[clang] [Clang][Cygwin] Link default-manifest.o if exists (PR #220875)

[Tomohiro Kashiwada via cfe-commits]

https://github.com/kikairoya created https://github.com/llvm/llvm-project/pull/220875

The Cygwin distribution provides an optional package to embed a manifest xml to disable the UAC escalation dialog.
Link automatically the manifest only if it exists when linking an executable.
This matches GCC's behavior.

>From edc1afbd2f37e877b921d5b7bd1360157d165b26 Mon Sep 17 00:00:00 2001
From: kikairoya <kikairoya at gmail.com>
Date: Thu, 3 Sep 2026 19:54:57 +0900
Subject: [PATCH] [Clang][Cygwin] Link default-manifest.o if exists

The Cygwin distribution provides an optional package to embed a manifest xml to disable the UAC escalation dialog.
Link automatically the manifest only if it exists when linking an executable.
This matches GCC's behavior.
---
 clang/lib/Driver/ToolChains/Cygwin.cpp             |  8 +++++++-
 .../basic_cygwin_tree/usr/lib/default-manifest.o   |  0
 clang/test/Driver/cygwin.cpp                       | 14 ++++++++++----
 3 files changed, 17 insertions(+), 5 deletions(-)
 create mode 100644 clang/test/Driver/Inputs/basic_cygwin_tree/usr/lib/default-manifest.o

diff --git a/clang/lib/Driver/ToolChains/Cygwin.cpp b/clang/lib/Driver/ToolChains/Cygwin.cpp
index 938f6c3b5f2db..7d4167372af27 100644
--- a/clang/lib/Driver/ToolChains/Cygwin.cpp
+++ b/clang/lib/Driver/ToolChains/Cygwin.cpp
@@ -375,8 +375,14 @@ void cygwin::Linker::ConstructJob(Compilation &C, const JobAction &JA,
         tools::AddRunTimeLibs(ToolChain, D, CmdArgs, Args);
     }
 
-    if (!Args.hasArg(options::OPT_nostartfiles))
+    if (!Args.hasArg(options::OPT_nostartfiles)) {
+      if (!Args.hasArg(options::OPT_mdll, options::OPT_shared)) {
+        if (std::string O = ToolChain.GetFilePath("default-manifest.o");
+            O != "default-manifest.o")
+          CmdArgs.push_back(Args.MakeArgString(std::move(O)));
+      }
       CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath("crtend.o")));
+    }
   }
 
   Args.addAllArgs(CmdArgs, {options::OPT_T, options::OPT_t});
diff --git a/clang/test/Driver/Inputs/basic_cygwin_tree/usr/lib/default-manifest.o b/clang/test/Driver/Inputs/basic_cygwin_tree/usr/lib/default-manifest.o
new file mode 100644
index 0000000000000..e69de29bb2d1d
diff --git a/clang/test/Driver/cygwin.cpp b/clang/test/Driver/cygwin.cpp
index c51a359bb35e2..66fa9fbcfc1e0 100644
--- a/clang/test/Driver/cygwin.cpp
+++ b/clang/test/Driver/cygwin.cpp
@@ -20,6 +20,7 @@
 // CHECK-SAME: "-m" "i386pe"
 // CHECK-SAME: "{{.*}}{{/|\\\\}}crt0.o"
 // CHECK-SAME: "{{.*}}i686-pc-cygwin{{/|\\\\}}{{[0-9.]*}}{{/|\\\\}}crtbegin.o"
+// CHECK-SAME: "[[SYSROOT]]{{/|\\\\}}usr{{/|\\\\}}lib{{/|\\\\}}default-manifest.o"
 // CHECK-SAME: "{{.*}}i686-pc-cygwin{{/|\\\\}}{{[0-9.]*}}{{/|\\\\}}crtend.o"
 
 // RUN: %clang -### %s --target=i686-pc-cygwin --sysroot=%S/Inputs/basic_cygwin_tree \
@@ -30,7 +31,7 @@
 // CHECK-STATIC-SAME: "-Bstatic"
 
 // RUN: %clang -### %s --target=i686-pc-cygwin --sysroot=%S/Inputs/basic_cygwin_tree \
-// RUN:   -shared 2>&1 | FileCheck --check-prefix=CHECK-SHARED %s
+// RUN:   -shared 2>&1 | FileCheck --check-prefix=CHECK-SHARED %s --implicit-check-not=default-manifest
 // CHECK-SHARED:      "{{.*}}ld{{(\.exe)?}}"
 // CHECK-SHARED-SAME: "--shared"
 // CHECK-SHARED-SAME: "-e" "__cygwin_dll_entry at 12"
@@ -67,6 +68,7 @@
 // CHECK-64-SAME: "-m" "i386pep"
 // CHECK-64-SAME: "{{.*}}{{/|\\\\}}crt0.o"
 // CHECK-64-SAME: "{{.*}}x86_64-pc-msys{{/|\\\\}}{{[0-9.]*}}{{/|\\\\}}crtbegin.o"
+// CHECK-64-SAME: "[[SYSROOT]]{{/|\\\\}}usr{{/|\\\\}}lib{{/|\\\\}}default-manifest.o"
 // CHECK-64-SAME: "{{.*}}x86_64-pc-msys{{/|\\\\}}{{[0-9.]*}}{{/|\\\\}}crtend.o"
 
 // RUN: %clang -### %s --target=x86_64-pc-cygwin --sysroot=%S/Inputs/basic_cygwin_tree \
@@ -77,7 +79,7 @@
 // CHECK-64-STATIC-SAME: "-Bstatic"
 
 // RUN: %clang -### %s --target=x86_64-pc-cygwin --sysroot=%S/Inputs/basic_cygwin_tree \
-// RUN:   -shared 2>&1 | FileCheck --check-prefix=CHECK-64-SHARED %s
+// RUN:   -shared 2>&1 | FileCheck --check-prefix=CHECK-64-SHARED %s --implicit-check-not=default-manifest
 // CHECK-64-SHARED:      "{{.*}}ld{{(\.exe)?}}"
 // CHECK-64-SHARED-SAME: "--shared"
 // CHECK-64-SHARED-SAME: "-e" "_cygwin_dll_entry"
@@ -94,13 +96,13 @@
 // CHECK-64-CROSS-SAME: "{{.*}}x86_64-pc-cygwin{{/|\\\\}}{{[0-9.]*}}{{/|\\\\}}crtend.o"
 
 // RUN: %clang -### %s --target=x86_64-pc-cygwin --sysroot=%S/Inputs/basic_cygwin_tree \
-// RUN:   -mdll 2>&1 | FileCheck --check-prefix=CHECK-64-DLL %s
+// RUN:   -mdll 2>&1 | FileCheck --check-prefix=CHECK-64-DLL %s --implicit-check-not=default-manifest
 // CHECK-64-DLL:      "{{.*}}ld{{(\.exe)?}}"
 // CHECK-64-DLL-SAME: "--dll"
 // CHECK-64-DLL-SAME: "-e" "_cygwin_dll_entry"
 
 // RUN: %clang -### %s --target=i686-pc-cygwin --sysroot=%S/Inputs/basic_cygwin_tree \
-// RUN:   -mdll 2>&1 | FileCheck --check-prefix=CHECK-DLL %s
+// RUN:   -mdll 2>&1 | FileCheck --check-prefix=CHECK-DLL %s --implicit-check-not=default-manifest
 // CHECK-DLL:      "{{.*}}ld{{(\.exe)?}}"
 // CHECK-DLL-SAME: "--dll"
 // CHECK-DLL-SAME: "-e" "__cygwin_dll_entry at 12"
@@ -176,3 +178,7 @@
 // RUN:   2>&1 | FileCheck --check-prefix=CHECK-64-RTLIB-PER-TARGET %s
 // CHECK-64-RTLIB-PER-TARGET:      "{{.*}}ld{{(\.exe)?}}"
 // CHECK-64-RTLIB-PER-TARGET-SAME: "{{.*}}{{/|\\\\}}lib{{/|\\\\}}x86_64-pc-windows-cygnus{{/|\\\\}}libclang_rt.builtins.a"
+
+// RUN: %clang -### %s --target=i686-pc-cygwin --sysroot=%S/Inputs/basic_cross_cygwin_tree \
+// RUN:   2>&1 | FileCheck --check-prefix=CHECK-MANIFEST-ABSENT %s
+// CHECK-MANIFEST-ABSENT-NOT: default-manifest