VM allows assignment in assert.

[lrhn]

Grammar of assert statements is:

'assert' '(' conditionalExpression ')' ';'

This does not allow assignment expressions directly as the expression.
The VM allows the syntax:

assert(x = true);

Analyzer now catches the syntax error.

[DartBot]

This comment was originally written by @chalin

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Related: https://code.google.com/p/dart/issues/detail?id=12289

[mhausner]

dart2js also allows assert(x = true). Both implementations are wrong. I suspect that there is code that may depend on this, maybe on purpose. For example, tests/standalone/io/file_constructor_test.dart.

void main() {
  bool developerMode = false;
  assert(developerMode = true);
  ....
  if (developerMode) ....

[mhausner]

@floitschG, please determine whether the language spec should be updated, or the two implementations should be fixed.

[eernstg]

We discussed this issue in the language team and came up with the following analysis which concludes that we will switch to assert(expression): https://gist.github.com/eernstg/50a327addd96035d5393a507c0ea2d9a.

This means that the vm and dart2js already implement the right semantics, but the analyzer should be adjusted. Created a new issue for the adjustment of the analyzer and one for the spec.