Dont require llvm for building generators (#4895)

* Dont require llvm for building generators

* Fetch slang-llvm.so from correct release (#4847)

* Fetch slang-llvm.so from correct release

Closes https://github.com/shader-slang/slang/issues/4648
Should close https://github.com/shader-slang/slang/issues/4812

* Update docs

* Correct documentation on cmake option

* Neaten cmake script

* Fix fetching on windows

---------

Co-authored-by: Yong He <yonghe@outlook.com>

* Be a bit more careful dealing with release list fetching failure

* clarify error messages

---------

Co-authored-by: Yong He <yonghe@outlook.com>

1 files changed, 100 insertions, 0 deletions

diff --git a/cmake/GitHubRelease.cmake b/cmake/GitHubRelease.cmake
new file mode 100644
index 000000000..e63fb7885
--- /dev/null
+++ b/cmake/GitHubRelease.cmake
@@ -0,0 +1,100 @@
+function(check_release_and_get_latest owner repo version os arch out_var)
+    # Construct the URL for the specified version's release API endpoint
+    set(version_url "https://api.github.com/repos/${owner}/${repo}/releases/tags/v${version}")
+
+    set(json_output_file "${CMAKE_CURRENT_BINARY_DIR}/${owner}_${repo}_release_info.json")
+
+    function(check_assets_for_file json_content filename found_var)
+        string(JSON asset_count LENGTH "${json_content}" "assets")
+        set(found "FALSE")
+        foreach(i RANGE 0 ${asset_count})
+            string(JSON asset_name GET "${json_content}" "assets" ${i} "name")
+            if("${asset_name}" STREQUAL "${filename}")
+                set(found "TRUE")
+                break()
+            endif()
+        endforeach()
+        set(${found_var} "${found}" PARENT_SCOPE)
+    endfunction()
+
+    # Download the specified release info from GitHub
+    file(DOWNLOAD "${version_url}" "${json_output_file}" STATUS download_statuses)
+    list(GET download_statuses 0 status_code)
+    if(status_code EQUAL 0)
+        file(READ "${json_output_file}" json_content)
+
+        # Check if the specified version contains the expected ZIP file
+        set(desired_zip "${repo}-${version}-${os}-${arch}.zip")
+        check_assets_for_file("${json_content}" "${desired_zip}" file_found)
+
+        if(file_found)
+            set(${out_var} "${version}" PARENT_SCOPE)
+            return()
+        endif()
+        message(WARNING "Failed to find ${desired_zip} in release assets for ${version} from ${version_url}\nFalling back to latest version if it differs")
+    else()
+        message(WARNING "Failed to download release info for version ${version} from ${version_url}\nFalling back to latest version if it differs")
+    endif()
+
+
+    # If not found, get the latest release tag
+    set(latest_release_url "https://api.github.com/repos/${owner}/${repo}/releases/latest")
+    file(DOWNLOAD "${latest_release_url}" "${json_output_file}" STATUS download_status)
+    list(GET download_status 0 status_code)
+    if(NOT status_code EQUAL 0)
+        message(WARNING "Failed to download latest release info from ${latest_release_url}")
+        return()
+    endif()
+
+    # Get the tag from this release json file
+    file(READ "${json_output_file}" latest_json_content)
+    string(JSON latest_release_tag GET "${latest_json_content}" "tag_name")
+    string(REGEX REPLACE "^v" "" latest_version "${latest_release_tag}")
+
+    if(latest_version EQUAL version)
+        # The versions are the same
+        message(WARNING "No release binary for ${os}-${arch} exists for ${version}")
+        return()
+    endif()
+
+    # Check if the expected ZIP file is in the latest release
+    set(desired_zip "${repo}-${latest_version}-${os}-${arch}.zip")
+    check_assets_for_file("${latest_json_content}" "${desired_zip}" file_found_latest)
+
+    if(file_found_latest)
+        # If we got it, we found a good version
+        set(${out_var} "${latest_version}" PARENT_SCOPE)
+    else()
+        message(WARNING "No release binary for ${os}-${arch} exists for ${version} or the latest version ${latest_version}")
+    endif()
+endfunction()
+
+function(get_best_slang_binary_release_url out_var)
+    if(CMAKE_SYSTEM_PROCESSOR MATCHES "x86_64|amd64|AMD64")
+        set(arch "x86_64")
+    elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "aarch64|ARM64|arm64")
+        set(arch "aarch64")
+    else()
+        message(WARNING "Unsupported architecture for slang binary releases: ${CMAKE_SYSTEM_PROCESSOR}")
+        return()
+    endif()
+
+    if(CMAKE_SYSTEM_NAME STREQUAL "Windows")
+        set(os "windows")
+    elseif(CMAKE_SYSTEM_NAME STREQUAL "Darwin")
+        set(os "macos")
+    elseif(CMAKE_SYSTEM_NAME STREQUAL "Linux")
+        set(os "linux")
+    else()
+        message(WARNING "Unsupported operating system for slang binary releases: ${CMAKE_SYSTEM_NAME}")
+        return()
+    endif()
+
+    set(owner "shader-slang")
+    set(repo "slang")
+
+    check_release_and_get_latest(${owner} ${repo} ${SLANG_VERSION_NUMERIC} ${os} ${arch} release_version)
+    if(DEFINED release_version)
+      set(${out_var} "https://github.com/${owner}/${repo}/releases/download/v${release_version}/slang-${release_version}-${os}-${arch}.zip" PARENT_SCOPE)
+    endif()
+endfunction()