Initial attempt (gzip -n and preserve post-processed manifest timestamp)reproducible-dist

Turns our this is not enough since tar saves timestamps (as well as owner
information, file order, etc) including for directories and getting rid of
that in a portable way is not going to be easy. Looks like the most plausible
way would be to switch to embedded libarchive (provided it's possible to
achieve everything we need).

3 files changed, 34 insertions, 10 deletions

diff --git a/libbuild2/dist/module.hxx b/libbuild2/dist/module.hxx
index 314dc96..e1af9fc 100644
--- a/libbuild2/dist/module.hxx
+++ b/libbuild2/dist/module.hxx
@@ -59,6 +59,10 @@ namespace build2
       // Note also that in the bootstrap distribution mode only callbacks
       // registered during bootstrap will be called.
       //
+      // If the callback is doing some sort of post-processing, then you may
+      // want to consider preserving the timestamps of the files being
+      // modified in order produce the same archive for the same distribution.
+      //
       using callback_func = void (const path&, const scope&, void*);
 
       void
diff --git a/libbuild2/dist/operation.cxx b/libbuild2/dist/operation.cxx
index 2fa953d..402f34b 100644
--- a/libbuild2/dist/operation.cxx
+++ b/libbuild2/dist/operation.cxx
@@ -719,13 +719,16 @@ namespace build2
         // On Windows we use libarchive's bsdtar with auto-compression (tar
         // itself and quite a few compressors are MSYS executables).
         //
-        const char* l (nullptr); // Compression level (option).
+        // For gzip we also suppress the timestamp with -n to produce the
+        // same archive for the same distribution.
+        //
+        const char* o (nullptr); // Option (compression level, etc).
 
 #ifdef _WIN32
         const char* tar = "bsdtar";
 
         if (e == "tar.gz")
-          l = "--options=compression-level=9";
+          o = "--options=compression-level=9,!timestamp";
 #else
         const char* tar = "tar";
 
@@ -739,9 +742,9 @@ namespace build2
         //
         const char* c (nullptr);
 
-        if      (e == "tar.gz")  { c = "gzip";  l = "-9"; }
-        else if (e == "tar.xz")  { c = "xz";              }
-        else if (e == "tar.bz2") { c = "bzip2";           }
+        if      (e == "tar.gz")  { c = "gzip";  o = "-9n"; }
+        else if (e == "tar.xz")  { c = "xz";               }
+        else if (e == "tar.bz2") { c = "bzip2";            }
 
         if (c != nullptr)
         {
@@ -753,8 +756,8 @@ namespace build2
 
           i = args.size ();
           args.push_back (c);
-          if (l != nullptr)
-            args.push_back (l);
+          if (o != nullptr)
+            args.push_back (o);
           args.push_back (nullptr);
           args.push_back (nullptr); // Pipe end.
 
@@ -784,8 +787,8 @@ namespace build2
                   "--format", "ustar",
                   "-a"};
 
-          if (l != nullptr)
-            args.push_back (l);
+          if (o != nullptr)
+            args.push_back (o);
 
           args.push_back ("-cf");
           args.push_back (ap.string ().c_str ());
diff --git a/libbuild2/version/init.cxx b/libbuild2/version/init.cxx
index ced9c68..88f1080 100644
--- a/libbuild2/version/init.cxx
+++ b/libbuild2/version/init.cxx
@@ -374,7 +374,24 @@ namespace build2
                                      path::temp_path ("manifest"),
                                      m.version));
 
-      mvfile (t.path, f, verb_never);
+
+
+      // Copy the original timestamps in order produce the same archive for
+      // the same distribution.
+      //
+      try
+      {
+        entry_time et (file_time (f));
+
+        mvfile (t.path, f, verb_never);
+
+        file_time (f, et);
+      }
+      catch (const system_error& e)
+      {
+        fail << "unable to get/set timestamp for " << f << ": " << e;
+      }
+
       t.cancel ();
     }