Completion should automatically add backquotes around names that conflict with keywords

[Glavo]

scala> object O {
         val `def` = 10
       } 
// defined object O
scala> O.d 
def
scala> O.def 
1 |O.def
  |  ^^^
  |  an identifier expected, but 'def' found
scala> scala.pa 
package
scala> scala.package 
1 |scala.package
  |      ^^^^^^^
  |      an identifier expected, but 'package' found
scala> 

Sometimes we will encounter names that conflict with keywords. When we complete such names, I think we should automatically add `` prevent conflicts for these names.

[dave-kav]

Hi folks. Interested in tackling this one, will be my first time contributing. Any advice on how to approach?

[smarter]

Welcome! The code that decides which completions to show is in https://github.com/lampepfl/dotty/blob/master/compiler/src/dotty/tools/dotc/interactive/Completion.scala, looking around quickly, it doesn't look like we have a convenience method to identifiy if a given string is a valid identifier or not, but you can easily make one from isIdentifierStart and isIdentifierPart in https://github.com/lampepfl/dotty/blob/master/library/src/scala/tasty/util/Chars.scala. Completion tests for the REPL go in https://github.com/lampepfl/dotty/blob/master/compiler/test/dotty/tools/repl/TabcompleteTests.scala, completion tests for the IDE support go in https://github.com/lampepfl/dotty/blob/master/language-server/test/dotty/tools/languageserver/CompletionTest.scala.

[dave-kav]

Perfect, thanks!

[dave-kav]

If you don't mind, can you dive a bit deeper into what the requirements are to construct a convenience method for validating identifiers from isIdentifierStart and isIdentifierPart?

[smarter]

An identifier that can be written without backquotes is one where isIdentifierStart returns true on the first character and isIdentifierPart returns true on every other character.

[dave-kav]

Perfect, just making sure there was nothing else to take into account.

[dave-kav]

To clarify - I only want to wrap the name in backticks if it is a valid identifier but clashes with a keyword, correct?

[smarter]

a name needs to be wrapped in backticks if it's not a valid identifier, which is the case when it's a keyword or when it can only be written with backticks (e.g. if you write object Foo { val a b = 1 } and do completion on Foo. you want to get back Foo.`a b` )

[dave-kav]

Is there a convenience method to determine whether an arbitrary string is a keyword in existence yet? I see all keywords defined in package dotty.tools.parsing.Tokens, maybe the allTokens: TokenSet will be useful if not.

[smarter]

I don't think there is one.