How can I reuse or override generateTerminalConstants to add custom generated texts?

[Shulabh-Prakash]

I want to modify the behavior of the generateTerminalConstants function from langium-cli.
I see that the function is located in langium-cli and used internally in generateAst. Since this is part of a node_module, I'm unsure of the best way to reuse or extend it without directly modifying the package. Is there any way that I am unaware of?

[msujew]

Hey @Shulabh-Prakash,

The generator package is closed down and it's not possible to change the generator in adopter/user code (at least right now). We wouldn't want to expose any API to change generated code, as this can quickly lead to unexplainable runtime errors that would be incredibly difficult to debug. We might add API though to allow to generate more code. See also the discussion in #818.

What is your specific use case for this? Can you give an example on what you want to change?

[Shulabh-Prakash]

as in linw 252 we are generating "export type ${config.projectName}KeywordNames = ${keywordStrings.length > 0 ? keywordStrings.map(keyword => ${EOL} | ${keyword}).join('') : 'never'};", I want to use this as a string array and am unable to convert or typecast it for the same as I can't use the 'type' while runtime. So I wanted to generate the same as string array too.

[msujew]

Getting an array of all keywords is a relatively trivial matter, see this collectKeywords:

langium/packages/langium-cli/src/generator/langium-util.ts

Lines 27 to 38 in c39bbf5

	export function collectKeywords(grammar: Grammar): string[] {
	const keywords = new Set<string>();
	const reachableRules = GrammarUtils.getAllReachableRules(grammar, false);
	for (const keyword of stream(reachableRules)
	.filter(rule => GrammarAST.isParserRule(rule) || GrammarAST.isInfixRule(rule))
	.flatMap(rule => AstUtils.streamAllContents(rule).filter(GrammarAST.isKeyword))) {
	keywords.add(keyword.value);
	}
	return Array.from(keywords).sort();
	}

You always have access to your own grammar via services.Grammar.