APPLE: Move HgiShaderProgramDesc operator== to header

[dgovil]

Description of Change(s)

This PR moves the HgiShaderProgramDesc's operator== to the header, since its marked inline, but is only defined in the cpp file, therefore cannot actually be inlined.

(Thanks to Maddy Adams)

pxr/imaging/hgi/shaderProgram.h contains:

HGI_API
inline bool operator==(
    const HgiShaderProgramDesc& lhs,
    const HgiShaderProgramDesc& rhs);

But, the definition is only in the .cpp file, so calling it results in a linker error:

Undefined symbols for architecture arm64:
  "pxrInternal_v0_25_5__pxrReserved__::operator==(pxrInternal_v0_25_5__pxrReserved__::HgiShaderProgramDesc const&, pxrInternal_v0_25_5__pxrReserved__::HgiShaderProgramDesc const&)", referenced from:
      reproducer(pxrInternal_v0_25_5__pxrReserved__::HgiShaderProgramDesc const&, pxrInternal_v0_25_5__pxrReserved__::HgiShaderProgramDesc const&) in main-d9ce5a.o
ld: symbol(s) not found for architecture arm64

Clang also emits this warning:

/opt/local/OpenUSD_no-python/include/pxr/imaging/hgi/shaderProgram.h:44:13: warning: inline function 'pxrInternal_v0_25_5__pxrReserved__::operator==' is not defined [-Wundefined-inline]
   44 | inline bool operator==(
      |             ^
main.cpp:44:16: note: used here
   44 |     bool x = l == r;
      |                ^

I think the inline keyword should be removed from the function declaration, or the function definition should be moved into the header file. (Note that the fix should also be applied to operator!=.)

Reproduction

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-W#pragma-messages" // Silence TBB deprecation warning from pxr/base/work/dispatcher.h

#include <iostream>
#include "pxr/usd/usd/stage.h"
#include "pxr/usd/sdf/layer.h"
#include "pxr/base/tf/token.h"
#include "pxr/usd/usdGeom/tokens.h"
#include "pxr/usd/sdf/path.h"
#include "pxr/usd/usd/prim.h"
#include "pxr/usd/usdPhysics/tokens.h"
#include "pxr/usd/usdPhysics/rigidBodyAPI.h"
#include "pxr/imaging/hgi/shaderProgram.h"

#pragma clang diagnostic pop


/// Basic smoke test that the OpenUSD install is usable
void smokeTest() {
    pxr::UsdStageRefPtr mainStage = pxr::UsdStage::CreateNew("main.usda");
    mainStage->DefinePrim(pxr::SdfPath("/hello"), pxr::UsdGeomTokens->Cube);
    mainStage->DefinePrim(pxr::SdfPath("/hello/world"), pxr::UsdGeomTokens->Sphere);
    std::string s;
    mainStage->ExportToString(&s);
    std::cout << s << std::endl;
}

/*
PXR_NAMESPACE_OPEN_SCOPE

bool operator==(
                const HgiShaderProgramDesc& lhs,
                const HgiShaderProgramDesc& rhs)
{
    return lhs.debugName == rhs.debugName &&
           lhs.shaderFunctions == rhs.shaderFunctions;
}

PXR_NAMESPACE_CLOSE_SCOPE
*/

void reproducer(const pxr::HgiShaderProgramDesc& l,
                const pxr::HgiShaderProgramDesc& r) {
    bool x = l == r;
}




int main() {
    smokeTest();
    return 0;
}

and compiled with

set -e

# Vanilla v25.05.01 with --no-python
OPENUSD_INSTALL=/opt/local/OpenUSD_no-python


# Remove stale files
rm -f ./a.out

# Compile
clang++ main.cpp -std=c++17 \
        -I $OPENUSD_INSTALL/include \
        -L $OPENUSD_INSTALL/lib \
        -Xlinker -rpath -Xlinker $OPENUSD_INSTALL/lib \
        -lusd_usd -lusd_sdf -lusd_tf -lusd_usdGeom -lusd_hgi

./a.out

Checklist

• I have created this PR based on the dev branch

• I have followed the coding conventions

• I have added unit tests that exercise this functionality (Reference:
  testing guidelines)

• I have verified that all unit tests pass with the proposed changes

• I have submitted a signed Contributor License Agreement (Reference:
  Contributor License Agreement instructions)

[jesschimein]

Filed as internal issue #USD-11120

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