component/golang: support environment variables during build

With this new environment option to gowork section, it is possible
to specify environment variables that will be set during the build,
more specifically when env.sh is sourced.

The implementation is a bit complex, so that the syntax is not strict
and whitespace are tolerated in the definition, ie. all these should be
understood:

    [gowork]
    environment =
      A=a
      B =b
      C= c
      D=d=d

component/golang/buildout.cfg

@@ -103,6 +103,13 @@ environment-extra =
 #   [gowork]
 #   buildflags = -race
 #
+# - If some environment variables are needed during the build, they can be
+#   added with environment option, e.g. this way:
+#
+#   [gowork]
+#   environment =
+#     CGO_ENABLED = 1
+#     FOO = bar
 #
 # Users can also add `install` field to [gowork] to request Go programs to be
 # automatically installed, for example:
@@ -143,6 +150,9 @@ cpkgpath =
 # by default don't `go install` anything
 install =
 
+# empty key=value environment by default
+environment =
+
 # everything is done by dependent parts
 recipe  = plone.recipe.command
 command = :

component/golang/buildout.hash.cfg

@@ -15,4 +15,4 @@
 
 [gowork-env.sh]
 filename = goenv.sh.in
-md5sum = 6efdf5d63381c240c7d206d7939a63f7
+md5sum = f6d0fc24e3f08f27bc2bd85003ca5ec2

component/golang/goenv.sh.in

@@ -2,6 +2,17 @@
 # Usage: env.sh [/path/to/env.sh]
 
 # ---- 8< ---- (buildout substitution here)
+# extend environment
+while read x ; do
+  k=$(echo $x | cut -d '=' -f 1  | sed -e 's/[[:space:]]*$//' )
+  v=$(echo $x | cut -d '=' -f 2- | sed -e 's/^[[:space:]]*//' )
+  if [ -n "$k" ]
+    then export $k="$v"
+  fi
+done <<-EOF
+  ${gowork:environment}
+EOF
+
 # PATH so that go & friends work out of the box
 export PATH=${gowork:golang}/bin:${git:location}/bin:${pkgconfig:location}/bin:${buildout:bin-directory}:${gcc:prefix}/bin:$PATH
 X=${gowork:directory}