Completion inside a string literal

Looks like your 

Patterns.protoDimensionString

does not match a middle of the string.

or prefix matcher is not `is_` in such case, but `is_moderator, is_` what is not looks like a good place for your completions.

 Thanks, Alexandr, you were right! Once I rewrote the prefix, it started working as expected (the code below).

 One question, it there anything I can do with the pattern to match a word inside string literal? Just curious.

class DimensionCompletionContributor : CompletionContributor() {
    init {
        extend(CompletionType.BASIC, Patterns.protoDimensionString, DimensionCompletionProvider())
    }
}

class DimensionCompletionProvider() : CompletionProvider<CompletionParameters>()
{
    override fun addCompletions(parameters: CompletionParameters, context: ProcessingContext, result: CompletionResultSet) {
        var resultSet = result

        val psiElement = parameters.originalPosition ?: return

        val psiElementOffset = psiElement.textOffset
        val withinTextOffset = parameters.offset - psiElementOffset - 1 // one for previous character
        if (withinTextOffset > 0) {
            val wordStart = findWordStart(withinTextOffset, psiElement.text)
            if (wordStart > 0) {
                val prefix = psiElement.text.slice(IntRange(wordStart + 1, withinTextOffset))
                Notification.debug("prefix: $prefix")

                resultSet = result.withPrefixMatcher(prefix)
            }
        }

        resultSet.addElement(LookupElementBuilder.create("is_test"))
        resultSet.addElement(LookupElementBuilder.create("is_test1"))
        resultSet.addElement(LookupElementBuilder.create("is_test2"))
        resultSet.addElement(LookupElementBuilder.create("is_test3"))
    }

    private fun findWordStart(offest: Int, str: String) : Int
    {
        var textOffset = offest
        while (textOffset > 0) {
            if (str[textOffset] == ' ' || str[textOffset] == ',') {
                break
            }
            -- textOffset
        }
        return textOffset
    }}

It depends on how literals are parsed. If whole string content is a single token, then probably not. If there are some literal chunks tokens, you should use them in pattern. 

negram, you can take a look at LookupElementDecorator abstract class. 

It lets you manipulate the lookup string and what is inserted. 

You want the lookup string to be prefixed with `is_moderator, is_` but choices presented to the user would be `is_..` only.

I used it to create a WrappingDecorator with options to add/remove prefix/suffix in lookup string or the inserted string. I use it in some cases to present "user friendly" choices while inserting strings which are messy because of their context, just like you have in your example.

It is a bit of hacked class I wrote a while back through trial and error. Using it is similarly trial and error since after getting it working I never went back to clean it up to be easier to use but it does solve the issue for my Markdown Navigator plugin, where completions can be done inside other completable elements, which the IDE does not really expect in a real language. For example a heading is a named element which can be referenced so the IDE treats it as the target of completion, but it can contain links and emoji shortcuts which are also completable, somewhere inside the heading text. Creates a similar issue to what you have.

I am not sure you can use the class directly but it may give you ideas on your own implementation. Let me know if you want me to post the source here, it is in Kotlin.