1 files changed, 455 insertions, 0 deletions

diff --git a/crates/syntax/src/parsing/reparsing.rs b/crates/syntax/src/parsing/reparsing.rs
new file mode 100644
index 000000000..4149f856a
--- /dev/null
+++ b/crates/syntax/src/parsing/reparsing.rs
@@ -0,0 +1,455 @@
+//! Implementation of incremental re-parsing.
+//!
+//! We use two simple strategies for this:
+//!   - if the edit modifies only a single token (like changing an identifier's
+//!     letter), we replace only this token.
+//!   - otherwise, we search for the nearest `{}` block which contains the edit
+//!     and try to parse only this block.
+
+use parser::Reparser;
+use text_edit::Indel;
+
+use crate::{
+    algo,
+    parsing::{
+        lexer::{lex_single_syntax_kind, tokenize, Token},
+        text_token_source::TextTokenSource,
+        text_tree_sink::TextTreeSink,
+    },
+    syntax_node::{GreenNode, GreenToken, NodeOrToken, SyntaxElement, SyntaxNode},
+    SyntaxError,
+    SyntaxKind::*,
+    TextRange, TextSize, T,
+};
+
+pub(crate) fn incremental_reparse(
+    node: &SyntaxNode,
+    edit: &Indel,
+    errors: Vec<SyntaxError>,
+) -> Option<(GreenNode, Vec<SyntaxError>, TextRange)> {
+    if let Some((green, new_errors, old_range)) = reparse_token(node, &edit) {
+        return Some((green, merge_errors(errors, new_errors, old_range, edit), old_range));
+    }
+
+    if let Some((green, new_errors, old_range)) = reparse_block(node, &edit) {
+        return Some((green, merge_errors(errors, new_errors, old_range, edit), old_range));
+    }
+    None
+}
+
+fn reparse_token<'node>(
+    root: &'node SyntaxNode,
+    edit: &Indel,
+) -> Option<(GreenNode, Vec<SyntaxError>, TextRange)> {
+    let prev_token = algo::find_covering_element(root, edit.delete).as_token()?.clone();
+    let prev_token_kind = prev_token.kind();
+    match prev_token_kind {
+        WHITESPACE | COMMENT | IDENT | STRING | RAW_STRING => {
+            if prev_token_kind == WHITESPACE || prev_token_kind == COMMENT {
+                // removing a new line may extends previous token
+                let deleted_range = edit.delete - prev_token.text_range().start();
+                if prev_token.text()[deleted_range].contains('\n') {
+                    return None;
+                }
+            }
+
+            let mut new_text = get_text_after_edit(prev_token.clone().into(), &edit);
+            let (new_token_kind, new_err) = lex_single_syntax_kind(&new_text)?;
+
+            if new_token_kind != prev_token_kind
+                || (new_token_kind == IDENT && is_contextual_kw(&new_text))
+            {
+                return None;
+            }
+
+            // Check that edited token is not a part of the bigger token.
+            // E.g. if for source code `bruh"str"` the user removed `ruh`, then
+            // `b` no longer remains an identifier, but becomes a part of byte string literal
+            if let Some(next_char) = root.text().char_at(prev_token.text_range().end()) {
+                new_text.push(next_char);
+                let token_with_next_char = lex_single_syntax_kind(&new_text);
+                if let Some((_kind, _error)) = token_with_next_char {
+                    return None;
+                }
+                new_text.pop();
+            }
+
+            let new_token =
+                GreenToken::new(rowan::SyntaxKind(prev_token_kind.into()), new_text.into());
+            Some((
+                prev_token.replace_with(new_token),
+                new_err.into_iter().collect(),
+                prev_token.text_range(),
+            ))
+        }
+        _ => None,
+    }
+}
+
+fn reparse_block<'node>(
+    root: &'node SyntaxNode,
+    edit: &Indel,
+) -> Option<(GreenNode, Vec<SyntaxError>, TextRange)> {
+    let (node, reparser) = find_reparsable_node(root, edit.delete)?;
+    let text = get_text_after_edit(node.clone().into(), edit);
+
+    let (tokens, new_lexer_errors) = tokenize(&text);
+    if !is_balanced(&tokens) {
+        return None;
+    }
+
+    let mut token_source = TextTokenSource::new(&text, &tokens);
+    let mut tree_sink = TextTreeSink::new(&text, &tokens);
+    reparser.parse(&mut token_source, &mut tree_sink);
+
+    let (green, mut new_parser_errors) = tree_sink.finish();
+    new_parser_errors.extend(new_lexer_errors);
+
+    Some((node.replace_with(green), new_parser_errors, node.text_range()))
+}
+
+fn get_text_after_edit(element: SyntaxElement, edit: &Indel) -> String {
+    let edit = Indel::replace(edit.delete - element.text_range().start(), edit.insert.clone());
+
+    let mut text = match element {
+        NodeOrToken::Token(token) => token.text().to_string(),
+        NodeOrToken::Node(node) => node.text().to_string(),
+    };
+    edit.apply(&mut text);
+    text
+}
+
+fn is_contextual_kw(text: &str) -> bool {
+    matches!(text, "auto" | "default" | "union")
+}
+
+fn find_reparsable_node(node: &SyntaxNode, range: TextRange) -> Option<(SyntaxNode, Reparser)> {
+    let node = algo::find_covering_element(node, range);
+
+    let mut ancestors = match node {
+        NodeOrToken::Token(it) => it.parent().ancestors(),
+        NodeOrToken::Node(it) => it.ancestors(),
+    };
+    ancestors.find_map(|node| {
+        let first_child = node.first_child_or_token().map(|it| it.kind());
+        let parent = node.parent().map(|it| it.kind());
+        Reparser::for_node(node.kind(), first_child, parent).map(|r| (node, r))
+    })
+}
+
+fn is_balanced(tokens: &[Token]) -> bool {
+    if tokens.is_empty()
+        || tokens.first().unwrap().kind != T!['{']
+        || tokens.last().unwrap().kind != T!['}']
+    {
+        return false;
+    }
+    let mut balance = 0usize;
+    for t in &tokens[1..tokens.len() - 1] {
+        match t.kind {
+            T!['{'] => balance += 1,
+            T!['}'] => {
+                balance = match balance.checked_sub(1) {
+                    Some(b) => b,
+                    None => return false,
+                }
+            }
+            _ => (),
+        }
+    }
+    balance == 0
+}
+
+fn merge_errors(
+    old_errors: Vec<SyntaxError>,
+    new_errors: Vec<SyntaxError>,
+    range_before_reparse: TextRange,
+    edit: &Indel,
+) -> Vec<SyntaxError> {
+    let mut res = Vec::new();
+
+    for old_err in old_errors {
+        let old_err_range = old_err.range();
+        if old_err_range.end() <= range_before_reparse.start() {
+            res.push(old_err);
+        } else if old_err_range.start() >= range_before_reparse.end() {
+            let inserted_len = TextSize::of(&edit.insert);
+            res.push(old_err.with_range((old_err_range + inserted_len) - edit.delete.len()));
+            // Note: extra parens are intentional to prevent uint underflow, HWAB (here was a bug)
+        }
+    }
+    res.extend(new_errors.into_iter().map(|new_err| {
+        // fighting borrow checker with a variable ;)
+        let offseted_range = new_err.range() + range_before_reparse.start();
+        new_err.with_range(offseted_range)
+    }));
+    res
+}
+
+#[cfg(test)]
+mod tests {
+    use test_utils::{assert_eq_text, extract_range};
+
+    use super::*;
+    use crate::{AstNode, Parse, SourceFile};
+
+    fn do_check(before: &str, replace_with: &str, reparsed_len: u32) {
+        let (range, before) = extract_range(before);
+        let edit = Indel::replace(range, replace_with.to_owned());
+        let after = {
+            let mut after = before.clone();
+            edit.apply(&mut after);
+            after
+        };
+
+        let fully_reparsed = SourceFile::parse(&after);
+        let incrementally_reparsed: Parse<SourceFile> = {
+            let before = SourceFile::parse(&before);
+            let (green, new_errors, range) =
+                incremental_reparse(before.tree().syntax(), &edit, before.errors.to_vec()).unwrap();
+            assert_eq!(range.len(), reparsed_len.into(), "reparsed fragment has wrong length");
+            Parse::new(green, new_errors)
+        };
+
+        assert_eq_text!(
+            &format!("{:#?}", fully_reparsed.tree().syntax()),
+            &format!("{:#?}", incrementally_reparsed.tree().syntax()),
+        );
+        assert_eq!(fully_reparsed.errors(), incrementally_reparsed.errors());
+    }
+
+    #[test] // FIXME: some test here actually test token reparsing
+    fn reparse_block_tests() {
+        do_check(
+            r"
+fn foo() {
+    let x = foo + <|>bar<|>
+}
+",
+            "baz",
+            3,
+        );
+        do_check(
+            r"
+fn foo() {
+    let x = foo<|> + bar<|>
+}
+",
+            "baz",
+            25,
+        );
+        do_check(
+            r"
+struct Foo {
+    f: foo<|><|>
+}
+",
+            ",\n    g: (),",
+            14,
+        );
+        do_check(
+            r"
+fn foo {
+    let;
+    1 + 1;
+    <|>92<|>;
+}
+",
+            "62",
+            31, // FIXME: reparse only int literal here
+        );
+        do_check(
+            r"
+mod foo {
+    fn <|><|>
+}
+",
+            "bar",
+            11,
+        );
+
+        do_check(
+            r"
+trait Foo {
+    type <|>Foo<|>;
+}
+",
+            "Output",
+            3,
+        );
+        do_check(
+            r"
+impl IntoIterator<Item=i32> for Foo {
+    f<|><|>
+}
+",
+            "n next(",
+            9,
+        );
+        do_check(r"use a::b::{foo,<|>,bar<|>};", "baz", 10);
+        do_check(
+            r"
+pub enum A {
+    Foo<|><|>
+}
+",
+            "\nBar;\n",
+            11,
+        );
+        do_check(
+            r"
+foo!{a, b<|><|> d}
+",
+            ", c[3]",
+            8,
+        );
+        do_check(
+            r"
+fn foo() {
+    vec![<|><|>]
+}
+",
+            "123",
+            14,
+        );
+        do_check(
+            r"
+extern {
+    fn<|>;<|>
+}
+",
+            " exit(code: c_int)",
+            11,
+        );
+    }
+
+    #[test]
+    fn reparse_token_tests() {
+        do_check(
+            r"<|><|>
+fn foo() -> i32 { 1 }
+",
+            "\n\n\n   \n",
+            1,
+        );
+        do_check(
+            r"
+fn foo() -> <|><|> {}
+",
+            "  \n",
+            2,
+        );
+        do_check(
+            r"
+fn <|>foo<|>() -> i32 { 1 }
+",
+            "bar",
+            3,
+        );
+        do_check(
+            r"
+fn foo<|><|>foo() {  }
+",
+            "bar",
+            6,
+        );
+        do_check(
+            r"
+fn foo /* <|><|> */ () {}
+",
+            "some comment",
+            6,
+        );
+        do_check(
+            r"
+fn baz <|><|> () {}
+",
+            "    \t\t\n\n",
+            2,
+        );
+        do_check(
+            r"
+fn baz <|><|> () {}
+",
+            "    \t\t\n\n",
+            2,
+        );
+        do_check(
+            r"
+/// foo <|><|>omment
+mod { }
+",
+            "c",
+            14,
+        );
+        do_check(
+            r#"
+fn -> &str { "Hello<|><|>" }
+"#,
+            ", world",
+            7,
+        );
+        do_check(
+            r#"
+fn -> &str { // "Hello<|><|>"
+"#,
+            ", world",
+            10,
+        );
+        do_check(
+            r##"
+fn -> &str { r#"Hello<|><|>"#
+"##,
+            ", world",
+            10,
+        );
+        do_check(
+            r"
+#[derive(<|>Copy<|>)]
+enum Foo {
+
+}
+",
+            "Clone",
+            4,
+        );
+    }
+
+    #[test]
+    fn reparse_str_token_with_error_unchanged() {
+        do_check(r#""<|>Unclosed<|> string literal"#, "Still unclosed", 24);
+    }
+
+    #[test]
+    fn reparse_str_token_with_error_fixed() {
+        do_check(r#""unterinated<|><|>"#, "\"", 12);
+    }
+
+    #[test]
+    fn reparse_block_with_error_in_middle_unchanged() {
+        do_check(
+            r#"fn main() {
+                if {}
+                32 + 4<|><|>
+                return
+                if {}
+            }"#,
+            "23",
+            105,
+        )
+    }
+
+    #[test]
+    fn reparse_block_with_error_in_middle_fixed() {
+        do_check(
+            r#"fn main() {
+                if {}
+                32 + 4<|><|>
+                return
+                if {}
+            }"#,
+            ";",
+            105,
+        )
+    }
+}