From 0247b135f8e67afccdd4c9600b7bc81c2abf362b Mon Sep 17 00:00:00 2001
From: Simon Lydell <simon.lydell@gmail.com>
Date: Fri, 10 Jun 2016 08:58:18 +0200
Subject: [PATCH] Improve naming of generated 'i-variables'

In for example `for` loops, a variable called `i` is generated (for the
loop index). If that name is unavailable, `j` is used instead, then `k`,
`l`, etc. all the way to `z`. Then, `aa`, `ab`, `ac` etc. are used.

This meant that, eventually, `do` would be used, but that's not a valid
variable name since `do` is a JavaScript keyword.

This logic was also inefficiently implemented. For example, going from
`aa` to `ab` or from `az` to `ba` required lots of loop iterations.

This commit changes the variable naming convention. Now, `i`, `j`, `k`,
etc. to `z` are used like before. Then comes `i1`, `j1`, `k1`, etc. Then
`i2`, `j2`, `k2` and so on. This is simpler, efficient and easier to
understand. `i1` is more obvious to be a loop index than `aa`.

Fixes #4267.
---
 lib/coffee-script/scope.js | 11 +++++++++--
 src/scope.litcoffee        | 10 ++++++++--
 test/control_flow.coffee   |  9 +++++++++
 3 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/lib/coffee-script/scope.js b/lib/coffee-script/scope.js
index 0f9835a0..fd1cefc7 100644
--- a/lib/coffee-script/scope.js
+++ b/lib/coffee-script/scope.js
@@ -66,13 +66,20 @@
     };
 
     Scope.prototype.temporary = function(name, index, single) {
+      var diff, endCode, letter, newCode, num, startCode;
       if (single == null) {
         single = false;
       }
       if (single) {
-        return (index + parseInt(name, 36)).toString(36).replace(/\d/g, 'a');
+        startCode = name.charCodeAt(0);
+        endCode = 'z'.charCodeAt(0);
+        diff = endCode - startCode;
+        newCode = startCode + index % (diff + 1);
+        letter = String.fromCharCode(newCode);
+        num = Math.floor(index / (diff + 1));
+        return "" + letter + (num || '');
       } else {
-        return name + (index || '');
+        return "" + name + (index || '');
       }
     };
 
diff --git a/src/scope.litcoffee b/src/scope.litcoffee
index e983a782..8135cf00 100644
--- a/src/scope.litcoffee
+++ b/src/scope.litcoffee
@@ -66,9 +66,15 @@ Generate a temporary variable name at the given index.
 
       temporary: (name, index, single=false) ->
         if single
-          (index + parseInt name, 36).toString(36).replace /\d/g, 'a'
+          startCode = name.charCodeAt(0)
+          endCode = 'z'.charCodeAt(0)
+          diff = endCode - startCode
+          newCode = startCode + index % (diff + 1)
+          letter = String.fromCharCode(newCode)
+          num = index // (diff + 1)
+          "#{letter}#{num or ''}"
         else
-          name + (index or '')
+          "#{name}#{index or ''}"
 
 Gets the type of a variable.
 
diff --git a/test/control_flow.coffee b/test/control_flow.coffee
index 9725f445..dc91c099 100644
--- a/test/control_flow.coffee
+++ b/test/control_flow.coffee
@@ -464,3 +464,12 @@ test "#2367: super in for-loop", ->
       @sum
 
   eq 10, (new Bar).add 2, 3, 5
+
+test "#4267: lots of for-loops in the same scope", ->
+  # This used to include the invalid JavaScript `var do = 0`.
+  code = """
+    do ->
+      #{Array(200).join('for [0..0] then\n  ')}
+      true
+  """
+  ok CoffeeScript.eval(code)