Detect erroneous multi-line strings.

[floitschG]

It is a (relatively) common error to forgot commas between two items of a string list:
var a = ["foo",
         "bar" // <===
         "gee"];

In this case "bar" and "gee" will be concatenated without any warning.
It would be nice if the editor offered some kind of warning for this.
In general this is difficult, but the following heuristics could potentially work:

• wrong number of arguments to a function call.
• in lists: if the two strings easily fit onto one line. Here, for example, the user could just as well write "bargee" if she wanted one string. Having concatenated strings is thus probably an error.

[floitschG]

Also it might be a good idea to do different syntax highlighting so that these strings stick out.

[floitschG]

Other ideas: https://groups.google.com/a/dartlang.org/forum/?fromgroups=#!topic/misc/86qY4F2FLGE

[danrubel]

Added this to the M2 milestone.

[clayberg]

Set owner to @bwilkerson.
Removed this from the M2 milestone.
Added this to the M3 milestone.

[danrubel]

To be added after AnalysisServer is in place

---

Set owner to @scheglov.
Removed this from the M3 milestone.
Added this to the Later milestone.

[scheglov]

Set owner to @bwilkerson.
Removed Area-Editor label.
Added Area-Analyzer label.

[bwilkerson]

Added Analyzer-Hint label.

[kasperl]

Removed this from the Later milestone.
Added Oldschool-Milestone-Later label.

[kasperl]

Removed Oldschool-Milestone-Later label.

[srawlins]

I don't think the analyzer is going to do either of the suggestions:

1. We already warn about wrong number of arguments to a function.
2. I don't think the analyzer is going to start looking at whether the two strings fit on one line together... does it do any positional/formatting analysis like this today?

[bwilkerson]

A request for this same functionality was just added to the linter project. It appears that it is a fairly common mistake, and we ought to provide support.

[srawlins]

Ah. #57318. The list literal case. I think we have to be careful in what we're fixing, to avoid generating noise warnings.

Should there just be a hint in List literals to never use "space"-concatenated String literals? I think the request in #57318 is based on the idea that trailing plus signs are much more visible than trailing (or missing) commas.

[bwilkerson]

Should there just be a hint in List literals to never use "space"-concatenated String literals?

That seems reasonable to me, although I'd make it a lint rather than a hint.

[srawlins]

This is now implemented as a lint: no_adjacent_strings_in_list, and the formatter also indents such that the error is noticeable.