[NFC] Integrate clang-format to hctgen (#5732)

This integrates formatting generated sources with clang-format with the
hctgen generation process.

This change makes a few small adjustments to how the build-time header
generation works. This change, disables automated build-time generation
for C++ sources if you don't have clang-format available on your system.

CMake can automatically detect clang-format installed as part of Visual
Studio, or based on your PATH. You can also explicitly set
`CLANG_FORMAT_EXE` when configuring to manually override. **Developers
on macOS** will need to install clang-format manually and place it on
their path to generate DXC's generated sources.

If clang-format cannot be found and `HLSL_COPY_GENERATED_SOURCES` is On
a fatal error will be reported at configuration time.

This change _does not_ make clang-format a requirement to build DXC, but
it does make it a requirement if you are modifying the generated
sources.

cmake/modules/HCT.cmake

@@ -2,6 +2,15 @@ option(HLSL_COPY_GENERATED_SOURCES "Copy generated sources if different" Off)
 
 add_custom_target(HCTGen)
 
+find_program(CLANG_FORMAT_EXE NAMES clang-format)
+
+if (NOT CLANG_FORMAT_EXE)
+  message(WARNING "Clang-format is not available. Generating included sources is not supported.")
+  if (HLSL_COPY_GENERATED_SOURCES)
+    message(FATAL_ERROR "Generating sources requires clang-format")
+  endif ()
+endif ()
+
 if (WIN32 AND NOT DEFINED HLSL_AUTOCRLF)
   find_program(git_executable NAMES git git.exe git.cmd)
   execute_process(COMMAND ${git_executable} config --get core.autocrlf
@@ -49,6 +58,12 @@ function(add_hlsl_hctgen mode)
                        ${hctdb}
                        ${hctdb_helper})
 
+  get_filename_component(output_extension ${full_output} LAST_EXT)
+
+  if (CLANG_FORMAT_EXE AND output_extension MATCHES "\.h|\.cpp|\.inl")
+    set(format_cmd COMMAND ${CLANG_FORMAT_EXE} -i ${temp_output})
+  endif ()
+
   set(copy_sources Off)
   if(ARG_BUILD_DIR OR HLSL_COPY_GENERATED_SOURCES)
     set(copy_sources On)
@@ -77,7 +92,9 @@ function(add_hlsl_hctgen mode)
   # file, and define the verification command
   if(NOT copy_sources)
     set(output ${temp_output})
-    set(verification COMMAND ${CMAKE_COMMAND} -E compare_files ${temp_output} ${full_output})
+    if (CLANG_FORMAT_EXE) # Only verify sources if clang-format is available.
+      set(verification COMMAND ${CMAKE_COMMAND} -E compare_files ${temp_output} ${full_output})
+    endif()
   endif()
   if(WIN32 AND NOT HLSL_AUTOCRLF)
     set(force_lf "--force-lf")
@@ -87,6 +104,7 @@ function(add_hlsl_hctgen mode)
                      COMMAND ${PYTHON_EXECUTABLE}
                              ${hctgen} ${force_lf}
                              ${mode} --output ${temp_output} ${input_flag}
+                     ${format_cmd}
                      COMMENT "Building ${ARG_OUTPUT}..."
                      DEPENDS ${hct_dependencies}
                      )