Assert if a node has been bound more than once

Author: jakebailey

src/compiler/binder.ts

@@ -227,6 +227,8 @@ namespace ts {
         const reportedUnreachableFlow: FlowNode = { flags: FlowFlags.Unreachable };
         const bindBinaryExpressionFlow = createBindBinaryExpressionFlow();
 
+        let alreadyBound: Set<Node>;
+
         /**
          * Inside the binder, we may create a diagnostic for an as-yet unbound node (with potentially no parent pointers, implying no accessible source file)
          * If so, the node _must_ be in the current file (as that's the only way anything could have traversed to it to yield it as the error node)
@@ -243,6 +245,7 @@ namespace ts {
             inStrictMode = bindInStrictMode(file, opts);
             classifiableNames = new Set();
             symbolCount = 0;
+            alreadyBound = new Set();
 
             Symbol = objectAllocator.getSymbolConstructor();
 
@@ -280,6 +283,7 @@ namespace ts {
             hasExplicitReturn = false;
             inAssignmentPattern = false;
             emitFlags = NodeFlags.None;
+            alreadyBound = undefined!;
         }
 
         return bindSourceFile;
@@ -2396,6 +2400,10 @@ namespace ts {
             if (!node) {
                 return;
             }
+
+            Debug.assert(!alreadyBound.has(node), "This node has already been bound.");
+            alreadyBound.add(node);
+
             setParent(node, parent);
             if (tracing) (node as TracingNode).tracingPath = file.path;
             const saveInStrictMode = inStrictMode;