Fix Windows build failure caused by extern "C" wrapper in oci.cpp

[Copilot]

Problem

The Windows build fails when compiling common/oci.cpp with the error:

error: templates must have C++ linkage

This occurs because oci.cpp wraps the include of liboci.h in an extern "C" block:

extern "C" {
#include "../oci-go/liboci.h"
}

Root Cause

The liboci.h file is generated by cgo and already provides its own extern "C" block for C function declarations. On Windows with MSVC, this generated header conditionally includes <complex> which contains C++ standard library templates:

#ifdef _MSC_VER
#if !defined(__cplusplus) || _MSVC_LANG <= 201402L
#include <complex.h>
typedef _Fcomplex GoComplex64;
#else
#include <complex>  // C++ header with templates
typedef std::complex<float> GoComplex64;
#endif
#endif

When these C++ templates are pulled in through the outer extern "C" block in oci.cpp, the compiler correctly rejects them since templates cannot have C linkage.

Solution

Remove the unnecessary extern "C" wrapper from oci.cpp. The cgo-generated liboci.h already provides the correct linkage specifications for its exported functions at lines 86-94:

#ifdef __cplusplus
extern "C" {
#endif

extern char* PullOCIModel(char* imageRef, char* cacheDir);
extern void FreeString(char* s);

#ifdef __cplusplus
}
#endif

This change also applies proper code formatting to the file according to the project's .clang-format rules (IndentPPDirectives: AfterHash).

Testing

• ✅ Builds successfully on Linux (CPU backend)
• ✅ No security vulnerabilities introduced
• ✅ Code review completed

The fix should resolve the Windows build failure while maintaining compatibility with all platforms.

Original prompt

Fix windows build, it fails with:

[98/253] Building CXX object common/CMakeFiles/common.dir/Release/oci.cpp.obj
FAILED: [code=1] common/CMakeFiles/common.dir/Release/oci.cpp.obj
ccache C:\PROGRA~1\LLVM\bin\CLANG_~1.EXE -DGGML_USE_CPU -DGGML_USE_RPC -DLLAMA_USE_CURL -DLLAMA_USE_OCI -D_CRT_SECURE_NO_WARNINGS -DCMAKE_INTDIR="Release" -ID:/a/llama.cpp/llama.cpp/oci-go -ID:/a/_temp/libcurl/include -ID:/a/llama.cpp/llama.cpp/common/. -ID:/a/llama.cpp/llama.cpp/common/../vendor -ID:/a/llama.cpp/llama.cpp/src/../include -ID:/a/llama.cpp/llama.cpp/ggml/src/../include -O3 -DNDEBUG -D_DLL -D_MT -Xclang --dependent-lib=msvcrt -std=gnu++17 -Wmissing-declarations -Wmissing-noreturn -Wall -Wextra -Wpedantic -Wcast-qual -Wno-unused-function -Wunreachable-code-break -Wunreachable-code-return -Wmissing-prototypes -Wextra-semi -MD -MT common/CMakeFiles/common.dir/Release/oci.cpp.obj -MF common\CMakeFiles\common.dir\Release\oci.cpp.obj.d -o common/CMakeFiles/common.dir/Release/oci.cpp.obj -c D:/a/llama.cpp/llama.cpp/common/oci.cpp
In file included from D:/a/llama.cpp/llama.cpp/common/oci.cpp:11:
In file included from cgo-gcc-export-header-prolog:19:
In file included from C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\ucrt\complex.h:15:
In file included from C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\include\ccomplex:11:
In file included from C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\include\complex:13:
C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\include\sstream:21:13: error: templates must have C++ linkage
21 | _EXPORT_STD template <class _Elem, class _Traits, class _Alloc>
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
D:/a/llama.cpp/llama.cpp/common/oci.cpp:10:1: note: extern "C" language linkage specification begins here
10 | extern "C" {
| ^
In file included from D:/a/llama.cpp/llama.cpp/common/oci.cpp:11:
In file included from cgo-gcc-export-header-prolog:19:
In file included from C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\ucrt\complex.h:15:
In file included from C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\include\ccomplex:11:
In file included from C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\include\complex:13:
C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\include\sstream:605:13: error: templates must have C++ linkage
605 | _EXPORT_STD template <class _Elem, class _Traits, class _Alloc>
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
D:/a/llama.cpp/llama.cpp/common/oci.cpp:10:1: note: extern "C" language linkage specification begins here
10 | extern "C" {
| ^
In file included from D:/a/llama.cpp/llama.cpp/common/oci.cpp:11:
In file included from cgo-gcc-export-header-prolog:19:
In file included from C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\ucrt\complex.h:15:
In file included from C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\include\ccomplex:11:
In file included from C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\include\complex:13:
C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\include\sstream:611:13: error: templates must have C++ linkage
611 | _EXPORT_STD template <class _Elem, class _Traits, class _Alloc>
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
D:/a/llama.cpp/llama.cpp/common/oci.cpp:10:1: note: extern "C" language linkage specification begins here
10 | extern "C" {
| ^
In file included from D:/a/llama.cpp/llama.cpp/common/oci.cpp:11:
In file included from cgo-gcc-export-header-prolog:19:
In file included from C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\ucrt\complex.h:15:
In file included from C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\include\ccomplex:11:
In file included from C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\include\complex:13:
C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\include\sstream:724:13: error: templates must have C++ linkage
724 | _EXPORT_STD template <class _Elem, class _Traits, class _Alloc>
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
D:/a/llama.cpp/llama.cpp/common/oci.cpp:10:1: note: extern "C" language linkage specification begins here
10 | extern "C" {
| ^
In file included from D:/a/llama.cpp/llama.cpp/common/oci.cpp:11:
In file included from cgo-gcc-export-header-prolog:19:
In file included from C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\ucrt\complex.h:15:
In file included from C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.44.35207\include\ccomplex:11:
In file included fr...

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.