cmTimestamp: Support SOURCE_DATE_EPOCH to override current time

See https://reproducible-builds.org/ for why this is good and
https://reproducible-builds.org/specs/source-date-epoch/ for the
definition of this variable.

1 files changed, 11 insertions, 0 deletions

diff --git a/Source/cmTimestamp.cxx b/Source/cmTimestamp.cxx
index 4a97114..1e5ac5b 100644
--- a/Source/cmTimestamp.cxx
+++ b/Source/cmTimestamp.cxx
@@ -5,6 +5,7 @@
 #include <cmConfigure.h>
 #include <cstring>
 #include <sstream>
+#include <stdlib.h>
 
 #include "cmSystemTools.h"
 
@@ -12,6 +13,16 @@ std::string cmTimestamp::CurrentTime(const std::string& formatString,
                                      bool utcFlag)
 {
   time_t currentTimeT = time(CM_NULLPTR);
+  std::string source_date_epoch;
+  cmSystemTools::GetEnv("SOURCE_DATE_EPOCH", source_date_epoch);
+  if (!source_date_epoch.empty()) {
+    std::istringstream iss(source_date_epoch);
+    iss >> currentTimeT;
+    if (iss.fail() || !iss.eof()) {
+      cmSystemTools::Error("Cannot parse SOURCE_DATE_EPOCH as integer");
+      exit(27);
+    }
+  }
   if (currentTimeT == time_t(-1)) {
     return std::string();
   }