tree-sitter-al

A tree-sitter parser for the AL programming language used in Microsoft Dynamics 365 Business Central.

Parser Status

Validated against 15,358 production AL files from the Business Central codebase:

Metric	Value
Success rate	100% (15,358 / 15,358 files)
Tests	1,451
parser.c size	~28 MB
grammar.js	~3,930 lines
Named keywords	82 (queryable via highlights/tags)
Scanner tokens	8 (stateful, depth-tracking)
Query files	6 (highlights, locals, tags, indents, folds, textobjects)

What's new in 3.0.0

Breaking parse-tree change for editor textobjects and code navigation. Every scoped construct now exposes its content as a single node via a body field (e.g. (page_declaration body: (declaration_body …)), (code_block (begin_keyword) body: (statement_block …) (end_keyword))), instead of a flat list of direct children. This powers Helix / nvim-treesitter textobjects (@class.inside, @function.inside, @parameter) via the new queries/textobjects.scm, plus a parameters field on procedures/triggers/events.

Tree-walkers and structural queries must descend through the body field — see CHANGELOG.md for the full migration guide.

Installation

Rust

cargo add tree-sitter-al

use tree_sitter::Parser;

let mut parser = Parser::new();
let language = tree_sitter_al::LANGUAGE;
parser.set_language(&language.into()).expect("Error loading AL grammar");
let tree = parser.parse("codeunit 50100 MyCodeunit { }", None).unwrap();
println!("{}", tree.root_node().to_sexp());

Query constants are also available:

use tree_sitter_al::{HIGHLIGHTS_QUERY, TAGS_QUERY, LOCALS_QUERY, FOLDS_QUERY, INDENTS_QUERY, TEXTOBJECTS_QUERY};

Python (tree-sitter 0.24+)

pip install tree-sitter-al

import tree_sitter
import tree_sitter_al

lang = tree_sitter.Language(tree_sitter_al.language())
parser = tree_sitter.Parser(lang)
tree = parser.parse(b'codeunit 50100 MyCodeunit { }')
print(tree.root_node.sexp())

Node.js

npm install tree-sitter-al

Pre-built binaries

Download from GitHub Releases:

File	Platform	Use case
`tree-sitter-al.wasm`	All	web-tree-sitter
`tree-sitter-al.so`	Linux x86_64	ast-grep, native bindings
`tree-sitter-al.dll`	Windows x86_64	ast-grep, native bindings
`tree-sitter-al.dylib`	macOS ARM64	ast-grep, native bindings

V2 Architecture

The grammar was rewritten from scratch in March 2026, achieving a major reduction in parser size while improving correctness.

Before / After

Metric	V1	V2 (current)
parser.c	106 MB (can't push to GitHub)	~25 MB
Errors	14	0
Success rate	99.91%	100%
Symbols	2,249	~814
States	29,126	~12,600
grammar.js	8,500 lines	~3,930 lines
Tests	1,225	1,451
Keywords	invisible in queries	82 named nodes
Query files	3 (partial)	6 (comprehensive)

Key design decisions

Stateful external scanner — 8 scanner tokens handle property disambiguation, depth tracking (#if/#endif nesting), named begin/end keywords at depth 0, and split-construct detection via lookahead.
Parse structure, don't validate — Accept any Name = Value ; as a property. Semantic validation belongs in linters/LSP servers, not the parser.
Generic preprocessor — One preproc_conditional rule + ~15 dedicated rules for genuinely complex split constructs (begin/end, var/begin, brace-close across #if/#else branches).
82 named keyword nodes — All keywords including begin/end are named nodes, enabling proper syntax highlighting and code navigation queries.

See docs/v2-blog-post-notes.md for the full rewrite narrative.

Development

Prerequisites

Node.js (v16+)
tree-sitter CLI: npm install -g tree-sitter-cli

Building

tree-sitter generate    # Generate parser from grammar.js
tree-sitter test        # Run test suite

Validation

./validate-grammar.sh        # Quick: generation, tests, orphan/duplicate detection
./validate-grammar.sh --full # Full: includes production AL file parsing

For grammar refactors, the parse-tree diff harness proves a change is zero-behavior-change by re-parsing every production file and asserting byte-identical trees:

./tools/tree-harness.sh snapshot ./BC.History .snapshots/bc   # baseline
./tools/tree-harness.sh verify   ./BC.History .snapshots/bc   # verify after a change

Parsing AL files

tree-sitter parse path/to/file.al
tree-sitter parse path/to/file.al -d    # Debug output
tree-sitter parse path/to/file.al -q    # Quiet (errors only)

Key files

File	Purpose
`grammar.js`	Main grammar definition
`src/scanner.c`	External scanner (8 tokens: property, depth tracking, named begin/end, split detection)
`test/corpus/`	Test suite (1,451 tests)
`queries/`	Syntax highlighting, code navigation, folding, indentation, textobjects

Contributing

See CLAUDE.md for detailed development guidelines including architecture, debugging, and conventions.

Author: Torben Leth (sshadows@sshadows.dk) License: MIT (see LICENSE)

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Release history Release notifications | RSS feed

4.0.0

Aug 11, 2026

3.3.1

Aug 9, 2026

3.3.0

Aug 8, 2026

3.2.1

Aug 8, 2026

This release

3.2.0

Aug 7, 2026

3.0.1

Jun 20, 2026

2.6.0

Jun 16, 2026

2.5.2

May 17, 2026

2.5.1

May 14, 2026

2.5.0

Apr 1, 2026

2.4.0

Apr 1, 2026

2.3.0

Mar 24, 2026

2.1.0

Mar 24, 2026

2.0.2

Mar 23, 2026

2.0.1

Mar 23, 2026

0.0.0

Mar 23, 2026

tree-sitter-al 3.2.0

tree-sitter-al

Parser Status

What's new in 3.0.0

Installation

Rust

Python (tree-sitter 0.24+)

Node.js

Pre-built binaries

V2 Architecture

Before / After

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Development

Prerequisites

Building

Validation

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Key files

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