IntelliJ missing comma causes code below it to be marked as dead instead of warning about missing comma

[devoncarew]

From @ScottS2017 on December 11, 2017 19:29

Some other unexpected behavior from IntelliJ. One would expect it to warn about a missing comma, the same way we're warned about a missing ; ] or }. However, instead of that, it just marks all code below that point as "dead code" and turns it gray. As you know, dead code also has tips disabled, which doesn't help matters.

Since I was getting warnings for missing ; ] and } I assumed that I wasn't missing anything since I wasn't getting a similar warning. Therefore, I chased my tail for hours trying to figure out what was wrong with other things in the code. Here is an example of code that this actually happened on, with the text changed for simplicity:

body: new Container(
        child: new Center(
          child: new Column(
            children: <Widget>[
              new Text("Placeholder Text") //Missed a comma here, 
                                            //all code below here
                                           // is gray "dead code"
              new RaisedButton(child: new Text("Press me!"))
            ],
          ),
        ),
      ),

Copied from original issue: flutter/flutter#13485

[devoncarew]

From @sethladd on December 11, 2017 19:35

cc @devoncarew @mit-mit

[devoncarew]

I do see analysis error in your sample, but they're too subtle in this case. They're associated with a 1-char missing location where the the ; / ] / ) might be.

In order to improve this, we'll either need to associate the error with a larger range of text (an enclosing expression?), or improve the in-line error display in IntelliJ. I think the 2nd one may be the right choice here.

[devoncarew]

/cc @alexander-doroshko for any ideas for how to improve in-line error display in IntelliJ

[alexander-doroshko]

I'm not sure we can fix it at the IDE end.
The first error range is new keyword - and that's ok. I'd expect analyzer to report Expected to find comma error here (currently it is Expected to find ) or ]).
Looks like parser recovery is not ideal because of the missing comma. In addition to red new keyword, analyzer reports dead code and a dozen of other errors in other places, and this confuses developer. I know parser recovery is one of the trickiest things.

[ScottS2017]

Well, from my standpoint it just pays to remind ones self that if you see dead code, quickly try a comma after the very last line of live code. I know it's far from ideal but if it's put out there as a tip then at least this might not lead to confused devs. It could end up being "just one of those things" that there's a 2 second work around for.

[mit-mit]

@devoncarew why can't the analyzer recover here and just present a more subtle 'missing comma' warning?

[alexander-doroshko]

@devoncarew I don't have permissions to change issue labels any more. I don't think anything needs to be done at the IDE end. Do you?