only rich display outputs have metadata

even affects v3, which had some bugs that didn't describe actual js behavior

IPython/nbconvert/exporters/tests/files/notebook2.ipynb

@@ -23,7 +23,6 b''
    },
    "outputs": [
     {
-     "metadata": {},
      "name": "stdout",
      "output_type": "stream",
      "text": [

IPython/nbconvert/preprocessors/tests/files/Clear Output.ipynb

@@ -19,7 +19,6 b''
    },
    "outputs": [
     {
-     "metadata": {},
      "name": "stdout",
      "output_type": "stream",
      "text": [

IPython/nbconvert/preprocessors/tests/files/Factorials.ipynb

@@ -19,7 +19,6 b''
    },
    "outputs": [
     {
-     "metadata": {},
      "name": "stdout",
      "output_type": "stream",
      "text": [

IPython/nbconvert/preprocessors/tests/files/HelloWorld.ipynb

@@ -8,7 +8,6 b''
    },
    "outputs": [
     {
-     "metadata": {},
      "name": "stdout",
      "output_type": "stream",
      "text": [

IPython/nbconvert/preprocessors/tests/files/Skip Exceptions.ipynb

@@ -10,7 +10,6 b''
     {
      "ename": "Exception",
      "evalue": "message",
-     "metadata": {},
      "output_type": "error",
      "traceback": [
       "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
@@ -32,7 +31,6 b''
    },
    "outputs": [
     {
-     "metadata": {},
      "name": "stdout",
      "output_type": "stream",
      "text": [

IPython/nbconvert/preprocessors/tests/files/Unicode.ipynb

@@ -8,7 +8,6 b''
    },
    "outputs": [
     {
-     "metadata": {},
      "name": "stdout",
      "output_type": "stream",
      "text": [

IPython/nbconvert/tests/files/notebook2.ipynb

@@ -23,7 +23,6 b''
    },
    "outputs": [
     {
-     "metadata": {},
      "name": "stdout",
      "output_type": "stream",
      "text": [

IPython/nbformat/tests/invalid.ipynb

@@ -36,7 +36,6 b''
       "print(\"hello\")"
      ],
      "language": "python",
-     "metadata": {},
      "outputs": [
       {
        "output_type": "stream",

IPython/nbformat/tests/test4.ipynb

@@ -31,7 +31,6 b''
    },
    "outputs": [
     {
-     "metadata": {},
      "name": "stdout",
      "output_type": "stream",
      "text": [

IPython/nbformat/v3/nbbase.py

@@ -54,6 +54,10 b' def new_output(output_type, output_text=None, output_png=None,'
     if not isinstance(metadata, dict):
         raise TypeError("metadata must be dict")
 
+
+    if output_type in {u'pyout', 'display_data'}:
+        output.metadata = metadata
+
     if output_type != 'pyerr':
         if output_text is not None:
             output.text = cast_unicode(output_text)
@@ -86,8 +90,6 b' def new_output(output_type, output_text=None, output_png=None,'
 
     if output_type == u'stream':
         output.stream = 'stdout' if stream is None else cast_unicode(stream)
-    else:
-        output.metadata = metadata
     
     return output
 

IPython/nbformat/v3/nbformat.v3.schema.json

@@ -295,7 +295,6 b''
                     "description": "Type of cell output.",
                     "enum": ["pyerr"]
                 },
-                "metadata": {"$ref": "#/definitions/misc/output_metadata"},
                 "ename": {
                     "description": "The name of the error.",
                     "type": "string"

IPython/nbformat/v4/convert.py

@@ -141,8 +141,8 b' def upgrade_output(output):'
     - mime-type keys
     - stream.stream -> stream.name
     """
-    output.setdefault('metadata', NotebookNode())
     if output['output_type'] in {'pyout', 'display_data'}:
+        output.setdefault('metadata', NotebookNode())
         if output['output_type'] == 'pyout':
             output['output_type'] = 'execute_result'
             output['execution_count'] = output.pop('prompt_number', None)
@@ -193,7 +193,6 b' def downgrade_output(output):'
         output['output_type'] = 'pyerr'
     elif output['output_type'] == 'stream':
         output['stream'] = output.pop('name')
-        output.pop('metadata')
     return output
 
 def upgrade_outputs(outputs):

IPython/nbformat/v4/nbbase.py

@@ -46,11 +46,11 b' def new_output(output_type, data=None, **kwargs):'
         output.data = from_dict(data)
 
     # populate defaults:
-    output.setdefault('metadata', NotebookNode())
     if output_type == 'stream':
         output.setdefault('name', 'stdout')
         output.setdefault('text', '')
     elif output_type in {'execute_result', 'display_data'}:
+        output.setdefault('metadata', NotebookNode())
         output.setdefault('data', NotebookNode())
     validate(output, output_type)
     return output

IPython/nbformat/v4/nbformat.v4.schema.json

@@ -235,13 +235,12 b''
             "description": "Stream output from a code cell.",
             "type": "object",
             "additionalProperties": false,
-            "required": ["output_type", "metadata", "name", "text"],
+            "required": ["output_type", "name", "text"],
             "properties": {
                 "output_type": {
                     "description": "Type of cell output.",
                     "enum": ["stream"]
                 },
-                "metadata": {"$ref": "#/definitions/misc/output_metadata"},
                 "name": {
                     "description": "The name of the stream (stdout, stderr).",
                     "type": "string"
@@ -257,13 +256,12 b''
             "description": "Output of an error that occurred during code cell execution.",
             "type": "object",
             "additionalProperties": false,
-            "required": ["output_type", "metadata", "ename", "evalue", "traceback"],
+            "required": ["output_type", "ename", "evalue", "traceback"],
             "properties": {
                 "output_type": {
                     "description": "Type of cell output.",
                     "enum": ["error"]
                 },
-                "metadata": {"$ref": "#/definitions/misc/output_metadata"},
                 "ename": {
                     "description": "The name of the error.",
                     "type": "string"