Add (prev) paragraph motion

Also improved testing facility.

Fix #1580

4 files changed, 238 insertions, 0 deletions

diff --git a/helix-core/src/lib.rs b/helix-core/src/lib.rs
index 1f43c266..0ae68f91 100644
--- a/helix-core/src/lib.rs
+++ b/helix-core/src/lib.rs
@@ -24,6 +24,7 @@ pub mod shellwords;
 mod state;
 pub mod surround;
 pub mod syntax;
+pub mod test;
 pub mod textobject;
 mod transaction;
 
diff --git a/helix-core/src/line_ending.rs b/helix-core/src/line_ending.rs
index 06ec2a45..f0cf3b10 100644
--- a/helix-core/src/line_ending.rs
+++ b/helix-core/src/line_ending.rs
@@ -119,6 +119,11 @@ pub fn str_is_line_ending(s: &str) -> bool {
     LineEnding::from_str(s).is_some()
 }
 
+#[inline]
+pub fn rope_is_line_ending(r: RopeSlice) -> bool {
+    r.chunks().all(str_is_line_ending)
+}
+
 /// Attempts to detect what line ending the passed document uses.
 pub fn auto_detect_line_ending(doc: &Rope) -> Option<LineEnding> {
     // Return first matched line ending. Not all possible line endings
diff --git a/helix-core/src/movement.rs b/helix-core/src/movement.rs
index e559f1ea..21d16931 100644
--- a/helix-core/src/movement.rs
+++ b/helix-core/src/movement.rs
@@ -10,6 +10,7 @@ use crate::{
         next_grapheme_boundary, nth_next_grapheme_boundary, nth_prev_grapheme_boundary,
         prev_grapheme_boundary,
     },
+    line_ending::{rope_is_line_ending, str_is_line_ending},
     pos_at_coords,
     syntax::LanguageConfiguration,
     textobject::TextObject,
@@ -149,6 +150,63 @@ fn word_move(slice: RopeSlice, range: Range, count: usize, target: WordMotionTar
     })
 }
 
+pub fn move_prev_para(slice: RopeSlice, range: Range, count: usize, behavior: Movement) -> Range {
+    let mut line = range.cursor_line(slice);
+    let first_char = slice.line_to_char(line) == range.cursor(slice);
+    let curr_line_empty = rope_is_line_ending(slice.line(line));
+    let last_line_empty = rope_is_line_ending(slice.line(line.saturating_sub(1)));
+    let line_to_empty = last_line_empty && !curr_line_empty;
+
+    // iterate current line if first character after paragraph boundary
+    if line_to_empty && !first_char {
+        line += 1;
+    }
+    let mut lines = slice.lines_at(line);
+    lines.reverse();
+    let mut lines = lines.map(rope_is_line_ending).peekable();
+    for _ in 0..count {
+        while lines.next_if(|&e| e).is_some() {
+            line -= 1;
+        }
+        while lines.next_if(|&e| !e).is_some() {
+            line -= 1;
+        }
+    }
+
+    let head = slice.line_to_char(line);
+    let anchor = if behavior == Movement::Move {
+        // exclude first character after paragraph boundary
+        if line_to_empty && first_char {
+            range.cursor(slice)
+        } else {
+            range.head
+        }
+    } else {
+        range.put_cursor(slice, head, true).anchor
+    };
+    Range::new(anchor, head)
+}
+
+pub fn move_next_para(slice: RopeSlice, range: Range, count: usize, behavior: Movement) -> Range {
+    let mut line = slice.char_to_line(range.head);
+    let lines = slice.lines_at(line);
+    let mut lines = lines.map(|l| l.chunks().all(str_is_line_ending)).peekable();
+    for _ in 0..count {
+        while lines.next_if(|&e| !e).is_some() {
+            line += 1;
+        }
+        while lines.next_if(|&e| e).is_some() {
+            line += 1;
+        }
+    }
+    let anchor = if behavior == Movement::Move {
+        range.cursor(slice)
+    } else {
+        range.anchor
+    };
+    Range::new(anchor, slice.line_to_char(line))
+}
+
 // ---- util ------------
 
 #[inline]
@@ -1179,4 +1237,67 @@ mod test {
             }
         }
     }
+
+    #[test]
+    fn test_behaviour_when_moving_to_prev_paragraph_single() {
+        let tests = [
+            ("^@", "@^"),
+            ("^s@tart at\nfirst char\n", "@s^tart at\nfirst char\n"),
+            ("start at\nlast char^\n@", "@start at\nlast char\n^"),
+            ("goto\nfirst\n\n^p@aragraph", "@goto\nfirst\n\n^paragraph"),
+            ("goto\nfirst\n^\n@paragraph", "@goto\nfirst\n\n^paragraph"),
+            ("goto\nsecond\n\np^a@ragraph", "goto\nsecond\n\n@pa^ragraph"),
+            (
+                "here\n\nhave\nmultiple\nparagraph\n\n\n\n\n^@",
+                "here\n\n@have\nmultiple\nparagraph\n\n\n\n\n^",
+            ),
+        ];
+
+        for (actual, expected) in tests {
+            let (s, selection) = crate::test::print(actual);
+            let text = Rope::from(s.as_str());
+            let selection =
+                selection.transform(|r| move_prev_para(text.slice(..), r, 1, Movement::Move));
+            let actual = crate::test::plain(&s, selection);
+            assert_eq!(actual, expected);
+        }
+    }
+
+    #[ignore]
+    #[test]
+    fn test_behaviour_when_moving_to_prev_paragraph_double() {}
+
+    #[test]
+    fn test_behaviour_when_moving_to_next_paragraph_single() {
+        let tests = [
+            ("^@", "@^"),
+            ("^s@tart at\nfirst char\n", "^start at\nfirst char\n@"),
+            ("start at\nlast char^\n@", "start at\nlast char^\n@"),
+            (
+                "a\nb\n\n^g@oto\nthird\n\nparagraph",
+                "a\nb\n\n^goto\nthird\n\n@paragraph",
+            ),
+            (
+                "a\nb\n^\n@goto\nthird\n\nparagraph",
+                "a\nb\n\n^goto\nthird\n\n@paragraph",
+            ),
+            (
+                "a\nb^\n@\ngoto\nsecond\n\nparagraph",
+                "a\nb^\n\n@goto\nsecond\n\nparagraph",
+            ),
+            (
+                "here\n\nhave\n^m@ultiple\nparagraph\n\n\n\n\n",
+                "here\n\nhave\n^multiple\nparagraph\n\n\n\n\n@",
+            ),
+        ];
+
+        for (actual, expected) in tests {
+            let (s, selection) = crate::test::print(actual);
+            let text = Rope::from(s.as_str());
+            let selection =
+                selection.transform(|r| move_next_para(text.slice(..), r, 1, Movement::Move));
+            let actual = crate::test::plain(&s, selection);
+            assert_eq!(actual, expected);
+        }
+    }
 }
diff --git a/helix-core/src/test.rs b/helix-core/src/test.rs
new file mode 100644
index 00000000..983c9a57
--- /dev/null
+++ b/helix-core/src/test.rs
@@ -0,0 +1,111 @@
+//! Test helpers.
+use crate::{Range, Selection};
+use smallvec::SmallVec;
+use std::cmp::Reverse;
+
+/// Convert annotated test string to test string and selection.
+///
+/// `^` for `anchor` and `|` for head (`@` for primary), both must appear
+/// or otherwise it will panic.
+///
+/// # Examples
+///
+/// ```
+/// use helix_core::{Range, Selection, test::print};
+/// use smallvec::smallvec;
+///
+/// assert_eq!(
+///     print("^a@b|c^"),
+///     ("abc".to_owned(), Selection::new(smallvec![Range::new(0, 1), Range::new(3, 2)], 0))
+/// );
+/// ```
+///
+/// # Panics
+///
+/// Panics when missing primary or appeared more than once.
+/// Panics when missing head or anchor.
+/// Panics when head come after head or anchor come after anchor.
+pub fn print(s: &str) -> (String, Selection) {
+    let mut anchor = None;
+    let mut head = None;
+    let mut primary = None;
+    let mut ranges = SmallVec::new();
+    let mut i = 0;
+    let s = s
+        .chars()
+        .filter(|c| {
+            match c {
+                '^' if anchor != None => panic!("anchor without head {s:?}"),
+                '^' if head == None => anchor = Some(i),
+                '^' => ranges.push(Range::new(i, head.take().unwrap())),
+                '|' if head != None => panic!("head without anchor {s:?}"),
+                '|' if anchor == None => head = Some(i),
+                '|' => ranges.push(Range::new(anchor.take().unwrap(), i)),
+                '@' if primary != None => panic!("head (primary) already appeared {s:?}"),
+                '@' if head != None => panic!("head (primary) without anchor {s:?}"),
+                '@' if anchor == None => {
+                    primary = Some(ranges.len());
+                    head = Some(i);
+                }
+                '@' => {
+                    primary = Some(ranges.len());
+                    ranges.push(Range::new(anchor.take().unwrap(), i));
+                }
+                _ => {
+                    i += 1;
+                    return true;
+                }
+            };
+            false
+        })
+        .collect();
+    if head.is_some() {
+        panic!("missing anchor (|) {s:?}");
+    }
+    if anchor.is_some() {
+        panic!("missing head (^) {s:?}");
+    }
+    let primary = match primary {
+        Some(i) => i,
+        None => panic!("missing primary (@) {s:?}"),
+    };
+    let selection = Selection::new(ranges, primary);
+    (s, selection)
+}
+
+/// Convert test string and selection to annotated test string.
+///
+/// `^` for `anchor` and `|` for head (`@` for primary).
+///
+/// # Examples
+///
+/// ```
+/// use helix_core::{Range, Selection, test::plain};
+/// use smallvec::smallvec;
+///
+/// assert_eq!(
+///     plain("abc", Selection::new(smallvec![Range::new(0, 1), Range::new(3, 2)], 0)),
+///     "^a@b|c^".to_owned()
+/// );
+/// ```
+pub fn plain(s: &str, selection: Selection) -> String {
+    let primary = selection.primary_index();
+    let mut out = String::with_capacity(s.len() + 2 * selection.len());
+    out.push_str(s);
+    let mut insertion: Vec<_> = selection
+        .iter()
+        .enumerate()
+        .flat_map(|(i, range)| {
+            [
+                (range.anchor, '^'),
+                (range.head, if i == primary { '@' } else { '|' }),
+            ]
+        })
+        .collect();
+    // insert in reverse order
+    insertion.sort_unstable_by_key(|k| Reverse(k.0));
+    for (i, c) in insertion {
+        out.insert(i, c);
+    }
+    out
+}