overlays: consolidate Abseil BMI2 workaround under patches

Extract the header fix into a standalone patch and colocate the
Electron, Deno, and Signal overrides in patches/abseil. Preserve the
x86-64-v3 restriction and document the accepted upstream fix while
waiting for bundled dependency updates.

Import the Abseil overrides through the patches overlay and register
the torchcodec override. Leave PostgreSQL output checks in
x86-64-v3-workarounds.nix.

overlays/patches/abseil/bmi2-public-header.patch

@@ -0,0 +1,20 @@
+Subject: [PATCH] abseil: include BMI2 intrinsics through the public header
+
+GCC and Clang reject direct inclusion of bmi2intrin.h. Include immintrin.h
+instead so that the compiler supplies the required intrinsic setup when
+BMI2 is enabled, including builds targeting x86-64-v3.
+
+This patch is shared by the vendored Abseil copies in Electron, rusty_v8
+(Deno), and Signal's WebRTC build.
+
+--- a/third_party/abseil-cpp/absl/container/internal/raw_hash_set.h
++++ b/third_party/abseil-cpp/absl/container/internal/raw_hash_set.h
+@@ -226,7 +226,7 @@
+ #endif
+ 
+ #ifdef __BMI2__
+-#include <bmi2intrin.h>
++#include <immintrin.h>
+ #endif  // __BMI2__
+ 
+ namespace absl {

overlays/patches/abseil/default.nix

@@ -0,0 +1,38 @@
+# Abseil accepted the upstream fix: https://github.com/abseil/abseil-cpp/pull/2071
+# Keep this workaround until Electron, Deno's rusty_v8, and Signal's WebRTC
+# update their bundled Abseil copies to include it.
+{ prev }:
+let
+  patchAbseilBmi2Include =
+    package:
+    package.overrideAttrs (old: {
+      # GCC and Clang require the public umbrella header for BMI2 intrinsics.
+      patches = (old.patches or [ ]) ++ [ ./bmi2-public-header.patch ];
+    });
+
+  electron43Unwrapped = patchAbseilBmi2Include prev.electron_43.unwrapped;
+  electron43 = prev.electron_43.override {
+    electron-unwrapped = electron43Unwrapped;
+  };
+
+  signalCallPackage =
+    path: args:
+    let
+      package = prev.callPackage path args;
+    in
+    if builtins.baseNameOf path == "webrtc.nix" then patchAbseilBmi2Include package else package;
+in
+prev.lib.optionalAttrs ((prev.stdenv.hostPlatform.gcc.arch or null) == "x86-64-v3") {
+  deno =
+    let
+      librusty_v8 = patchAbseilBmi2Include prev.deno.passthru.librusty_v8;
+    in
+    prev.deno.override { inherit librusty_v8; };
+
+  electron_43 = electron43;
+
+  signal-desktop = prev.signal-desktop.override {
+    electron_43 = electron43;
+    callPackage = signalCallPackage;
+  };
+}

overlays/patches/default.nix

@@ -1,9 +1,12 @@
-_final: prev: {
+_final: prev:
+(import ./abseil { inherit prev; })
+// {
   gnutls = import ./gnutls { inherit (prev) gnutls; };
 
   pythonPackagesExtensions = prev.pythonPackagesExtensions ++ [
     (_pythonFinal: pythonPrev: {
       scipy = import ./scipy { inherit (pythonPrev) scipy; };
+      torchcodec = import ./torchcodec { inherit (pythonPrev) torchcodec; };
     })
   ];
 }

overlays/x86-64-v3-workarounds.nix

@@ -1,22 +1,6 @@
-# Compatibility fixes for packages rebuilt with x86-64-v3.
-#
-# The v3 baseline enables instructions that expose source assumptions hidden
-# by the generic x86-64 build. Keep compile fixes here, separate from test
-# exclusions, until upstream or nixpkgs incorporates them.
+# Output-validation workarounds for packages rebuilt with x86-64-v3.
 _final: prev:
 let
-  patchAbseilBmi2Include =
-    package:
-    package.overrideAttrs (old: {
-      # GCC and Clang prohibit including their internal BMI2 header directly.
-      # The public umbrella provides the same intrinsics with the required
-      # compiler setup.
-      postPatch = (old.postPatch or "") + ''
-        substituteInPlace third_party/abseil-cpp/absl/container/internal/raw_hash_set.h \
-          --replace-fail "#include <bmi2intrin.h>" "#include <immintrin.h>"
-      '';
-    });
-
   removeSiblingOutputChecks =
     package:
     package.overrideAttrs (old: {
@@ -29,32 +13,8 @@ let
       ) (old.outputChecks or { });
     });
 
-  electron43Unwrapped = patchAbseilBmi2Include prev.electron_43.unwrapped;
-  electron43 = prev.electron_43.override {
-    electron-unwrapped = electron43Unwrapped;
-  };
-
-  signalCallPackage =
-    path: args:
-    let
-      package = prev.callPackage path args;
-    in
-    if builtins.baseNameOf path == "webrtc.nix" then patchAbseilBmi2Include package else package;
 in
 prev.lib.optionalAttrs ((prev.stdenv.hostPlatform.gcc.arch or null) == "x86-64-v3") {
-  deno =
-    let
-      librusty_v8 = patchAbseilBmi2Include prev.deno.passthru.librusty_v8;
-    in
-    prev.deno.override { inherit librusty_v8; };
-
-  electron_43 = electron43;
-
   postgresql = removeSiblingOutputChecks prev.postgresql;
   postgresql_18 = removeSiblingOutputChecks prev.postgresql_18;
-
-  signal-desktop = prev.signal-desktop.override {
-    electron_43 = electron43;
-    callPackage = signalCallPackage;
-  };
 }