cmake: enforce USE_HTTP_PARSER validity

When `-DUSE_HTTP_PARSER=...` is specified, ensure that the specified
HTTP Parser is valid, do not fallback to builtin.

Restore `-DUSE_HTTP_PARSER=system` for backcompatibility.

Author: ethomson

CMakeLists.txt

@@ -34,8 +34,8 @@ option(USE_SSH                 "Enable SSH support. Can be set to a specific bac
 option(USE_HTTPS               "Enable HTTPS support. Can be set to a specific backend" ON)
 option(USE_SHA1                "Enable SHA1. Can be set to CollisionDetection(ON)/HTTPS" ON)
 option(USE_SHA256              "Enable SHA256. Can be set to HTTPS/Builtin" ON)
-option(USE_GSSAPI              "Link with libgssapi for SPNEGO auth"      OFF)
-   set(USE_HTTP_PARSER         "" CACHE STRING "Specifies the HTTP Parser implementation; either system or builtin.")
+option(USE_GSSAPI              "Link with libgssapi for SPNEGO auth"       OFF)
+   set(USE_HTTP_PARSER         "" CACHE STRING "Specifies the HTTP Parser implementation. One of http-parser, llhttp, or builtin. (Defaults to builtin.)")
 #  set(USE_XDIFF               "" CACHE STRING "Specifies the xdiff implementation; either system or builtin.")
    set(REGEX_BACKEND           "" CACHE STRING "Regular expression implementation. One of regcomp_l, pcre2, pcre, regcomp, or builtin.")
 option(USE_BUNDLED_ZLIB        "Use the bundled version of zlib. Can be set to one of Bundled(ON)/Chromium. The Chromium option requires a x86_64 processor with SSE4.2 and CLMUL" OFF)

cmake/FindHTTPParser.cmake cmake/FindHTTP_Parser.cmakecmake/FindHTTPParser.cmake renamed to cmake/FindHTTP_Parser.cmake

@@ -1,6 +1,6 @@
 # Optional external dependency: http-parser
-if(USE_HTTP_PARSER STREQUAL "http-parser")
-	find_package(HTTPParser)
+if(USE_HTTP_PARSER STREQUAL "http-parser" OR USE_HTTP_PARSER STREQUAL "system")
+	find_package(HTTP_Parser)
 
 	if(HTTP_PARSER_FOUND AND HTTP_PARSER_VERSION_MAJOR EQUAL 2)
 		list(APPEND LIBGIT2_SYSTEM_INCLUDES ${HTTP_PARSER_INCLUDE_DIRS})
@@ -23,10 +23,12 @@ elseif(USE_HTTP_PARSER STREQUAL "llhttp")
 	else()
 		message(FATAL_ERROR "llhttp support was requested but not found")
 	endif()
-else()
+elseif(USE_HTTP_PARSER STREQUAL "" OR USE_HTTP_PARSER STREQUAL "builtin")
 	add_subdirectory("${PROJECT_SOURCE_DIR}/deps/llhttp" "${PROJECT_BINARY_DIR}/deps/llhttp")
 	list(APPEND LIBGIT2_DEPENDENCY_INCLUDES "${PROJECT_SOURCE_DIR}/deps/llhttp")
 	list(APPEND LIBGIT2_DEPENDENCY_OBJECTS "$<TARGET_OBJECTS:llhttp>")
 	set(GIT_HTTPPARSER_BUILTIN 1)
 	add_feature_info(http-parser ON "using bundled parser")
+else()
+	message(FATAL_ERROR "unknown http-parser: ${USE_HTTP_PARSER}")
 endif()