tests: Ensure vk_enum_string_helper.h is C compatible

Added ifdef checks for backcompat

Intended to properly address these issue(s):
- https://github.com/KhronosGroup/Vulkan-ValidationLayers/issues/3233
- https://github.com/KhronosGroup/Vulkan-ValidationLayers/issues/1211

scripts/generators/enum_string_helper_generator.py

@@ -27,7 +27,9 @@ class EnumStringHelperOutputGenerator(BaseGenerator):
 
         out.append('''
 #pragma once
+#ifdef __cplusplus
 #include <string>
+#endif
 #include <vulkan/vulkan.h>
 ''')
 
@@ -53,8 +55,16 @@ class EnumStringHelperOutputGenerator(BaseGenerator):
         # If there are no flags (empty bitmask) ignore
         for bitmask in [x for x in self.vk.bitmasks.values() if len(x.flags) > 0]:
             groupType = bitmask.name if bitmask.bitWidth == 32 else 'uint64_t'
+
+            # switch labels must be constant expressions. In C a const-qualified variable is not a constant expression.
+            use_switch_statement = True
+            if groupType == 'uint64_t':
+                use_switch_statement = False
+
             out.extend([f'#ifdef {bitmask.protect}\n'] if bitmask.protect else [])
             out.append(f'static inline const char* string_{bitmask.name}({groupType} input_value) {{\n')
+
+            if use_switch_statement:
                 out.append('    switch (input_value) {\n')
                 for flag in [x for x in bitmask.flags if not x.multiBit]:
                     out.extend([f'#ifdef {flag.protect}\n'] if flag.protect else [])
@@ -64,6 +74,14 @@ class EnumStringHelperOutputGenerator(BaseGenerator):
                 out.append('        default:\n')
                 out.append(f'            return "Unhandled {bitmask.name}";\n')
                 out.append('    }\n')
+            else:
+                # We need to use if statements
+                for flag in [x for x in bitmask.flags if not x.multiBit]:
+                    out.extend([f'#ifdef {flag.protect}\n'] if flag.protect else [])
+                    out.append(f'    if (input_value == {flag.name}) return "{flag.name}";\n')
+                    out.extend([f'#endif //{flag.protect}\n'] if flag.protect else [])
+                out.append(f'    return "Unhandled {bitmask.name}";\n')
+            
             out.append('}\n')
 
             mulitBitChecks = ''
@@ -71,6 +89,7 @@ class EnumStringHelperOutputGenerator(BaseGenerator):
                 mulitBitChecks += f'    if (input_value == {flag.name}) {{ return "{flag.name}"; }}\n'
             intSuffix = 'U' if bitmask.bitWidth == 32 else 'ULL'
 
+            out.append('\n#ifdef __cplusplus')
             out.append(f'''
 static inline std::string string_{bitmask.flagName}({bitmask.flagName} input_value) {{
 {mulitBitChecks}    std::string ret;
@@ -87,6 +106,7 @@ static inline std::string string_{bitmask.flagName}({bitmask.flagName} input_val
     return ret;
 }}\n''')
             out.extend([f'#endif //{bitmask.protect}\n'] if bitmask.protect else [])
+            out.append('#endif // __cplusplus\n')
 
         out.append('// NOLINTEND') # Wrap for clang-tidy to ignore
         self.write("".join(out))

tests/add_subdirectory/CMakeLists.txt

@@ -9,10 +9,13 @@ project(TEST_ADD_SUBDIRECTORY LANGUAGES C)
 
 add_library(add_subdirectory_example STATIC)
 
-# Test c99 support as well as find_package support
+# Test c99 support
 target_compile_features(add_subdirectory_example PRIVATE c_std_99)
 
-target_sources(add_subdirectory_example PRIVATE client.c)
+target_sources(add_subdirectory_example PRIVATE
+    client.c
+    vk_enum_string_helper.c
+)
 
 # NOTE: Because VulkanHeaders is a PUBLIC dependency it needs to be found prior to VulkanUtilityLibraries
 add_subdirectory(${GITHUB_VULKAN_HEADER_SOURCE_DIR} ${PROJECT_BINARY_DIR}/headers)

tests/add_subdirectory/vk_enum_string_helper.c

@@ -0,0 +1,14 @@
+// Copyright 2023 The Khronos Group Inc.
+// Copyright 2023 Valve Corporation
+// Copyright 2023 LunarG, Inc.
+//
+// SPDX-License-Identifier: Apache-2.0
+#include <vulkan/vk_enum_string_helper.h>
+
+// Ensure vk_enum_string_helper.h can be compiled with a C compiler
+const char* foobar() { return string_VkResult(VK_SUCCESS); }
+
+// Ensure string_VkPipelineStageFlagBits2 is callable by C users
+const char* vk_format_feature_2_sampled_image_bit() {
+    return string_VkPipelineStageFlagBits2(VK_FORMAT_FEATURE_2_SAMPLED_IMAGE_BIT);
+}

tests/find_package/CMakeLists.txt

@@ -14,6 +14,7 @@ target_compile_features(find_package_example PRIVATE c_std_99)
 
 target_sources(find_package_example PRIVATE
     ${CMAKE_CURRENT_LIST_DIR}/../add_subdirectory/client.c
+    ${CMAKE_CURRENT_LIST_DIR}/../add_subdirectory/vk_enum_string_helper.c
 )
 
 # NOTE: Because VulkanHeaders is a PUBLIC dependency it needs to be found prior to VulkanUtilityLibraries

tests/generated/vk_enum_string_helper.cpp

@@ -74,3 +74,12 @@ TEST(vk_enum_string_helper, string_VkFormat) {
         EXPECT_STREQ(magic_str.data(), str);
     }
 }
+
+// string_VkPipelineStageFlagBits2 can't use a switch statement due to C not treating const-qualified variables as constant
+// expressions. As a result test the codegen for this function explicitly.
+TEST(vk_enum_string_helper, string_VkFormatFeatureFlagBits2) {
+    EXPECT_STREQ(string_VkFormatFeatureFlagBits2(VK_FORMAT_FEATURE_2_SAMPLED_IMAGE_BIT), "VK_FORMAT_FEATURE_2_SAMPLED_IMAGE_BIT");
+    EXPECT_STREQ(string_VkFormatFeatureFlagBits2(VK_FORMAT_FEATURE_2_STORAGE_IMAGE_BIT), "VK_FORMAT_FEATURE_2_STORAGE_IMAGE_BIT");
+    EXPECT_STREQ(string_VkFormatFeatureFlagBits2(VK_FORMAT_FEATURE_2_VERTEX_BUFFER_BIT), "VK_FORMAT_FEATURE_2_VERTEX_BUFFER_BIT");
+    EXPECT_STREQ(string_VkFormatFeatureFlagBits2(3), "Unhandled VkFormatFeatureFlagBits2");
+}