gnu: python-2: Honor 'SOURCE_DATE_EPOCH'.

* gnu/packages/patches/python-2.7-source-date-epoch.patch: New file.
* gnu/packages/python.scm (python-2)[source]: Use it.
  [arguments]: Set SOURCE_DATE_EPOCH in 'patch-lib-shells' phase.
* guix/build/python-build-system.scm (set-SOURCE-DATE-EPOCH): New
  procedure.
  (%standard-phases): Add it.
* gnu-system.am (dist_patch_DATA): Add patch.

4 files changed, 49 insertions, 1 deletions

diff --git a/gnu-system.am b/gnu-system.am
index 1fdbd00731..c7a17a42e9 100644
--- a/gnu-system.am
+++ b/gnu-system.am
@@ -670,6 +670,7 @@ dist_patch_DATA =						\
   gnu/packages/patches/pybugz-stty.patch			\
   gnu/packages/patches/pyqt-configure.patch			\
   gnu/packages/patches/python-2.7-search-paths.patch		\
+  gnu/packages/patches/python-2.7-source-date-epoch.patch	\
   gnu/packages/patches/python-3-search-paths.patch		\
   gnu/packages/patches/python-disable-ssl-test.patch		\
   gnu/packages/patches/python-fix-tests.patch			\
diff --git a/gnu/packages/patches/python-2.7-source-date-epoch.patch b/gnu/packages/patches/python-2.7-source-date-epoch.patch
new file mode 100644
index 0000000000..be1f8e010e
--- /dev/null
+++ b/gnu/packages/patches/python-2.7-source-date-epoch.patch
@@ -0,0 +1,33 @@
+Honor the 'SOURCE_DATE_EPOCH' environment variable to allow for
+determinitic builds.
+
+--- a/Lib/py_compile.py
++++ b/Lib/py_compile.py
+@@ -105,7 +105,10 @@ def compile(file, cfile=None, dfile=None, doraise=False):
+     """
+     with open(file, 'U') as f:
+         try:
+-            timestamp = long(os.fstat(f.fileno()).st_mtime)
++            if 'SOURCE_DATE_EPOCH' in os.environ:
++                timestamp = long(os.environ['SOURCE_DATE_EPOCH'])
++            else:
++                timestamp = long(os.fstat(f.fileno()).st_mtime)
+         except AttributeError:
+             timestamp = long(os.stat(file).st_mtime)
+         codestring = f.read()
+diff --git a/Python/import.c b/Python/import.c
+index e47ce63..7eecf9c 100644
+--- a/Python/import.c
++++ b/Python/import.c
+@@ -945,6 +945,11 @@ write_compiled_module(PyCodeObject *co, char *cpathname, struct stat *srcstat, t
+     /* Now write the true mtime (as a 32-bit field) */
+     fseek(fp, 4L, 0);
+     assert(mtime <= 0xFFFFFFFF);
++    if (Py_GETENV("SOURCE_DATE_EPOCH") != NULL) {
++	const char *epoch = Py_GETENV("SOURCE_DATE_EPOCH");
++	mtime = atoi(epoch);
++    }
++
+     PyMarshal_WriteLongToFile((long)mtime, fp, Py_MARSHAL_VERSION);
+     fflush(fp);
+     fclose(fp);
diff --git a/gnu/packages/python.scm b/gnu/packages/python.scm
index 001d00e9be..07725c727a 100644
--- a/gnu/packages/python.scm
+++ b/gnu/packages/python.scm
@@ -92,7 +92,9 @@
       (sha256
        (base32
         "1h7zbrf9pkj29hlm18b10548ch9757f75m64l47sy75rh43p7lqw"))
-      (patches (list (search-patch "python-2.7-search-paths.patch")))))
+      (patches (map search-patch
+                    '("python-2.7-search-paths.patch"
+                      "python-2.7-source-date-epoch.patch")))))
     (build-system gnu-build-system)
     (arguments
      `(#:tests? #f
@@ -158,6 +160,11 @@
                                     "Lib/distutils/tests/test_spawn.py"
                                     "Lib/test/test_subprocess.py"))
                (("/bin/sh") (which "sh")))
+
+             ;; Use zero as the timestamp in .pyc files so that builds are
+             ;; deterministic.  TODO: Remove it when this variable is set in
+             ;; gnu-build-system.scm.
+             (setenv "SOURCE_DATE_EPOCH" "0")
              #t))
           (add-before
            'check 'pre-check
diff --git a/guix/build/python-build-system.scm b/guix/build/python-build-system.scm
index 1ae42c00b4..6775cc4396 100644
--- a/guix/build/python-build-system.scm
+++ b/guix/build/python-build-system.scm
@@ -136,11 +136,18 @@ installed with setuptools."
                #t))
     #t))
 
+(define* (set-SOURCE-DATE-EPOCH #:rest _)
+  "Set the 'SOURCE_DATE_EPOCH' environment variable."
+  ;; Use zero as the timestamp in .pyc files so that builds are deterministic.
+  ;; TODO: Remove it when this variable is set in GNU:%STANDARD-PHASES.
+  (setenv "SOURCE_DATE_EPOCH" "0"))
+
 (define %standard-phases
   ;; 'configure' and 'build' phases are not needed.  Everything is done during
   ;; 'install'.
   (modify-phases gnu:%standard-phases
     (add-after 'unpack 'ensure-no-mtimes-pre-1980 ensure-no-mtimes-pre-1980)
+    (add-after 'unpack 'set-SOURCE-DATE-EPOCH set-SOURCE-DATE-EPOCH)
     (delete 'configure)
     (replace 'install install)
     (replace 'check check)