Comments and neighbors

5 files changed, 281 insertions, 239 deletions

diff --git a/src/parse/mod.rs b/src/parse/mod.rs
index 1f1ac266..f2fae5f2 100644
--- a/src/parse/mod.rs
+++ b/src/parse/mod.rs
@@ -26,14 +26,14 @@ pub fn parse(src: &str) -> Rc<GreenNode> {
 }
 
 /// Parse an atomic primary. Returns `Some` if all of the input was consumed.
-pub fn parse_atomic(src: &str, _: bool) -> Option<Vec<Green>> {
+pub fn parse_atomic(src: &str, _: bool) -> Option<(Vec<Green>, bool)> {
     let mut p = Parser::new(src, TokenMode::Code);
     primary(&mut p, true).ok()?;
     p.eject_partial()
 }
 
 /// Parse some markup. Returns `Some` if all of the input was consumed.
-pub fn parse_markup(src: &str, _: bool) -> Option<Vec<Green>> {
+pub fn parse_markup(src: &str, _: bool) -> Option<(Vec<Green>, bool)> {
     let mut p = Parser::new(src, TokenMode::Markup);
     markup(&mut p);
     p.eject()
@@ -41,7 +41,10 @@ pub fn parse_markup(src: &str, _: bool) -> Option<Vec<Green>> {
 
 /// Parse some markup without the topmost node. Returns `Some` if all of the
 /// input was consumed.
-pub fn parse_markup_elements(src: &str, mut at_start: bool) -> Option<Vec<Green>> {
+pub fn parse_markup_elements(
+    src: &str,
+    mut at_start: bool,
+) -> Option<(Vec<Green>, bool)> {
     let mut p = Parser::new(src, TokenMode::Markup);
     while !p.eof() {
         markup_node(&mut p, &mut at_start);
@@ -50,7 +53,7 @@ pub fn parse_markup_elements(src: &str, mut at_start: bool) -> Option<Vec<Green>
 }
 
 /// Parse a template literal. Returns `Some` if all of the input was consumed.
-pub fn parse_template(source: &str, _: bool) -> Option<Vec<Green>> {
+pub fn parse_template(source: &str, _: bool) -> Option<(Vec<Green>, bool)> {
     let mut p = Parser::new(source, TokenMode::Code);
     if !matches!(p.peek(), Some(NodeKind::LeftBracket)) {
         return None;
@@ -61,7 +64,7 @@ pub fn parse_template(source: &str, _: bool) -> Option<Vec<Green>> {
 }
 
 /// Parse a code block. Returns `Some` if all of the input was consumed.
-pub fn parse_block(source: &str, _: bool) -> Option<Vec<Green>> {
+pub fn parse_block(source: &str, _: bool) -> Option<(Vec<Green>, bool)> {
     let mut p = Parser::new(source, TokenMode::Code);
     if !matches!(p.peek(), Some(NodeKind::LeftBrace)) {
         return None;
@@ -72,7 +75,7 @@ pub fn parse_block(source: &str, _: bool) -> Option<Vec<Green>> {
 }
 
 /// Parse a comment. Returns `Some` if all of the input was consumed.
-pub fn parse_comment(source: &str, _: bool) -> Option<Vec<Green>> {
+pub fn parse_comment(source: &str, _: bool) -> Option<(Vec<Green>, bool)> {
     let mut p = Parser::new(source, TokenMode::Code);
     comment(&mut p).ok()?;
     p.eject()
diff --git a/src/parse/parser.rs b/src/parse/parser.rs
index 31c918a8..a37cb9c6 100644
--- a/src/parse/parser.rs
+++ b/src/parse/parser.rs
@@ -48,9 +48,9 @@ impl<'s> Parser<'s> {
     }
 
     /// End the parsing process and return multiple children.
-    pub fn eject(self) -> Option<Vec<Green>> {
+    pub fn eject(self) -> Option<(Vec<Green>, bool)>{
         if self.eof() && self.group_success() {
-            Some(self.children)
+            Some((self.children, self.tokens.was_unterminated()))
         } else {
             None
         }
@@ -97,8 +97,9 @@ impl<'s> Parser<'s> {
 
     /// End the parsing process and return multiple children, even if there
     /// remains stuff in the string.
-    pub fn eject_partial(self) -> Option<Vec<Green>> {
-        self.group_success().then(|| self.children)
+    pub fn eject_partial(self) -> Option<(Vec<Green>, bool)> {
+        self.group_success()
+            .then(|| (self.children, self.tokens.was_unterminated()))
     }
 
     /// Whether the end of the source string or group is reached.
diff --git a/src/parse/tokens.rs b/src/parse/tokens.rs
index 27ec046d..7be31fe1 100644
--- a/src/parse/tokens.rs
+++ b/src/parse/tokens.rs
@@ -13,6 +13,7 @@ use crate::util::EcoString;
 pub struct Tokens<'s> {
     s: Scanner<'s>,
     mode: TokenMode,
+    has_unterminated: bool,
 }
 
 /// What kind of tokens to emit.
@@ -28,7 +29,11 @@ impl<'s> Tokens<'s> {
     /// Create a new token iterator with the given mode.
     #[inline]
     pub fn new(src: &'s str, mode: TokenMode) -> Self {
-        Self { s: Scanner::new(src), mode }
+        Self {
+            s: Scanner::new(src),
+            mode,
+            has_unterminated: false,
+        }
     }
 
     /// Get the current token mode.
@@ -63,6 +68,12 @@ impl<'s> Tokens<'s> {
     pub fn scanner(&self) -> Scanner<'s> {
         self.s
     }
+
+    /// Whether the last token was unterminated.
+    #[inline]
+    pub fn was_unterminated(&self) -> bool {
+        self.has_unterminated
+    }
 }
 
 impl<'s> Iterator for Tokens<'s> {
@@ -248,6 +259,7 @@ impl<'s> Tokens<'s> {
                             )
                         }
                     } else {
+                        self.has_unterminated = true;
                         NodeKind::Error(
                             ErrorPos::End,
                             "expected closing brace".into(),
@@ -346,6 +358,7 @@ impl<'s> Tokens<'s> {
             let remaining = backticks - found;
             let noun = if remaining == 1 { "backtick" } else { "backticks" };
 
+            self.has_unterminated = true;
             NodeKind::Error(
                 ErrorPos::End,
                 if found == 0 {
@@ -393,6 +406,7 @@ impl<'s> Tokens<'s> {
                 display,
             }))
         } else {
+            self.has_unterminated = true;
             NodeKind::Error(
                 ErrorPos::End,
                 if !display || (!escaped && dollar) {
@@ -481,18 +495,23 @@ impl<'s> Tokens<'s> {
         if self.s.eat_if('"') {
             NodeKind::Str(string)
         } else {
+            self.has_unterminated = true;
             NodeKind::Error(ErrorPos::End, "expected quote".into())
         }
     }
 
     fn line_comment(&mut self) -> NodeKind {
         self.s.eat_until(is_newline);
+        if self.s.peek().is_none() {
+            self.has_unterminated = true;
+        }
         NodeKind::LineComment
     }
 
     fn block_comment(&mut self) -> NodeKind {
         let mut state = '_';
         let mut depth = 1;
+        let mut terminated = false;
 
         // Find the first `*/` that does not correspond to a nested `/*`.
         while let Some(c) = self.s.eat() {
@@ -500,6 +519,7 @@ impl<'s> Tokens<'s> {
                 ('*', '/') => {
                     depth -= 1;
                     if depth == 0 {
+                        terminated = true;
                         break;
                     }
                     '_'
@@ -512,6 +532,10 @@ impl<'s> Tokens<'s> {
             }
         }
 
+        if !terminated {
+            self.has_unterminated = true;
+        }
+
         NodeKind::BlockComment
     }
 
diff --git a/src/source.rs b/src/source.rs
index 797e815b..7eb1d3a7 100644
--- a/src/source.rs
+++ b/src/source.rs
@@ -128,7 +128,6 @@ pub struct SourceFile {
     src: String,
     line_starts: Vec<usize>,
     root: Rc<GreenNode>,
-    was_incremental: bool,
 }
 
 impl SourceFile {
@@ -142,7 +141,6 @@ impl SourceFile {
             root: parse(&src),
             src,
             line_starts,
-            was_incremental: false,
         }
     }
 
@@ -268,7 +266,7 @@ impl SourceFile {
     /// Edit the source file by replacing the given range.
     ///
     /// This panics if the `replace` range is out of bounds.
-    pub fn edit(&mut self, replace: Range<usize>, with: &str) {
+    pub fn edit(&mut self, replace: Range<usize>, with: &str) -> Range<usize> {
         let start = replace.start;
         self.src.replace_range(replace.clone(), with);
 
@@ -287,11 +285,13 @@ impl SourceFile {
 
         // Update the root node.
         let span = Span::new(self.id, replace.start, replace.end);
-        if Rc::make_mut(&mut self.root).incremental(&self.src, span, with.len()) {
-            self.was_incremental = true;
+        if let Ok(range) =
+            Rc::make_mut(&mut self.root).incremental(&self.src, span, with.len())
+        {
+            range
         } else {
             self.root = parse(&self.src);
-            self.was_incremental = false;
+            0 .. self.src.len()
         }
     }
 
@@ -485,93 +485,108 @@ mod tests {
     #[test]
     fn test_incremental_parse() {
         #[track_caller]
-        fn test(prev: &str, range: Range<usize>, with: &str, incr: bool) {
+        fn test(prev: &str, range: Range<usize>, with: &str, incr: Range<usize>) {
             let mut source = SourceFile::detached(prev);
-            source.edit(range, with);
+            let range = source.edit(range, with);
+            assert_eq!(range, incr);
 
-            if incr {
-                assert!(source.was_incremental);
-                let incr_tree = source.root.clone();
-                assert_eq!(parse(source.src()), incr_tree);
-            } else {
-                assert!(!source.was_incremental);
-            }
+            let incr_tree = source.root.clone();
+            assert_eq!(parse(source.src()), incr_tree);
         }
 
         // Test simple replacements.
-        test("hello world", 6 .. 11, "wankers", true);
-        test("a d e", 1 .. 3, " b c d", true);
-        test("a #f() e", 1 .. 6, " b c d", false);
-        test("{(0, 1, 2)}", 5 .. 6, "11pt", true);
-        test("= A heading", 3 .. 3, "n evocative", true);
+        test("hello world", 6 .. 11, "wankers", 5 .. 13);
+        test("a d e", 1 .. 3, " b c d", 0 .. 8);
+        test("a #f() e", 1 .. 6, " b c d", 0 .. 8);
+        test("{(0, 1, 2)}", 5 .. 6, "11pt", 5 .. 9);
+        test("= A heading", 3 .. 3, "n evocative", 2 .. 15);
+        test("your thing", 5 .. 5, "a", 4 .. 11);
+        test("a your thing a", 6 .. 7, "a", 2 .. 12);
         test(
             "#grid(columns: (auto, 1fr, 40%), [*plonk*], rect(width: 100%, height: 1pt, fill: conifer), [thing])",
             16 .. 20,
             "none",
-            true,
+            16 .. 20,
         );
         test(
             "#grid(columns: (auto, 1fr, 40%), [*plonk*], rect(width: 100%, height: 1pt, fill: conifer), [thing])",
             33 .. 42,
             "[_gronk_]",
-            true,
+            33 .. 42,
         );
         test(
             "#grid(columns: (auto, 1fr, 40%), [*plonk*], rect(width: 100%, height: 1pt, fill: conifer), [thing])",
             34 .. 41,
             "_bar_",
-            true,
+            34 .. 39,
         );
-        test("{let i=1; for x in range(5) {i}}", 6 .. 6, " ", true);
-        test("{let i=1; for x in range(5) {i}}", 13 .. 14, "  ", true);
-        test("hello {x}", 6 .. 9, "#f()", false);
+        test("{let i=1; for x in range(5) {i}}", 6 .. 6, " ", 1 .. 9);
+        test("{let i=1; for x in range(5) {i}}", 13 .. 14, "  ", 13 .. 15);
+        test("hello {x}", 6 .. 9, "#f()", 5 .. 10);
         test(
             "this is -- in my opinion -- spectacular",
             8 .. 10,
             "---",
-            true,
+            7 .. 12,
+        );
+        test(
+            "understanding `code` is complicated",
+            15 .. 15,
+            "C ",
+            14 .. 22,
         );
-        test("understanding `code` is complicated", 15 .. 15, "C ", true);
-        test("{ let x = g() }", 10 .. 12, "f(54", true);
+        test("{ let x = g() }", 10 .. 12, "f(54", 2 .. 15);
         test(
-            "#let rect with (fill: eastern)",
-            14 .. 29,
+            "a #let rect with (fill: eastern)\nb",
+            16 .. 31,
             " (stroke: conifer",
-            true,
+            2 .. 34,
         );
-        test("a b c", 1 .. 1, " /* letters */", false);
 
         // Test the whitespace invariants.
-        test("hello \\ world", 7 .. 8, "a ", false);
-        test("hello \\ world", 7 .. 8, "\n\n", true);
-        test("x = y", 2 .. 2, "+ y ", true);
-        test("x = y", 2 .. 2, "+ y \n ", false);
-        test("abc\n= a heading", 3 .. 4, "\nsome more test\n\n", true);
-        test("abc\n= a heading", 3 .. 4, "\nnot ", false);
-        test("hey #myfriend", 4 .. 4, "\\", false);
-        test("hey  #myfriend", 4 .. 4, "\\", true);
+        test("hello \\ world", 7 .. 8, "a ", 6 .. 14);
+        test("hello \\ world", 7 .. 8, " a", 6 .. 14);
+        test("x = y", 1 .. 1, " + y", 0 .. 6);
+        test("x = y", 1 .. 1, " + y\n", 0 .. 10);
+        test("abc\n= a heading\njoke", 3 .. 4, "\nmore\n\n", 0 .. 21);
+        test("abc\n= a heading\njoke", 3 .. 4, "\nnot ", 0 .. 19);
+        test("hey #myfriend", 4 .. 4, "\\", 0 .. 14);
+        test("hey  #myfriend", 4 .. 4, "\\", 3 .. 6);
 
         // Test type invariants.
-        test("#for x in array {x}", 16 .. 19, "[#x]", true);
-        test("#let x = 1 {5}", 1 .. 4, "if", false);
-        test("{let x = 1 {5}}", 1 .. 4, "if", true);
-        test("#let x = 1 {5}", 4 .. 4, " if", false);
-        test("{let x = 1 {5}}", 4 .. 4, " if", true);
-        test("a // b c #f()", 3 .. 4, "", false);
-        test("{\nf()\n//g(a)\n}", 6 .. 8, "", true);
-        test("{(1, 2)}", 1 .. 1, "while ", true);
-
-        // this appearantly works but the assertion fails.
-        test("a b c", 1 .. 1, "{[}", true);
+        test("a #for x in array {x}", 18 .. 21, "[#x]", 2 .. 22);
+        test("a #let x = 1 {5}", 3 .. 6, "if", 0 .. 15);
+        test("a {let x = 1 {5}} b", 3 .. 6, "if", 2 .. 16);
+        test("#let x = 1 {5}", 4 .. 4, " if", 0 .. 17);
+        test("{let x = 1 {5}}", 4 .. 4, " if", 0 .. 18);
+        test("a // b c #f()", 3 .. 4, "", 0 .. 12);
+        test("{\nf()\n//g(a)\n}", 6 .. 8, "", 0 .. 12);
+        test("a{\nf()\n//g(a)\n}b", 7 .. 9, "", 1 .. 13);
+        test("a #while x {\n g(x) \n}  b", 11 .. 11, "//", 0 .. 26);
+        test("{(1, 2)}", 1 .. 1, "while ", 0 .. 14);
+        test("a b c", 1 .. 1, "{[}", 0 .. 5);
 
         // Test unclosed things.
-        test(r#"{"hi"}"#, 4 .. 5, "c", false);
-        test(r"this \u{abcd}", 8 .. 9, "", true);
-        test(r"this \u{abcd} that", 12 .. 13, "", false);
-        test(r"{{let x = z}; a = 1} b", 6 .. 6, "//", false);
-
-        // these appearantly works but the assertion fails.
-        test(r#"a ```typst hello``` b"#, 16 .. 17, "", false);
-        test(r#"a ```typst hello```"#, 16 .. 17, "", true);
+        test(r#"{"hi"}"#, 4 .. 5, "c", 0 .. 6);
+        test(r"this \u{abcd}", 8 .. 9, "", 5 .. 12);
+        test(r"this \u{abcd} that", 12 .. 13, "", 0 .. 17);
+        test(r"{{let x = z}; a = 1} b", 6 .. 6, "//", 0 .. 24);
+        test("a b c", 1 .. 1, " /* letters */", 0 .. 16);
+        test("a b c", 1 .. 1, " /* letters", 0 .. 16);
+        test(
+            "{if i==1 {a} else [b]; b()}",
+            12 .. 12,
+            " /* letters */",
+            1 .. 35,
+        );
+        test(
+            "{if i==1 {a} else [b]; b()}",
+            12 .. 12,
+            " /* letters",
+            0 .. 38,
+        );
+
+        test(r#"a ```typst hello``` b"#, 16 .. 17, "", 0 .. 20);
+        test(r#"a ```typst hello```"#, 16 .. 17, "", 2 .. 18);
     }
 }
diff --git a/src/syntax/mod.rs b/src/syntax/mod.rs
index d1ca3674..cfb44376 100644
--- a/src/syntax/mod.rs
+++ b/src/syntax/mod.rs
@@ -6,6 +6,7 @@ mod pretty;
 mod span;
 
 use std::fmt::{self, Debug, Display, Formatter};
+use std::ops::Range;
 use std::rc::Rc;
 
 pub use highlight::*;
@@ -88,7 +89,7 @@ impl Green {
     }
 
     /// Find the innermost child that is incremental safe.
-    fn incremental_int(
+    fn incremental(
         &mut self,
         edit: &str,
         replace: Span,
@@ -96,7 +97,7 @@ impl Green {
         offset: usize,
         parent_mode: TokenMode,
         outermost: bool,
-    ) -> bool {
+    ) -> Result<Range<usize>, ()> {
         match self {
             Green::Node(n) => Rc::make_mut(n).incremental_int(
                 edit,
@@ -106,21 +107,7 @@ impl Green {
                 parent_mode,
                 outermost,
             ),
-            Green::Token(_) => false,
-        }
-    }
-
-    /// The error messages for this node and its descendants.
-    pub fn errors(&self) -> Vec<NodeKind> {
-        match self {
-            Green::Node(n) => n.errors(),
-            Green::Token(t) => {
-                if t.kind().is_error() {
-                    vec![t.kind().clone()]
-                } else {
-                    vec![]
-                }
-            }
+            Green::Token(_) => Err(()),
         }
     }
 }
@@ -198,15 +185,23 @@ impl GreenNode {
         self.data().len()
     }
 
-    /// The error messages for this node and its descendants.
-    pub fn errors(&self) -> Vec<NodeKind> {
-        let mut res = self.children.iter().flat_map(|c| c.errors()).collect::<Vec<_>>();
+    pub fn replace_child_range(
+        &mut self,
+        child_idx_range: Range<usize>,
+        replacement: Vec<Green>,
+    ) {
+        let old_len: usize =
+            self.children[child_idx_range.clone()].iter().map(Green::len).sum();
+        let new_len: usize = replacement.iter().map(Green::len).sum();
 
-        if self.kind().is_error() {
-            res.push(self.kind().clone());
-        }
+        self.children.splice(child_idx_range, replacement);
+        self.erroneous = self.children.iter().any(|x| x.erroneous());
+        self.data.set_len(self.data.len + new_len - old_len);
+    }
 
-        res
+    pub fn update_child_len(&mut self, new_len: usize, old_len: usize) {
+        self.data.len = self.data.len() + new_len - old_len;
+        self.erroneous = self.children.iter().any(|x| x.erroneous());
     }
 
     /// Find the innermost child that is incremental safe.
@@ -215,12 +210,7 @@ impl GreenNode {
         src: &str,
         replace: Span,
         replacement_len: usize,
-    ) -> bool {
-        let edit = &src[replace.inserted(replace, replacement_len).to_range()];
-        if edit.contains("//") || edit.contains("/*") || edit.contains("*/") {
-            return false;
-        }
-
+    ) -> Result<Range<usize>, ()> {
         self.incremental_int(src, replace, replacement_len, 0, TokenMode::Markup, true)
     }
 
@@ -232,10 +222,9 @@ impl GreenNode {
         mut offset: usize,
         parent_mode: TokenMode,
         outermost: bool,
-    ) -> bool {
+    ) -> Result<Range<usize>, ()> {
         let kind = self.kind().clone();
         let mode = kind.mode().contextualize(parent_mode);
-        eprintln!("in {:?} (mode {:?})", kind, mode);
 
         let mut loop_result = None;
         let mut child_at_start = true;
@@ -243,13 +232,16 @@ impl GreenNode {
         let mut start = None;
         for (i, child) in self.children.iter_mut().enumerate() {
             let child_span = Span::new(replace.source, offset, offset + child.len());
-            if child_span.surrounds(replace) {
-                eprintln!("found correct child");
-
+            if child_span.surrounds(replace)
+                && start.is_none()
+                && ((replace.start != child_span.end && replace.end != child_span.start)
+                    || mode == TokenMode::Code
+                    || i == last)
+            {
                 let old_len = child.len();
                 // First, we try if the child has another, more specific applicable child.
                 if !kind.incremental_safety().unsafe_interior() {
-                    if child.incremental_int(
+                    if let Ok(range) = child.incremental(
                         src,
                         replace,
                         replacement_len,
@@ -257,21 +249,17 @@ impl GreenNode {
                         kind.mode().child_mode(),
                         i == last && outermost,
                     ) {
-                        eprintln!("child success");
                         let new_len = child.len();
-                        self.data.set_len(self.data.len() + new_len - old_len);
-                        self.erroneous = self.children.iter().any(|x| x.erroneous());
-                        return true;
+                        self.update_child_len(new_len, old_len);
+                        return Ok(range);
                     }
                 }
 
                 // This didn't work, so we try to replace the child at this
                 // level.
                 let (function, policy) =
-                    match child.kind().reparsing_function(kind.mode().child_mode()) {
-                        Ok(p) => p,
-                        _ => return false,
-                    };
+                    child.kind().reparsing_function(kind.mode().child_mode());
+                let function = function?;
                 loop_result = Some((
                     i .. i + 1,
                     child_span,
@@ -280,23 +268,21 @@ impl GreenNode {
                     policy,
                 ));
                 break;
-            } else if child_span.contains(replace.start)
+            } else if start.is_none()
+                && child_span.contains(replace.start)
                 && mode == TokenMode::Markup
                 && child.kind().incremental_safety().markup_safe()
             {
-                eprintln!("found safe start");
                 start = Some((i, offset));
             } else if child_span.contains(replace.end)
+                && (replace.end != child_span.end || i == last)
                 && mode == TokenMode::Markup
                 && child.kind().incremental_safety().markup_safe()
             {
-                eprintln!("found safe end");
                 if let Some((start, start_offset)) = start {
                     let (function, policy) =
-                        match child.kind().reparsing_function(kind.mode().child_mode()) {
-                            Ok(p) => p,
-                            _ => return false,
-                        };
+                        child.kind().reparsing_function(kind.mode().child_mode());
+                    let function = function?;
                     loop_result = Some((
                         start .. i + 1,
                         Span::new(replace.source, start_offset, offset + child.len()),
@@ -310,7 +296,6 @@ impl GreenNode {
                 && (mode != TokenMode::Markup
                     || !child.kind().incremental_safety().markup_safe())
             {
-                eprintln!("unsafe inbetweeen {:?}", child.kind());
                 break;
             }
 
@@ -322,15 +307,7 @@ impl GreenNode {
         // We now have a child that we can replace and a function to do so if
         // the loop found any results at all.
         let (child_idx_range, child_span, child_outermost, func, policy) =
-            if let Some(loop_result) = loop_result {
-                loop_result
-            } else {
-                // No child fully contains the replacement.
-                eprintln!("no child match");
-                return false;
-            };
-
-        eprintln!("aquired function, policy {:?}", policy);
+            loop_result.ok_or(())?;
 
         let src_span = child_span.inserted(replace, replacement_len);
         let recompile_range = if policy == IncrementalSafety::AtomicPrimary {
@@ -339,121 +316,137 @@ impl GreenNode {
             src_span.to_range()
         };
 
-        let new_children = if let Some(new_children) =
-            func(&src[recompile_range], child_at_start)
-        {
-            if policy != IncrementalSafety::AtomicPrimary
-                || new_children.iter().map(Green::len).sum::<usize>() == src_span.len()
-            {
-                new_children
-            } else {
-                eprintln!("wrong atomic len");
-                return false;
-            }
+        let (mut new_children, unterminated) =
+            func(&src[recompile_range], child_at_start).ok_or(())?;
+
+        let insertion = match check_invariants(
+            &new_children,
+            self.children(),
+            unterminated,
+            child_idx_range.clone(),
+            child_outermost,
+            child_at_start,
+            mode,
+            src_span,
+            policy,
+        ) {
+            InvariantResult::Ok => Ok(new_children),
+            InvariantResult::UseFirst => Ok(vec![std::mem::take(&mut new_children[0])]),
+            InvariantResult::Error => Err(()),
+        }?;
+
+        self.replace_child_range(child_idx_range, insertion);
+
+        Ok(src_span.to_range())
+    }
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+enum InvariantResult {
+    Ok,
+    UseFirst,
+    Error,
+}
+
+fn check_invariants(
+    use_children: &[Green],
+    old_children: &[Green],
+    unterminated: bool,
+    child_idx_range: Range<usize>,
+    outermost: bool,
+    child_at_start: bool,
+    mode: TokenMode,
+    src_span: Span,
+    policy: IncrementalSafety,
+) -> InvariantResult {
+    let (new_children, ok) = if policy == IncrementalSafety::AtomicPrimary {
+        if use_children.iter().map(Green::len).sum::<usize>() == src_span.len() {
+            (use_children, InvariantResult::Ok)
+        } else if use_children[0].len() == src_span.len() {
+            (&use_children[0 .. 1], InvariantResult::UseFirst)
         } else {
-            eprintln!("function failed");
-            return false;
-        };
-        let child_mode = self.children[child_idx_range.start].kind().mode().child_mode();
-        eprintln!("child mode {:?}", child_mode);
+            return InvariantResult::Error;
+        }
+    } else {
+        (use_children, InvariantResult::Ok)
+    };
+
+    let child_mode = old_children[child_idx_range.start].kind().mode().child_mode();
+
+    // Check if the children / child has the right type.
+    let require_single = match policy {
+        IncrementalSafety::AtomicPrimary | IncrementalSafety::SameKind => true,
+        IncrementalSafety::SameKindInCode if child_mode == TokenMode::Code => true,
+        _ => false,
+    };
+
+    if require_single {
+        if new_children.len() != 1 {
+            return InvariantResult::Error;
+        }
 
-        // Check if the children / child has the right type.
-        let require_single = match policy {
-            IncrementalSafety::AtomicPrimary | IncrementalSafety::SameKind => true,
-            IncrementalSafety::SameKindInCode if child_mode == TokenMode::Code => true,
+        if match policy {
+            IncrementalSafety::SameKind => true,
+            IncrementalSafety::SameKindInCode => child_mode == TokenMode::Code,
             _ => false,
-        };
-
-        if require_single {
-            eprintln!("must be a single replacement");
-            if new_children.len() != 1 {
-                eprintln!("not a single replacement");
-                return false;
+        } {
+            if old_children[child_idx_range.start].kind() != new_children[0].kind() {
+                return InvariantResult::Error;
             }
+        }
+    }
 
-            if match policy {
-                IncrementalSafety::SameKind => true,
-                IncrementalSafety::SameKindInCode if child_mode == TokenMode::Code => {
-                    true
-                }
-                _ => false,
-            } {
-                if self.children[child_idx_range.start].kind() != new_children[0].kind() {
-                    eprintln!("not the same kind");
-                    return false;
-                }
+    // Do not accept unclosed nodes if the old node did not use to be at the
+    // right edge of the tree.
+    if !outermost && unterminated {
+        return InvariantResult::Error;
+    }
+
+    // Check if the neighbor invariants are still true.
+    if mode == TokenMode::Markup {
+        if child_idx_range.start > 0 {
+            if old_children[child_idx_range.start - 1].kind().incremental_safety()
+                == IncrementalSafety::EnsureRightWhitespace
+                && !new_children[0].kind().is_whitespace()
+            {
+                return InvariantResult::Error;
             }
         }
 
-        // Do not accept unclosed nodes if the old node did not use to be at the
-        // right edge of the tree.
-        if !child_outermost
-            && new_children
-                .iter()
-                .flat_map(|x| x.errors())
-                .any(|x| matches!(x, NodeKind::Error(ErrorPos::End, _)))
-        {
-            eprintln!("unclosed node");
-            return false;
+        let mut new_at_start = child_at_start;
+        for child in new_children {
+            new_at_start = child.kind().is_at_start(new_at_start);
         }
 
-        // Check if the neighbor invariants are still true.
-        if mode == TokenMode::Markup {
-            if child_idx_range.start > 0 {
-                if self.children[child_idx_range.start - 1].kind().incremental_safety()
-                    == IncrementalSafety::EnsureRightWhitespace
-                    && !new_children[0].kind().is_whitespace()
-                {
-                    eprintln!("left whitespace missing");
-                    return false;
-                }
-            }
-
-            let mut new_at_start = child_at_start;
-            for child in &new_children {
+        for child in &old_children[child_idx_range.end ..] {
+            if child.kind().is_trivia() {
                 new_at_start = child.kind().is_at_start(new_at_start);
+                continue;
             }
 
-            for child in &self.children[child_idx_range.end ..] {
-                if child.kind().is_trivia() {
-                    new_at_start = child.kind().is_at_start(new_at_start);
-                    continue;
+            match child.kind().incremental_safety() {
+                IncrementalSafety::EnsureAtStart if !new_at_start => {
+                    return InvariantResult::Error;
                 }
-
-                match child.kind().incremental_safety() {
-                    IncrementalSafety::EnsureAtStart if !new_at_start => {
-                        return false;
-                    }
-                    IncrementalSafety::EnsureNotAtStart if new_at_start => {
-                        return false;
-                    }
-                    _ => {}
+                IncrementalSafety::EnsureNotAtStart if new_at_start => {
+                    return InvariantResult::Error;
                 }
-                break;
+                _ => {}
             }
+            break;
+        }
 
-            if new_children.last().map(|x| x.kind().incremental_safety())
-                == Some(IncrementalSafety::EnsureRightWhitespace)
-                && self.children.len() > child_idx_range.end
-            {
-                if !self.children[child_idx_range.end].kind().is_whitespace() {
-                    eprintln!("right whitespace missing");
-                    return false;
-                }
+        if new_children.last().map(|x| x.kind().incremental_safety())
+            == Some(IncrementalSafety::EnsureRightWhitespace)
+            && old_children.len() > child_idx_range.end
+        {
+            if !old_children[child_idx_range.end].kind().is_whitespace() {
+                return InvariantResult::Error;
             }
         }
-
-        eprintln!("... replacing");
-
-        let old_len: usize =
-            self.children[child_idx_range.clone()].iter().map(Green::len).sum();
-        let new_len: usize = new_children.iter().map(Green::len).sum();
-
-        self.children.splice(child_idx_range, new_children);
-        self.erroneous = self.children.iter().any(|x| x.erroneous());
-        self.data.set_len(self.data.len + new_len - old_len);
-        true
     }
+
+    ok
 }
 
 impl From<GreenNode> for Green {
@@ -1025,6 +1018,7 @@ impl NodeKind {
         match self {
             Self::Markup
             | Self::Space(_)
+            | Self::Linebreak
             | Self::Parbreak
             | Self::Text(_)
             | Self::TextInLine(_)
@@ -1034,6 +1028,10 @@ impl NodeKind {
             | Self::Escape(_)
             | Self::Strong
             | Self::Emph
+            | Self::Heading
+            | Self::Enum
+            | Self::EnumNumbering(_)
+            | Self::List
             | Self::Raw(_)
             | Self::Math(_) => NodeMode::Markup,
             Self::Template
@@ -1058,24 +1056,24 @@ impl NodeKind {
     pub fn reparsing_function(
         &self,
         parent_mode: TokenMode,
-    ) -> Result<
-        (fn(&str, bool) -> Option<Vec<Green>>, IncrementalSafety),
+    ) -> (
+        Result<fn(&str, bool) -> Option<(Vec<Green>, bool)>, ()>,
         IncrementalSafety,
-    > {
+    ) {
         let policy = self.incremental_safety();
         if policy.is_unsafe() {
-            return Err(policy);
+            return (Err(()), policy);
         }
 
         let contextualized = self.mode().contextualize(parent_mode);
         let is_code = contextualized == TokenMode::Code;
 
         if is_code && policy == IncrementalSafety::UnsafeLayer {
-            return Err(policy);
+            return (Err(()), policy);
         }
 
         if is_code && policy == IncrementalSafety::AtomicPrimary {
-            return Ok((parse_atomic, policy));
+            return (Ok(parse_atomic), policy);
         }
 
         if policy == IncrementalSafety::SameKind
@@ -1085,19 +1083,19 @@ impl NodeKind {
                 NodeKind::Template => parse_template,
                 NodeKind::Block => parse_block,
                 NodeKind::LineComment | NodeKind::BlockComment => parse_comment,
-                _ => return Err(policy),
+                _ => return (Err(()), policy),
             };
 
-            return Ok((parser, policy));
+            return (Ok(parser), policy);
         }
 
         let parser: fn(&str, bool) -> _ = match contextualized {
             TokenMode::Markup if self == &Self::Markup => parse_markup,
             TokenMode::Markup => parse_markup_elements,
-            _ => return Err(policy),
+            _ => return (Err(()), policy),
         };
 
-        Ok((parser, policy))
+        (Ok(parser), policy)
     }
 
     /// Whether it is safe to do incremental parsing on this node. Never allow
@@ -1434,6 +1432,8 @@ impl IncrementalSafety {
             Self::Safe
             | Self::SameKindInCode
             | Self::EnsureAtStart
+            | Self::EnsureNotAtStart
+            | Self::EnsureRightWhitespace
             | Self::UnsafeLayer => true,
             _ => false,
         }
@@ -1458,8 +1458,7 @@ impl NodeMode {
         match self {
             Self::Markup => TokenMode::Markup,
             Self::Code => TokenMode::Code,
-            Self::Universal if old != TokenMode::Markup => TokenMode::Code,
-            Self::Universal => TokenMode::Markup,
+            Self::Universal => old,
         }
     }