Change Placeholder to support partial shapes and enforce scalar shapes.

Adds tests; testScalar failed before with the original placeholder because
it treated [] as "?" instead of scalar.  Now you can actually specify
[] and it means 'scalar'.

Added a backwards compatibility test using a graph_def generated
from a previous tf version.

RELNOTES: tf.placeholder can represent scalar shapes and partially known
shapes accurately. Note, this change can break already buggy programs because
it makes placeholder shape handling more consistent across graph serializations.

Note: There are some buggy cases where this change can break a buggy pipeline: namely those that serialize a graph using an unknown shape (e.g., [None, 10] in a tf.placeholder, but then reload the graph using import_graph_def and feed it a different shape.  Prior to this change, serializing the graph_def loses the [None, 10] shape requirement, so you can feed anything you want. This change makes it so that you serialize the graph with [None, 10], and so when you reload it, it would fail if you fed it a different shape.  In these cases, the fix is to correct the original placeholder shape to match what you feed it, which is not a bug in TF but in the user's program.

Note 2: A python user that did tf.placeholder(shape=[]) would get scalar checking
in the same process due to python shape inference code.  However, a C++ user that did Placeholder(shape=[]) would not have gotten
scalar shape checking; a C++ program that passed Placeholder(shape=[]) that expects
to interpret this as "UnknownShape" would break -- however, that user could have
already used an {unknown_shape: true} proto, and should not have expected the legacy behavior.

Backwards compatibility: Old graphs that have shape = {} in the proto will also have a
graph_def_version <= 21, so the default value of shape prior to this change will be interpreted by new binaries as "UnknownShape" just as before.

Forwards compatibility: new graphs will produce, by default, shape={ unknown rank: true}; old binaries will use PartialTensorShape's parsing code to parse that proto
into an object whose shape.dims() <= 0, and so these binaries will continue to interpret
the default shape as "unknown shape" without crashing and without producing new errors.

Fixes #9103
Change: 152751019

1 files changed, 1 insertions, 1 deletions

diff --git a/tensorflow/cc/client/client_session_test.cc b/tensorflow/cc/client/client_session_test.cc
index 9c0f00f2b1..dfbac9788e 100644
--- a/tensorflow/cc/client/client_session_test.cc
+++ b/tensorflow/cc/client/client_session_test.cc
@@ -49,7 +49,7 @@ TEST(ClientSessionTest, Feed) {
 
 TEST(ClientSessionTest, Extend) {
   Scope root = Scope::NewRootScope();
-  auto a = Placeholder(root, DT_INT32);
+  auto a = Placeholder(root, DT_INT32, Placeholder::Shape({2}));
   auto c = Add(root, a, {2, 2});
   ClientSession session(root);
   std::vector<Tensor> outputs;