From 7d546e52b21c94e1d4f6669d2d4d64f79bff0d7b Mon Sep 17 00:00:00 2001
From: Kai Pastor <dg0yt@darc.de>
Date: Sat, 9 May 2026 07:23:37 +0200
Subject: [PATCH] cmake: export/forward `NGTCP2_CRYPTO_BACKEND`

Exporting the component name as passed in is somewhat boring. OTOH it is
convenient for reuse.

- FindNGTCP2: export crypto backend in `NGTCP2_CRYPTO_BACKEND`.
- pass `COMPONENTS` `NGTCP2_CRYPTO_BACKEND` in `curl-config.cmake`.
- FindNGTCP2: fix to skip Config detection when optional `COMPONENTS` is
  not passed.

Co-authored-by: Viktor Szakats
Reported-by: x-xiang on github
Fixes #21523
Follow-up to 8fce3e17e6cb310cd6dbe38ff14869b8fe5827d2 #20814

Closes #21540
---
 CMake/FindNGTCP2.cmake     | 21 +++++++++++----------
 CMake/curl-config.in.cmake |  2 +-
 CMakeLists.txt             |  2 +-
 3 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/CMake/FindNGTCP2.cmake b/CMake/FindNGTCP2.cmake
index 70dae14b86..bf2f488777 100644
--- a/CMake/FindNGTCP2.cmake
+++ b/CMake/FindNGTCP2.cmake
@@ -49,27 +49,28 @@
 #
 # - `NGTCP2_FOUND`:                     System has ngtcp2.
 # - `NGTCP2_VERSION`:                   Version of ngtcp2.
+# - `NGTCP2_CRYPTO_BACKEND`:            Name of the crypto library component. (Empty if COMPONENTS was not used.)
 # - `CURL::ngtcp2`:                     ngtcp2 library target.
 
+set(NGTCP2_CRYPTO_BACKEND "")
 if(NGTCP2_FIND_COMPONENTS)
-  set(_ngtcp2_crypto_backend "")
   foreach(_component IN LISTS NGTCP2_FIND_COMPONENTS)
     if(_component MATCHES "^(BoringSSL|GnuTLS|LibreSSL|ossl|quictls|wolfSSL)")
-      if(_ngtcp2_crypto_backend)
+      if(NGTCP2_CRYPTO_BACKEND)
         message(FATAL_ERROR "NGTCP2: Only one crypto library can be selected")
       endif()
-      set(_ngtcp2_crypto_backend ${_component})
+      set(NGTCP2_CRYPTO_BACKEND ${_component})
     endif()
   endforeach()
 
-  if(_ngtcp2_crypto_backend)
-    string(TOLOWER "ngtcp2_crypto_${_ngtcp2_crypto_backend}" _crypto_library_lower)
-    string(TOUPPER "ngtcp2_crypto_${_ngtcp2_crypto_backend}" _crypto_library_upper)
+  if(NGTCP2_CRYPTO_BACKEND)
+    string(TOLOWER "ngtcp2_crypto_${NGTCP2_CRYPTO_BACKEND}" _crypto_library_lower)
+    string(TOUPPER "ngtcp2_crypto_${NGTCP2_CRYPTO_BACKEND}" _crypto_library_upper)
   endif()
 endif()
 
 set(_ngtcp2_pc_requires "libngtcp2")
-if(_ngtcp2_crypto_backend)
+if(NGTCP2_CRYPTO_BACKEND)
   list(APPEND _ngtcp2_pc_requires "lib${_crypto_library_lower}")
 endif()
 
@@ -81,7 +82,7 @@ if(NOT DEFINED NGTCP2_INCLUDE_DIR AND
     pkg_check_modules(_ngtcp2 ${_ngtcp2_pc_requires})
     set(_tried_pkgconfig TRUE)
   endif()
-  if(NOT _ngtcp2_FOUND AND CURL_USE_CMAKECONFIG)
+  if(NOT _ngtcp2_FOUND AND CURL_USE_CMAKECONFIG AND NGTCP2_CRYPTO_BACKEND)
     find_package(ngtcp2 CONFIG QUIET)
     # Skip using it if the crypto library target is not available
     if(ngtcp2_CONFIG AND
@@ -130,7 +131,7 @@ else()
     unset(_version_str)
   endif()
 
-  if(_ngtcp2_crypto_backend)
+  if(NGTCP2_CRYPTO_BACKEND)
     if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.20)
       cmake_path(GET NGTCP2_LIBRARY PARENT_PATH _ngtcp2_library_dir)
     else()
@@ -145,7 +146,7 @@ else()
     endif()
 
     if(${_crypto_library_upper}_LIBRARY)
-      set(NGTCP2_${_ngtcp2_crypto_backend}_FOUND TRUE)
+      set(NGTCP2_${NGTCP2_CRYPTO_BACKEND}_FOUND TRUE)
       set(NGTCP2_CRYPTO_LIBRARY ${${_crypto_library_upper}_LIBRARY})
     endif()
   endif()
diff --git a/CMake/curl-config.in.cmake b/CMake/curl-config.in.cmake
index 317477197f..1c0eec36ed 100644
--- a/CMake/curl-config.in.cmake
+++ b/CMake/curl-config.in.cmake
@@ -122,7 +122,7 @@ if("@USE_NGHTTP3@")
   list(APPEND _curl_libs CURL::nghttp3)
 endif()
 if("@USE_NGTCP2@")
-  find_dependency(NGTCP2 MODULE)
+  find_dependency(NGTCP2 MODULE COMPONENTS @NGTCP2_CRYPTO_BACKEND@)
   list(APPEND _curl_libs CURL::ngtcp2)
 endif()
 if("@USE_GNUTLS@")
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 506dfeb305..f8d7a0b86e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -2374,7 +2374,7 @@ if(NOT CURL_DISABLE_INSTALL)
   #   USE_MBEDTLS
   #   USE_NGHTTP2
   #   USE_NGHTTP3
-  #   USE_NGTCP2
+  #   USE_NGTCP2 NGTCP2_CRYPTO_BACKEND
   #   USE_OPENSSL OPENSSL_VERSION_MAJOR
   #   USE_QUICHE
   #   USE_RUSTLS