feat: Support requirements overrides files (#186)

Closes #128

#128 gives a workaround, but it only works when the overrides file is at
the root because `args` does not seem to support [Predefined
source/output path
variables](https://bazel.build/reference/be/make-variables#predefined_label_variables).

This PR makes `requirements_overrides` as a dedicated attr so in the
rule can access its `short_path`.

readme.md

diff --git a/readme.md b/readme.md
index 1a14316..2023491 100644
--- a/readme.md
+++ b/readme.md
@@ -43,6 +43,7 @@
 - `data`: pass additional files to be present when generating and testing requirements txt files (see also [examples/multiple-inputs](examples/multiple-inputs/))
 - `tags`: tags to apply to the test target
 - `target_compatible_with`: restrict targets to running on the specified Bazel platform
+- `requirements_overrides`: a label for the file that is used to override dependencies (passed to uv via `--overrides`)
 
 ### create_venv
 

uv/pip.bzl

diff --git a/uv/pip.bzl b/uv/pip.bzl
index 26e04d1..3ddf4c5 100644
--- a/uv/pip.bzl
+++ b/uv/pip.bzl
@@ -7,6 +7,7 @@
 def pip_compile(
         name,
         requirements_in = None,
+        requirements_overrides = None,
         requirements_txt = None,
         target_compatible_with = None,
         python_platform = None,
@@ -23,6 +24,7 @@
         name: name of the primary compilation target.
         requirements_in: (optional, default "//:requirements.in") a label for the requirements.in file.
             May also be provided as a list of strings which represent the requirements file lines.
+        requirements_overrides: (optional, default None) a label for the file that is used to override dependencies.
         requirements_txt: (optional, default "//:requirements.txt") a label for the requirements.txt file.
         python_platform: (optional) a uv pip compile compatible value for --python-platform.
         universal: (optional, default False) use uv's `--universal` option
@@ -58,6 +60,7 @@
     _pip_compile(
         name = name,
         requirements_in = requirements_in,
+        requirements_overrides = requirements_overrides,
         requirements_txt = requirements_txt,
         python_platform = python_platform,
         universal = universal,
@@ -78,6 +81,7 @@
         name = name + "_test",
         generator_label = name,
         requirements_in = requirements_in,
+        requirements_overrides = requirements_overrides,
         requirements_txt = requirements_txt,
         python_platform = python_platform or "",
         universal = universal,

uv/private/pip.bzl

diff --git a/uv/private/pip.bzl b/uv/private/pip.bzl
index 2239ec7..aef3fbe 100644
--- a/uv/private/pip.bzl
+++ b/uv/private/pip.bzl
@@ -13,6 +13,7 @@
 
 _COMMON_ATTRS = {
     "requirements_in": attr.label(mandatory = True, allow_single_file = True),
+    "requirements_overrides": attr.label(mandatory = False, allow_single_file = True),
     "requirements_txt": attr.label(mandatory = True, allow_single_file = True),
     "python_platform": attr.string(),
     "universal": attr.bool(),
@@ -55,6 +56,8 @@
         args.append("--python-platform={platform}".format(platform = ctx.attr.python_platform))
     elif ctx.attr.universal:
         args.append("--universal")
+    if ctx.attr.requirements_overrides:
+        args.append("--overrides={overrides_file}".format(overrides_file = ctx.file.requirements_overrides.short_path))
 
     ctx.actions.expand_template(
         template = template,
@@ -70,8 +73,9 @@
 
 def _runfiles(ctx):
     py3_runtime = _python_runtime(ctx)
+    overrides_file = [ctx.file.requirements_overrides] if ctx.attr.requirements_overrides else []
     runfiles = ctx.runfiles(
-        files = [ctx.file.requirements_in, ctx.file.requirements_txt] + ctx.files.data,
+        files = [ctx.file.requirements_in, ctx.file.requirements_txt] + overrides_file + ctx.files.data,
         transitive_files = py3_runtime.files,
     )
     runfiles = runfiles.merge(ctx.attr._uv[0].default_runfiles)