# tree-sitter-django A [tree-sitter](https://tree-sitter.github.io/tree-sitter/) grammar for the Django Template Language (DTL) — the `{% %}` tags, `{{ }}` variables and `{# #}` comments used in Django templates. ## Coverage Every tag and filter Django ships as a builtin is modelled — 28 tags and 57 filters as of Django 6.1 — and so is every tag and filter of the five libraries below. Arguments are part of the grammar rather than something a linter checks later, so a builtin written with the wrong ones is a parse error: `{{ x|length:2 }}` and `{% now %}` do not parse, because `length` takes no argument and `now` requires one. The target is Django 6.1, including the builtins Django 6 added (`{% partial %}`, `{% partialdef %}`, `{% querystring %}`, `{% csp_nonce_attr %}`). Rather than being written from the documentation, the grammar is checked against a real Django — `Pipfile.lock` pins the version — by enumerating `Engine.default_builtins` for the tag and filter lists and their arities, and by running candidate snippets through both `django.template.Template()` and this parser to compare what each accepts. Where the two deliberately disagree is listed under [Divergences](#divergences-from-django). ## Using it There is no published package yet, and no language bindings — those are coming. What is here today: - **`src/parser.c` and `src/scanner.c` are generated and committed**, so any tree-sitter host can compile them directly without running the CLI. The scanner is required: block-name matching (`{% block a %}…{% endblock a %}`), the repeated-argument guards and the missing-tag markers live in it. - **`npm run parser-build`** produces `tree-sitter-django.wasm` for a `web-tree-sitter` host or an editor that loads Wasm grammars. It is a build artifact rather than a checked-in one, so it has to be built (or shipped by a release) before anything can load it. - **`queries/`** holds the highlight, locals, tags, injection and error queries an editor loads, plus three files meant for a linter. See [Queries](#queries). - **`tree-sitter.json`** names the grammar `django`, scopes it `source.django`, and points at the query files, which is what a tree-sitter host reads to wire all of the above together. ## Development ```sh npm install npm run parser-generate # regenerate the parser from grammar.js npm run parser-test # run the corpus tests in test/corpus npm run parser-build # build the WASM binary npm run playground # interactively explore the grammar ``` `src/parser.c`, `src/grammar.json` and `src/node-types.json` are generated **and committed**, so a change to `grammar.js` or `src/scanner.c` is only half made until `parser-generate` has run and the result is committed alongside it. `tree-sitter test` compiles the parser itself, so a stale `src/` shows up as tests that pass against the wrong grammar. ## Queries Five of the files in `queries/` are query files an editor loads: - **`highlights.scm`** — syntax highlighting. Tag and filter names are listed one by one, so a name the grammar knows is captured as `@function` and a name it is only tolerating as `@function.call`. - **`locals.scm`** — scopes, definitions and references, so an editor can resolve a variable to the tag that bound it. A definition is a `variable:` field; the scopes are the clauses whose bindings do not outlive them (`{% with %}`, `{% for %}`, `{% empty %}`, `{% block %}`, `{% partialdef %}`, `{% blocktranslate %}`). - **`tags.scm`** — the symbol index behind `tree-sitter tag`. A `{% partialdef %}` and the names a `{% load %}` brings in are definitions; every tag and filter used is a reference. - **`injections.scm`** — marks template text and `{% verbatim %}` bodies as another language's content, so the HTML around the tags can be parsed by its own grammar. It names no language, leaving the editor to supply one. - **`errors.scm`** — what to report as a problem: `(ERROR)` as `@error.syntax`, tree-sitter's own `(MISSING)` as `@error.missing`, and `@error.missing_block` for the marker placed where a group's required tag is missing. An unterminated `{% if a %}x` parses as an `if_group` ending in a zero-width `missing_endif_block` rather than as an `ERROR`, so completion and the scope queries keep working while a template is being written — and the tree reports no error of its own, so this query is how to find it. A marker is placed only where the scanner can tell: at the end of input, before an end tag that belongs to an enclosing group, or before an `{% endblock %}` naming a block further out. A group's tag written where no open group can hold it, such as `{% else %}` inside a `{% for %}`, is an `unexpected_block`, captured as `@error.unexpected_block`. The other three are data for a tool rather than queries an editor runs. Each captures the two halves of a relation a tree-sitter query cannot express, and the tool does the join: - **`libraries.scm`** — which library each tag or filter is registered in, and what each `{% load %}` brings in. The grammar never requires the load, so reporting a missing one is a linter's job; a query has no ordering predicate to compare the positions itself. - **`exports.scm`** — a name a tag binds in the scope _around_ it rather than the scope it opens. Only `{% blocktranslate %}`'s `asvar` does that, and a locals query cannot say so: it places a definition in the innermost scope containing it and offers no way out again. - **`conditionals.scm`** — which bodies render on only some passes, as `@conditional.group` / `@conditional.branch` / `@conditional.default`, so a checker can tell that `{% if a %}{% now "Y" as n %}{% endif %}{{ n }}` may reach `{{ n }}` with nothing bound. A group is exhaustive exactly when one of its branches is a default. A locals query has no notion of a path not taken. `tree-sitter test` loads every file in the directory, so a pattern naming a node that no longer exists fails the suite rather than quietly matching nothing. ## Django libraries Five of Django's template libraries are not builtins: their names have to be `{% load %}`ed, or preloaded through the engine's `OPTIONS: {"builtins": [...]}`. Every tag and filter all five register is modelled, with the same argument and arity rules as a builtin: | library | tags | filters | | -------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------- | | `i18n` | `trans`, `translate`, `blocktrans`, `blocktranslate`, `language`, `get_available_languages`, `get_current_language`, `get_current_language_bidi`, `get_language_info`, `get_language_info_list` | `language_bidi`, `language_name`, `language_name_local`, `language_name_translated` | | `l10n` | `localize` | `localize`, `unlocalize` | | `static` | `static`, `get_static_prefix`, `get_media_prefix` | — | | `cache` | `cache` | — | | `tz` | `localtime`, `timezone`, `get_current_timezone` | `localtime`, `timezone`, `utc` | **The `{% load %}` is never required**, because an engine may have preloaded the library. Whether one is present is a question about the order of nodes rather than about how the template parses, so it is left to a tool: `queries/libraries.scm` marks each name with the library it came from and each `{% load %}` with what it brings in, and the tool joins the two. Such a tool needs to know that loading is positional (`{% trans "x" %}{% load i18n %}` is an error), that it is per file rather than inherited through `{% extends %}` or `{% include %}`, and that `{% load trans from i18n %}` brings in only the names it lists. Because these names are modelled, they win over the fallbacks below: a project that registers its own tag under one of them with a different signature gets a parse error. They are common enough that shadowing them is treated as the mistake. ## Custom tags and filters A library's tags and filters are registered in Python, so the grammar cannot know their names, their arity, or whether a tag opens a body. Two fallback rules accept them: - **Tags.** Any tag the grammar does not recognise parses as `custom_tag_block`, with the shape `simple_tag` and `inclusion_tag` give: positional filter expressions, then `name=value` keyword arguments, then an optional `as name`. So `{% mytag a b|upper "s" k=1 as out %}` parses, with the name on the `tag:` field. A keyword argument written twice is refused, as `parse_bits` refuses it. - **Filters.** An unknown filter parses as `(filter name: (identifier))` with at most one `:argument`, which is all Django's expression regex allows. No arity check is possible. Both are captured as `@function.call` rather than `@function`, so an editor can distinguish a name the grammar knows from one it is only tolerating. What the fallbacks cannot do: - **A block tag is not nested.** `{% mytag %}…{% endmytag %}` is two sibling `custom_tag_block`s; pairing them would mean guessing that an unknown tag opens a body. - **A tag registered with `@register.tag` may parse anything**, since it receives the raw token, so one whose arguments are not the `simple_tag` shape — `{% mytag <<>> %}` — is an error here and not in Django. - **A misspelled name cannot be caught.** `{{ x|lenght }}` is indistinguishable from a filter some library registered. Cross-referencing names against `{% load %}` needs the project's Python, so it belongs in a linter; `queries/libraries.scm` and the `load_block` rule supply what one needs. - **Names that only exist inside a tag group are reserved**, so `{% endif %}` or `{% empty %}` standing on its own is an `unexpected_block`, reported by `errors.scm`, rather than a call to a custom tag of that name. ### Adding rules for your own tags and filters For a project whose custom tags deserve real rules rather than the fallbacks, use this grammar as a base grammar. `grammar(base, {...})` merges your rules into it, and a rule that redefines one the base already has receives it as `previous`. A tag is an alternative of `tag_block_group`; a filter is an alternative of `filter`. ```js import django from "tree-sitter-django/grammar"; export default grammar(django, { name: "djangox", conflicts: ($, previous) => [...previous, [$.loop_clause]], rules: { tag_block_group: ($, previous) => choice(previous, $.map_block, $.loop_group), // {% map items over rows %} map_block: ($) => seq( $.simpleBlockOpen, field("tag", "map"), $._sep, $.filtered_value, $._sep, "over", $._sep, $.filtered_value, $.simpleBlockClose, ), // {% loop x %}…{% endloop %} loop_block: ($) => seq( $.startBlockOpen, field("tag", "loop"), $._sep, $.identifier, $.startBlockClose, ), loop_clause: ($) => seq($.loop_block, optional($.template)), endloop_block: ($) => seq($.endBlockOpen, field("tag", "endloop"), $.endBlockClose), loop_group: ($) => seq( $.loop_clause, choice( $.endloop_block, alias($._missing_block, $.missing_endloop_block), ), ), // {{ value|shout:"!" }} filter: ($, previous) => choice( previous, seq(field("name", "shout"), ":", field("argument", $.value)), ), }, }); ``` Seven things to know: - **Whitespace is explicit.** `extras` is empty, because Django splits a tag's contents before parsing any argument, so every separator has to be written out. The `part`/`block`/`simpleTag` helpers the base grammar is built from are private to it, but the separator is the hidden rule `$._sep`, and it and the tag utilities (`simpleBlockOpen` and the rest) are rules, so an extending grammar uses them as they are. - **Every tag begins with one of the opens**: `$.simpleBlockOpen`, with `$.simpleBlockClose` at its end, for a tag outside any group such as `map_block`, and `startBlockOpen`, `followBlockOpen`, `repeatBlockOpen` or `endBlockOpen` for the tags of a group. Its zero-width token hands the tag's name to the scanner and is taken wherever a tag can start, so a tag written from a bare `"{%"` never matches: `{% map items over rows %}` would quietly parse as a `custom_tag_block` instead. - **A new name wins over the fallback.** `shout` becomes a token of its own, so it commits to your alternative and your arity applies — `{{ x|shout }}` is now an error, while names you have not modelled still fall through to `(filter name: (identifier))`. - **A tag with a body is split the way the base grammar's are**, so every `{% %}` is a node of its own: a `loop_block` ending in `$.startBlockClose`, a `loop_clause` of that block and the body, an `endloop_block` built from `$.endBlockOpen` and `$.endBlockClose`, and a `loop_group` of the clause and the end block. A middle tag uses `followBlockOpen`/`followBlockClose` if the group holds it at most once, and `repeatBlockOpen`/`repeatBlockClose` if it may repeat; the scanner trusts that choice. The clause needs a `conflicts` entry, as every clause in the base grammar does. The generator offers an associativity instead; taking it silently discards the parse in which the body continues. - **End tags are not reserved**, a stray `{% endmap %}` parses as a `custom_tag_block` rather than an error — `reserved` takes no `previous`, so the `tag_name` list cannot be added to a name at a time. Instead you may drop the `custom_tag_block` rule to avoid parsing end tags as custom tags. - **Your groups get missing-tag markers.** The scanner knows no group by name — a group is closed by `end` followed by its opening tag's name — so the `alias($._missing_block, $.missing_endloop_block)` choice above is all it takes: an unclosed `{% loop x %}`, or one left open inside an `{% if %}` that `{% endif %}` closes, holds a `missing_endloop_block`. Add the name to your copy of `errors.scm`. - **The external scanner has to be re-exported under your grammar's name**, or block-name matching and the repeated-argument guards will not link. Give your grammar a `src/scanner.c` that renames the base's five entry points to the ones your generated `parser.c` calls, and includes it: ```c #define tree_sitter_django_external_scanner_create tree_sitter_djangox_external_scanner_create #define tree_sitter_django_external_scanner_destroy tree_sitter_djangox_external_scanner_destroy #define tree_sitter_django_external_scanner_scan tree_sitter_djangox_external_scanner_scan #define tree_sitter_django_external_scanner_serialize tree_sitter_djangox_external_scanner_serialize #define tree_sitter_django_external_scanner_deserialize tree_sitter_djangox_external_scanner_deserialize #include "../node_modules/tree-sitter-django/src/scanner.c" ``` The base's `tree_sitter/parser.h` then resolves to your own generated copy, and the externals keep the order they have here, so the scanner's token enum stays valid. `tree-sitter build` takes no include path, hence the relative `#include`; the package also exports `tree-sitter-django/src/scanner.c`, so a build step can hand the compiler an absolute path from `import.meta.resolve` where a package manager's layout makes the relative one unreliable. **Turning the fallbacks off.** A grammar that models every tag and filter its project uses probably does not want `custom_tag_block` and `_custom_filter` accepting unrecognized names as they allow typos to parse. `previous` is the base rule whose `members` are filterable. We can filter out these rules to make the grammar more strict: ```js tag_block_group: ($, previous) => choice( ...previous.members.filter((m) => m.name !== "custom_tag_block"), $.map_block, ), filter: ($, previous) => choice( ...previous.members.filter((m) => m.name !== "_custom_filter"), seq(field("name", "shout"), ":", field("argument", $.value)), ), ``` `{% mytag %}` and `{{ x|unknown }}` are then errors, while the builtins, the libraries and your own rules carry on as before. ## Divergences from Django The grammar aims to accept what Django accepts, with one deliberate exception. Where Django takes an input without complaint but the input is almost certainly a mistake — it parses, and then silently renders nothing or quietly ignores half of what was written — the grammar reports an error instead. Every case below is input Django itself accepts: - **Number-shaped names.** Django has no number token: a word is a literal if `int()` or `float()` parses it and a variable lookup otherwise, so `0x1f`, `1a`, `1.`, `1.2.3` and `1__0` look up a variable of that name and render nothing. (`1.` really is a lookup there and not a float — `Variable` rejects a trailing dot after parsing it — while `1.e5` is a float, and both are treated that way here.) - **An attribute of `True`, `False` or `None`.** Every Django context is seeded with those three names, so `{{ True.x }}` is an ordinary two-part lookup that can never resolve. - **A keyword argument written twice.** `{% with a=1 a=2 %}`, and the same in `{% include %}` and `{% blocktranslate %}`, where Django builds a dict and lets the last value win. - **Anything after a `{% static %}` path.** `StaticNode.handle_token` looks for `as` two words from the end and ignores the rest, so `{% static "a" junk %}` and `{% static "a" as url junk %}` render as if the extra words were not there. - **A `{% cache %}` argument meant as something other than the fragment name.** Django takes the raw word in that position, so `{% cache 500 using="c" %}` names a fragment called `using="c"` rather than choosing a cache, and `{% cache 500 sidebar.name %}` names one with a dot in it. In the other direction the grammar is more permissive only where it cannot know better, which is what the fallbacks above are for. ## License MIT — see [LICENSE](LICENSE).