move all parsing related bits to a separate module

crates/ra_syntax/src/parsing/builder.rs

@@ -0,0 +1,41 @@
+use crate::{
+    parsing::parser_impl::Sink,
+    syntax_node::{GreenNode, RaTypes, SyntaxError},
+    SmolStr, SyntaxKind,
+};
+use rowan::GreenNodeBuilder;
+
+pub(crate) struct GreenBuilder {
+    errors: Vec<SyntaxError>,
+    inner: GreenNodeBuilder<RaTypes>,
+}
+
+impl GreenBuilder {
+    pub(crate) fn new() -> GreenBuilder {
+        GreenBuilder { errors: Vec::new(), inner: GreenNodeBuilder::new() }
+    }
+}
+
+impl Sink for GreenBuilder {
+    type Tree = (GreenNode, Vec<SyntaxError>);
+
+    fn leaf(&mut self, kind: SyntaxKind, text: SmolStr) {
+        self.inner.leaf(kind, text);
+    }
+
+    fn start_branch(&mut self, kind: SyntaxKind) {
+        self.inner.start_internal(kind)
+    }
+
+    fn finish_branch(&mut self) {
+        self.inner.finish_internal();
+    }
+
+    fn error(&mut self, error: SyntaxError) {
+        self.errors.push(error)
+    }
+
+    fn finish(self) -> (GreenNode, Vec<SyntaxError>) {
+        (self.inner.finish(), self.errors)
+    }
+}