chore: upgrade to Langium v4 and TypeScript v5.8

[aloisklink]

📑 Summary

Note

This PR targets the master branch, not develop.

Upgrade the @mermaid-js/parser package to use Langium v4.

There were a couple of breaking changes we had to fix to do this upgrade:

• Rename all the grammers from Abc to AbcGrammar, as rules within grammars cannot have the same name as the grammar.
• Update the tests, since the generated type names from ast.ts have been moved from <typeName> to <typeName>.$type.
• Turn the EOL fragment into a rule, as in Langium v4, it's no longer allowed and throws an error.
• Upgrade to using TypeScript v5.8, since Langium v4 is not compatible with older versions
  • TypeScript v5.8 also required switching our import assertions with import attributes.

v3.5.0 of Langium also had a breaking change with treemap diagrams, but I've moved the terminal INDENTATION in front of the hidden terminal WS and that seems to have fixed it!

Because of this, I've made the changeset for @mermaid-js/parser to be a major version, so we'd release v1.0.0 of it.

However, I don't believe any of these changes will be breaking to any user of mermaid, since mermaid doesn't re-export anything from @mermaid-js/parser, so just the default patch release that changeset makes would be okay for it.

Resolves #7345

📏 Design Decisions

Since there's some merge conflicts with develop and the master branch, I've also made https://github.com/aloisklink/mermaid/tree/chore/upgrade-to-langium-v4-develop so we can easily merge the changes into develop.

Also, due to @argos-ci failing, I've updated it so we can see the status of it on this PR.

📋 Tasks

Make sure you

• 📖 have read the contribution guidelines
• 💻 have added necessary unit/e2e tests.
  • Our existing tests cover this
• 📓 have added documentation. Make sure MERMAID_RELEASE_VERSION is used for all new features.
  • Not needed, other than the changeset entry.
• 🦋 If your PR makes a change that should be noted in one or more packages' changelogs, generate a changeset by running pnpm changeset and following the prompts. Changesets that add features should be minor and those that fix bugs should be patch. Please prefix changeset messages with feat:, fix:, or chore:.

[changeset-bot]

🦋 Changeset detected

Latest commit: 426a616

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@mermaid-js/parser	Major
mermaid	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[codecov]

Codecov Report

❌ Patch coverage is 0% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 3.59%. Comparing base (1f8669a) to head (426a616).
⚠️ Report is 10 commits behind head on master.

Files with missing lines	Patch %	Lines
...ackages/mermaid/src/diagrams/git/gitGraphParser.ts	0.00%	6 Missing ⚠️
packages/mermaid/src/diagrams/info/infoDb.ts	0.00%	1 Missing ⚠️
packages/mermaid/src/docs/.vitepress/config.ts	0.00%	1 Missing ⚠️
packages/mermaid/src/mermaidAPI.ts	0.00%	1 Missing ⚠️
...ackages/parser/src/language/architecture/module.ts	0.00%	1 Missing ⚠️
packages/parser/src/language/gitGraph/module.ts	0.00%	1 Missing ⚠️
packages/parser/src/language/info/module.ts	0.00%	1 Missing ⚠️
packages/parser/src/language/packet/module.ts	0.00%	1 Missing ⚠️
packages/parser/src/language/pie/module.ts	0.00%	1 Missing ⚠️
packages/parser/src/language/radar/module.ts	0.00%	1 Missing ⚠️
... and 1 more

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #7377      +/-   ##
=========================================
- Coverage    3.59%   3.59%   -0.01%     
=========================================
  Files         474     475       +1     
  Lines       47168   47185      +17     
  Branches      734     734              
=========================================
  Hits         1696    1696              
- Misses      45472   45489      +17     

Flag	Coverage Δ
unit	3.59% <0.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
packages/parser/src/language/index.ts	0.00% <ø> (ø)
packages/mermaid/src/diagrams/info/infoDb.ts	14.28% <0.00%> (ø)
packages/mermaid/src/docs/.vitepress/config.ts	0.40% <0.00%> (ø)
packages/mermaid/src/mermaidAPI.ts	0.30% <0.00%> (ø)
...ackages/parser/src/language/architecture/module.ts	4.54% <0.00%> (ø)
packages/parser/src/language/gitGraph/module.ts	4.76% <0.00%> (ø)
packages/parser/src/language/info/module.ts	5.00% <0.00%> (ø)
packages/parser/src/language/packet/module.ts	4.76% <0.00%> (ø)
packages/parser/src/language/pie/module.ts	5.00% <0.00%> (ø)
packages/parser/src/language/radar/module.ts	5.00% <0.00%> (ø)
... and 2 more

... and 1 file with indirect coverage changes

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[aloisklink]

I'm moving this into draft. Argos CI doesn't seem to be working since this PR is a) from a fork, and b) using an older version of Argos.

But when testing this manually with git clean -fxd && clear && pnpm install && pnpm run e2e; git switch chore/upgrade-to-langium-v4 && pnpm install && pnpm run e2e, there seems to be some sort of regression with treemap diagrams:

[argos-ci]

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Build	Status	Details	Updated (UTC)
default (Inspect)	👍 Changes approved	2 changed	Feb 13, 2026, 12:14 PM

[aloisklink]

Marking this as ready for review again! I went through and fixed a bunch of issues in treemap diagrams before finally finding the one that was breaking this. Apparently, the INDENTATION terminal was never being triggered (instead the hidden terminal WS was being triggered), so none of the treemap entries had any indentation associated with them.

I've also updated @argos-ci in this PR, just so we can see the result.

[slorber]

Not a big deal for us, but upgrading to Langium in a minor release means requiring a newer Node version, which is kind of a breaking change for Mermaid consumers (see facebook/docusaurus#11812)

error [email protected]: The engine "node" is incompatible with this module. Expected version ">=20.10.0". Got "20.0.0"

I'm not sure what your commitment to semver is, but maybe it could be useful to use GitHub actions with node matrices with min/max supported versions so that you detect early when a dependency require.