GN hack to tag targets as poisonous (and use it with audio codecs)

Only specially taggged targets may transitively depend on poisonous
targets. We first apply it to audio codecs.

This makes it much clearer exactly what parts of the code still have
dependencies on the audio codecs (and we want to eventually get rid of
pretty much all of them).

Bug: webrtc:8396, webrtc:9121
Change-Id: Iba5c2e806c702b5cfe881022674705f647896d43
Reviewed-on: https://webrtc-review.googlesource.com/69520
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22979}

BUILD.gn

@@ -587,3 +587,15 @@ if (rtc_include_tests) {
     }
   }
 }
+
+# ---- Poisons ----
+#
+# Here is one empty dummy target for each poison type (needed because
+# "being poisonous with poison type foo" is implemented as "depends on
+# //:poison_foo").
+#
+# The set of poison_* targets needs to be kept in sync with the
+# `all_poison_types` list in webrtc.gni.
+#
+group("poison_audio_codecs") {
+}

api/BUILD.gn

@@ -268,6 +268,7 @@ rtc_source_set("video_stream_decoder") {
 
 rtc_source_set("video_stream_decoder_create") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   sources = [
     "video/video_stream_decoder_create.cc",
     "video/video_stream_decoder_create.h",

api/audio/BUILD.gn

@@ -44,6 +44,7 @@ rtc_source_set("aec3_config") {
 
 rtc_source_set("aec3_factory") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   configs += [ "../../modules/audio_processing:apm_debug_dump" ]
   sources = [
     "echo_canceller3_factory.cc",

api/audio_codecs/BUILD.gn

@@ -44,6 +44,7 @@ rtc_source_set("audio_codecs_api") {
 
 rtc_static_library("builtin_audio_decoder_factory") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]
   sources = [
     "builtin_audio_decoder_factory.cc",
     "builtin_audio_decoder_factory.h",
@@ -73,6 +74,7 @@ rtc_static_library("builtin_audio_decoder_factory") {
 
 rtc_static_library("builtin_audio_encoder_factory") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]
   sources = [
     "builtin_audio_encoder_factory.cc",
     "builtin_audio_encoder_factory.h",

api/audio_codecs/L16/BUILD.gn

@@ -14,6 +14,7 @@ if (is_android) {
 
 rtc_static_library("audio_encoder_L16") {
   visibility = [ "*" ]
+  poisonous = [ "audio_codecs" ]
   sources = [
     "audio_encoder_L16.cc",
     "audio_encoder_L16.h",
@@ -29,6 +30,7 @@ rtc_static_library("audio_encoder_L16") {
 
 rtc_static_library("audio_decoder_L16") {
   visibility = [ "*" ]
+  poisonous = [ "audio_codecs" ]
   sources = [
     "audio_decoder_L16.cc",
     "audio_decoder_L16.h",

api/audio_codecs/g711/BUILD.gn

@@ -14,6 +14,7 @@ if (is_android) {
 
 rtc_static_library("audio_encoder_g711") {
   visibility = [ "*" ]
+  poisonous = [ "audio_codecs" ]
   sources = [
     "audio_encoder_g711.cc",
     "audio_encoder_g711.h",
@@ -30,6 +31,7 @@ rtc_static_library("audio_encoder_g711") {
 
 rtc_static_library("audio_decoder_g711") {
   visibility = [ "*" ]
+  poisonous = [ "audio_codecs" ]
   sources = [
     "audio_decoder_g711.cc",
     "audio_decoder_g711.h",

api/audio_codecs/g722/BUILD.gn

@@ -21,6 +21,7 @@ rtc_source_set("audio_encoder_g722_config") {
 
 rtc_static_library("audio_encoder_g722") {
   visibility = [ "*" ]
+  poisonous = [ "audio_codecs" ]
   sources = [
     "audio_encoder_g722.cc",
     "audio_encoder_g722.h",
@@ -38,6 +39,7 @@ rtc_static_library("audio_encoder_g722") {
 
 rtc_static_library("audio_decoder_g722") {
   visibility = [ "*" ]
+  poisonous = [ "audio_codecs" ]
   sources = [
     "audio_decoder_g722.cc",
     "audio_decoder_g722.h",

api/audio_codecs/ilbc/BUILD.gn

@@ -21,6 +21,7 @@ rtc_source_set("audio_encoder_ilbc_config") {
 
 rtc_static_library("audio_encoder_ilbc") {
   visibility = [ "*" ]
+  poisonous = [ "audio_codecs" ]
   sources = [
     "audio_encoder_ilbc.cc",
     "audio_encoder_ilbc.h",
@@ -38,6 +39,7 @@ rtc_static_library("audio_encoder_ilbc") {
 
 rtc_static_library("audio_decoder_ilbc") {
   visibility = [ "*" ]
+  poisonous = [ "audio_codecs" ]
   sources = [
     "audio_decoder_ilbc.cc",
     "audio_decoder_ilbc.h",

api/audio_codecs/isac/BUILD.gn

@@ -19,6 +19,7 @@ if (is_android) {
 
 rtc_source_set("audio_encoder_isac") {
   visibility = [ "*" ]
+  poisonous = [ "audio_codecs" ]
   public = [
     "audio_encoder_isac.h",
   ]
@@ -36,6 +37,7 @@ rtc_source_set("audio_encoder_isac") {
 
 rtc_source_set("audio_decoder_isac") {
   visibility = [ "*" ]
+  poisonous = [ "audio_codecs" ]
   public = [
     "audio_decoder_isac.h",
   ]
@@ -68,6 +70,7 @@ config("isac_config") {
 
 rtc_static_library("audio_encoder_isac_fix") {
   visibility = [ "*" ]
+  poisonous = [ "audio_codecs" ]
   sources = [
     "audio_encoder_isac_fix.cc",
     "audio_encoder_isac_fix.h",
@@ -83,6 +86,7 @@ rtc_static_library("audio_encoder_isac_fix") {
 
 rtc_static_library("audio_decoder_isac_fix") {
   visibility = [ "*" ]
+  poisonous = [ "audio_codecs" ]
   sources = [
     "audio_decoder_isac_fix.cc",
     "audio_decoder_isac_fix.h",
@@ -98,6 +102,7 @@ rtc_static_library("audio_decoder_isac_fix") {
 
 rtc_static_library("audio_encoder_isac_float") {
   visibility = [ "*" ]
+  poisonous = [ "audio_codecs" ]
   sources = [
     "audio_encoder_isac_float.cc",
     "audio_encoder_isac_float.h",
@@ -113,6 +118,7 @@ rtc_static_library("audio_encoder_isac_float") {
 
 rtc_static_library("audio_decoder_isac_float") {
   visibility = [ "*" ]
+  poisonous = [ "audio_codecs" ]
   sources = [
     "audio_decoder_isac_float.cc",
     "audio_decoder_isac_float.h",

api/audio_codecs/opus/BUILD.gn

@@ -32,6 +32,7 @@ rtc_static_library("audio_encoder_opus_config") {
 
 rtc_source_set("audio_encoder_opus") {
   visibility = [ "*" ]
+  poisonous = [ "audio_codecs" ]
   public = [
     "audio_encoder_opus.h",
   ]
@@ -49,6 +50,7 @@ rtc_source_set("audio_encoder_opus") {
 
 rtc_static_library("audio_decoder_opus") {
   visibility = [ "*" ]
+  poisonous = [ "audio_codecs" ]
   sources = [
     "audio_decoder_opus.cc",
     "audio_decoder_opus.h",

media/BUILD.gn

@@ -64,6 +64,7 @@ rtc_source_set("rtc_media_config") {
 
 rtc_static_library("rtc_media_base") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   defines = []
   libs = []
   deps = [
@@ -155,6 +156,7 @@ rtc_static_library("rtc_constants") {
 
 rtc_static_library("rtc_internal_video_codecs") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   defines = []
   libs = []
   deps = [
@@ -253,6 +255,7 @@ rtc_static_library("rtc_software_fallback_wrappers") {
 
 rtc_static_library("rtc_audio_video") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   defines = []
   libs = []
   deps = [
@@ -420,6 +423,7 @@ rtc_static_library("rtc_data") {
 
 rtc_source_set("rtc_media") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   deps = [
     ":rtc_audio_video",
     ":rtc_data",

modules/audio_coding/BUILD.gn

@@ -104,6 +104,7 @@ rtc_source_set("audio_coding_module_typedefs") {
 
 rtc_static_library("audio_coding") {
   visibility += [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   sources = [
     "acm2/acm_receiver.cc",
     "acm2/acm_receiver.h",
@@ -220,6 +221,7 @@ config("g711_config") {
 
 rtc_static_library("g711") {
   visibility += [ "*" ]
+  poisonous = [ "audio_codecs" ]
   sources = [
     "codecs/g711/audio_decoder_pcm.cc",
     "codecs/g711/audio_decoder_pcm.h",
@@ -242,6 +244,7 @@ rtc_static_library("g711") {
 }
 
 rtc_source_set("g711_c") {
+  poisonous = [ "audio_codecs" ]
   sources = [
     "codecs/g711/g711.c",
     "codecs/g711/g711.h",
@@ -260,6 +263,7 @@ config("g722_config") {
 
 rtc_static_library("g722") {
   visibility += [ "*" ]
+  poisonous = [ "audio_codecs" ]
   sources = [
     "codecs/g722/audio_decoder_g722.cc",
     "codecs/g722/audio_decoder_g722.h",
@@ -283,6 +287,7 @@ rtc_static_library("g722") {
 }
 
 rtc_source_set("g722_c") {
+  poisonous = [ "audio_codecs" ]
   sources = [
     "codecs/g722/g722_decode.c",
     "codecs/g722/g722_enc_dec.h",
@@ -302,6 +307,7 @@ config("ilbc_config") {
 
 rtc_static_library("ilbc") {
   visibility += webrtc_default_visibility
+  poisonous = [ "audio_codecs" ]
   sources = [
     "codecs/ilbc/audio_decoder_ilbc.cc",
     "codecs/ilbc/audio_decoder_ilbc.h",
@@ -326,6 +332,7 @@ rtc_static_library("ilbc") {
 }
 
 rtc_source_set("ilbc_c") {
+  poisonous = [ "audio_codecs" ]
   sources = [
     "codecs/ilbc/abs_quant.c",
     "codecs/ilbc/abs_quant.h",
@@ -483,6 +490,7 @@ rtc_source_set("ilbc_c") {
 }
 
 rtc_static_library("isac_common") {
+  poisonous = [ "audio_codecs" ]
   sources = [
     "codecs/isac/audio_decoder_isac_t.h",
     "codecs/isac/audio_decoder_isac_t_impl.h",
@@ -508,6 +516,7 @@ config("isac_config") {
 
 rtc_static_library("isac") {
   visibility += [ "*" ]
+  poisonous = [ "audio_codecs" ]
   sources = [
     "codecs/isac/main/include/audio_decoder_isac.h",
     "codecs/isac/main/include/audio_encoder_isac.h",
@@ -525,6 +534,7 @@ rtc_static_library("isac") {
 }
 
 rtc_static_library("isac_c") {
+  poisonous = [ "audio_codecs" ]
   sources = [
     "codecs/isac/main/include/isac.h",
     "codecs/isac/main/source/arith_routines.c",
@@ -602,6 +612,7 @@ config("isac_fix_config") {
 
 rtc_static_library("isac_fix") {
   visibility += [ "*" ]
+  poisonous = [ "audio_codecs" ]
   sources = [
     "codecs/isac/fix/source/audio_decoder_isacfix.cc",
     "codecs/isac/fix/source/audio_encoder_isacfix.cc",
@@ -625,6 +636,7 @@ rtc_static_library("isac_fix") {
 }
 
 rtc_source_set("isac_fix_common") {
+  poisonous = [ "audio_codecs" ]
   sources = [
     "codecs/isac/fix/source/codec.h",
     "codecs/isac/fix/source/entropy_coding.h",
@@ -645,6 +657,7 @@ rtc_source_set("isac_fix_common") {
 }
 
 rtc_source_set("isac_fix_c_arm_asm") {
+  poisonous = [ "audio_codecs" ]
   sources = []
   if (current_cpu == "arm" && arm_version >= 7) {
     sources += [
@@ -659,6 +672,7 @@ rtc_source_set("isac_fix_c_arm_asm") {
 }
 
 rtc_source_set("isac_fix_c") {
+  poisonous = [ "audio_codecs" ]
   sources = [
     "codecs/isac/fix/include/audio_decoder_isacfix.h",
     "codecs/isac/fix/include/audio_encoder_isacfix.h",
@@ -760,6 +774,7 @@ rtc_source_set("isac_fix_c") {
 
 if (rtc_build_with_neon) {
   rtc_static_library("isac_neon") {
+    poisonous = [ "audio_codecs" ]
     sources = [
       "codecs/isac/fix/source/entropy_coding_neon.c",
       "codecs/isac/fix/source/filterbanks_neon.c",
@@ -801,6 +816,7 @@ config("pcm16b_config") {
 
 rtc_static_library("pcm16b") {
   visibility += [ "*" ]
+  poisonous = [ "audio_codecs" ]
   sources = [
     "codecs/pcm16b/audio_decoder_pcm16b.cc",
     "codecs/pcm16b/audio_decoder_pcm16b.h",
@@ -825,6 +841,7 @@ rtc_static_library("pcm16b") {
 }
 
 rtc_source_set("pcm16b_c") {
+  poisonous = [ "audio_codecs" ]
   sources = [
     "codecs/pcm16b/pcm16b.c",
     "codecs/pcm16b/pcm16b.h",
@@ -839,6 +856,7 @@ rtc_source_set("pcm16b_c") {
 
 rtc_static_library("webrtc_opus") {
   visibility += webrtc_default_visibility
+  poisonous = [ "audio_codecs" ]
   sources = [
     "codecs/opus/audio_decoder_opus.cc",
     "codecs/opus/audio_decoder_opus.h",
@@ -874,6 +892,7 @@ rtc_static_library("webrtc_opus") {
 }
 
 rtc_source_set("webrtc_opus_c") {
+  poisonous = [ "audio_codecs" ]
   sources = [
     "codecs/opus/opus_inst.h",
     "codecs/opus/opus_interface.c",

modules/audio_processing/BUILD.gn

@@ -29,6 +29,7 @@ config("apm_debug_dump") {
 
 rtc_static_library("audio_processing") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   configs += [ ":apm_debug_dump" ]
   sources = [
     "aec/aec_resampler.cc",

modules/audio_processing/aec3/BUILD.gn

@@ -11,6 +11,7 @@ import("../../../webrtc.gni")
 
 rtc_static_library("aec3") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   configs += [ "..:apm_debug_dump" ]
   sources = [
     "adaptive_fir_filter.cc",

modules/video_capture/BUILD.gn

@@ -14,6 +14,7 @@ import("../../webrtc.gni")
 # use the internal capturer.
 rtc_static_library("video_capture_module") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   sources = [
     "device_info_impl.cc",
     "device_info_impl.h",
@@ -50,6 +51,7 @@ rtc_static_library("video_capture_module") {
 
 rtc_static_library("video_capture") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   sources = [
     "external/device_info_external.cc",
     "external/video_capture_external.cc",

modules/video_coding/BUILD.gn

@@ -38,6 +38,7 @@ rtc_static_library("encoded_frame") {
 
 rtc_static_library("video_coding") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   deps = []
 
   sources = [
@@ -249,6 +250,7 @@ rtc_source_set("video_coding_utility") {
 
 rtc_static_library("webrtc_h264") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   sources = [
     "codecs/h264/h264.cc",
     "codecs/h264/include/h264.h",

pc/BUILD.gn

@@ -27,6 +27,7 @@ config("rtc_pc_config") {
 
 rtc_static_library("rtc_pc_base") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   defines = []
   sources = [
     "audiomonitor.h",
@@ -102,6 +103,7 @@ rtc_static_library("rtc_pc_base") {
 
 rtc_source_set("rtc_pc") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   deps = [
     ":rtc_pc_base",
     "../media:rtc_audio_video",
@@ -119,6 +121,7 @@ config("libjingle_peerconnection_warnings_config") {
 
 rtc_static_library("peerconnection") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   cflags = []
   sources = [
     "audiotrack.cc",
@@ -250,6 +253,7 @@ rtc_static_library("create_pc_factory") {
 
 rtc_source_set("libjingle_peerconnection") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   deps = [
     ":create_pc_factory",
     ":peerconnection",

rtc_tools/BUILD.gn

@@ -203,6 +203,7 @@ if (!build_with_chromium) {
 
     rtc_static_library("event_log_visualizer_utils") {
       visibility = [ "*" ]
+      allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
       sources = [
         "event_log_visualizer/analyzer.cc",
         "event_log_visualizer/analyzer.h",

sdk/BUILD.gn

@@ -229,6 +229,7 @@ if (is_ios || is_mac) {
 
     rtc_static_library("ui_objc") {
       visibility = [ "*" ]
+      allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
       if (is_ios) {
         sources = [
           "objc/Framework/Classes/UI/RTCCameraPreviewView.m",
@@ -255,6 +256,7 @@ if (is_ios || is_mac) {
     if (rtc_use_metal_rendering) {
       rtc_static_library("metal_objc") {
         visibility = [ "*" ]
+        allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
         sources = [
           "objc/Framework/Classes/Metal/RTCMTLI420Renderer.h",
           "objc/Framework/Classes/Metal/RTCMTLI420Renderer.mm",
@@ -316,6 +318,7 @@ if (is_ios || is_mac) {
 
     rtc_static_library("videocapture_objc") {
       visibility = [ "*" ]
+      allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
       sources = [
         "objc/Framework/Classes/PeerConnection/RTCCameraVideoCapturer.m",
         "objc/Framework/Headers/WebRTC/RTCCameraVideoCapturer.h",
@@ -347,6 +350,8 @@ if (is_ios || is_mac) {
     }
 
     rtc_static_library("videocodec_objc") {
+      visibility = [ "*" ]
+      allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
       sources = [
         "objc/Framework/Classes/PeerConnection/RTCEncodedImage.mm",
         "objc/Framework/Classes/PeerConnection/RTCRtpFragmentationHeader.mm",
@@ -363,7 +368,6 @@ if (is_ios || is_mac) {
         # (bugs.webrtc.org/163).
         suppressed_configs += [ "//build/config/clang:find_bad_constructs" ]
       }
-      visibility = [ "*" ]
       public_configs = [ ":common_config_objc" ]
       deps = [
         ":common_objc",
@@ -398,6 +402,7 @@ if (is_ios || is_mac) {
 
     rtc_static_library("vp8") {
       visibility = [ "*" ]
+      allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
       sources = [
         "objc/Framework/Classes/PeerConnection/RTCVideoCodecVP8.mm",
         "objc/Framework/Headers/WebRTC/RTCVideoDecoderVP8.h",
@@ -419,6 +424,7 @@ if (is_ios || is_mac) {
 
     rtc_static_library("vp9") {
       visibility = [ "*" ]
+      allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
       sources = [
         "objc/Framework/Classes/PeerConnection/RTCVideoCodecVP9.mm",
         "objc/Framework/Headers/WebRTC/RTCVideoDecoderVP9.h",
@@ -447,6 +453,7 @@ if (is_ios || is_mac) {
     # The applications which only use WebRTC DataChannel can depend on this.
     rtc_static_library("peerconnectionfactory_no_media_objc") {
       visibility = [ "*" ]
+      allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
       defines = [ "HAVE_NO_MEDIA" ]
 
       sources = [
@@ -500,6 +507,8 @@ if (is_ios || is_mac) {
     }
 
     rtc_static_library("videorendereradapter_objc") {
+      visibility = [ "*" ]
+      allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
       sources = [
         "objc/Framework/Classes/PeerConnection/RTCVideoRendererAdapter+Private.h",
         "objc/Framework/Classes/PeerConnection/RTCVideoRendererAdapter.h",
@@ -507,7 +516,6 @@ if (is_ios || is_mac) {
       ]
 
       configs += [ "..:common_objc" ]
-      visibility = [ "*" ]
       public_configs = [ ":common_config_objc" ]
 
       deps = [
@@ -537,6 +545,8 @@ if (is_ios || is_mac) {
     }
 
     rtc_static_library("peerconnectionfactory_base_objc") {
+      visibility = [ "*" ]
+      allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
       sources = [
         "objc/Framework/Classes/PeerConnection/RTCAudioSource+Private.h",
         "objc/Framework/Classes/PeerConnection/RTCAudioSource.mm",
@@ -624,7 +634,6 @@ if (is_ios || is_mac) {
       ]
 
       configs += [ "..:common_objc" ]
-      visibility = [ "*" ]
       public_configs = [ ":common_config_objc" ]
 
       if (!build_with_chromium && is_clang) {
@@ -958,6 +967,7 @@ if (is_ios || is_mac) {
     # The native API is currently experimental and may change without notice.
     rtc_static_library("native_api") {
       visibility = [ "*" ]
+      allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
       sources = [
         "objc/Framework/Native/api/video_capturer.h",
         "objc/Framework/Native/api/video_capturer.mm",
@@ -1067,6 +1077,7 @@ if (is_ios || is_mac) {
 
     rtc_static_library("videotoolbox_objc") {
       visibility = [ "*" ]
+      allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
       sources = [
         "objc/Framework/Classes/VideoToolbox/RTCVideoDecoderH264.mm",
         "objc/Framework/Classes/VideoToolbox/RTCVideoEncoderH264.mm",

sdk/android/BUILD.gn

@@ -519,6 +519,7 @@ rtc_static_library("peerconnection_jni") {
   # made public because we don't have a proper NDK yet. Header APIs here are not
   # considered public and are subject to change.
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
 
   sources = [
     "src/jni/androidnetworkmonitor_jni.h",
@@ -611,6 +612,7 @@ rtc_static_library("peerconnection_jni") {
 
 rtc_static_library("libjingle_peerconnection_jni") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   public_deps = [
     ":audio_jni",
     ":base_jni",
@@ -631,6 +633,7 @@ generate_jni("generated_metrics_jni") {
 
 rtc_static_library("libjingle_peerconnection_metrics_default_jni") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   sources = [
     "src/jni/androidmetrics.cc",
   ]
@@ -1143,6 +1146,7 @@ rtc_static_library("native_api_jni") {
 # objects.
 rtc_static_library("native_api_codecs") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   sources = [
     "native_api/codecs/wrapper.cc",
     "native_api/codecs/wrapper.h",
@@ -1160,6 +1164,7 @@ rtc_static_library("native_api_codecs") {
 # API for creating Java PeerConnectionFactory from C++ equivalents.
 rtc_static_library("native_api_peerconnection") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   sources = [
     "native_api/peerconnection/peerconnectionfactory.cc",
     "native_api/peerconnection/peerconnectionfactory.h",
@@ -1186,6 +1191,7 @@ rtc_static_library("native_api_peerconnection") {
 # video interfaces from their Java equivalents.
 rtc_static_library("native_api_video") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   sources = [
     "native_api/video/wrapper.cc",
     "native_api/video/wrapper.h",

video/BUILD.gn

@@ -108,6 +108,7 @@ rtc_static_library("video") {
 
 rtc_source_set("video_stream_decoder_impl") {
   visibility = [ "*" ]
+  allow_poison = [ "audio_codecs" ]  # TODO(bugs.webrtc.org/8396): Remove.
   sources = [
     "video_stream_decoder_impl.cc",
     "video_stream_decoder_impl.h",

webrtc.gni

@@ -278,6 +278,41 @@ if (build_with_chromium) {
   webrtc_default_visibility += [ webrtc_root + "/../webrtc_overrides/*" ]
 }
 
+# ---- Poisons ----
+#
+# The general idea is that some targets declare that they contain some
+# kind of poison, which makes it impossible for other targets to
+# depend on them (even transitively) unless they declare themselves
+# immune to that particular type of poison.
+#
+# Targets that *contain* poison of type foo should contain the line
+#
+#   poisonous = [ "foo" ]
+#
+# and targets that *are immune but arent't themselves poisonous*
+# should contain
+#
+#   allow_poison = [ "foo" ]
+#
+# This useful in cases where we have some large target or set of
+# targets and want to ensure that most other targets do not
+# transitively depend on them. For example, almost no high-level
+# target should depend on the audio codecs, since we want WebRTC users
+# to be able to inject any subset of them and actually end up with a
+# binary that doesn't include the codecs they didn't inject.
+#
+# Test-only targets (`testonly` set to true) and non-public targets
+# (`visibility` not containing "*") are automatically immune to all
+# types of poison.
+#
+# Here's the complete list of all types of poison. It must be kept in
+# 1:1 correspondence with the set of //:poison_* targets.
+#
+all_poison_types = [
+  # Encoders and decoders for specific audio codecs such as Opus and iSAC.
+  "audio_codecs",
+]
+
 template("rtc_test") {
   test(target_name) {
     forward_variables_from(invoker,
@@ -321,6 +356,45 @@ template("rtc_source_set") {
     if (!defined(visibility)) {
       visibility = webrtc_default_visibility
     }
+
+    # What's your poison?
+    if (defined(testonly) && testonly) {
+      assert(!defined(poisonous))
+      assert(!defined(allow_poison))
+    } else {
+      if (!defined(poisonous)) {
+        poisonous = []
+      }
+      if (!defined(allow_poison)) {
+        allow_poison = []
+      }
+      if (!defined(assert_no_deps)) {
+        assert_no_deps = []
+      }
+      if (!defined(deps)) {
+        deps = []
+      }
+      foreach(p, poisonous) {
+        deps += [ webrtc_root + ":poison_" + p ]
+      }
+      foreach(poison_type, all_poison_types) {
+        allow_dep = true
+        foreach(v, visibility) {
+          if (v == "*") {
+            allow_dep = false
+          }
+        }
+        foreach(p, allow_poison + poisonous) {
+          if (p == poison_type) {
+            allow_dep = true
+          }
+        }
+        if (!allow_dep) {
+          assert_no_deps += [ webrtc_root + ":poison_" + poison_type ]
+        }
+      }
+    }
+
     configs += invoker.configs
     configs -= rtc_remove_configs
     configs -= invoker.suppressed_configs
@@ -375,6 +449,45 @@ template("rtc_static_library") {
     if (!defined(visibility)) {
       visibility = webrtc_default_visibility
     }
+
+    # What's your poison?
+    if (defined(testonly) && testonly) {
+      assert(!defined(poisonous))
+      assert(!defined(allow_poison))
+    } else {
+      if (!defined(poisonous)) {
+        poisonous = []
+      }
+      if (!defined(allow_poison)) {
+        allow_poison = []
+      }
+      if (!defined(assert_no_deps)) {
+        assert_no_deps = []
+      }
+      if (!defined(deps)) {
+        deps = []
+      }
+      foreach(p, poisonous) {
+        deps += [ webrtc_root + ":poison_" + p ]
+      }
+      foreach(poison_type, all_poison_types) {
+        allow_dep = true
+        foreach(v, visibility) {
+          if (v == "*") {
+            allow_dep = false
+          }
+        }
+        foreach(p, allow_poison + poisonous) {
+          if (p == poison_type) {
+            allow_dep = true
+          }
+        }
+        if (!allow_dep) {
+          assert_no_deps += [ webrtc_root + ":poison_" + poison_type ]
+        }
+      }
+    }
+
     configs += invoker.configs
     configs -= rtc_remove_configs
     configs -= invoker.suppressed_configs
@@ -399,6 +512,45 @@ template("rtc_shared_library") {
     if (!defined(visibility)) {
       visibility = webrtc_default_visibility
     }
+
+    # What's your poison?
+    if (defined(testonly) && testonly) {
+      assert(!defined(poisonous))
+      assert(!defined(allow_poison))
+    } else {
+      if (!defined(poisonous)) {
+        poisonous = []
+      }
+      if (!defined(allow_poison)) {
+        allow_poison = []
+      }
+      if (!defined(assert_no_deps)) {
+        assert_no_deps = []
+      }
+      if (!defined(deps)) {
+        deps = []
+      }
+      foreach(p, poisonous) {
+        deps += [ webrtc_root + ":poison_" + p ]
+      }
+      foreach(poison_type, all_poison_types) {
+        allow_dep = true
+        foreach(v, visibility) {
+          if (v == "*") {
+            allow_dep = false
+          }
+        }
+        foreach(p, allow_poison + poisonous) {
+          if (p == poison_type) {
+            allow_dep = true
+          }
+        }
+        if (!allow_dep) {
+          assert_no_deps += [ webrtc_root + ":poison_" + poison_type ]
+        }
+      }
+    }
+
     configs += invoker.configs
     configs -= rtc_remove_configs
     configs -= invoker.suppressed_configs