[openwrt/openwrt] build: store SOURCE_DATE_EPOCH in JSON info files

[LEDE Commits]

aparcar pushed a commit to openwrt/openwrt.git, branch openwrt-19.07:
https://git.openwrt.org/524cbcf6f5b07f3d9ee45e445da12760947e232e

commit 524cbcf6f5b07f3d9ee45e445da12760947e232e
Author: Paul Spooren <mail at aparcar.org>
AuthorDate: Sun Nov 1 11:53:39 2020 -1000

    build: store SOURCE_DATE_EPOCH in JSON info files
    
    The source date epoch is the only reproducible date close to the actual
    build date. It can be used for tooling like the firmware wizard to show
    the image age.
    
    Signed-off-by: Paul Spooren <mail at aparcar.org>
    (cherry picked from commit 165f0b00cdd2f763c1d478c2f58c535fc19b13bd)
    [store source_date_epoch as integer]
    Signed-off-by: Paul Spooren <mail at aparcar.org>
---
 include/image.mk               | 1 +
 scripts/json_add_image_info.py | 1 +
 2 files changed, 2 insertions(+)

diff --git a/include/image.mk b/include/image.mk
index ee9885c8f7..1c37d5839f 100644
--- a/include/image.mk
+++ b/include/image.mk
@@ -532,6 +532,7 @@ define Device/Build/image
 	@mkdir -p $$(shell dirname $$@)
 	DEVICE_ID="$(DEVICE_NAME)" \
 	BIN_DIR="$(BIN_DIR)" \
+	SOURCE_DATE_EPOCH=$(SOURCE_DATE_EPOCH) \
 	IMAGE_NAME="$(IMAGE_NAME)" \
 	IMAGE_TYPE=$(word 1,$(subst ., ,$(2))) \
 	IMAGE_FILESYSTEM="$(1)" \
diff --git a/scripts/json_add_image_info.py b/scripts/json_add_image_info.py
index 9a640ad468..23d816916c 100755
--- a/scripts/json_add_image_info.py
+++ b/scripts/json_add_image_info.py
@@ -31,6 +31,7 @@ image_info = {
     "target": "{}/{}".format(getenv("TARGET"), getenv("SUBTARGET")),
     "version_code": getenv("VERSION_CODE"),
     "version_number": getenv("VERSION_NUMBER"),
+    "source_date_epoch": int(getenv("SOURCE_DATE_EPOCH")),
     "profiles": {
         device_id: {
             "image_prefix": getenv("IMAGE_PREFIX"),