Add conf-root variable to builds

Adding the conf-root variable makes creating out of source builds
slightly easier.

buildstream/data/projectconfig.yaml

@@ -52,6 +52,12 @@ variables:
   # normally staged
   build-root: /buildstream/%{project-name}/%{element-name}
 
+  # now that we have build-root we can define some more helpful
+  # vars for build elements.
+  source-directory: . 
+  source-subdir: .
+  conf-root: "%{source-directory}/%{source-subdir}/"
+
   # Indicates the build installation directory in the sandbox
   install-root: /buildstream-install
 

buildstream/plugins/elements/autotools.yaml

@@ -6,11 +6,11 @@ variables:
     export NOCONFIGURE=1;
 
     if [ -x %{conf-cmd} ]; then true;
-    elif [ -x autogen ]; then ./autogen;
-    elif [ -x autogen.sh ]; then ./autogen.sh;
-    elif [ -x bootstrap ]; then ./bootstrap;
-    elif [ -x bootstrap.sh ]; then ./bootstrap.sh;
-    else autoreconf -ivf;
+    elif [ -x %{conf-root}/autogen ]; then %{conf-root}/./autogen;
+    elif [ -x %{conf-root}/autogen.sh ]; then %{conf-root}/./autogen.sh;
+    elif [ -x %{conf-root}/bootstrap ]; then %{conf-root}/./bootstrap;
+    elif [ -x %{conf-root}/bootstrap.sh ]; then %{conf-root}/./bootstrap.sh;
+    else autoreconf -ivf %{conf-root};
     fi
 
   # Project-wide extra arguments to be passed to `configure`
@@ -22,7 +22,8 @@ variables:
   # For backwards compatibility only, do not use.
   conf-extra: ''
 
-  conf-cmd: ./configure
+  conf-cmd: "%{conf-root}./configure"
+  
   conf-args: |
 
     --prefix=%{prefix} \

buildstream/plugins/elements/cmake.yaml

@@ -23,7 +23,7 @@ variables:
 
   cmake: |
 
-    cmake -B%{build-dir} -H. -G"%{generator}" %{cmake-args}
+    cmake -B%{build-dir} -H"%{conf-root}" -G"%{generator}" %{cmake-args}
 
   make: cmake --build %{build-dir} -- ${JOBS}
   make-install: env DESTDIR="%{install-root}" cmake --build %{build-dir} --target install

tests/format/variables.py

@@ -19,7 +19,7 @@ DATA_DIR = os.path.join(
 @pytest.mark.parametrize("target,varname,expected", [
     ('autotools.bst', 'make-install', "make -j1 DESTDIR=\"/buildstream-install\" install"),
     ('cmake.bst', 'cmake',
-     "cmake -B_builddir -H. -G\"Unix Makefiles\" -DCMAKE_INSTALL_PREFIX:PATH=\"/usr\" \\\n" +
+     "cmake -B_builddir -H\"././\" -G\"Unix Makefiles\" " + "-DCMAKE_INSTALL_PREFIX:PATH=\"/usr\" \\\n" +
      "-DCMAKE_INSTALL_LIBDIR=lib   "),
     ('distutils.bst', 'python-install',
      "python3 setup.py install --prefix \"/usr\" \\\n" +
@@ -45,7 +45,7 @@ def test_defaults(cli, datafiles, tmpdir, target, varname, expected):
 @pytest.mark.parametrize("target,varname,expected", [
     ('autotools.bst', 'make-install', "make -j1 DESTDIR=\"/custom/install/root\" install"),
     ('cmake.bst', 'cmake',
-     "cmake -B_builddir -H. -G\"Ninja\" -DCMAKE_INSTALL_PREFIX:PATH=\"/opt\" \\\n" +
+     "cmake -B_builddir -H\"././\" -G\"Ninja\" " + "-DCMAKE_INSTALL_PREFIX:PATH=\"/opt\" \\\n" +
      "-DCMAKE_INSTALL_LIBDIR=lib   "),
     ('distutils.bst', 'python-install',
      "python3 setup.py install --prefix \"/opt\" \\\n" +