Bug #365439: Add set_unless_changed() and unset_unless_changed().

3 files changed, 47 insertions, 5 deletions

diff --git a/bin/ebuild.sh b/bin/ebuild.sh
index c79d4c3d0..e652cb55b 100755
--- a/bin/ebuild.sh
+++ b/bin/ebuild.sh
@@ -1639,6 +1639,34 @@ _ebuild_phase_funcs() {
 	esac
 }
 
+# Set given variable unless this variable has been already set (e.g. during emerge
+# invocation) to a value different than value set in make.conf.
+set_unless_changed() {
+	if [[ $# -ne 2 ]]; then
+		die "${FUNCNAME}() requires 2 arguments: VARIABLE VALUE"
+	fi
+
+	local variable="$1" value="$2"
+
+	if eval "[[ \${${variable}} == \$(env -u ${variable} portageq envvar ${variable}) ]]"; then
+		eval "${variable}=\"${value}\""
+	fi
+}
+
+# Unset given variable unless this variable has been set (e.g. during emerge
+# invocation) to a value different than value set in make.conf.
+unset_unless_changed() {
+	if [[ $# -ne 1 ]]; then
+		die "${FUNCNAME}() requires 1 argument: VARIABLE"
+	fi
+
+	local variable="$1"
+
+	if eval "[[ \${${variable}} == \$(env -u ${variable} portageq envvar ${variable}) ]]"; then
+		unset ${variable}
+	fi
+}
+
 PORTAGE_BASHRCS_SOURCED=0
 
 # @FUNCTION: source_all_bashrcs
diff --git a/bin/isolated-functions.sh b/bin/isolated-functions.sh
index 2f144a084..24443ac1b 100644
--- a/bin/isolated-functions.sh
+++ b/bin/isolated-functions.sh
@@ -585,8 +585,8 @@ save_ebuild_env() {
 			dyn_preinst dyn_help debug-print debug-print-function \
 			debug-print-section inherit EXPORT_FUNCTIONS remove_path_entry \
 			save_ebuild_env filter_readonly_variables preprocess_ebuild_env \
-			source_all_bashrcs ebuild_main \
-			ebuild_phase ebuild_phase_with_hooks \
+			set_unless_changed unset_unless_changed source_all_bashrcs \
+			ebuild_main ebuild_phase ebuild_phase_with_hooks \
 			_ebuild_arg_to_phase _ebuild_phase_funcs default \
 			_pipestatus \
 			${QA_INTERCEPTORS}
diff --git a/man/portage.5 b/man/portage.5
index fc51481d1..a210e8d2d 100644
--- a/man/portage.5
+++ b/man/portage.5
@@ -1,4 +1,4 @@
-.TH "PORTAGE" "5" "Feb 2011" "Portage VERSION" "Portage"
+.TH "PORTAGE" "5" "May 2011" "Portage VERSION" "Portage"
 .SH NAME
 portage \- the heart of Gentoo
 .SH "DESCRIPTION"
@@ -674,8 +674,22 @@ In this directory additional package\-specific bashrc files can be created.
 Note that if package\-specific environment variable settings are all that's
 needed, then \fB/etc/portage/package.env\fR should be used instead of the
 bashrc approach that is described here.
-Portage will source all of them after \fB/etc/portage/bashrc\fR in the following
-order:
+
+set_unless_changed and unset_unless_changed functions can be used to set or
+unset given variables only if these variable have not been set to values
+different than values set in make.conf. This functionality can be useful for
+temporary overriding of these variables during emerge invocation. Variables
+set in the usual VARIABLE=VALUE style will unconditionally override variables
+set during emerge invocation.
+
+.I Syntax:
+.nf
+set_unless_changed VARIABLE VALUE
+unset_unless_changed VALUE
+.fi
+
+Portage will source all of these bashrc files after \fB/etc/portage/bashrc\fR
+in the following order:
 .nr step 1 1
 .IP \n[step]. 3
 /etc/portage/env/${CATEGORY}/${PN}