Bug#912299: blender: make the build reproducible

[Nicholas M Gregory]

Source: blender
Version: 2.79.b+dfsg0-4
Severity: wishlist
Tags: patch
X-Debbugs-Cc: reproducible-builds at lists.alioth.debian.org

Hi there,

While working on the reproducible builds project
(https://wiki.debian.org/ReproducibleBuilds), we noticed that blender
could not be built reproducibly.

The attached patch changes the build system to use the
SOURCE_DATE_EPOCH envvar (if set) in place of the current build
date/time to make blender build reproducibly.

Best,
-Nick Gregory

================ begin patch ================
diff --git a/build_files/cmake/buildinfo.cmake
b/build_files/cmake/buildinfo.cmake
index a43b99f..ab7d3e3 100644
--- a/build_files/cmake/buildinfo.cmake
+++ b/build_files/cmake/buildinfo.cmake
@@ -148,12 +148,21 @@ endif()
 # BUILD_PLATFORM and BUILD_PLATFORM are taken from CMake
 # but BUILD_DATE and BUILD_TIME are platform dependent
 if(UNIX)
-       if(NOT BUILD_DATE)
-               execute_process(COMMAND date "+%Y-%m-%d"
OUTPUT_VARIABLE BUILD_DATE OUTPUT_STRIP_TRAILING_WHITESPACE)
-       endif()
-       if(NOT BUILD_TIME)
-               execute_process(COMMAND date "+%H:%M:%S"
OUTPUT_VARIABLE BUILD_TIME OUTPUT_STRIP_TRAILING_WHITESPACE)
-       endif()
+    if(DEFINED ENV{SOURCE_DATE_EPOCH})
+        execute_process(COMMAND "date" "-u" "-d"
"@$ENV{SOURCE_DATE_EPOCH}" "+%Y-%m-%d"
+                        OUTPUT_VARIABLE BUILD_DATE
+                        OUTPUT_STRIP_TRAILING_WHITESPACE)
+        execute_process(COMMAND "date" "-u" "-d"
"@$ENV{SOURCE_DATE_EPOCH}" "+%H:%M:%S"
+                        OUTPUT_VARIABLE BUILD_TIME
+                        OUTPUT_STRIP_TRAILING_WHITESPACE)
+    else()
+        if(NOT BUILD_DATE)
+            execute_process(COMMAND date "+%Y-%m-%d" OUTPUT_VARIABLE
BUILD_DATE OUTPUT_STRIP_TRAILING_WHITESPACE)
+        endif()
+        if(NOT BUILD_TIME)
+            execute_process(COMMAND date "+%H:%M:%S" OUTPUT_VARIABLE
BUILD_TIME OUTPUT_STRIP_TRAILING_WHITESPACE)
+        endif()
+    endif()
 elseif(WIN32)
        if(NOT BUILD_DATE)
                execute_process(COMMAND cmd /c date /t OUTPUT_VARIABLE
BUILD_DATE OUTPUT_STRIP_TRAILING_WHITESPACE)