add stimcirq tags

[emma-louise-rosenfeld]

When a particular cirq operation has a tag, convert it to stim according to the tag's value.

[Strilanc]

I can't accept this as currently designed.

The basic issue is you are hardcoding your particular usage of tags into the library (replace a gate based on a tag), rather than making a tool that other people would also use. Stim and stimcirq should attach as little semantic meaning to tags as possible; there should be no kind of replacement logic triggered by the presence of a tag. Instead, the conversion should attempt to preserve the tags while making as few changes as possible.

For example, when stimcirq is converting from a stim circuit to a cirq circuit, it could add the tags appearing on the stim instruction to the resulting cirq gates as a string or as a custom class stimcirq.StimTag. Then, when converting from cirq to stim, it could look for stimcirq.CirqTag tags and turn them into tags in the stim circuit. For handling more general cases (since cirq allows a wide variety of tagging), the user should be able to specify custom tag conversion functions that take a cirq tag and return a stim tag (or vice versa).

[emma-louise-rosenfeld]

I can't accept this as currently designed.

The basic issue is you are hardcoding your particular usage of tags into the library (replace a gate based on a tag), rather than making a tool that other people would also use. Stim and stimcirq should attach as little semantic meaning to tags as possible; there should be no kind of replacement logic triggered by the presence of a tag. Instead, the conversion should attempt to preserve the tags while making as few changes as possible.

For example, when stimcirq is converting from a stim circuit to a cirq circuit, it could add the tags appearing on the stim instruction to the resulting cirq gates as a string or as a custom class stimcirq.StimTag. Then, when converting from cirq to stim, it could look for stimcirq.CirqTag tags and turn them into tags in the stim circuit. For handling more general cases (since cirq allows a wide variety of tagging), the user should be able to specify custom tag conversion functions that take a cirq tag and return a stim tag (or vice versa).

The use case here is not related to the tags in STIM. Instead, here I'm working on the cirq to stim conversion, when the cirq circuit has non-standard gates

[Strilanc]

Do a test where the stim circuit ends up containing a tag.

[emma-louise-rosenfeld]

@Strilanc this required some extra functionality (persisting cirq tags through to stim tags) beyond our use case here but I gave a stab at it. See my most recent commit for an example of what I'm thinking. I haven't run/written tests on it yet.

[emma-louise-rosenfeld]

@Strilanc , done, check my latest commit. Note that tags on cirq.CircuitOperation's aren't persisted through - only tags associated with cirq.TaggedOperations are maintained