260 lines
16 KiB
Markdown
260 lines
16 KiB
Markdown
# 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 %}`) and the repeated-argument guards 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 and injection 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
|
|
|
|
Four of the files in `queries/` are the standard 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.
|
|
|
|
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`, 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`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` 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 error 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 `template_block_groups`; a filter is an
|
|
alternative of `filter`.
|
|
|
|
```js
|
|
import django from "tree-sitter-django/grammar";
|
|
|
|
const SEP = /[ \t\r\n]+/;
|
|
|
|
export default grammar(django, {
|
|
name: "djangox",
|
|
|
|
rules: {
|
|
// {% map items over rows %}
|
|
template_block_groups: ($, previous) => choice(previous, $.map_tag),
|
|
map_tag: ($) =>
|
|
seq(
|
|
"{%",
|
|
optional(SEP),
|
|
"map",
|
|
SEP,
|
|
$.filtered_value,
|
|
SEP,
|
|
"over",
|
|
SEP,
|
|
$.filtered_value,
|
|
optional(SEP),
|
|
"%}",
|
|
),
|
|
|
|
// {{ value|shout:"!" }}
|
|
filter: ($, previous) =>
|
|
choice(
|
|
previous,
|
|
seq(field("name", "shout"), ":", field("argument", $.value)),
|
|
),
|
|
},
|
|
});
|
|
```
|
|
|
|
Five things to know:
|
|
|
|
- **Whitespace is explicit.** `extras` is empty, because Django splits a tag's contents before parsing any
|
|
argument, so every separator has to be written out. The `part`/`block`/`simpleTag` helpers the base
|
|
grammar is built from are private to it, hence the `SEP` above.
|
|
- **A new name wins over the fallback.** `shout` becomes a token of its own, so it commits to your
|
|
alternative and your arity applies — `{{ x|shout }}` is now an error, while names you have not modelled
|
|
still fall through to `(filter name: (identifier))`.
|
|
- **A tag with a body needs a `conflicts` entry**, as every clause in the base grammar does:
|
|
`conflicts: ($, previous) => [...previous, [$.map_clause]]` for a `map_clause` holding the body. 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` 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` rule to avoid parsing end tags as custom tags.
|
|
- **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` 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
|
|
template_block_groups: ($, previous) =>
|
|
choice(
|
|
...previous.members.filter((m) => m.name !== "custom_tag"),
|
|
$.map_tag,
|
|
),
|
|
|
|
filter: ($, 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).
|