Allow to opt-out from library evolution (#2484)

As the title says. A followup on #2401 (closed as I reorganised my fork
a bit).

apple/internal/partials/swift_framework.bzl

@@ -70,14 +70,25 @@ issue with a reproducible error case.
 
         found_module_name = swift_module.name
 
-        bundle_interface = swift_info_support.declare_swiftinterface(
-            actions = actions,
-            arch = arch,
-            label_name = label_name,
-            output_discriminator = output_discriminator,
-            swiftinterface = swift_module.swift.swiftinterface,
-        )
-        bundle_files.append((processor.location.bundle, modules_parent, depset([bundle_interface])))
+        # A swiftinterface will not be present when library evolution is disabled, if so, fallback to swiftmodule.
+        if swift_module.swift.swiftinterface:
+            bundle_interface = swift_info_support.declare_swiftinterface(
+                actions = actions,
+                arch = arch,
+                label_name = label_name,
+                output_discriminator = output_discriminator,
+                swiftinterface = swift_module.swift.swiftinterface,
+            )
+            bundle_files.append((processor.location.bundle, modules_parent, depset([bundle_interface])))
+        else:
+            bundle_swiftmodule = swift_info_support.declare_swiftmodule(
+                actions = actions,
+                arch = arch,
+                label_name = label_name,
+                output_discriminator = output_discriminator,
+                swiftmodule = swift_module.swift.swiftmodule,
+            )
+            bundle_files.append((processor.location.bundle, modules_parent, depset([bundle_swiftmodule])))
 
         bundle_doc = swift_info_support.declare_swiftdoc(
             actions = actions,

apple/internal/swift_info_support.bzl

@@ -81,7 +81,7 @@ swift_library dependencies.\
 """,
             )
 
-        if not all([module.name, module.swift.swiftdoc, module.swift.swiftinterface]):
+        if not all([module.name, module.swift.swiftdoc]) or not (module.swift.swiftmodule or module.swift.swiftinterface):
             fail(
                 """\
 error: Could not find all required artifacts and information to build a Swift framework. \
@@ -246,6 +246,38 @@ def _declare_swiftinterface(
     )
     return bundle_interface
 
+def _declare_swiftmodule(
+        *,
+        actions,
+        arch,
+        label_name,
+        output_discriminator,
+        swiftmodule):
+    """Declares the swiftmodule for this Swift framework.
+
+    Args:
+        actions: The actions provider from `ctx.actions`.
+        arch: The cpu architecture that the generated swiftdoc belongs to.
+        label_name: Name of the target being built.
+        output_discriminator: A string to differentiate between different target intermediate files
+            or `None`.
+        swiftmodule: A File referencing the swiftmodule file from a SwiftInfo provider.
+
+    Returns:
+        A File referencing the intermediate swiftmodule.
+    """
+    bundle_module = intermediates.file(
+        actions = actions,
+        target_name = label_name,
+        output_discriminator = output_discriminator,
+        file_name = "{}.swiftmodule".format(arch),
+    )
+    actions.symlink(
+        target_file = swiftmodule,
+        output = bundle_module,
+    )
+    return bundle_module
+
 swift_info_support = struct(
     verify_found_module_name = _verify_found_module_name,
     modules_from_avoid_deps = _modules_from_avoid_deps,
@@ -254,4 +286,5 @@ swift_info_support = struct(
     declare_generated_header = _declare_generated_header,
     declare_swiftdoc = _declare_swiftdoc,
     declare_swiftinterface = _declare_swiftinterface,
+    declare_swiftmodule = _declare_swiftmodule,
 )

apple/internal/transition_support.bzl

@@ -320,6 +320,7 @@ def _resolved_environment_arch_for_arch(*, arch, environment, platform_type):
 
 def _command_line_options_for_xcframework_platform(
         *,
+        attr,
         minimum_os_version,
         platform_attr,
         platform_type,
@@ -328,6 +329,7 @@ def _command_line_options_for_xcframework_platform(
     """Generates a dictionary of command line options keyed by 1:2+ transition for this platform.
 
     Args:
+        attr: The attributes passed to the transition function.
         minimum_os_version: A string representing the minimum OS version specified for this
             platform, represented as a dotted version number (for example, `"9.0"`).
         platform_attr: The attribute for the apple platform specifying in dictionary form which
@@ -361,7 +363,10 @@ def _command_line_options_for_xcframework_platform(
                     environment = target_environment,
                     platform_type = platform_type,
                 ): _command_line_options(
-                    emit_swiftinterface = True,
+                    emit_swiftinterface = _should_emit_swiftinterface(
+                        attr,
+                        is_xcframework = True,
+                    ),
                     environment_arch = resolved_environment_arch,
                     minimum_os_version = minimum_os_version,
                     platform_type = platform_type,
@@ -372,11 +377,28 @@ def _command_line_options_for_xcframework_platform(
 
     return output_dictionary
 
+def _should_emit_swiftinterface(attr, is_xcframework = False):
+    """Determines if a .swiftinterface file should be generated for Swift dependencies.
+
+    Needed until users of the framework rules are allowed to enable
+    library evolution on specific targets instead of having it automatically
+    applied to the entire dependency subgraph.
+    """
+
+    features = getattr(attr, "features", [])
+    if type(features) == "list" and "apple.no_legacy_swiftinterface" in features:
+        return False
+
+    # iOS and tvOS static frameworks require underlying swift_library targets generate a Swift
+    # interface file. These rules define a private attribute called `_emitswiftinterface` that
+    # let's this transition flip rules_swift config down the build graph.
+    return is_xcframework or hasattr(attr, "_emitswiftinterface")
+
 def _apple_rule_base_transition_impl(settings, attr):
     """Rule transition for Apple rules using Bazel CPUs and a valid Apple split transition."""
     platform_type = attr.platform_type
     return _command_line_options(
-        emit_swiftinterface = hasattr(attr, "_emitswiftinterface"),
+        emit_swiftinterface = _should_emit_swiftinterface(attr),
         environment_arch = _environment_archs(platform_type, settings)[0],
         minimum_os_version = attr.minimum_os_version,
         platform_type = platform_type,
@@ -447,7 +469,7 @@ def _apple_platforms_rule_base_transition_impl(settings, attr):
         environment_arch = _environment_archs(platform_type, settings)[0]
     return _command_line_options(
         apple_platforms = settings["//command_line_option:apple_platforms"],
-        emit_swiftinterface = hasattr(attr, "_emitswiftinterface"),
+        emit_swiftinterface = _should_emit_swiftinterface(attr),
         environment_arch = environment_arch,
         minimum_os_version = minimum_os_version,
         platform_type = platform_type,
@@ -470,7 +492,7 @@ def _apple_platforms_rule_bundle_output_base_transition_impl(settings, attr):
         environment_arch = _environment_archs(platform_type, settings)[0]
     return _command_line_options(
         apple_platforms = settings["//command_line_option:apple_platforms"],
-        emit_swiftinterface = hasattr(attr, "_emitswiftinterface"),
+        emit_swiftinterface = _should_emit_swiftinterface(attr),
         environment_arch = environment_arch,
         force_bundle_outputs = True,
         minimum_os_version = minimum_os_version,
@@ -550,7 +572,7 @@ def _apple_platform_split_transition_impl(settings, attr):
     # iOS and tvOS static frameworks require underlying swift_library targets generate a Swift
     # interface file. These rules define a private attribute called `_emitswiftinterface` that
     # let's this transition flip rules_swift config down the build graph.
-    emit_swiftinterface = hasattr(attr, "_emitswiftinterface")
+    emit_swiftinterface = _should_emit_swiftinterface(attr)
 
     if settings["//command_line_option:incompatible_enable_apple_toolchain_resolution"]:
         platforms = (
@@ -665,6 +687,7 @@ def _xcframework_transition_impl(settings, attr):
             target_environments.append("simulator")
 
         command_line_options = _command_line_options_for_xcframework_platform(
+            attr = attr,
             minimum_os_version = attr.minimum_os_versions.get(platform_type),
             platform_attr = getattr(attr, platform_type),
             platform_type = platform_type,

test/starlark_tests/targets_under_test/apple/BUILD

@@ -863,9 +863,6 @@ apple_xcframework(
     name = "ios_swift_3p_xcframework_with_generated_header",
     bundle_id = "com.google.example",
     bundle_name = "Swift3PFmwkWithGenHeader",
-    # TODO(b/239957001): Remove this when the rule no longer forces library
-    # evolution.
-    features = ["apple.no_legacy_swiftinterface"],
     infoplists = [
         "//test/starlark_tests/resources:Info.plist",
     ],
@@ -1271,7 +1268,6 @@ swift_library(
 swift_library(
     name = "Swift3PFmwkWithGenHeader",
     srcs = ["DummyFmwk.swift"],
-    features = ["swift.enable_library_evolution"],
     generates_header = True,
     module_name = "Swift3PFmwkWithGenHeader",
     tags = common.fixture_tags,

test/starlark_tests/targets_under_test/ios/BUILD

@@ -4071,9 +4071,6 @@ ios_static_framework(
 ios_static_framework(
     name = "static_framework_with_generated_header",
     bundle_name = "SwiftStaticFmwkWithGenHeader",
-    # TODO(b/239957001): Remove this when the rule no longer forces library
-    # evolution.
-    features = ["apple.no_legacy_swiftinterface"],
     minimum_os_version = common.min_os_ios.baseline,
     tags = common.fixture_tags,
     deps = [":SwiftStaticFmwkWithGenHeader"],
@@ -4171,7 +4168,6 @@ swift_library(
 swift_library(
     name = "SwiftStaticFmwkWithGenHeader",
     srcs = [":dummy_swift"],
-    features = ["swift.enable_library_evolution"],
     generates_header = True,
     module_name = "SwiftStaticFmwkWithGenHeader",
     tags = common.fixture_tags,