feat: load jq filter from file

docs/jq.md

@@ -7,7 +7,7 @@ Public API for jq
 ## jq
 
 <pre>
-jq(<a href="#jq-name">name</a>, <a href="#jq-srcs">srcs</a>, <a href="#jq-filter">filter</a>, <a href="#jq-args">args</a>, <a href="#jq-out">out</a>, <a href="#jq-kwargs">kwargs</a>)
+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-kwargs">kwargs</a>)
 </pre>
 
 Invoke jq with a filter on a set of json input files.
@@ -50,6 +50,15 @@ jq(
     """,
     args = ["--slurp"],
 )
+
+# Load filter from a file
+jq(
+    name = "merged",
+    srcs = ["foo.json", "bar.json"],
+    filter_file = "filter.txt",
+    args = ["--slurp"],
+    out = "foobar.json",
+)
 ```
 
 
@@ -60,9 +69,10 @@ jq(
 | :------------- | :------------- | :------------- |
 | <a id="jq-name"></a>name |  Name of the rule   |  none |
 | <a id="jq-srcs"></a>srcs |  List of input json files   |  none |
-| <a id="jq-filter"></a>filter |  mandatory jq filter specification (https://stedolan.github.io/jq/manual/#Basicfilters)   |  none |
-| <a id="jq-args"></a>args |  additional args to pass to jq   |  <code>[]</code> |
+| <a id="jq-filter"></a>filter |  Filter expression (https://stedolan.github.io/jq/manual/#Basicfilters)   |  <code>None</code> |
+| <a id="jq-filter_file"></a>filter_file |  File containing filter expression (alternative to <code>filter</code>)   |  <code>None</code> |
+| <a id="jq-args"></a>args |  Additional args to pass to jq   |  <code>[]</code> |
 | <a id="jq-out"></a>out |  Name of the output json file; defaults to the rule name plus ".json"   |  <code>None</code> |
-| <a id="jq-kwargs"></a>kwargs |  other common named parameters such as <code>tags</code> or <code>visibility</code>   |  none |
+| <a id="jq-kwargs"></a>kwargs |  Other common named parameters such as <code>tags</code> or <code>visibility</code>   |  none |
 
 

lib/jq.bzl

@@ -8,7 +8,7 @@ _jq_rule = rule(
     toolchains = ["@aspect_bazel_lib//lib:jq_toolchain_type"],
 )
 
-def jq(name, srcs, filter, args = [], out = None, **kwargs):
+def jq(name, srcs, filter = None, filter_file = None, args = [], out = None, **kwargs):
     """Invoke jq with a filter on a set of json input files.
 
     For jq documentation, see https://stedolan.github.io/jq/.
@@ -49,15 +49,25 @@ def jq(name, srcs, filter, args = [], out = None, **kwargs):
         \"\"\",
         args = ["--slurp"],
     )
+
+    # Load filter from a file
+    jq(
+        name = "merged",
+        srcs = ["foo.json", "bar.json"],
+        filter_file = "filter.txt",
+        args = ["--slurp"],
+        out = "foobar.json",
+    )
     ```
 
     Args:
         name: Name of the rule
         srcs: List of input json files
-        filter: mandatory jq filter specification (https://stedolan.github.io/jq/manual/#Basicfilters)
-        args: additional args to pass to jq
+        filter: Filter expression (https://stedolan.github.io/jq/manual/#Basicfilters)
+        filter_file: File containing filter expression (alternative to `filter`)
+        args: Additional args to pass to jq
         out: Name of the output json file; defaults to the rule name plus ".json"
-        **kwargs: other common named parameters such as `tags` or `visibility`
+        **kwargs: Other common named parameters such as `tags` or `visibility`
     """
     if not out:
         out = name + ".json"
@@ -66,6 +76,7 @@ def jq(name, srcs, filter, args = [], out = None, **kwargs):
         name = name,
         srcs = srcs,
         filter = filter,
+        filter_file = filter_file,
         args = args,
         out = out,
         **kwargs

lib/private/jq.bzl

@@ -6,9 +6,8 @@ _jq_attrs = {
         mandatory = True,
         allow_empty = True,
     ),
-    "filter": attr.string(
-        mandatory = True,
-    ),
+    "filter": attr.string(),
+    "filter_file": attr.label(allow_single_file = True),
     "args": attr.string_list(),
     "out": attr.output(mandatory = True),
 }
@@ -18,22 +17,32 @@ def _jq_impl(ctx):
 
     out = ctx.outputs.out
     args = ctx.attr.args
+    inputs = ctx.files.srcs[:]
+
+    if not ctx.attr.filter and not ctx.attr.filter_file:
+        fail("Must provide a filter or a filter_file")
+    if ctx.attr.filter and ctx.attr.filter_file:
+        fail("Cannot provide both a filter and a filter_file")
 
     # jq hangs when there are no input sources unless --null-input flag is passed
     if len(ctx.attr.srcs) == 0 and "-n" not in args and "--null-input" not in args:
         args = args + ["--null-input"]
 
-    cmd = "{jq} {args} '{filter}' {sources} > {out}".format(
+    if ctx.attr.filter_file:
+        args = args + ["--from-file '%s'" % ctx.file.filter_file.path]
+        inputs.append(ctx.file.filter_file)
+
+    cmd = "{jq} {args} {filter} {sources} > {out}".format(
         jq = jq_bin.path,
         args = " ".join(args),
-        filter = ctx.attr.filter,
+        filter = "'%s'" % ctx.attr.filter if ctx.attr.filter else "",
         sources = " ".join(["'%s'" % file.path for file in ctx.files.srcs]),
         out = out.path,
     )
 
     ctx.actions.run_shell(
         tools = [jq_bin],
-        inputs = ctx.files.srcs,
+        inputs = inputs,
         outputs = [out],
         command = cmd,
     )

lib/tests/jq/BUILD.bazel

@@ -72,6 +72,20 @@ diff_test(
     file2 = "null.json",
 )
 
+# Load filter from file
+jq(
+    name = "case_filter_file",
+    srcs = ["a.json", "b.json"],
+    args = ["--slurp"],
+    filter_file = "merge_filter.txt",
+)
+
+diff_test(
+    name = "case_filter_file_test",
+    file1 = "a_b_merged.json",
+    file2 = ":case_filter_file",
+)
+
 # Call jq within a genrule
 genrule(
     name = "case_genrule",

lib/tests/jq/merge_filter.txt

@@ -0,0 +1,2 @@
+# Merge the second object onto the first
+.[0] * .[1]