From babc9c90b46ae36eb670a2b487b23103ec3a2647 Mon Sep 17 00:00:00 2001
From: Sebastian McKenzie <sebmck@gmail.com>
Date: Tue, 7 Jul 2015 11:11:58 +0100
Subject: [PATCH] fix tail call recursion on functions with less arguments than
 parameters - fixes #1938

---
 .../transformers/es6/tail-call.js             | 25 +++++++++++------
 .../transformation/transformers/other/flow.js |  1 +
 .../es6.tail-call/parameter-exceeds/actual.js | 15 ++++++++++
 .../es6.tail-call/parameter-exceeds/exec.js   |  9 ++++++
 .../parameter-exceeds/expected.js             | 28 +++++++++++++++++++
 5 files changed, 70 insertions(+), 8 deletions(-)
 create mode 100644 test/core/fixtures/transformation/es6.tail-call/parameter-exceeds/actual.js
 create mode 100644 test/core/fixtures/transformation/es6.tail-call/parameter-exceeds/exec.js
 create mode 100644 test/core/fixtures/transformation/es6.tail-call/parameter-exceeds/expected.js

diff --git a/src/babel/transformation/transformers/es6/tail-call.js b/src/babel/transformation/transformers/es6/tail-call.js
index 610b63f8e5..15738db793 100644
--- a/src/babel/transformation/transformers/es6/tail-call.js
+++ b/src/babel/transformation/transformers/es6/tail-call.js
@@ -337,10 +337,6 @@ class TailCallTransformer {
       args = t.arrayExpression(node.arguments);
     }
 
-    if (t.isArrayExpression(args) && args.elements.length > this.node.params.length) {
-      this.needsArguments = true;
-    }
-
     var argumentsId = this.getArgumentsId();
     var params      = this.getParams();
 
@@ -354,17 +350,30 @@ class TailCallTransformer {
 
     if (t.isArrayExpression(args)) {
       var elems = args.elements;
-      for (let i = 0; i < elems.length && i < params.length; i++) {
+
+      // pad out the args so all the function args are reset - https://github.com/babel/babel/issues/1938
+      while (elems.length < params.length) {
+        elems.push(t.identifier("undefined"));
+      }
+
+      for (let i = 0; i < elems.length; i++) {
         let param = params[i];
-        let elem = elems[i] || (elems[i] = t.identifier("undefined"));
-        if (!param._isDefaultPlaceholder) {
+        let elem  = elems[i];
+
+        if (param && !param._isDefaultPlaceholder) {
           elems[i] = t.assignmentExpression("=", param, elem);
+        } else {
+          // exceeds parameters but push it anyway to ensure correct execution
         }
       }
 
       if (!this.needsArguments) {
         for (let elem of (elems: Array)) {
-          body.push(t.expressionStatement(elem));
+          // only push expressions that we really need, this will skip pure arguments that exceed the
+          // parameter length of the current function
+          if (!this.scope.isPure(elem)) {
+            body.push(t.expressionStatement(elem));
+          }
         }
       }
     } else {
diff --git a/src/babel/transformation/transformers/other/flow.js b/src/babel/transformation/transformers/other/flow.js
index 84dda2a7d5..bb7184576f 100644
--- a/src/babel/transformation/transformers/other/flow.js
+++ b/src/babel/transformation/transformers/other/flow.js
@@ -12,6 +12,7 @@ export var visitor = {
       }
     }
   },
+
   Flow() {
     this.dangerouslyRemove();
   },
diff --git a/test/core/fixtures/transformation/es6.tail-call/parameter-exceeds/actual.js b/test/core/fixtures/transformation/es6.tail-call/parameter-exceeds/actual.js
new file mode 100644
index 0000000000..1887c13c91
--- /dev/null
+++ b/test/core/fixtures/transformation/es6.tail-call/parameter-exceeds/actual.js
@@ -0,0 +1,15 @@
+function foo(a, b) {
+  if (b) {
+    return foo(b);
+  } else {
+    return a;
+  }
+}
+
+function foo(a, b) {
+  if (b) {
+    return foo("a", "b", "c");
+  } else {
+    return a;
+  }
+}
diff --git a/test/core/fixtures/transformation/es6.tail-call/parameter-exceeds/exec.js b/test/core/fixtures/transformation/es6.tail-call/parameter-exceeds/exec.js
new file mode 100644
index 0000000000..5053794f69
--- /dev/null
+++ b/test/core/fixtures/transformation/es6.tail-call/parameter-exceeds/exec.js
@@ -0,0 +1,9 @@
+function foo(a, b) {
+  if (b) {
+    return foo(b);
+  } else {
+    return a;
+  }
+}
+
+assert.equal(foo("Michael", "Jackson"), "Jackson");
diff --git a/test/core/fixtures/transformation/es6.tail-call/parameter-exceeds/expected.js b/test/core/fixtures/transformation/es6.tail-call/parameter-exceeds/expected.js
new file mode 100644
index 0000000000..c666b193c7
--- /dev/null
+++ b/test/core/fixtures/transformation/es6.tail-call/parameter-exceeds/expected.js
@@ -0,0 +1,28 @@
+"use strict";
+
+function foo(a, b) {
+  if (b) {
+    return foo(b);
+  } else {
+    return a;
+  }
+}
+
+function foo(_x, _x2) {
+  var _again = true;
+
+  _function: while (_again) {
+    var a = _x,
+        b = _x2;
+    _again = false;
+
+    if (b) {
+      _x = "a";
+      _x2 = "b";
+      _again = true;
+      continue _function;
+    } else {
+      return a;
+    }
+  }
+}