Use cmake instead of pkg-config to find packages in dunecontrol

The library pkg-config is used to distinguish if a module is already installed or not. With this information, it gives precedence for the modules to include in case of double definitions.

The issue with pkg-config

• De-facto dependency: The website hints that pkg-config is an optional dependency. However, the reality is that using DUNE without dunecontrol requires you to know how several internal things about DUNE. So, most of our users (specially newcomers), require dunecontrol to use DUNE at all Now, the problem is that dunecontrol depends in pkg-config even though all of our documentations say its optional. I have fallen into this trap several times when creating minimal setups.
• Finds packages the pkg-config way: It tries to find information extracting information from the .pc files. But this is not how the build system in dune works. Our build system is built with cmake, that is to say that if cmake cannot find a package, it doesn't matter how does the .pc file looks like. In other words, that's just a proxy for the real way to find dune modules.

Proposal

Make dune control find packages using cmake and use this to distinguish if a module is installed or not.

lib/dunemodules.lib

@@ -43,6 +43,28 @@ SPACE="$space$formfeed$newline$cr$tab$vtab"
 BLANK="$space$tab"
 NOBLANK="^$space$tab"
 
+cmake_package_exists() {
+  $CMAKE -DMODULE=$1 -P << EOF 2>/dev/null
+  find_package(${MODULE} REQUIRED QUIET)
+EOF
+}
+
+cmake_package_prefix() {
+  prefix="$CMAKE -DMODULE=$1 -P << EOF 2>/dev/null
+find_package(${MODULE} REQUIRED QUIET)
+message(NOTICE ${${MODULE}_PREFIX})
+EOF"
+  echo "$prefix"
+}
+
+cmake_package_version() {
+  version="$CMAKE -DMODULE=$1 -P << EOF 2>/dev/null
+find_package(${MODULE} REQUIRED QUIET)
+message(NOTICE ${${MODULE}_VERSION})
+EOF"
+  echo "$version"
+}
+
 #
 # read parameters from a $CONTROL file
 #
@@ -81,18 +103,18 @@ parse_control() {
   local vers="$($GREP "^[BLANK]*Version:" "$1" | cut -d ':' -f2 | eval $PARSER_TRIM)"
   local main="$($GREP "^[BLANK]*Maintainer:" "$1" | cut -d ':' -f2 | eval $PARSER_TRIM)"
   # check whether the module is installed.
-  # - installed modules can be found via pkg-config
-  # - pkg-config --var=prefix should be the same as $path
+  # - installed modules can be found via cmake
   #
   # the path contains a different sub structure
   # for installed and source modules
   # - installed module: ${path}/lib/dunecontrol/${name}/dune.module
-  #   and there is a file ${path}/lib/pkgconfig/${name}.pc
+  #   configuration file: ${path}/lib*/cmake/${name}/${name}-config.cmake
   # - source module: ${path}/dune.module
-  #   and there is a file ${path}/${name}.pc.in
+  #   source configuration file ${path}/$CMakeLists.txt
   local path="$(canonicalpath "$1")"
-  if pkg-config $name; then
-    local prefix="$(pkg-config --variable=prefix $name)"
+
+  if cmake_package_exists $name; then
+    local prefix="$(cmake_package_prefix $name)"
     local pkgpath=$(canonicalname "$prefix/lib/dunecontrol/$name")
     if test x"$pkgpath" = x"$path"; then
 	  path="$prefix"
@@ -223,8 +245,8 @@ extract_multiarch_pkg_config_path(){
 setup_control_path() {
   if test -z "$DUNE_CONTROL_PATH"; then
     DUNE_CONTROL_PATH=.
-    # try pkg-config locations
-    if ! pkg-config dune-common; then
+    # try to find dune-common
+    if ! cmake_package_exists dune-common; then
       # try usual locations of installed modules
       for i in /usr/local/lib/dunecontrol/ /usr/lib/dunecontrol/; do
         if test -d $i; then
@@ -237,7 +259,7 @@ setup_control_path() {
         fi
       done
     else
-      NEW_DUNE_CONTROL_DIR=$(pkg-config dune-common --variable=prefix)/lib/dunecontrol
+      NEW_DUNE_CONTROL_DIR=$(cmake_package_prefix dune-common)/lib/dunecontrol
       # There might be old version of DUNE lying around, that do not contain
       # lib/dunecontrol, yet. To prevent failur at a later stage of dunecontrol
       # we check that the directory really exists.
@@ -418,12 +440,12 @@ _check_deps()
       _sort_module $dep $depmode
     else
       # perhaps this module is installed,
-      # then it should be handled via pkg-config
-      if ! pkg-config $name; then
+      # then it should be handled as a cmake package
+      if ! cmake_package_exists $name; then
         if test "$requires" == "requires" || test "$DUNE_CONTROL_VERBOSE" == "yes"; then
           echo $'\n'"$report could not find module '$name'," >&2
-          echo "       module is also unknown to pkg-config." >&2
-          echo "       Maybe you need to adjust PKG_CONFIG_PATH!" >&2
+          echo "       module is also unknown to CMake." >&2
+          echo "       Maybe you need to adjust CMAKE_PREFIX_PATH!" >&2
           echo "       '$name' is $required by $modname" >&2
         fi
         if test "x$mode" = "xDEPS"; then
@@ -432,7 +454,7 @@ _check_deps()
           continue
         fi
       else
-        eval ver=$(pkg-config $name --modversion)
+        eval ver=$(cmake_package_version $name)
         if test "$SKIPVERSIONCHECK" != "yes" && ! check_version "$ver" "$depver"; then
           echo $'\n'"$report version mismatch." >&2
           echo "       $modname $requires '$name $depver'," >&2
@@ -445,7 +467,7 @@ _check_deps()
           fi
         fi
         # update module list
-        parse_control $(pkg-config $name --variable=prefix)/lib/dunecontrol/$name/dune.module
+        parse_control $(cmake_package_prefix $name)/lib/dunecontrol/$name/dune.module
         _sort_module $dep $depmode
       fi
     fi