Parsing errors on invalid templates are uncaught, unclear, and unhelpful
shonfeder opened this issue · 4 comments
A minimal example:
let () =
ignore (Mustache.of_string "{{.name}}")Which crashes with
Fatal error: exception Mustache_parser.MenhirBasics.Error
A first-level fix would be to catch this error and raise something a bit more informative (e.g., Invalid_mustache_template). A better fix would be to identify the location of the syntax error.
I'm happy to help with the first part, at least, if that would be welcome.
When I've managed to trigger tracebacks, they look like this:
Uncaught exception:
Mustache_parser.MenhirBasics.Error
Raised at file "lib/mustache_parser.ml", line 347, characters 8-18
Called from file "lib/mustache.ml" (inlined), line 151, characters 18-49
Called from file "lib/mustache.ml", line 212, characters 31-44
Proper error messages would definitely be welcome.
I added support for reporting of lexing and parsing errors in #47, and then more support for render-time errors in #51 (and some more on #52). I also propose to add reference outputs for various error messages in #55. (As mentioned in #55, the error messages I have proposed so far do a reasonable job when the mistake is in the template file, not when the mistake is in the JSON, but this issue is on invalid templates.)
The particular example given by @shonfeder, however, is trickier than most and still badly handled with all these PRs. I don't understand all the details, but I think that this is related to the (somewhat unorthodox) way the lexer is setup. (.name is not a valid section name, but . is.) What happens in practice is that the error is only noticed at the very end of the file: a location is shown, but it is not helpful.