Merge pull request #19071 from icecrime/incremental_builds

Enable incremental builds

hack/make.sh

@@ -151,8 +151,17 @@ LDFLAGS_STATIC=''
 EXTLDFLAGS_STATIC='-static'
 # ORIG_BUILDFLAGS is necessary for the cross target which cannot always build
 # with options like -race.
-ORIG_BUILDFLAGS=( -a -tags "autogen netgo static_build sqlite_omit_load_extension $DOCKER_BUILDTAGS" -installsuffix netgo )
+ORIG_BUILDFLAGS=( -tags "autogen netgo static_build sqlite_omit_load_extension $DOCKER_BUILDTAGS" -installsuffix netgo )
 # see https://github.com/golang/go/issues/9369#issuecomment-69864440 for why -installsuffix is necessary here
+
+# When $DOCKER_INCREMENTAL_BINARY is set in the environment, enable incremental
+# builds by installing dependent packages to the GOPATH.
+REBUILD_FLAG="-a"
+if [ "$DOCKER_INCREMENTAL_BINARY" ]; then
+	REBUILD_FLAG="-i"
+fi
+ORIG_BUILDFLAGS+=( $REBUILD_FLAG )
+
 BUILDFLAGS=( $BUILDFLAGS "${ORIG_BUILDFLAGS[@]}" )
 # Test timeout.