Refactor semantic token walker to use explicit traversal

Sources/hylo-lsp/AST+NodeFinder.swift → Sources/hylo-lsp/AST+FindNode.swift

@@ -3,7 +3,7 @@ import FrontEnd
 import IR
 
 extension AST {
-  struct NodeFinder: ASTWalkObserver {
+  private struct NodeFinder: ASTWalkObserver {
     // var outermostFunctions: [FunctionDecl.ID] = []
     let query: SourcePosition
     private(set) var match: AnyNodeID?

Sources/hylo-lsp/AST+FindTranslationUnit.swift

@@ -0,0 +1,43 @@
+import Foundation
+import Core
+import FrontEnd
+import IR
+import LanguageServerProtocol
+
+extension AST {
+  private struct TranslationUnitFinder: ASTWalkObserver {
+    // var outermostFunctions: [FunctionDecl.ID] = []
+    let query: DocumentUri
+    private(set) var match: TranslationUnit?
+
+
+    public init(_ query: DocumentUri) {
+      self.query = query
+    }
+
+    mutating func willEnter(_ n: AnyNodeID, in ast: AST) -> Bool {
+      let node = ast[n]
+      let site = node.site
+
+      if let t = node as? TranslationUnit {
+        if site.file.url.absoluteString == query {
+          match = t
+        }
+        return false
+      }
+
+      return true
+    }
+  }
+
+  public func findTranslationUnit(_ url: DocumentUri) -> TranslationUnit? {
+    var finder = TranslationUnitFinder(url)
+    for m in modules {
+      walk(m, notifying: &finder)
+      if finder.match != nil {
+        break
+      }
+    }
+    return finder.match
+  }
+}