Dart2Js does wrong check of types

[DartBot]

This issue was originally filed by @budde377

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What steps will reproduce the problem?
1.
Compile

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import "dart:math";

dynamic a;
Function f;

void test({String s1, String s2}) {
  s1 = ?s1 ? s1 : "string1";
  s1 = ?s2 ? s2 : "string2";
  if(new Random().nextBool()){
   f = (){
      print("$s1 $s2");
   };
  }
}

main() {
  test(s2:a);
}

---

with dart2js
2.
Run

What is the expected output? What do you see instead?
Expected:
No errors

Got:

Uncaught type 'anonymous' is not a subtype of type 'String'
main.dart.js:300
$.stringTypeCheck main.dart.js:300
$.test main.dart.js:178
$.main main.dart.js:187
(anonymous function) main.dart.js:624

What version of the product are you using? On what operating system?
dartium-lucid64-full-trunk-22223.0
on Ubuntu 12.10 64bit
I have dart-sdk revision 22231 installed

Please provide any additional information below.
The program compiles to:

---

...

$.test = function(s1, s2) {
  var t1, t2, t3;
  t1 = {};
  t1.s1_0 = s1;
  t2 = $ === s1;
  if (t2)
    t1.s1_0 = null;
  t3 = $ === s2;
  if (t3)
    s2 = null;
  $.stringTypeCheck(s1);
  $.stringTypeCheck(s2);
  t1.s1_0 = $.stringTypeCheck(!t2 ? t1.s1_0 : "string1");
  t1.s1_0 = !t3 ? s2 : "string2";
  if (Math.random() < 0.5)
    $.f = new $.test_anon(t1, s2);
};

$.main = function() {
  $.test($, $.a);
};

...

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The checks

  $.stringTypeCheck(s1);
  $.stringTypeCheck(s2);

should be

  $.stringTypeCheck(t1.s1_0);
  $.stringTypeCheck(t1.s2_0);

[DartBot]

This comment was originally written by @budde377

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This will also fail on the code:

void test({String s1, String s2}) {
  s1 = ?s1 ? s1 : "string1";
  s1 = ?s2 ? s2 : "string2";
  f = (){
    print("$s1 $s2");
  };
}

[dgrove]

The unary ? operator is being removed from the language shortly, so if this is related only to "?", this will not be fixed.

Can you try this test with some sort of sentinel default value to see if that works (since that will be the recommended pattern for this sort of thing going forward)?

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Added NeedsInfo label.

[DartBot]

This comment was originally written by @budde377

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It that I can't reproduce the error without the ? operator.
Why will the operator be removed?

[dgrove]

see issue #10466 for more detail

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Added WontFix label.