Detect duplicate declaration during one-use replacement (#626)

* Detect duplicate declaration during one-use replacement

Fix #611

* FnDecls always have id

packages/babel-plugin-minify-dead-code-elimination/__tests__/dead-code-elimination-test.js

@@ -2448,4 +2448,18 @@ describe("dce-plugin", () => {
       }
     `
   );
+
+  thePlugin(
+    "should fix issue#611 - transforming fn decl to expr",
+    `
+      function foo() {
+        function count() {
+          let count = 1;
+          bar(count);
+          return count;
+        }
+        return count;
+      }
+    `
+  );
 });

packages/babel-plugin-minify-dead-code-elimination/src/index.js

@@ -400,7 +400,8 @@ module.exports = ({ types: t, traverse }) => {
               const replaced = replace(binding.referencePaths[0], {
                 binding,
                 scope,
-                replacement
+                replacement,
+                replacementPath
               });
 
               if (replaced) {
@@ -936,7 +937,7 @@ module.exports = ({ types: t, traverse }) => {
   }
 
   function replace(path, options) {
-    const { replacement, scope, binding } = options;
+    const { replacement, replacementPath, scope, binding } = options;
 
     // Same name, different binding.
     if (scope.getBinding(path.node.name) !== binding) {
@@ -976,6 +977,18 @@ module.exports = ({ types: t, traverse }) => {
       return;
     }
 
+    // https://github.com/babel/babili/issues/611
+    // this is valid only for FunctionDeclaration where we convert
+    // function declaration to expression in the next step
+    if (replacementPath.isFunctionDeclaration()) {
+      const fnName = replacementPath.get("id").node.name;
+      for (let name in replacementPath.scope.bindings) {
+        if (name === fnName) {
+          return;
+        }
+      }
+    }
+
     // https://github.com/babel/babili/issues/130
     if (!t.isExpression(replacement)) {
       t.toExpression(replacement);