bazel-lib/docs/jq.md

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Wrapper rule around the popular `jq` utility.

For jq documentation, see https://stedolan.github.io/jq/.

## Usage examples

```starlark
load("@aspect_bazel_lib//lib:jq.bzl", "jq")
```

Create a new file `bazel-out/.../no_srcs.json` containing some JSON data:
```starlark
jq(
    name = "no_srcs",
    srcs = [],
    filter = ".name = "Alice"",
)
```

Remove a field from `package.json`:

> The output path `bazel-out/.../package.json` matches the path of the source file,
> which means you must refer to the label `:no_dev_deps` to reference the output,
> since Bazel doesn't provide a label for an output file that collides with an input file.

```starlark
jq(
    name = "no_dev_deps",
    srcs = ["package.json"],
    filter = "del(.devDependencies)",
)
```

Merge data from `bar.json` on top of `foo.json`, producing `foobar.json`:
```starlark
jq(
    name = "merged",
    srcs = ["foo.json", "bar.json"],
    filter = ".[0] * .[1]",
    args = ["--slurp"],
    out = "foobar.json",
)
```

Long filters can be split over several lines with comments:
```starlark
jq(
    name = "complex",
    srcs = ["a.json", "b.json"],
    filter = """
        .[0] as $a
        # Take select fields from b.json
        | (.[1] | {foo, bar, tags}) as $b
        # Merge b onto a
        | ($a * $b)
        # Combine 'tags' array from both
        | .tags = ($a.tags + $b.tags)
        # Add new field
        + {\"aspect_is_cool\": true}
    """,
    args = ["--slurp"],
)
```

Load filter from a file `filter.jq`, making it easier to edit complex filters:
```starlark
jq(
    name = "merged",
    srcs = ["foo.json", "bar.json"],
    filter_file = "filter.jq",
    args = ["--slurp"],
    out = "foobar.json",
)
```

Convert [genquery](https://bazel.build/reference/be/general#genquery) output to JSON.
```starlark
genquery(
    name = "deps",
    expression = "deps(//some:target)",
    scope = ["//some:target"],
)

jq(
    name = "deps_json",
    srcs = [":deps"],
    args = [
        "--raw-input",
        "--slurp",
    ],
    filter = "{ deps: split("\n") | map(select(. | length > 0)) }",
)
```

When Bazel is run with `--stamp`, replace some properties with version control info:
```starlark
jq(
    name = "stamped",
    srcs = ["package.json"],
    filter = "|".join([
        # Don't directly reference $STAMP as it's only set when stamping
        # This 'as' syntax results in $stamp being null in unstamped builds.
        "$ARGS.named.STAMP as $stamp",
        # Provide a default using the "alternative operator" in case $stamp is null.
        ".version = ($stamp[0].BUILD_EMBED_LABEL // "<unstamped>")",
    ]),
)
```

jq is exposed as a "Make variable", so you could use it directly from a `genrule` by referencing the toolchain.

```starlark
genrule(
    name = "case_genrule",
    srcs = ["a.json"],
    outs = ["genrule_output.json"],
    cmd = "$(JQ_BIN) '.' $(location a.json) > $@",
    toolchains = ["@jq_toolchains//:resolved_toolchain"],
)
```

<a id="jq"></a>

## jq

<pre>
jq(<a href="#jq-name">name</a>, <a href="#jq-srcs">srcs</a>, <a href="#jq-filter">filter</a>, <a href="#jq-filter_file">filter_file</a>, <a href="#jq-args">args</a>, <a href="#jq-out">out</a>, <a href="#jq-data">data</a>, <a href="#jq-expand_args">expand_args</a>, <a href="#jq-kwargs">kwargs</a>)
</pre>

Invoke jq with a filter on a set of json input files.

**PARAMETERS**


| Name  | Description | Default Value |
| :------------- | :------------- | :------------- |
| <a id="jq-name"></a>name |  Name of the rule   |  none |
| <a id="jq-srcs"></a>srcs |  List of input files. May be empty.   |  none |
| <a id="jq-filter"></a>filter |  Filter expression (https://stedolan.github.io/jq/manual/#Basicfilters). Subject to stamp variable replacements, see [Stamping](./stamping.md). When stamping is enabled, a variable named "STAMP" will be available in the filter.<br><br>Be careful to write the filter so that it handles unstamped builds, as in the example above.   |  `None` |
| <a id="jq-filter_file"></a>filter_file |  File containing filter expression (alternative to `filter`)   |  `None` |
| <a id="jq-args"></a>args |  Additional args to pass to jq   |  `[]` |
| <a id="jq-out"></a>out |  Name of the output json file; defaults to the rule name plus ".json"   |  `None` |
| <a id="jq-data"></a>data |  List of additional files. May be empty.   |  `[]` |
| <a id="jq-expand_args"></a>expand_args |  Run bazel's location-expansion on the args.   |  `False` |
| <a id="jq-kwargs"></a>kwargs |  Other common named parameters such as `tags` or `visibility`   |  none |