String concatenation does not work with empty string literals

[DartBot]

This issue was originally filed by [email protected]

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Some adjacent string literals are not concatenated and produce a compile-time error (Dart parses them as an unterminated multi-line string literal):

main() {
  //two empty string literals not separated by a whitespace
  '''';
  """";
  @­'''';
  @­"""";
   //the first string literal is empty.
  '''a';
}

A compile-time error is produced in DartVM and Frog, r5311.
OS: Ubuntu 10.04.

[madsager]

Added Area-Frog label.

[madsager]

Added Triaged label.

[lrhn]

This is an unterminated string literal. You are accidentally starting multiline strings where you intend an empty single line string followed by another string.

main() {
  //two empty string literals not separated by a whitespace
  '''';
//^^^ multiline string literal starts here ...
  """";
  @­'''';
// ^^^ and ends here.
// ^ Single line string starts here, and is unterminated before end of string.
  @­"""";
//^^^^ Second multline string starts here and is also unterminated.
   //the first string literal is empty.
  '''a';
}

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Added AsDesigned label.