langium common attributes require a custom valueconverter

[dandaviesbrackett]

Description

While developing a new chart type, I came across some awkwardness in common.langium. As currently specified, the common attributes title, accTitle, and accDescr are terminals whose regex captures the initial literal. This causes two problems:

1. it requires a custom ValueConverter to capture only the "actual" values, which is unnecessary complexity and also introduces repeated regular expressions between common.langium and the valueconverter
2. It is confusing when using Langium's online playground as the values for title, accTitle, and accDescr in the playground AST don't match the ones that Mermaid will result in.

Steps to reproduce

1. paste any diagram type's .langium into the Langium playground
2. replace the import of common.langium with the content of common.langium
3. write a diagram in the middle pane that includes a title, accessible title, and accessible description
4. BUG: note that the values for title, accTitle, and accDescr begin with the words "title", "accTitle", and "accDescr" respectively

Screenshots

No response

Code Sample

Setup

• Mermaid version: main, as of 3 april 2025

Suggested Solutions

rejig the grammar in common.langium to avoid needing the value converter

Additional Context

I'll post a PR that closes this soon :)

[dandaviesbrackett]

I was overly ambitious with this - I had 85% of a solution, but it doesn't actually work. The existing grammar functions, this is a superfluous issue.