Add error message - Parsers.scala:1180

[jyotman]

Part of #1589.
Explanation for the error on line Parsers.scala:1180.
Adds the sematic object for the error illiegal start of simple expression.
@felixmulder kindly review.

[felixmulder]

I would call this something like: IllegalStartSimpleExpr since it is simple expressions and not all valid expressions. I'm assuming you chose 14 to coordinate with Shane's PR? :)

[felixmulder]

If the explanation is printed, the user is most likely a beginner. In this case we need to educate them by providing a hint as to how they can make their program valid. If I don't know that expressions are things which return values then I, the user, need to be given some examples.

This error also occurs frequently when a user has forgotten a parenthesis somewhere which makes it sort of tricky to give a 100% concrete solution in this case. Perhaps in the future we could have some machinery to discover this.

I would try to write something similar to:

An expression yields a value. In the case of the simple expression, this error
commonly occurs when there's a missing parenthesis or brace. The reason being
that a simple expression is one of the following:

- Block
- Expression in parenthesis
- Identifier
- Object creation
- Literal

Which cannot start with a `}` or a `)`.

[jyotman]

Hey so I'm trying to get the illegal string so that the above explanation's last line would read like -
Which cannot start with a //the illegal string comes here.

Now to get this string in Parsers.scala I'm gonna have to use the tokenString() method -
syntaxErrorOrIncomplete(IllegalStartSimpleExpr(tokenString(in.token)))

What do you think of this? Will tokenString() method always return a value or could it produce an exception?

if my usage is fine then currently it looks like this -

scala> val a = ;
-- [E014] Syntax Error: <console> --------------------------------------------------------------------------------------
1 |val a = ;
  |        ^
  |        illegal start of simple expression

Explanation
===========
An expression yields a value. In the case of the simple expression, this error
commonly occurs when there's a missing parenthesis or brace. The reason being
that a simple expression is one of the following:

- Block
- Expression in parenthesis
- Identifier
- Object creation
- Literal

which cannot start with ';'.

[felixmulder]

It won't produce an exception if the token is defined no - so it shouldn't be a problem. Good thinking on including user code 👍

[felixmulder]

Also a quick note on commit messages, we prefer the form:

Add explanation for "illegal start of simple expression"

instead of:

Added explanation for "illegal start of simple expression"

:)

[felixmulder]

Otherwise things are looking great 👍

[jyotman]

Thanks @felixmulder all points noted :) I'll try to give a better explanation using the one you've suggested. Do you want me to include code samples also to explain both - probable wrong ways and the correct ways? But there could be many examples for that.

Also yes I kept the message number 14 to coordinate with Shane's PR.

[felixmulder]

@jyotman94 - hmm, yeah I don't know, that's really subjective right? IMHO this explanation probably doesn't need any code examples - but you know, have fun with it and experiment :)

[jyotman]

@felixmulder I've made the changes. Kindly review. Also I've resolved conflicts with Shane's #1611 .

[felixmulder]

I would rename illegalString to illegalToken :)

[felixmulder]

So when I said the the git commit should be in "imperative form" I meant do a rebase and reword the commit. If you didn't know how, it can be done like this:

$ git remote add upstream [email protected]:lampepfl/dotty.git
$ git fetch upstream
$ git rebase -i upstream/master

Then choose to reword your commit message and call it something like: Add explanation for "illegal start of simple expression". Makes sense? After that everything looks good to me, great job!

[jyotman]

Sorry, actually I got confused whether you referred to my commit message or the pull request title earlier so I had just renamed the pull request title. I've made the new changes. Thank you for being so patient :)

[felixmulder]

No problem - thank you for putting in all the hard work :)

Once this passes CI, I'll merge it - cheers!

[felixmulder]

Hey @jyotman94 - could you rebase so I can merge? :) (Don't forget to check that your errorId is correct)

[jyotman]

@felixmulder done!

[felixmulder]

Great! Thanks a lot for the PR :)