Fix coverage exclusion syntax (#6241)

* switch to standard opt-out comments for code exclusion from coverage
* fix placement of `# pragma: no cover` markup comments,
  so they are either on the affected line or at the preceding block
 * remove no-cover comments for code that is covered
 * remove redundant no-cover comments

Author: pavoljuhas

CONTRIBUTING.md

@@ -1,9 +1,9 @@
 # How to Contribute
 
 We'd love to accept your patches and contributions to this project.
-We do have some guidelines to follow, covered in this document, but don't 
+We do have some guidelines to follow, covered in this document, but don't
 worry about (or expect to) get everything right the first time!
-Create a pull request and we'll nudge you in the right direction. Please also 
+Create a pull request and we'll nudge you in the right direction. Please also
 note that we have a [code of conduct](CODE_OF_CONDUCT.md) to make Cirq an
 open and welcoming environment.
 
@@ -83,7 +83,7 @@ on setting up your local development environment.
 
 ## Code Testing Standards
 
-When a pull request is created or updated, various automatic checks will 
+When a pull request is created or updated, various automatic checks will
 run to ensure that the change won't break Cirq and meets our coding standards.
 
 Cirq contains a continuous integration tool to verify testing.  See our
@@ -94,36 +94,36 @@ Please be aware of the following code standards that will be applied to any
 new changes.
 
 - **Tests**.
-Existing tests must continue to pass (or be updated) when new changes are 
-introduced. We use [pytest](https://docs.pytest.org/en/latest/) to run our 
+Existing tests must continue to pass (or be updated) when new changes are
+introduced. We use [pytest](https://docs.pytest.org/en/latest/) to run our
 tests.
 - **Coverage**.
 Code should be covered by tests.
-We use [pytest-cov](https://pytest-cov.readthedocs.io/en/latest/) to compute 
+We use [pytest-cov](https://pytest-cov.readthedocs.io/en/latest/) to compute
 coverage, and custom tooling to filter down the output to only include new or
-changed code. We don't require 100% coverage, but any uncovered code must 
-be annotated with `# coverage: ignore`. To ignore coverage of a single line, 
-place `# coverage: ignore` at the end of the line. To ignore coverage for 
-an entire block, start the block with a `# coverage: ignore` comment on its 
+changed code. We don't require 100% coverage, but any uncovered code must
+be annotated with `# pragma: no cover`. To ignore coverage of a single line,
+place `# pragma: no cover` at the end of the line. To ignore coverage for
+an entire block, start the block with a `# pragma: no cover` comment on its
 own line.
 - **Lint**.
-Code should meet common style standards for python and be free of error-prone 
+Code should meet common style standards for python and be free of error-prone
 constructs. We use [pylint](https://www.pylint.org/) to check for lint.
-To see which lint checks we enforce, see the 
+To see which lint checks we enforce, see the
 [dev_tools/conf/.pylintrc](dev_tools/conf/.pylintrc) file. When pylint produces
-a false positive, it can be squashed with annotations like 
+a false positive, it can be squashed with annotations like
 `# pylint: disable=unused-import`.
 - **Types**.
 Code should have [type annotations](https://www.python.org/dev/peps/pep-0484/).
 We use [mypy](http://mypy-lang.org/) to check that type annotations are correct.
-When type checking produces a false positive, it can be ignored with 
+When type checking produces a false positive, it can be ignored with
 annotations like `# type: ignore`.
 
 ## Request For Comment Process for New Major Features
 
-For larger contributions that will benefit from design reviews, please use the 
+For larger contributions that will benefit from design reviews, please use the
 [Request for Comment](docs/dev/rfc_process.md) process.
 
-## Developing notebooks 
+## Developing notebooks
 
-Please refer to our [notebooks guide](docs/dev/notebooks.md) on how to develop iPython notebooks for documentation.
+Please refer to our [notebooks guide](docs/dev/notebooks.md) on how to develop iPython notebooks for documentation.

cirq-core/cirq/_version.py

@@ -17,8 +17,7 @@
 
 import sys
 
-if sys.version_info < (3, 9, 0):
-    # coverage: ignore
+if sys.version_info < (3, 9, 0):  # pragma: no cover
     raise SystemError(
         "You installed the latest version of cirq but aren't on python 3.9+.\n"
         'To fix this error, you need to either:\n'

cirq-core/cirq/circuits/circuit_operation.py

@@ -61,9 +61,9 @@ def _full_join_string_lists(
     list1: Optional[Sequence[str]], list2: Optional[Sequence[str]]
 ) -> Optional[Sequence[str]]:
     if list1 is None and list2 is None:
-        return None  # coverage: ignore
+        return None  # pragma: no cover
     if list1 is None:
-        return list2  # coverage: ignore
+        return list2  # pragma: no cover
     if list2 is None:
         return list1
     return [f'{first}{REPETITION_ID_SEPARATOR}{second}' for first in list1 for second in list2]

cirq-core/cirq/circuits/qasm_output_test.py

@@ -257,7 +257,7 @@ def _qasm_(self, args: cirq.QasmArgs) -> str:
 
         def _decompose_(self):
             # Only used by test_output_unitary_same_as_qiskit
-            return ()  # coverage: ignore
+            return ()  # pragma: no cover
 
     class DummyCompositeOperation(cirq.Operation):
         qubits = (q0,)

cirq-core/cirq/conftest.py

@@ -27,8 +27,7 @@ def pytest_configure(config):
 
 def pytest_pyfunc_call(pyfuncitem):
     if inspect.iscoroutinefunction(pyfuncitem._obj):
-        # coverage: ignore
-        raise ValueError(
+        raise ValueError(  # pragma: no cover
             f'{pyfuncitem._obj.__name__} is a bare async function. '
             f'It should be decorated with "@duet.sync".'
         )

cirq-core/cirq/contrib/acquaintance/devices.py

@@ -68,7 +68,7 @@ class _UnconstrainedAcquaintanceDevice(AcquaintanceDevice):
     """An acquaintance device with no constraints other than of the gate types."""
 
     def __repr__(self) -> str:
-        return 'UnconstrainedAcquaintanceDevice'  # coverage: ignore
+        return 'UnconstrainedAcquaintanceDevice'  # pragma: no cover
 
 
 UnconstrainedAcquaintanceDevice = _UnconstrainedAcquaintanceDevice()

cirq-core/cirq/contrib/hacks/disable_validation_test.py

@@ -29,7 +29,7 @@ def test_disable_op_validation():
     with pytest.raises(ValueError, match='mysterious and terrible'):
         with disable_op_validation():
             # This does not run - the with condition errors out first.
-            _ = cirq.H(q0, q1)  # coverage: ignore
+            _ = cirq.H(q0, q1)  # pragma: no cover
 
     # Passes, skipping validation.
     with disable_op_validation(accept_debug_responsibility=True):

cirq-core/cirq/contrib/noise_models/noise_models.py

@@ -41,8 +41,7 @@ def __init__(self, depol_prob: float, prepend: bool = False):
         self._prepend = prepend
 
     def noisy_moment(self, moment: 'cirq.Moment', system_qubits: Sequence['cirq.Qid']):
-        if validate_all_measurements(moment) or self.is_virtual_moment(moment):
-            # coverage: ignore
+        if validate_all_measurements(moment) or self.is_virtual_moment(moment):  # pragma: no cover
             return moment
 
         output = [

cirq-core/cirq/contrib/paulistring/clifford_optimize.py

@@ -161,7 +161,7 @@ def try_merge_cz(cz_op: ops.GateOperation, start_i: int) -> int:
             else:
                 # Two CZ gates that share one qubit
                 # Pass through and keep looking
-                continue  # coverage: ignore
+                continue  # pragma: no cover
                 # The above line is covered by test_remove_staggered_czs but the
                 # coverage checker disagrees.
         return 0

cirq-core/cirq/contrib/qcircuit/qcircuit_pdf.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-# coverage: ignore
+# pragma: no cover
 
 import errno
 import os