introduce syntax-ptr

crates/ra_analysis/src/syntax_ptr.rs

@@ -0,0 +1,67 @@
+use ra_syntax::{
+    File, TextRange, SyntaxKind, SyntaxNode, SyntaxNodeRef,
+    ast::{self, AstNode},
+};
+
+use crate::FileId;
+use crate::db::SyntaxDatabase;
+
+/// SyntaxPtr is a cheap `Copy` id which identifies a particular syntax node,
+/// without retainig syntax tree in memory. You need to explicitelly `resovle`
+/// `SyntaxPtr` to get a `SyntaxNode`
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) struct SyntaxPtr {
+    file_id: FileId,
+    local: LocalSyntaxPtr,
+}
+
+impl SyntaxPtr {
+    pub(crate) fn new(file_id: FileId, node: SyntaxNodeRef) -> SyntaxPtr {
+        let local = LocalSyntaxPtr::new(node);
+        SyntaxPtr { file_id, local }
+    }
+
+    pub(crate) fn resolve(self, db: &impl SyntaxDatabase) -> SyntaxNode {
+        let syntax = db.file_syntax(self.file_id);
+        self.local.resolve(&syntax)
+    }
+}
+
+
+/// A pionter to a syntax node inside a file.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+struct LocalSyntaxPtr {
+    range: TextRange,
+    kind: SyntaxKind,
+}
+
+impl LocalSyntaxPtr {
+    fn new(node: SyntaxNodeRef) -> LocalSyntaxPtr {
+        LocalSyntaxPtr {
+            range: node.range(),
+            kind: node.kind(),
+        }
+    }
+
+    fn resolve(self, file: &File) -> SyntaxNode {
+        let mut curr = file.syntax();
+        loop {
+            if curr.range() == self.range && curr.kind() == self.kind {
+                return curr.owned();
+            }
+            curr = curr.children()
+                .find(|it| self.range.is_subrange(&it.range()))
+                .unwrap_or_else(|| panic!("can't resovle local ptr to SyntaxNode: {:?}", self))
+        }
+    }
+}
+
+
+#[test]
+fn test_local_syntax_ptr() {
+    let file = File::parse("struct Foo { f: u32, }");
+    let field = file.syntax().descendants().find_map(ast::NamedFieldDef::cast).unwrap();
+    let ptr = LocalSyntaxPtr::new(field.syntax());
+    let field_syntax = ptr.resolve(&file);
+    assert_eq!(field.syntax(), field_syntax);
+}