[Frontend] Recognize environment variable SOURCE_DATE_EPOCH

See https://reproducible-builds.org/docs/source-date-epoch/ . The environment
variable ``SOURCE_DATE_EPOCH`` been recognized by many compilers.

In GCC, if `SOURCE_DATE_EPOCH` is set, it specifies a UNIX timestamp to be used
in replacement of the current date and time in the `__DATE__` and `__TIME__`
macros. Note: GCC as of today does not update `__TIMESTAMP__` (the modification
time of the current source file) but
https://wiki.debian.org/ReproducibleBuilds/TimestampsFromCPPMacros expresses the
intention to update it.

This patches parses SOURCE_DATE_EPOCH and changes all the three macros.

In addition, in case gmtime/localtime returns null (e.g. on 64-bit Windows
gmtime returns null when the timestamp is larger than 32536850399
(3001-01-19T21:59:59Z)), use `??? ?? ????` as used by GCC.

Reviewed By: ychen

Differential Revision: https://reviews.llvm.org/D135045

1 files changed, 17 insertions, 0 deletions

diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 656e595..bcd5359 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -94,7 +94,9 @@
 #include <cassert>
 #include <cstddef>
 #include <cstring>
+#include <ctime>
 #include <fstream>
+#include <limits>
 #include <memory>
 #include <string>
 #include <tuple>
@@ -4307,6 +4309,21 @@ static bool ParsePreprocessorArgs(PreprocessorOptions &Opts, ArgList &Args,
     Opts.addRemappedFile(Split.first, Split.second);
   }
 
+  if (const char *Epoch = std::getenv("SOURCE_DATE_EPOCH")) {
+    // SOURCE_DATE_EPOCH, if specified, must be a non-negative decimal integer.
+    // On time64 systems, pick 253402300799 (the UNIX timestamp of
+    // 9999-12-31T23:59:59Z) as the upper bound.
+    const uint64_t MaxTimestamp =
+        std::min<uint64_t>(std::numeric_limits<time_t>::max(), 253402300799);
+    uint64_t V;
+    if (StringRef(Epoch).getAsInteger(10, V) || V > MaxTimestamp) {
+      Diags.Report(diag::err_fe_invalid_source_date_epoch)
+          << Epoch << MaxTimestamp;
+    } else {
+      Opts.SourceDateEpoch = V;
+    }
+  }
+
   // Always avoid lexing editor placeholders when we're just running the
   // preprocessor as we never want to emit the
   // "editor placeholder in source file" error in PP only mode.