Parsing of Snippets / with subrule

[cdietrich]

Hi, is there a way to parse a string into a ast/document with a subrule?
constructing a on the fly grammar with.
createServicesForGrammar seems to work but also to be tedious when you need to merge with the original grammar

[spoenemann]

Currently the only way is to create a clone of the grammar, change the entry rule, and derive a new LangiumServices from that.

We could look into adding an optional parameter to the parser's parse method so you can change the main rule. But I don't know how feasible that is. For sure it would require to pass the rules map from the parser builder (createParser function) to the LangiumParser.

[cdietrich]

can i programmatically clone the grammar? (with document) so i could pass the grammar object instead of grammar text to the createServicesForGrammar

[cdietrich]

rn i do something like

const originalGrammar = XxxxxGrammar()
// create a new grammar with different entry rule
const { shared, grammar: grammarServices } = createLangiumGrammarServices(EmptyFileSystem)
const linker = grammarServices.references.Linker
const buildReference = linker.buildReference.bind(linker)
const copiedGrammar: Grammar = AstUtils.copyAstNode(originalGrammar, buildReference)
for (const rule of copiedGrammar.rules) {
  if (GrammarAST.isParserRule(rule)) {
    if (rule.name === "Xxxxxx") {
      rule.entry = false
    }
    if (rule.name === "Expression") {
      rule.entry = true
    }
  }
}

const doc = shared.workspace.LangiumDocumentFactory.fromModel(copiedGrammar, URI.parse("dummy.langium"))

services = await createServicesForGrammar({
  grammar: doc.parseResult.value,
  grammarServices: grammarServices,
})

[spoenemann]

I made an experiment in #1407 to simplify this. Could you check whether it works for you?

[cdietrich]

need to figure out how to consume this in our env.

[cdietrich]

cool it seems to work. can we expose this on parseHelper via flag in ParseHelperOptions?