1 files changed, 188 insertions, 0 deletions

diff --git a/crates/libsyntax2/src/reparsing.rs b/crates/libsyntax2/src/reparsing.rs
new file mode 100644
index 000000000..723ea2b8b
--- /dev/null
+++ b/crates/libsyntax2/src/reparsing.rs
@@ -0,0 +1,188 @@
+use algo;
+use grammar;
+use lexer::{tokenize, Token};
+use text_unit::{TextRange, TextUnit};
+use yellow::{self, SyntaxNodeRef, GreenNode, SyntaxError};
+use parser_impl;
+use parser_api::Parser;
+use {
+    SyntaxKind::*,
+};
+use text_utils::replace_range;
+
+#[derive(Debug, Clone)]
+pub struct AtomEdit {
+    pub delete: TextRange,
+    pub insert: String,
+}
+
+impl AtomEdit {
+    pub fn replace(range: TextRange, replace_with: String) -> AtomEdit {
+        AtomEdit { delete: range, insert: replace_with }
+    }
+
+    pub fn delete(range: TextRange) -> AtomEdit {
+        AtomEdit::replace(range, String::new())
+    }
+
+    pub fn insert(offset: TextUnit, text: String) -> AtomEdit {
+        AtomEdit::replace(TextRange::offset_len(offset, 0.into()), text)
+    }
+}
+
+pub(crate) fn incremental_reparse(
+    node: SyntaxNodeRef,
+    edit: &AtomEdit,
+    errors: Vec<SyntaxError>,
+) -> Option<(GreenNode, Vec<SyntaxError>)> {
+    let (node, green, new_errors) =
+        reparse_leaf(node, &edit).or_else(|| reparse_block(node, &edit))?;
+    let green_root = node.replace_with(green);
+    let errors = merge_errors(errors, new_errors, node, edit);
+    Some((green_root, errors))
+}
+
+fn reparse_leaf<'node>(
+    node: SyntaxNodeRef<'node>,
+    edit: &AtomEdit,
+) -> Option<(SyntaxNodeRef<'node>, GreenNode, Vec<SyntaxError>)> {
+    let node = algo::find_covering_node(node, edit.delete);
+    match node.kind() {
+        | WHITESPACE
+        | COMMENT
+        | DOC_COMMENT
+        | IDENT
+        | STRING
+        | RAW_STRING => {
+            let text = get_text_after_edit(node, &edit);
+            let tokens = tokenize(&text);
+            let token = match tokens[..] {
+                [token] if token.kind == node.kind() => token,
+                _ => return None,
+            };
+
+            if token.kind == IDENT && is_contextual_kw(&text) {
+                return None;
+            }
+
+            let green = GreenNode::new_leaf(node.kind(), &text);
+            let new_errors = vec![];
+            Some((node, green, new_errors))
+        }
+        _ => None,
+    }
+}
+
+fn reparse_block<'node>(
+    node: SyntaxNodeRef<'node>,
+    edit: &AtomEdit,
+) -> Option<(SyntaxNodeRef<'node>, GreenNode, Vec<SyntaxError>)> {
+    let (node, reparser) = find_reparsable_node(node, edit.delete)?;
+    let text = get_text_after_edit(node, &edit);
+    let tokens = tokenize(&text);
+    if !is_balanced(&tokens) {
+        return None;
+    }
+    let (green, new_errors) =
+        parser_impl::parse_with::<yellow::GreenBuilder>(
+            &text, &tokens, reparser,
+        );
+    Some((node, green, new_errors))
+}
+
+fn get_text_after_edit(node: SyntaxNodeRef, edit: &AtomEdit) -> String {
+    replace_range(
+        node.text().to_string(),
+        edit.delete - node.range().start(),
+        &edit.insert,
+    )
+}
+
+fn is_contextual_kw(text: &str) -> bool {
+    match text {
+        | "auto"
+        | "default"
+        | "union" => true,
+        _ => false,
+    }
+}
+
+fn find_reparsable_node<'node>(
+    node: SyntaxNodeRef<'node>,
+    range: TextRange,
+) -> Option<(SyntaxNodeRef<'node>, fn(&mut Parser))> {
+    let node = algo::find_covering_node(node, range);
+    return algo::ancestors(node)
+        .filter_map(|node| reparser(node).map(|r| (node, r)))
+        .next();
+
+    fn reparser(node: SyntaxNodeRef) -> Option<fn(&mut Parser)> {
+        let res = match node.kind() {
+            BLOCK => grammar::block,
+            NAMED_FIELD_DEF_LIST => grammar::named_field_def_list,
+            NAMED_FIELD_LIST => grammar::named_field_list,
+            ENUM_VARIANT_LIST => grammar::enum_variant_list,
+            MATCH_ARM_LIST => grammar::match_arm_list,
+            USE_TREE_LIST => grammar::use_tree_list,
+            EXTERN_ITEM_LIST => grammar::extern_item_list,
+            TOKEN_TREE if node.first_child().unwrap().kind() == L_CURLY => grammar::token_tree,
+            ITEM_LIST => {
+                let parent = node.parent().unwrap();
+                match parent.kind() {
+                    IMPL_ITEM => grammar::impl_item_list,
+                    TRAIT_DEF => grammar::trait_item_list,
+                    MODULE => grammar::mod_item_list,
+                    _ => return None,
+                }
+            }
+            _ => return None,
+        };
+        Some(res)
+    }
+}
+
+fn is_balanced(tokens: &[Token]) -> bool {
+    if tokens.len() == 0
+        || tokens.first().unwrap().kind != L_CURLY
+        || tokens.last().unwrap().kind != R_CURLY {
+        return false;
+    }
+    let mut balance = 0usize;
+    for t in tokens.iter() {
+        match t.kind {
+            L_CURLY => balance += 1,
+            R_CURLY => 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>,
+    old_node: SyntaxNodeRef,
+    edit: &AtomEdit,
+) -> Vec<SyntaxError> {
+    let mut res = Vec::new();
+    for e in old_errors {
+        if e.offset <= old_node.range().start() {
+            res.push(e)
+        } else if e.offset >= old_node.range().end() {
+            res.push(SyntaxError {
+                msg: e.msg,
+                offset: e.offset + TextUnit::of_str(&edit.insert) - edit.delete.len(),
+            })
+        }
+    }
+    for e in new_errors {
+        res.push(SyntaxError {
+            msg: e.msg,
+            offset: e.offset + old_node.range().start(),
+        })
+    }
+    res
+}