Fix SLANG_USE_SYSTEM_SPIRV_HEADERS (#7371)

* Use aliased SPIRV-Headers::SPIRV-Headers to also work with an installed SPIRV-Headers

SPIRV-Headers standalone is only defined when using sources directly.
When consuming an installed SPIRV-Headers via find_package, the full SPIRV-Headers::SPIRV-Headers must be used.

The full syntax is supported by both source and installed builds.

* Fix SLANG_USE_SYSTEM_SPIRV_HEADERS

- Use find_package to bring in SPIRV-Headers cmake targets
- Set SPIRV-Headers_SOURCE_DIR as a workaround when including
  spirv-tools
- Query cmake for SLANG_SPIRV_HEADERS_INCLUDE_DIR location, supporting
  default, SLANG_OVERRIDE_SPIRV_HEADERS_PATH and find_package builds.
- Cleanup unnecessary SPIRV_HEADER_DIR (unconditionally overwritten in
  spirv-tools)

3 files changed, 5 insertions, 15 deletions

diff --git a/source/compiler-core/CMakeLists.txt b/source/compiler-core/CMakeLists.txt
index d3a88fddd..1873b21d4 100644
--- a/source/compiler-core/CMakeLists.txt
+++ b/source/compiler-core/CMakeLists.txt
@@ -5,7 +5,7 @@ slang_add_target(
     EXCLUDE_FROM_ALL
     USE_EXTRA_WARNINGS
     LINK_WITH_PRIVATE core
-    INCLUDE_FROM_PUBLIC SPIRV-Headers
+    INCLUDE_FROM_PUBLIC SPIRV-Headers::SPIRV-Headers
 )
 if(NOT MSVC)
     # This is necessary to compile the DXC headers
diff --git a/source/slang-core-module/CMakeLists.txt b/source/slang-core-module/CMakeLists.txt
index 600190161..d7f29be0a 100644
--- a/source/slang-core-module/CMakeLists.txt
+++ b/source/slang-core-module/CMakeLists.txt
@@ -61,7 +61,7 @@ set(core_module_source_common_args
     core
     slang-capability-defs
     slang-fiddle-output
-    SPIRV-Headers
+    SPIRV-Headers::SPIRV-Headers
     INCLUDE_DIRECTORIES_PRIVATE
     ../slang
     ${core_module_meta_output_dir}
diff --git a/source/slang/CMakeLists.txt b/source/slang/CMakeLists.txt
index 9ebf6b2bd..6c9b9c0b3 100644
--- a/source/slang/CMakeLists.txt
+++ b/source/slang/CMakeLists.txt
@@ -100,17 +100,7 @@ slang_add_target(
 # generated lookup tables
 #
 
-if(NOT SLANG_USE_SYSTEM_SPIRV_HEADERS)
-    if(NOT SLANG_OVERRIDE_SPIRV_HEADERS_PATH)
-        set(SLANG_SPIRV_HEADERS_INCLUDE_DIR
-            "${slang_SOURCE_DIR}/external/spirv-headers/include"
-        )
-    else()
-        set(SLANG_SPIRV_HEADERS_INCLUDE_DIR
-            "${SLANG_OVERRIDE_SPIRV_HEADERS_PATH}/spirv-headers/include"
-        )
-    endif()
-endif()
+get_target_property(SLANG_SPIRV_HEADERS_INCLUDE_DIR SPIRV-Headers::SPIRV-Headers INTERFACE_INCLUDE_DIRECTORIES)
 
 set(SLANG_LOOKUP_GENERATOR_INPUT_JSON
     "${SLANG_SPIRV_HEADERS_INCLUDE_DIR}/spirv/unified1/extinst.glsl.std.450.grammar.json"
@@ -164,7 +154,7 @@ slang_add_target(
         ${SLANG_LOOKUP_GENERATED_SOURCE}
         ${SLANG_SPIRV_CORE_GRAMMAR_SOURCE}
     EXPORT_TYPE_AS ${SLANG_LIB_TYPE}
-    LINK_WITH_PRIVATE core SPIRV-Headers
+    LINK_WITH_PRIVATE core SPIRV-Headers::SPIRV-Headers
     EXCLUDE_FROM_ALL
     FOLDER generated
 )
@@ -226,7 +216,7 @@ set(slang_link_args
     slang-capability-lookup
     slang-fiddle-output
     slang-lookup-tables
-    SPIRV-Headers
+    SPIRV-Headers::SPIRV-Headers
 )
 set(slang_interface_args INCLUDE_DIRECTORIES_PUBLIC ${slang_SOURCE_DIR}/include)
 set(slang_public_lib_args