Updates to device specfication and program validation (#661)

* update gate params and layout

* updates

* add to changelog

* remove unused import

* more changelog

* minor spelling

* Apply suggestions from code review

Co-authored-by: Mikhail Andrenkov <Mandrenkov@users.noreply.github.com>

* updates from code review

* add test

* add test

* update changelog

* Apply suggestions from code review

Co-authored-by: Mikhail Andrenkov <Mandrenkov@users.noreply.github.com>

* suggestions from code review

* fix passing empty params dict to validation

* fix tests

* add test

Co-authored-by: Mikhail Andrenkov <Mandrenkov@users.noreply.github.com>

.github/CHANGELOG.md

@@ -2,16 +2,27 @@
 
 <h3>New features since last release</h3>
 
+* `DeviceSpec.layout` and `DeviceSpec.gate_parameters` may now return `None`. This can happen
+  when a remote simulator device is used.
+  [(#661)](https://github.com/XanaduAI/strawberryfields/pull/661)
+
 <h3>Breaking Changes</h3>
 
 <h3>Bug fixes</h3>
 
+* `program.compile` now raises an error if the device specification contains gate parameters but no
+  circuit layout. Without a layout, the gate parameters cannot be validated against the device
+  specification.
+  [(#661)](https://github.com/XanaduAI/strawberryfields/pull/661)
+
 <h3>Documentation</h3>
 
 <h3>Contributors</h3>
 
 This release contains contributions from (in alphabetical order):
 
+Theodor Isacsson
+
 # Release 0.21.0 (current release)
 
 <h3>New features since last release</h3>
@@ -492,7 +503,7 @@ Quesada, Antal Száva, Yuan Yao.
   modes = 4
   cutoff_dim = 6
 
-  # prepare an intial state with 4 photons in as many modes
+  # prepare an initial state with 4 photons in as many modes
   initial_state = np.zeros([cutoff_dim] * modes, dtype=complex)
   initial_state[1, 1, 1, 1] = 1
 
@@ -584,7 +595,7 @@ Quesada, Antal Száva, Yuan Yao.
 * `measure_threshold` in the `gaussian` backend now supports displaced Gaussian states.
   [(#615)](https://github.com/XanaduAI/strawberryfields/pull/615)
 
-* Speed improvements are addded to ``gaussian_unitary`` compiler.
+* Speed improvements are added to ``gaussian_unitary`` compiler.
   [(#603)](https://github.com/XanaduAI/strawberryfields/pull/603)
 
 * Adds native support in the Fock backend for the MZgate.

strawberryfields/devicespec.py

@@ -15,7 +15,7 @@
 This module contains a class that represents the specifications of
 a device available via the API.
 """
-from typing import Sequence, Mapping, Any
+from typing import Sequence, Mapping, Any, Optional
 
 import blackbird
 from blackbird.error import BlackbirdSyntaxError
@@ -52,7 +52,7 @@ def target(self) -> str:
         return self._spec["target"]
 
     @property
-    def layout(self) -> str:
+    def layout(self) -> Optional[str]:
         """str: Returns a string containing the Blackbird circuit layout."""
         return self._spec["layout"]
 
@@ -78,7 +78,7 @@ def default_compiler(self) -> str:
         return "Xunitary"
 
     @property
-    def gate_parameters(self) -> Mapping[str, Ranges]:
+    def gate_parameters(self) -> Optional[Mapping[str, Ranges]]:
         """dict[str, strawberryfields.compilers.Ranges]: A dictionary of gate parameters
         and allowed ranges.
 
@@ -89,8 +89,10 @@ def gate_parameters(self) -> Mapping[str, Ranges]:
         >>> spec.gate_parameters
         {'squeezing_amplitude_0': x=0, x=1, 'phase_0': x=0, 0≤x≤6.283185307179586}
         """
-        gate_parameters = {}
+        if self._spec["gate_parameters"] is None:
+            return None
 
+        gate_parameters = {}
         for gate_name, param_ranges in self._spec["gate_parameters"].items():
             # convert gate parameter allowed ranges to Range objects
             range_list = [[i] if not isinstance(i, Sequence) else i for i in param_ranges]
@@ -107,6 +109,9 @@ def validate_parameters(self, **parameters: complex) -> None:
         Raises:
             ValueError: if an invalid parameter is passed
         """
+        if self.gate_parameters is None:
+            return
+
         # check that all provided parameters are valid
         for p, v in parameters.items():
             if p in self.gate_parameters and v not in self.gate_parameters[p]:
@@ -141,19 +146,23 @@ def create_program(self, **parameters: complex):
         Returns:
             strawberryfields.program.Program: program compiled to the device
         """
+        if not self.layout:
+            raise ValueError("Cannot create program. Specification is missing a circuit layout.")
+
         try:
             bb = blackbird.loads(self.layout)
         except BlackbirdSyntaxError as e:
             raise BlackbirdSyntaxError("Layout is not formatted correctly.") from e
         self.validate_parameters(**parameters)
 
-        # determine parameter value if not provided
-        extra_params = set(self.gate_parameters) - set(parameters)
+        if self.gate_parameters:
+            # determine parameter value if not provided
+            extra_params = set(self.gate_parameters) - set(parameters)
 
-        for p in extra_params:
-            # Set parameter value as the first allowed
-            # value in the gate parameters dictionary.
-            parameters[p] = self.gate_parameters[p].ranges[0].x
+            for p in extra_params:
+                # Set parameter value as the first allowed
+                # value in the gate parameters dictionary.
+                parameters[p] = self.gate_parameters[p].ranges[0].x
 
         # evaluate the blackbird template
         bb = bb(**parameters)

strawberryfields/program.py

@@ -680,8 +680,13 @@ def _get_compiler(compiler_or_name):
         backend_options = {k: kwargs[k] for k in kwargs if k not in ALLOWED_RUN_OPTIONS}
         compiled.backend_options.update(backend_options)
 
-        # validate gate parameters
-        if device is not None and device.gate_parameters:
+        # if device spec has allowed gate parameters, validate the applied gate parameters
+        if device and device.gate_parameters:
+            if not device.layout:
+                raise ValueError(
+                    "Gate parameters cannot be validated. Device specification is missing a "
+                    "circuit layout."
+                )
             bb_device = bb.loads(device.layout)
             bb_compiled = sf.io.to_blackbird(compiled)
 

tests/api/test_devicespec.py

@@ -121,6 +121,24 @@ def test_create_program(self):
         assert prog.circuit
         assert [str(cmd) for cmd in prog.circuit] == circuit
 
+    def test_create_program_no_layout(self):
+        """Test that the program creation raises an error if the device spec contains no layout"""
+
+        params = {"phase_0": 1.23}
+        device_dict_no_layout = {
+            "target": "abc",
+            "layout": None,
+            "modes": 2,
+            "compiler": ["Xcov"],
+            "gate_parameters": {
+                "squeezing_amplitude_0": [0, 1],
+                "phase_0": [0, [0, 6.3]],
+                "phase_1": [[0.5, 1.4]],
+            },
+        }
+        with pytest.raises(ValueError, match="missing a circuit layout"):
+            DeviceSpec(spec=device_dict_no_layout).create_program(**params)
+
     @pytest.mark.parametrize(
         "params", [{"phase_0": 7.5}, {"phase_1": 0.4}, {"squeezing_amplitude_0": 0.5}]
     )
@@ -148,3 +166,46 @@ def test_invalid_spec(self):
             ValueError, match=r"missing the following keys: \['gate_parameters', 'layout'\]"
         ):
             DeviceSpec(spec=invalid_spec)
+
+    @pytest.mark.parametrize(
+        "params",
+        [
+            {"phase_0": 1.23},
+            {"phase_0": 0},
+            {"phase_0": 6.29999},
+        ],
+    )
+    def test_valid_parameters(self, params):
+        """Test that valid parameters pass the validate_parameters validation"""
+        DeviceSpec(spec=device_dict).validate_parameters(**params)
+
+    def test_invalid_parameter(self):
+        """Test that invalid parameter names raise an error in validate_parameters"""
+        with pytest.raises(ValueError, match=r"not a valid parameter for this device"):
+            DeviceSpec(spec=device_dict).validate_parameters(phase_42=0)
+
+    def test_invalid_parameters_value(self):
+        """Test that invalid parameter values raise an error in validate_parameters"""
+        with pytest.raises(ValueError, match=r"has invalid value"):
+            DeviceSpec(spec=device_dict).validate_parameters(phase_0=123)
+
+    @pytest.mark.parametrize(
+        "params",
+        [
+            {"phase_0": 1.23},
+            {"phase_0": 0},
+            {"phase_0": 6.29999},
+            {"phase_0": 123},
+            {"phase_42": 123},
+        ],
+    )
+    def test_gate_parameters_none(self, params):
+        """Test that any parameters a valid when gate_parameters is None"""
+        device_dict = {
+            "target": "abc",
+            "layout": mock_layout,
+            "modes": 2,
+            "compiler": ["Xcov"],
+            "gate_parameters": None,
+        }
+        DeviceSpec(spec=device_dict).validate_parameters(**params)