core/src/local/derive.rs

@@ -19,10 +19,13 @@
 //! Also derived `[[wiki-links]]` until they were removed (note 2897) — this is a
 //! capture-and-recall surface, and a linking system is organization.
 
-/// Extract every `#tag` name (without the leading `#`) from `body`.
-pub fn extract_tags(body: &str) -> Vec<String> {
-    let chars: Vec<char> = body.chars().collect();
-    let mut out: Vec<String> = Vec::new();
+/// Every `#tag` in ONE line, as `(start, end, name)` in char indices.
+///
+/// Char indices rather than byte offsets so the spans can be used to cut the tags
+/// back out of the line without ever landing mid-codepoint — see
+/// [`lift_standalone_tags`], which is the only reason the spans exist.
+fn line_tags(chars: &[char]) -> Vec<(usize, usize, String)> {
+    let mut out: Vec<(usize, usize, String)> = Vec::new();
     let mut i = 0;
     while i < chars.len() {
         if chars[i] == '#' {
@@ -33,8 +36,7 @@ pub fn extract_tags(body: &str) -> Vec<String> {
                 while j < chars.len() && is_tag_char(chars[j]) {
                     j += 1;
                 }
-                let tag: String = chars[i + 1..j].iter().collect();
-                push_unique(&mut out, &tag);
+                out.push((i, j, chars[i + 1..j].iter().collect()));
                 i = j;
                 continue;
             }
@@ -44,6 +46,127 @@ pub fn extract_tags(body: &str) -> Vec<String> {
     out
 }
 
+/// Extract every `#tag` name (without the leading `#`) from `body`.
+///
+/// Line by line, which changes nothing: a line start and a `\n` are both boundaries,
+/// so the same tags come out. It means there is ONE scanner rather than two — this and
+/// [`lift_standalone_tags`] cannot disagree about what a tag is.
+pub fn extract_tags(body: &str) -> Vec<String> {
+    let mut out: Vec<String> = Vec::new();
+    for line in body.split('\n') {
+        let chars: Vec<char> = line.chars().collect();
+        for (_, _, name) in line_tags(&chars) {
+            push_unique(&mut out, &name);
+        }
+    }
+    out
+}
+
+/// Whether a line opens or closes a fenced code block.
+fn is_fence(line: &str) -> bool {
+    let trimmed = line.trim_start();
+    trimmed.starts_with("```") || trimmed.starts_with("~~~")
+}
+
+/// Runs of three or more newlines become two, and the ends are trimmed.
+///
+/// Removing a line must not leave a hole where it was.
+fn collapse_blank_runs(text: &str) -> String {
+    let mut out = String::with_capacity(text.len());
+    let mut run = 0;
+    for c in text.chars() {
+        if c == '\n' {
+            run += 1;
+            if run <= 2 {
+                out.push(c);
+            }
+        } else {
+            run = 0;
+            out.push(c);
+        }
+    }
+    out.trim_matches('\n').to_string()
+}
+
+/// Split a body's tags by whether the text around them can be taken away.
+///
+/// Returns `(standalone, inline, lifted_body)`.
+///
+/// THE RULE: a line containing nothing but tags and whitespace is removed. Anything
+/// else is left exactly as written.
+///
+/// The MIRROR of `split_body_tags` in the server's `notes/tags.py`, and it has to stay
+/// one: a note lifted differently here than there would change under the operator the
+/// moment it synced. Same discipline, and the same reason, as `DerivedTint`.
+///
+/// The conservative reading of "standalone" is deliberate. A trailing tag is
+/// ambiguous and the text does not say which it is — `buy milk #grocery` is filing,
+/// `remember to call #mom` is the sentence's object, and lifting the second leaves
+/// "remember to call". A tag sharing a line with words keeps its words.
+///
+/// `standalone` tags become ORDINARY labels (`via_tag = 0`): nothing is left to derive
+/// them from, so the row becomes the record and the chip's × becomes the way to remove
+/// one. `inline` tags stay derived exactly as before. That is what `via_tag` means from
+/// here on — backed by text still in the body.
+pub fn lift_standalone_tags(body: &str) -> (Vec<String>, Vec<String>, String) {
+    let mut standalone: Vec<String> = Vec::new();
+    let mut inline: Vec<String> = Vec::new();
+    let mut kept: Vec<&str> = Vec::new();
+    let mut in_fence = false;
+
+    for line in body.split('\n') {
+        if is_fence(line) {
+            in_fence = !in_fence;
+            kept.push(line);
+            continue;
+        }
+        let chars: Vec<char> = line.chars().collect();
+        let spans = line_tags(&chars);
+        // Cut the tags out and see whether anything is left. That is what
+        // "standalone" means, and it is the whole rule.
+        let mut remainder = String::new();
+        let mut pos = 0;
+        for (start, end, _) in &spans {
+            remainder.extend(chars[pos..*start].iter());
+            pos = *end;
+        }
+        remainder.extend(chars[pos..].iter());
+
+        // A fence's contents are CODE: a `#tag` there is a shell comment in somebody's
+        // snippet, and deleting the line would eat part of their example.
+        if in_fence || spans.is_empty() || !remainder.trim().is_empty() {
+            for (_, _, name) in &spans {
+                push_unique(&mut inline, name);
+            }
+            kept.push(line);
+        } else {
+            for (_, _, name) in &spans {
+                push_unique(&mut standalone, name);
+            }
+        }
+    }
+
+    let lifted = collapse_blank_runs(&kept.join("\n"));
+    if !body.trim().is_empty() && lifted.trim().is_empty() {
+        // The note was NOTHING but tags. Lifting would leave a blank card, which is a
+        // worse outcome than a duplicated chip — so leave it alone.
+        let mut all = standalone;
+        for name in &inline {
+            push_unique(&mut all, name);
+        }
+        return (Vec::new(), all, body.to_string());
+    }
+
+    // A tag that ALSO appears in prose stays derived: the prose copy still backs it,
+    // so deleting that copy should still detach the label.
+    let inline_lower: Vec<String> = inline.iter().map(|n| n.to_lowercase()).collect();
+    let standalone = standalone
+        .into_iter()
+        .filter(|n| !inline_lower.contains(&n.to_lowercase()))
+        .collect();
+    (standalone, inline, lifted)
+}
+
 fn is_tag_char(c: char) -> bool {
     c.is_alphanumeric() || c == '_' || c == '-'
 }
@@ -315,6 +438,89 @@ mod tests {
         assert!(extract_tags("").is_empty());
     }
 
+    // ── lifting standalone tags ──────────────────────────────────────────────
+    //
+    // The MIRROR of `split_body_tags` in the server's notes/tags.py, case for case.
+    // A note lifted differently here than there would change under the operator the
+    // moment it synced, so these are the cases that file agrees to.
+
+    #[test]
+    fn lifts_a_line_that_is_nothing_but_tags() {
+        let (standalone, inline, body) = lift_standalone_tags("#todo\nreorganize the homepage");
+        assert_eq!(standalone, vec!["todo"]);
+        assert!(inline.is_empty());
+        assert_eq!(body, "reorganize the homepage");
+
+        let (standalone, _, body) = lift_standalone_tags("needs a tauri app\n#todo");
+        assert_eq!(standalone, vec!["todo"]);
+        assert_eq!(body, "needs a tauri app");
+
+        let (standalone, _, body) = lift_standalone_tags("#todo #work\nreal text");
+        assert_eq!(standalone, vec!["todo", "work"]);
+        assert_eq!(body, "real text");
+    }
+
+    /// The cases that must come back byte-identical. Getting any of these wrong
+    /// destroys somebody's words, which is why the rule is the conservative one:
+    /// a trailing tag is ambiguous and the text does not say which kind it is.
+    #[test]
+    fn leaves_a_tag_that_shares_its_line_with_words() {
+        for prose in [
+            "remember to call #mom tomorrow",
+            "buy milk #grocery",
+            "#2024\nreal",
+        ] {
+            let (standalone, _, body) = lift_standalone_tags(prose);
+            assert!(standalone.is_empty(), "{prose}");
+            assert_eq!(body, prose, "{prose}");
+        }
+    }
+
+    #[test]
+    fn removing_a_line_leaves_no_hole() {
+        let (_, _, body) = lift_standalone_tags("foo\n\n#todo\n\nbar");
+        assert_eq!(body, "foo\n\nbar");
+    }
+
+    /// A `#tag` in a fence is a shell comment in somebody's snippet. It still becomes
+    /// a label — it always has — but the line is never touched.
+    #[test]
+    fn never_touches_a_fenced_line() {
+        let fenced = "code:\n```\n#!/bin/sh\n#deploy\n```\ndone";
+        let (standalone, inline, body) = lift_standalone_tags(fenced);
+        assert!(standalone.is_empty());
+        assert_eq!(inline, vec!["deploy"]);
+        assert_eq!(body, fenced);
+    }
+
+    /// Lifting would leave a blank card, which is worse than the duplication this
+    /// removes. So the note keeps its text and its tags stay derived.
+    #[test]
+    fn will_not_blank_a_note_that_is_only_tags() {
+        let (standalone, inline, body) = lift_standalone_tags("#todo");
+        assert!(standalone.is_empty());
+        assert_eq!(inline, vec!["todo"]);
+        assert_eq!(body, "#todo");
+    }
+
+    /// Appearing on its own line does NOT lift a tag also written in a sentence — the
+    /// sentence still backs it, so deleting the sentence should still detach it.
+    #[test]
+    fn a_tag_still_in_prose_stays_derived() {
+        let (standalone, inline, body) = lift_standalone_tags("#todo\nremember the #todo list");
+        assert!(standalone.is_empty());
+        assert_eq!(inline, vec!["todo"]);
+        assert_eq!(body, "remember the #todo list");
+    }
+
+    #[test]
+    fn lifting_an_empty_body_is_a_no_op() {
+        let (standalone, inline, body) = lift_standalone_tags("");
+        assert!(standalone.is_empty());
+        assert!(inline.is_empty());
+        assert_eq!(body, "");
+    }
+
     // ── checklist items ─────────────────────────────────────────────────────
 
     fn item(text: &str, checked: bool, line: u32) -> DerivedItem {

core/src/local/store.rs

@@ -205,34 +205,89 @@ fn find_or_create_label(conn: &Connection, name: &str) -> rusqlite::Result<Strin
     Ok(id)
 }
 
-/// Re-sync the note's `via_tag` labels to exactly the `#tags` in its body.
-fn sync_tags(conn: &Connection, note_id: &str, body: &str) -> rusqlite::Result<()> {
-    let tags = derive::extract_tags(body);
-    let mut desired: Vec<String> = Vec::with_capacity(tags.len());
-    for t in &tags {
-        desired.push(find_or_create_label(conn, t)?);
+/// Attach the note's tag labels, LIFT its standalone tags out of the body, and write
+/// the shortened body back.
+///
+/// NAMED FOR THE MUTATION. It used to be `sync_tags` and only touched label rows; it
+/// now rewrites `notes.body`, and every caller writes the body just before calling —
+/// so this overwrites what they wrote, on purpose.
+///
+/// `display_title` needs no attention here, unlike on the server: the core derives it
+/// on READ (see `display_title` above, called from `load_note`) rather than storing
+/// it, so there is no persisted copy to go stale.
+///
+/// The two kinds of tag are handled differently, and that difference IS what `via_tag`
+/// means from here on — backed by text still in the body:
+///
+///   standalone  lifted out, attached as an ORDINARY label. Nothing derives it any
+///               more, and the way to remove it becomes the chip's ×.
+///   inline      left in place, attached via_tag = 1, still detached when its text
+///               goes. Unchanged from before.
+///
+/// Mirrors `_lift_and_reconcile_tags` in the server's `notes/tags.py`.
+fn lift_and_sync_tags(conn: &Connection, note_id: &str, body: &str) -> rusqlite::Result<()> {
+    let (standalone, inline, lifted) = derive::lift_standalone_tags(body);
+
+    let mut standalone_ids: Vec<String> = Vec::with_capacity(standalone.len());
+    for name in &standalone {
+        standalone_ids.push(find_or_create_label(conn, name)?);
+    }
+    let mut inline_ids: Vec<String> = Vec::with_capacity(inline.len());
+    for name in &inline {
+        inline_ids.push(find_or_create_label(conn, name)?);
     }
 
-    let current: Vec<String> = {
+    let current: Vec<(String, bool)> = {
         let mut stmt =
-            conn.prepare("SELECT label_id FROM note_labels WHERE note_id = ?1 AND via_tag = 1")?;
-        let rows = stmt.query_map([note_id], |r| r.get::<_, String>(0))?;
-        rows.collect::<rusqlite::Result<Vec<String>>>()?
+            conn.prepare("SELECT label_id, via_tag FROM note_labels WHERE note_id = ?1")?;
+        let rows = stmt.query_map([note_id], |r| {
+            Ok((r.get::<_, String>(0)?, r.get::<_, bool>(1)?))
+        })?;
+        rows.collect::<rusqlite::Result<Vec<(String, bool)>>>()?
     };
-    for lid in &current {
-        if !desired.contains(lid) {
+
+    for (lid, via_tag) in &current {
+        if !*via_tag {
+            continue; // manual already: a #tag of the same name changes nothing
+        }
+        if standalone_ids.contains(lid) {
+            // It GRADUATED. The text backing it is about to go, so the row has to
+            // become the record instead — and BEFORE the delete below, or the same row
+            // is dropped for no longer being in the body. That is the bug a naive lift
+            // has, and it silently loses the tag.
+            conn.execute(
+                "UPDATE note_labels SET via_tag = 0 WHERE note_id = ?1 AND label_id = ?2",
+                params![note_id, lid],
+            )?;
+        } else if !inline_ids.contains(lid) {
             conn.execute(
                 "DELETE FROM note_labels WHERE note_id = ?1 AND label_id = ?2 AND via_tag = 1",
                 params![note_id, lid],
             )?;
         }
     }
-    for lid in &desired {
+
+    // OR IGNORE leaves a label already attached in ANY form alone, which is what keeps
+    // a manually-added label of the same name manual.
+    for lid in &standalone_ids {
+        conn.execute(
+            "INSERT OR IGNORE INTO note_labels (note_id, label_id, via_tag) VALUES (?1, ?2, 0)",
+            params![note_id, lid],
+        )?;
+    }
+    for lid in &inline_ids {
         conn.execute(
             "INSERT OR IGNORE INTO note_labels (note_id, label_id, via_tag) VALUES (?1, ?2, 1)",
             params![note_id, lid],
         )?;
     }
+
+    if lifted != body {
+        conn.execute(
+            "UPDATE notes SET body = ?1 WHERE id = ?2",
+            params![lifted, note_id],
+        )?;
+    }
     Ok(())
 }
 
@@ -378,7 +433,7 @@ pub fn create_note(conn: &Connection, input: &NoteCreateInput) -> rusqlite::Resu
         params![id, body, input.color, position, ts],
     )?;
     // The FOLDED body, not the input one: an item can carry a #tag too.
-    sync_tags(conn, &id, &body)?;
+    lift_and_sync_tags(conn, &id, &body)?;
     load_note(conn, &id)
 }
 
@@ -451,7 +506,7 @@ pub fn update_note(conn: &Connection, id: &str, changes: &Value) -> rusqlite::Re
                     "UPDATE notes SET body = ?1 WHERE id = ?2",
                     params![body, id],
                 )?;
-                sync_tags(conn, id, body)?;
+                lift_and_sync_tags(conn, id, body)?;
             }
             "color" => {
                 if let Some(s) = v.as_str() {
@@ -727,7 +782,7 @@ pub fn restore_revision(conn: &Connection, id: &str, rev_id: &str) -> rusqlite::
         "UPDATE notes SET body = ?1 WHERE id = ?2",
         params![body, id],
     )?;
-    sync_tags(conn, id, &body)?;
+    lift_and_sync_tags(conn, id, &body)?;
     touch(conn, id)?;
     load_note(conn, id)
 }