Honor SOURCE_DATE_EPOCH in bootstrapping

Currently, a stamped bazel binary contains the actual timestamp at build
time. This means, that building bazel we either include no version
information at all, or the binary contains a not reproducible time
stamp. Both are not acceptable from the point of view of a downstream
maintainer of a bazel package, where the requirement is that the package
be reproducible, but the binary still provide sensible version information.
Fortunately, there is a suggested standard to solve this problem taking
the "current time" from the SOURCE_DATE_EPOCH environment variable, if
set, rather than the actual time.
See https://reproducible-builds.org/specs/source-date-epoch/.

Honor this proposed standard, so that bazel can reasonably be packaged
downstream. See issue #2240.

Note that we only use the environment variable in our bootstrap script;
for bazel itself we communicate that information via an appropriate
option.

--
Change-Id: I55409a117285b9a3446421179c20f4e8c59088f8
Reviewed-on: https://cr.bazel.build/9467
PiperOrigin-RevId: 150896326
MOS_MIGRATED_REVID=150896326

1 files changed, 4 insertions, 1 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/analysis/BuildInfo.java b/src/main/java/com/google/devtools/build/lib/analysis/BuildInfo.java
index 681818bfc1..7af9837012 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/BuildInfo.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/BuildInfo.java
@@ -23,7 +23,10 @@ public class BuildInfo {
    * Named constants for the BuildInfo keys.
    */
   public static final String BUILD_EMBED_LABEL = "BUILD_EMBED_LABEL";
-  
+
+  /** Named constant for the reference timestamp to be included. */
+  public static final String SOURCE_DATE_EPOCH = "SOURCE_DATE_EPOCH";
+
   /**
    * The name of the user that performs the build.
    */