CMake: clean up and improve build procedures

- remove check for unsupported old CMake versions

- do not link to c-ares library twice

- modernize custom Find modules

    - FindLibSSH2:
        - pass version to FPHSA to show it in the output
        - use LIBSSH2_VERSION define to extract the version number in
          one shot. This variable exists in the header for 10 years.
        - remove unneeded code

    - FindNGHTTP2.cmake:
        - drop needless FPHSA argument
        - mark found variables as advanced

    - FindNSS.cmake:
        - show version number

    - FindCARES.cmake:
        - drop default paths
        - use FPHSA instead of checking things by hand

- remove needless explict variable dereference

- simplify count_true()

- allow all policies up to version 3.16 to be set to NEW

- do not rerun check for -Wstrict-aliasing=3 every time

In contrast to every other compiler flag this has a = in it, which CMake
can't have in a variable name.

- only read the interesting strings from curlver.h

Reviewed-by: Peter Wu

Closes https://github.com/curl/curl/pull/4975

1 files changed, 10 insertions, 9 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index b13616fc7..8b6d77542 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -38,7 +38,8 @@
 # To check:
 # (From Daniel Stenberg) The cmake build selected to run gcc with -fPIC on my box while the plain configure script did not.
 # (From Daniel Stenberg) The gcc command line use neither -g nor any -O options. As a developer, I also treasure our configure scripts's --enable-debug option that sets a long range of "picky" compiler options.
-cmake_minimum_required(VERSION 3.0 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.0...3.16 FATAL_ERROR)
+
 set(CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/CMake;${CMAKE_MODULE_PATH}")
 include(Utilities)
 include(Macros)
@@ -49,7 +50,7 @@ project(CURL C)
 
 message(WARNING "the curl cmake build system is poorly maintained. Be aware")
 
-file(READ ${CURL_SOURCE_DIR}/include/curl/curlver.h CURL_VERSION_H_CONTENTS)
+file(STRINGS ${CURL_SOURCE_DIR}/include/curl/curlver.h CURL_VERSION_H_CONTENTS REGEX "#define LIBCURL_VERSION( |_NUM )")
 string(REGEX MATCH "#define LIBCURL_VERSION \"[^\"]*"
   CURL_VERSION ${CURL_VERSION_H_CONTENTS})
 string(REGEX REPLACE "[^\"]+\"" "" CURL_VERSION ${CURL_VERSION})
@@ -104,8 +105,9 @@ if(CMAKE_COMPILER_IS_GNUCC OR CMAKE_COMPILER_IS_CLANG)
     foreach(_CCOPT -pedantic -Wall -W -Wpointer-arith -Wwrite-strings -Wunused -Wshadow -Winline -Wnested-externs -Wmissing-declarations -Wmissing-prototypes -Wno-long-long -Wfloat-equal -Wno-multichar -Wsign-compare -Wundef -Wno-format-nonliteral -Wendif-labels -Wstrict-prototypes -Wdeclaration-after-statement -Wstrict-aliasing=3 -Wcast-align -Wtype-limits -Wold-style-declaration -Wmissing-parameter-type -Wempty-body -Wclobbered -Wignored-qualifiers -Wconversion -Wno-sign-conversion -Wvla -Wdouble-promotion -Wno-system-headers -Wno-pedantic-ms-format)
       # surprisingly, CHECK_C_COMPILER_FLAG needs a new variable to store each new
       # test result in.
-      check_c_compiler_flag(${_CCOPT} OPT${_CCOPT})
-      if(OPT${_CCOPT})
+      string(MAKE_C_IDENTIFIER "OPT${_CCOPT}" _optvarname)
+      check_c_compiler_flag(${_CCOPT} ${_optvarname})
+      if(${_optvarname})
         set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${_CCOPT}")
       endif()
     endforeach()
@@ -134,7 +136,6 @@ if(ENABLE_ARES)
   set(USE_ARES 1)
   find_package(CARES REQUIRED)
   list(APPEND CURL_LIBS ${CARES_LIBRARY})
-  set(CURL_LIBS ${CURL_LIBS} ${CARES_LIBRARY})
 endif()
 
 include(CurlSymbolHiding)
@@ -1229,12 +1230,12 @@ endif()
 
 # Helper to populate a list (_items) with a label when conditions (the remaining
 # args) are satisfied
-function(_add_if label)
-  # TODO need to disable policy CMP0054 (CMake 3.1) to allow this indirection
+macro(_add_if label)
+  # needs to be a macro to allow this indirection
   if(${ARGN})
-    set(_items ${_items} "${label}" PARENT_SCOPE)
+    set(_items ${_items} "${label}")
   endif()
-endfunction()
+endmacro()
 
 # Clear list and try to detect available features
 set(_items)