From 7c7000347a51f577f44024e6c8e1a7bac626ac05 Mon Sep 17 00:00:00 2001
From: Rolf Bjarne Kvinge <rolf@xamarin.com>
Date: Thu, 12 Sep 2024 18:49:17 +0200
Subject: [PATCH 1/3] [dotnet] Change the usage of the classic linker to be
 opt-in.

Fixes https://github.com/xamarin/xamarin-macios/issues/20711.
---
 dotnet/targets/Xamarin.Shared.Sdk.targets | 4 ++--
 tools/common/Application.cs               | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/dotnet/targets/Xamarin.Shared.Sdk.targets b/dotnet/targets/Xamarin.Shared.Sdk.targets
index b1b307862a84..5c624f08312a 100644
--- a/dotnet/targets/Xamarin.Shared.Sdk.targets
+++ b/dotnet/targets/Xamarin.Shared.Sdk.targets
@@ -1630,8 +1630,8 @@
 			<_AllLinkerFlags Condition="'$(_ExportSymbolsExplicitly)' != 'true'" Include="@(_ProcessedReferenceNativeSymbol->'-u%(Identity)')" />
 
 			<!-- check if needs to be removed: https://github.com/xamarin/xamarin-macios/issues/18693 -->
-			<_AllLinkerFlags Condition="$([MSBuild]::VersionGreaterThanOrEquals('$(_XcodeVersion)', '15.0')) And '$(_UseClassicLinker)' != 'false'" Include="-Xlinker" />
-			<_AllLinkerFlags Condition="$([MSBuild]::VersionGreaterThanOrEquals('$(_XcodeVersion)', '15.0')) And '$(_UseClassicLinker)' != 'false'" Include="-ld_classic" />
+			<_AllLinkerFlags Condition="$([MSBuild]::VersionGreaterThanOrEquals('$(_XcodeVersion)', '15.0')) And '$(_UseClassicLinker)' != 'true'" Include="-Xlinker" />
+			<_AllLinkerFlags Condition="$([MSBuild]::VersionGreaterThanOrEquals('$(_XcodeVersion)', '15.0')) And '$(_UseClassicLinker)' != 'true'" Include="-ld_classic" />
 		</ItemGroup>
 
 		<LinkNativeCode
diff --git a/tools/common/Application.cs b/tools/common/Application.cs
index 385773aa1cab..fa43bcaa5615 100644
--- a/tools/common/Application.cs
+++ b/tools/common/Application.cs
@@ -175,7 +175,7 @@ public bool IsDefaultMarshalManagedExceptionMode {
 		public bool SkipMarkingNSObjectsInUserAssemblies { get; set; }
 
 		// check if needs to be removed: https://github.com/xamarin/xamarin-macios/issues/18693
-		public bool DisableAutomaticLinkerSelection { get; set; }
+		public bool DisableAutomaticLinkerSelection { get; set; } = true;
 
 		// assembly_build_targets describes what kind of native code each assembly should be compiled into for mobile targets (iOS, tvOS, watchOS).
 		// An assembly can be compiled into: static object (.o), dynamic library (.dylib) or a framework (.framework).

From b9dc59af9e7957dc5a94eaf47e974e928a9d2f96 Mon Sep 17 00:00:00 2001
From: Rolf Bjarne Kvinge <rolf@xamarin.com>
Date: Sat, 14 Sep 2024 00:55:22 +0200
Subject: [PATCH 2/3] Only use the new linker in Xcode 16+

---
 dotnet/targets/Xamarin.Shared.Sdk.targets | 12 +++++++++---
 tools/common/Application.cs               |  3 +--
 tools/common/CompilerFlags.cs             |  5 +++--
 3 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/dotnet/targets/Xamarin.Shared.Sdk.targets b/dotnet/targets/Xamarin.Shared.Sdk.targets
index 5c624f08312a..61b32c561f43 100644
--- a/dotnet/targets/Xamarin.Shared.Sdk.targets
+++ b/dotnet/targets/Xamarin.Shared.Sdk.targets
@@ -1625,13 +1625,19 @@
 
 		<WriteLinesToFile SessionId="$(BuildSessionId)" File="$(_MtouchSymbolsList)" Lines="@(_ProcessedReferenceNativeSymbol)" Overwrite="true" />
 
+		<PropertyGroup>
+			<!-- There are known bugs in the classic linker with Xcode 15, so keep use the classic linker in that case -->
+			<!-- In Xcode 16 we don't know of any problems for now, so enable the new linker by default -->
+			<_UseClassicLinker Condition="'$(_UseClassicLinker)' == '' And $([MSBuild]::VersionGreaterThanOrEquals('$(_XcodeVersion)', '16.0'))">false</_UseClassicLinker>
+			<_UseClassicLinker Condition="'$(_UseClassicLinker)' == '' And $([MSBuild]::VersionGreaterThanOrEquals('$(_XcodeVersion)', '15.0'))">true</_UseClassicLinker>
+		</PropertyGroup>
+
 		<ItemGroup>
 			<_AllLinkerFlags Include="@(_AssemblyLinkerFlags);@(_MainLinkerFlags);@(_CustomLinkFlags)" />
 			<_AllLinkerFlags Condition="'$(_ExportSymbolsExplicitly)' != 'true'" Include="@(_ProcessedReferenceNativeSymbol->'-u%(Identity)')" />
 
-			<!-- check if needs to be removed: https://github.com/xamarin/xamarin-macios/issues/18693 -->
-			<_AllLinkerFlags Condition="$([MSBuild]::VersionGreaterThanOrEquals('$(_XcodeVersion)', '15.0')) And '$(_UseClassicLinker)' != 'true'" Include="-Xlinker" />
-			<_AllLinkerFlags Condition="$([MSBuild]::VersionGreaterThanOrEquals('$(_XcodeVersion)', '15.0')) And '$(_UseClassicLinker)' != 'true'" Include="-ld_classic" />
+			<_AllLinkerFlags Condition="'$(_UseClassicLinker)' == 'true'" Include="-Xlinker" />
+			<_AllLinkerFlags Condition="'$(_UseClassicLinker)' == 'true'" Include="-ld_classic" />
 		</ItemGroup>
 
 		<LinkNativeCode
diff --git a/tools/common/Application.cs b/tools/common/Application.cs
index fa43bcaa5615..5b5f38098feb 100644
--- a/tools/common/Application.cs
+++ b/tools/common/Application.cs
@@ -174,8 +174,7 @@ public bool IsDefaultMarshalManagedExceptionMode {
 
 		public bool SkipMarkingNSObjectsInUserAssemblies { get; set; }
 
-		// check if needs to be removed: https://github.com/xamarin/xamarin-macios/issues/18693
-		public bool DisableAutomaticLinkerSelection { get; set; } = true;
+		public bool DisableAutomaticLinkerSelection { get; set; };
 
 		// assembly_build_targets describes what kind of native code each assembly should be compiled into for mobile targets (iOS, tvOS, watchOS).
 		// An assembly can be compiled into: static object (.o), dynamic library (.dylib) or a framework (.framework).
diff --git a/tools/common/CompilerFlags.cs b/tools/common/CompilerFlags.cs
index 5956cd08864c..7bf08e067f86 100644
--- a/tools/common/CompilerFlags.cs
+++ b/tools/common/CompilerFlags.cs
@@ -239,8 +239,9 @@ public void WriteArguments (IList<string> args)
 				}
 			}
 
-			// check if needs to be removed: https://github.com/xamarin/xamarin-macios/issues/18693
-			if (Driver.XcodeVersion.Major >= 15 && !Application.DisableAutomaticLinkerSelection) {
+			// There are known bugs in the classic linker with Xcode 15, so keep use the classic linker in that case
+			//  In Xcode 16 we don't know of any problems for now, so enable the new linker by default
+			if (Driver.XcodeVersion.Major >= 15 && Driver.XcodeVersion.Major < 16 && !Application.DisableAutomaticLinkerSelection) {
 				args.Insert (0, "-Xlinker");
 				args.Insert (1, "-ld_classic");
 			}

From a1592c8f45d09586f96aba5341f0d1b5de528e9f Mon Sep 17 00:00:00 2001
From: Rolf Bjarne Kvinge <rolf@xamarin.com>
Date: Mon, 16 Sep 2024 09:19:57 +0200
Subject: [PATCH 3/3] Fix build

---
 tools/common/Application.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/common/Application.cs b/tools/common/Application.cs
index 5b5f38098feb..19685c7a962c 100644
--- a/tools/common/Application.cs
+++ b/tools/common/Application.cs
@@ -174,7 +174,7 @@ public bool IsDefaultMarshalManagedExceptionMode {
 
 		public bool SkipMarkingNSObjectsInUserAssemblies { get; set; }
 
-		public bool DisableAutomaticLinkerSelection { get; set; };
+		public bool DisableAutomaticLinkerSelection { get; set; }
 
 		// assembly_build_targets describes what kind of native code each assembly should be compiled into for mobile targets (iOS, tvOS, watchOS).
 		// An assembly can be compiled into: static object (.o), dynamic library (.dylib) or a framework (.framework).