Tree Sitter Grammar for ASN.1

This is a complete and working ASN.1 grammar for tree-sitter. It is based off of the BNF provided in the ITU-T Recommendations X.680 through X.683.

It fully supports parameterization, XML values, information objects, defined syntax, encoding control notation (ECN), etc.

The queries highlights.scm and folds.scm works with nvim-treesitter to provide highlighting and folding. Indents are currently experimental with nvim-treesitter, and didn't work quite right from my experience, and I don't think textobjects.scm is really used anywhere.

Building and testing

Install Node.js dependencies (this also compiles the Node addon):

npm install

After changing grammar.js (or src/scanner.c), regenerate the parser and rebuild the Node addon. tree-sitter test uses the CLI parser; the Node tests in bindings/node load build/Release/tree_sitter_asn1_binding.node, which is not updated by tree-sitter generate alone.

npx tree-sitter generate
npx node-gyp rebuild

There are three overlapping test entry points:

make test and npx tree-sitter test both use the CLI parser. npm test uses that CLI for the corpus, then the Node addon for everything else, so regenerate and npx node-gyp rebuild after grammar changes before relying on npm test.

CMake’s ts-test target matches make test. Other language bindings have their own tests (cargo test, go test, and so on).

The playground is npm start (tree-sitter build --wasm then tree-sitter playground).

Why did you have to include an external parser?

This custom parser exists to deal with a very specific issue. If the AssignedIdentifier is not used in the GlobalModuleReference production, and the GlobalModuleReference production is followed by another SymbolsFromModule production that starts with an imported symbol that starts with a lowercased letter, said symbol may be interpreted as the DefinedValue alternative of the AssignedIdentifier production. Then the parser would read a comma or FROM after the symbol and fail, because it expected another symbol.

The solution to this is to read ahead and check if the next non-whitespace token is a comma or FROM. If either of these cases are true, we know that we just read a symbol from the subsequent SymbolsFromModule production rather than a DefinedValue for the AssignedIdentifier production.

Releasing a new Version

Run

# Set the version
npx tree-sitter version $DESIRED_VERSION
# Re-generate the C files, because the version number is incorporate into them.
npx tree-sitter generate

Publishing to Various Package Repositories

• Maven Central (I would have to create the bindings myself, and I have not used Java in 10 years.)
• jsr.io The NodeJS bindings currently use CommonJS, but JSR requires ESM.
• NPM
• PyPI
• Crates