Provide a way for aspects to participate in swift_feature_allowlist…

… checking

This lets aspects enable/disable features without having to add every package where that aspect might be applied to targets to the `packages` of the allowlist.

PiperOrigin-RevId: 596900977
(cherry picked from commit 0206011)
Signed-off-by: Brentley Jones <github@brentleyjones.com>

doc/rules.md

@@ -212,7 +212,7 @@ the future, this rule is not recommended for other widespread use.
 ## swift_feature_allowlist
 
 <pre>
-swift_feature_allowlist(<a href="#swift_feature_allowlist-name">name</a>, <a href="#swift_feature_allowlist-managed_features">managed_features</a>, <a href="#swift_feature_allowlist-packages">packages</a>)
+swift_feature_allowlist(<a href="#swift_feature_allowlist-name">name</a>, <a href="#swift_feature_allowlist-aspect_ids">aspect_ids</a>, <a href="#swift_feature_allowlist-managed_features">managed_features</a>, <a href="#swift_feature_allowlist-packages">packages</a>)
 </pre>
 
 Limits the ability to request or disable certain features to a set of packages
@@ -233,7 +233,8 @@ package.
 | Name  | Description | Type | Mandatory | Default |
 | :------------- | :------------- | :------------- | :------------- | :------------- |
 | <a id="swift_feature_allowlist-name"></a>name |  A unique name for this target.   | <a href="https://bazel.build/concepts/labels#target-names">Name</a> | required |  |
-| <a id="swift_feature_allowlist-managed_features"></a>managed_features |  A list of feature strings that are permitted to be specified by the targets in the packages matched by the `packages` attribute. This list may include both feature names and/or negations (a name with a leading `-`); a regular feature name means that the targets in the matching packages may explicitly request that the feature be enabled, and a negated feature means that the target may explicitly request that the feature be disabled.<br><br>For example, `managed_features = ["foo", "-bar"]` means that targets in the allowlist's packages may request that feature `"foo"` be enabled and that feature `"bar"` be disabled.   | List of strings | optional |  `[]`  |
+| <a id="swift_feature_allowlist-aspect_ids"></a>aspect_ids |  A list of strings representing the identifiers of aspects that are allowed to enable/disable the features in `managed_features`, even when the aspect is applied to packages not covered by the `packages` attribute.<br><br>Aspect identifiers are each expected to be of the form `<.bzl file label>%<aspect top-level name>` (i.e., the form one would use if invoking it from the command line, as described at https://bazel.build/extending/aspects#invoking_the_aspect_using_the_command_line).   | List of strings | optional |  `[]`  |
+| <a id="swift_feature_allowlist-managed_features"></a>managed_features |  A list of feature strings that are permitted to be specified by the targets in the packages matched by the `packages` attribute *or* an aspect whose name matches the `aspect_ids` attribute (in any package). This list may include both feature names and/or negations (a name with a leading `-`); a regular feature name means that the matching targets/aspects may explicitly request that the feature be enabled, and a negated feature means that the target may explicitly request that the feature be disabled.<br><br>For example, `managed_features = ["foo", "-bar"]` means that targets in the allowlist's packages/aspects may request that feature `"foo"` be enabled and that feature `"bar"` be disabled.   | List of strings | optional |  `[]`  |
 | <a id="swift_feature_allowlist-packages"></a>packages |  A list of strings representing packages (possibly recursive) whose targets are allowed to enable/disable the features in `managed_features`. Each package pattern is written in the syntax used by the `package_group` function:<br><br>*   `//foo/bar`: Targets in the package `//foo/bar` but not in subpackages.<br><br>*   `//foo/bar/...`: Targets in the package `//foo/bar` and any of its     subpackages.<br><br>*   A leading `-` excludes packages that would otherwise have been included by     the patterns in the list.<br><br>Exclusions always take priority over inclusions; order in the list is irrelevant.   | List of strings | required |  |
 
 

swift/internal/features.bzl

@@ -87,9 +87,25 @@ def configure_features(
         "parse_headers",
     ])
 
+    # HACK: This is the only way today to check whether the caller is inside an
+    # aspect. We have to do this because accessing `ctx.aspect_ids` halts the
+    # build if called from outside an aspect, but we can't use `hasattr` to
+    # check if it's safe because the attribute is always present on both rule
+    # and aspect contexts.
+    # TODO: b/319132714 - Replace this with a real API.
+    is_aspect = repr(ctx).startswith("<aspect context ")
+    if is_aspect and ctx.aspect_ids:
+        # It doesn't appear to be documented anywhere, but according to the
+        # Bazel team, the last element in this list is the currently running
+        # aspect.
+        aspect_id = ctx.aspect_ids[len(ctx.aspect_ids) - 1]
+    else:
+        aspect_id = None
+
     if swift_toolchain.feature_allowlists:
         _check_allowlists(
             allowlists = swift_toolchain.feature_allowlists,
+            aspect_id = aspect_id,
             label = ctx.label,
             requested_features = requested_features,
             unsupported_features = unsupported_features,
@@ -194,6 +210,7 @@ def is_feature_enabled(feature_configuration, feature_name):
 def _check_allowlists(
         *,
         allowlists,
+        aspect_id,
         label,
         requested_features,
         unsupported_features):
@@ -206,6 +223,9 @@ def _check_allowlists(
     Args:
         allowlists: A list of `SwiftFeatureAllowlistInfo` providers that will be
             checked.
+        aspect_id: The identifier of the currently running aspect that has been
+            applied to the target that is creating the feature configuration, or
+            `None` if it is not being called from an aspect.
         label: The label of the target being checked against the allowlist.
         requested_features: The list of features to be enabled. This is
             typically obtained using the `ctx.features` field in a rule
@@ -225,6 +245,11 @@ def _check_allowlists(
             if feature_string not in allowlist.managed_features:
                 continue
 
+            # If the current aspect is permitted by the allowlist, we can allow
+            # the usage without looking at the package specs.
+            if aspect_id in allowlist.aspect_ids:
+                continue
+
             if not label_matches_package_specs(
                 label = label,
                 package_specs = allowlist.package_specs,

swift/providers.bzl

@@ -45,8 +45,8 @@ arbitrary libraries/binaries to depend on a plugin.
 
 SwiftFeatureAllowlistInfo = provider(
     doc = """\
-Describes a set of features and the packages that are allowed to request or
-disable them.
+Describes a set of features and the packages and aspects that are allowed to
+request or disable them.
 
 This provider is an internal implementation detail of the rules; users should
 not rely on it or assume that its structure is stable.
@@ -55,6 +55,11 @@ not rely on it or assume that its structure is stable.
         "allowlist_label": """\
 A string containing the label of the `swift_feature_allowlist` target that
 created this provider.
+""",
+        "aspect_ids": """\
+A list of strings representing identifiers of aspects that are allowed to
+request or disable a feature managed by the allowlist, even when the target the
+aspect is being applied to does not match `package_specs`.
 """,
         "managed_features": """\
 A list of strings representing feature names or their negations that packages in

swift/swift_feature_allowlist.bzl

@@ -20,6 +20,7 @@ load(":providers.bzl", "SwiftFeatureAllowlistInfo")
 def _swift_feature_allowlist_impl(ctx):
     return [SwiftFeatureAllowlistInfo(
         allowlist_label = str(ctx.label),
+        aspect_ids = ctx.attr.aspect_ids,
         managed_features = ctx.attr.managed_features,
         package_specs = parse_package_specs(
             package_specs = ctx.attr.packages,
@@ -29,19 +30,33 @@ def _swift_feature_allowlist_impl(ctx):
 
 swift_feature_allowlist = rule(
     attrs = {
+        "aspect_ids": attr.string_list(
+            allow_empty = True,
+            doc = """\
+A list of strings representing the identifiers of aspects that are allowed to
+enable/disable the features in `managed_features`, even when the aspect is
+applied to packages not covered by the `packages` attribute.
+
+Aspect identifiers are each expected to be of the form
+`<.bzl file label>%<aspect top-level name>` (i.e., the form one would use if
+invoking it from the command line, as described at
+https://bazel.build/extending/aspects#invoking_the_aspect_using_the_command_line).
+""",
+        ),
         "managed_features": attr.string_list(
             allow_empty = True,
             doc = """\
 A list of feature strings that are permitted to be specified by the targets in
-the packages matched by the `packages` attribute. This list may include both
+the packages matched by the `packages` attribute *or* an aspect whose name
+matches the `aspect_ids` attribute (in any package). This list may include both
 feature names and/or negations (a name with a leading `-`); a regular feature
-name means that the targets in the matching packages may explicitly request that
-the feature be enabled, and a negated feature means that the target may
-explicitly request that the feature be disabled.
+name means that the matching targets/aspects may explicitly request that the
+feature be enabled, and a negated feature means that the target may explicitly
+request that the feature be disabled.
 
 For example, `managed_features = ["foo", "-bar"]` means that targets in the
-allowlist's packages may request that feature `"foo"` be enabled and that
-feature `"bar"` be disabled.
+allowlist's packages/aspects may request that feature `"foo"` be enabled and
+that feature `"bar"` be disabled.
 """,
             mandatory = False,
         ),