Error messages not always propagated from F* to Emacs about fstar-mode.el

[beurdouche]

By the way, maybe always having a feedback would be nice ?
Printing "OK" or "Success" in emacs when everything goes fine
Printing "ERROR : blabla" in emacs on failure

[cpitclaudel]

Thanks for that feedback! I'll look at it now.

[cpitclaudel]

Ok, I see where the problem is from: this is another case of F*'s error messages not being consistent:

Error: Could not parse a valid build configuration from ; Invalid options : unrecognized option '--admit-fsi'

and

heap.fst(14,37-14,40) : Error
Identifier not found: [set] 

as opposed to

<input>(5,21-5,32): Name "FStar.All.ML" not found

(notice the extra space in the second message). Also notice that it doesn't point to the current file, but to another file.

[cpitclaudel]

Ah, I see the actual issue here. The problem is that the F* subprocess exits after that error, but before printing the #done flag, so the Emacs mode never knows that the message is complete. I'm not sure what I can do about this particular issue; it would seem better for the interactive mode to print one last #done before exiting :/

[cpitclaudel]

I looked at the code in a bit more detail, and I think this shouldn't be too hard to fix on the F* side. The problem is that F* exits right after starting with an error message if it can't parse the current document. fstar-mode doesn't know why it exited, and doesn't know what to do with that output.

I can fix it partially on the Emacs side by displaying the remaining output, but it won't be very nice.

Instead, the F* side could be changed to delay looking for dependencies (that's the part that causes a parse) until it receives a "#init" query, or something like this. Then if the parsing failed F* would print the error (as it does now), print a #done-nok, and exit. F*-mode would process the error message just fine, because it would come in response to an IDE query ("#init").

I think that should be a pretty simple patch (all in FStar.Interactive.fs).

[cpitclaudel]

Fixing this would be nice: there are tutorial entries and README tips about this bug.