byte_idx, slice.len_bytes(), true);
+
+    // Determine if the given position is a grapheme cluster boundary.
+    loop {
+        match gc.is_boundary(chunk, chunk_byte_idx) {
+            Ok(n) => return n,
+            Err(GraphemeIncomplete::PreContext(n)) => {
+                let (ctx_chunk, ctx_byte_start, _, _) = slice.chunk_at_byte(n - 1);
+                gc.provide_context(ctx_chunk, ctx_byte_start);
+            }
+            _ => unreachable!(),
+        }
+    }
+}
+
+/// An iterator over the graphemes of a RopeSlice.
+#[derive(Clone)]
+pub struct RopeGraphemes<'a> {
+    text: RopeSlice<'a>,
+    chunks: Chunks<'a>,
+    cur_chunk: &'a str,
+    cur_chunk_start: usize,
+    cursor: GraphemeCursor,
+}
+
+impl<'a> RopeGraphemes<'a> {
+    pub fn new<'b>(slice: &RopeSlice<'b>) -> RopeGraphemes<'b> {
+        let mut chunks = slice.chunks();
+        let first_chunk = chunks.next().unwrap_or("");
+        RopeGraphemes {
+            text: *slice,
+            chunks: chunks,
+            cur_chunk: first_chunk,
+            cur_chunk_start: 0,
+            cursor: GraphemeCursor::new(0, slice.len_bytes(), true),
+        }
+    }
+}
+
+impl<'a> Iterator for RopeGraphemes<'a> {
+    type Item = RopeSlice<'a>;
+
+    fn next(&mut self) -> Option<RopeSlice<'a>> {
+        let a = self.cursor.cur_cursor();
+        let b;
+        loop {
+            match self
+                .cursor
+                .next_boundary(self.cur_chunk, self.cur_chunk_start)
+            {
+                Ok(None) => {
+                    return None;
+                }
+                Ok(Some(n)) => {
+                    b = n;
+                    break;
+                }
+                Err(GraphemeIncomplete::NextChunk) => {
+                    self.cur_chunk_start += self.cur_chunk.len();
+                    self.cur_chunk = self.chunks.next().unwrap_or("");
+                }
+                _ => unreachable!(),
+            }
+        }
+
+        if a < self.cur_chunk_start {
+            let a_char = self.text.byte_to_char(a);
+            let b_char = self.text.byte_to_char(b);
+
+            Some(self.text.slice(a_char..b_char))
+        } else {
+            let a2 = a - self.cur_chunk_start;
+            let b2 = b - self.cur_chunk_start;
+            Some((&self.cur_chunk[a2..b2]).into())
+        }
+    }
+}