Workaround symengine serialization payload incompatibility #13251
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In QPY we rely on symengine's internal serialization to represent the internal symbolic expression stored inside a ParameterExpression object. However, this format is nominally symengine version specific and will raise an error if there is a mismatch between the version used to generate the payload and what is trying to read it. This became an issue in the recent symengine 0.13 release which started to raise an error when people installed it and tried to load QPY payloads across the versions. This makes the symengine serialization unsuitable for use in QPY because it's supposed to be independent of these kind of concerns, especially when QPY is used in a server-client model where you don't necessarily control the installed environment of symengine. To correctly address this issue we'll need a new version of the QPY format that owns the serialization format of ParameterExpressions directly instead of relying on symengine which doesn't offer a compatibility guarantee on the format. However this won't be quick solution and users are encountering issues since the release of 0.13. This commit introduces a workaround for this specific instance of the mismatch. It turns out the payload format between 0.11 and 0.13 is completely unchanged except for the version number. So before passing the parameter expression payload to symengine for deserialization this commit checks the versions numbers are the same, if they're not it checks that we're dealing with 0.11 or 0.13, and if so it changes the version number in the payloads header appropriately. If the version number is outside those bounds it raises an exception because while this hack is known to be safe for translating between symengine 0.11 and 0.13, it's not possible to know for a future version whether the payload format changed or not. Longer term we will need a proper fix in qpy version 13 that introduces a qiskit native serialization format for parameter expression instead of relying on symengine or sympy to do it for us.
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| if int(symengine_version[1]) != minor: | ||
| if minor not in (11, 13): | ||
| raise exceptions.QpyError( | ||
| f"Incompatible symengine version {major}.{minor} used to generate the QPY " | ||
| "payload" | ||
| ) | ||
| minor_version = int(symengine_version[1]) | ||
| if minor_version not in (11, 13): | ||
| raise exceptions.QpyError( | ||
| f"Incompatible installed symengine version {symengine.__version__} to load " | ||
| "this QPY payload" | ||
| ) |
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The ordering of this means that we can cope with generation and load from (say) a hypothetical symengine 0.14, but is it worth us risking that? We could put symengine>=0.11,<=0.13 in our requirements, potentially.
Not sure how I feel about that, just asking the question.
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Can we, did I do the logic incorrectly? My intent was that if we have a version mismatch between the payload and the installed library and if either the payload or the installed version is not using 0.11 or 0.13 we'll raise the error.
There is an edge case here if the major version != 0, but I figured this was unlikely to be an issue (especially with a minor version of 11 or 13) in any reasonable timescale.
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Yeah, I'm saying we can attempt to load if there's no payload mismatch and both were 0.14, but given we know there's problems, would we prefer just to forbid 0.14 from entering at all, rather than have it work iff there's a match?
Yeah, I saw the major version thing too, but was just assuming that we'll fix this before that happened.
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(and by "yeah" I mean I'm agreeing with you - I think you did the logic right)
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Ah ok, now I get what you're saying. My initial thought was if there is no mismatch I think we're fine as symengine should be totally fine if everything is the same version. I guess it's more a question of whether we think it's sufficiently a risk of foot gunning by generating a payload with 0.14.0 that will fail if someone is using any other version later
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Yeah, I was kind of hoping you'd have a strong opinion about that last point so I'd be absolved of needing to develop one. In lieu of anything better, let's stick with the PR as written - upper bounds aren't ideal, and I don't particularly like introducing one within a patch release.
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Yeah I think that's what we're talking about. That's the only option really is either add a cap to the requirements file in 1.2.3, or we do it in the python code so that qpy.dump() fails if you have symenging > 0.14 installed. It might be prudent. I was hesitant to do that in this PR because I was worried about python 3.13 support. But since 0.13 has 3.13 support maybe it's worth it here.
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I opted to add the cap in: 7aae984
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For future posterity: Matt and I talked offline before this, and thought that pre-emptively capping is actually the lesser of the two evils. We don't like introducing an upper bound in a patch release, but we've had upper bounds on symengine before, and the hack we're doing to enable compatibility is pretty dangerous, since symengine's deserialisation code can hard crash on malformed payloads. It feels safer to try and restrict symengine 0.14 from entering (as best as we can), rather than hoping that nothing will break when it's released.
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In local testing, I generated the QPY backwards compatibility tests using this branch, with Symengine 0.11 and Symengine 0.13, and then attempted to reload them with both. I found that the schedule code ( |
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Probably we can find a way to slightly unify those two code paths, since they looked pretty similar to me. |
Fixed in: ea69a45 |
This commit updates the schedule serialization path too, as it was also directly loading symengine expressions. The code handling the workaround is extracted to a standalone function which is used in both spots now instead of calling symengine directly.
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I tested this again locally with the same procedure as above, and verified that it works. The last question before I approve:
The use_symengine argument to QPY serialisation was introduced in #10820, released in Terra 0.45.0, which allowed symengine>=0.9. use_symengine=False was the default back then, but it was possible to set use_symengine=True, and if I set that during the QPY file generation, then this branch will fail to load the files. I can't just add 9 to the allowed minor versions we can load from, because it seems like between 0.9 and 0.11 the format did change, and we segfault symengine if we patch the version.
Are we prepared to accept this problem as "good enough", or do we want to look for anything deeper? Ideologically it's not nice to call it "good enough", but pragmatically I don't think I can see an alternative solution for us in the short term. Assuming we accept that issue, should we put a "known issues" release note in about it, or potentially document it in the QPY documentation about the backwards compatibility guarantees?
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To finish the thought - |
During the discovery on the fix in this PR we discovered that setting the ``use_symengine`` flag from Qiskit 0.45.x and 0.46.x would result in newer versions of Qiskit being unable to parse the QPY file for the same issue as being addressed here. This commit expands the logic to account for this and raise a useful warning. It also updates the release notes and documentation to document these limitations.
Out of an abundance of caution this commit places a cap on the allowed version of symengine users can install to be compatible with Qiskit. Due to the symengine version dependence discovered in QPY around serializing ParameterExpressions, we'll likely have a similar issue when symengine 0.14.0 releases. Pre-emptively capping this means we aren't going to be in this situation until we can confirm compatibility with QPY serialization. The real solution for this will come in Qiskit#13252, although as this behavior is embedded in QPY formats 10, 11, and 12 at this point we'll have to handle this edge case moving forward regardless of whether we introduce a better solution in 1.3.0 or not. Although realistically in that case we will likely need to just document this as a limitation when exporting QPY payloads with Qiskit 0.45.0 through 1.2.3 (and with the ``version`` flag set to >= 10 and < 13) and have explicit error checking around the symengine version (which this PR adds) when in that code path.
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Ok, I've updated the PR in: e089d5c to be more explicit about the symengine versions coming from 0.45.x and 0.46.x with |
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Co-authored-by: Matthew Treinish <[email protected]>
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* Workaround symengine serialization payload incompatibility In QPY we rely on symengine's internal serialization to represent the internal symbolic expression stored inside a ParameterExpression object. However, this format is nominally symengine version specific and will raise an error if there is a mismatch between the version used to generate the payload and what is trying to read it. This became an issue in the recent symengine 0.13 release which started to raise an error when people installed it and tried to load QPY payloads across the versions. This makes the symengine serialization unsuitable for use in QPY because it's supposed to be independent of these kind of concerns, especially when QPY is used in a server-client model where you don't necessarily control the installed environment of symengine. To correctly address this issue we'll need a new version of the QPY format that owns the serialization format of ParameterExpressions directly instead of relying on symengine which doesn't offer a compatibility guarantee on the format. However this won't be quick solution and users are encountering issues since the release of 0.13. This commit introduces a workaround for this specific instance of the mismatch. It turns out the payload format between 0.11 and 0.13 is completely unchanged except for the version number. So before passing the parameter expression payload to symengine for deserialization this commit checks the versions numbers are the same, if they're not it checks that we're dealing with 0.11 or 0.13, and if so it changes the version number in the payloads header appropriately. If the version number is outside those bounds it raises an exception because while this hack is known to be safe for translating between symengine 0.11 and 0.13, it's not possible to know for a future version whether the payload format changed or not. Longer term we will need a proper fix in qpy version 13 that introduces a qiskit native serialization format for parameter expression instead of relying on symengine or sympy to do it for us. * Handle schedules too This commit updates the schedule serialization path too, as it was also directly loading symengine expressions. The code handling the workaround is extracted to a standalone function which is used in both spots now instead of calling symengine directly. * Remove unused imports * Gracefully handle failure to parse historical symengine files During the discovery on the fix in this PR we discovered that setting the ``use_symengine`` flag from Qiskit 0.45.x and 0.46.x would result in newer versions of Qiskit being unable to parse the QPY file for the same issue as being addressed here. This commit expands the logic to account for this and raise a useful warning. It also updates the release notes and documentation to document these limitations. * Cap upper version of symengine in requirements list Out of an abundance of caution this commit places a cap on the allowed version of symengine users can install to be compatible with Qiskit. Due to the symengine version dependence discovered in QPY around serializing ParameterExpressions, we'll likely have a similar issue when symengine 0.14.0 releases. Pre-emptively capping this means we aren't going to be in this situation until we can confirm compatibility with QPY serialization. The real solution for this will come in #13252, although as this behavior is embedded in QPY formats 10, 11, and 12 at this point we'll have to handle this edge case moving forward regardless of whether we introduce a better solution in 1.3.0 or not. Although realistically in that case we will likely need to just document this as a limitation when exporting QPY payloads with Qiskit 0.45.0 through 1.2.3 (and with the ``version`` flag set to >= 10 and < 13) and have explicit error checking around the symengine version (which this PR adds) when in that code path. * Fix release note upgrade section label * Rewrite support documentation * Fix mistakes in release note Co-authored-by: Matthew Treinish <[email protected]> --------- Co-authored-by: Jake Lishman <[email protected]> Co-authored-by: Jake Lishman <[email protected]> (cherry picked from commit fee9f77)
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…13251) (#13255) * Workaround symengine serialization payload incompatibility (#13251) * Workaround symengine serialization payload incompatibility In QPY we rely on symengine's internal serialization to represent the internal symbolic expression stored inside a ParameterExpression object. However, this format is nominally symengine version specific and will raise an error if there is a mismatch between the version used to generate the payload and what is trying to read it. This became an issue in the recent symengine 0.13 release which started to raise an error when people installed it and tried to load QPY payloads across the versions. This makes the symengine serialization unsuitable for use in QPY because it's supposed to be independent of these kind of concerns, especially when QPY is used in a server-client model where you don't necessarily control the installed environment of symengine. To correctly address this issue we'll need a new version of the QPY format that owns the serialization format of ParameterExpressions directly instead of relying on symengine which doesn't offer a compatibility guarantee on the format. However this won't be quick solution and users are encountering issues since the release of 0.13. This commit introduces a workaround for this specific instance of the mismatch. It turns out the payload format between 0.11 and 0.13 is completely unchanged except for the version number. So before passing the parameter expression payload to symengine for deserialization this commit checks the versions numbers are the same, if they're not it checks that we're dealing with 0.11 or 0.13, and if so it changes the version number in the payloads header appropriately. If the version number is outside those bounds it raises an exception because while this hack is known to be safe for translating between symengine 0.11 and 0.13, it's not possible to know for a future version whether the payload format changed or not. Longer term we will need a proper fix in qpy version 13 that introduces a qiskit native serialization format for parameter expression instead of relying on symengine or sympy to do it for us. * Handle schedules too This commit updates the schedule serialization path too, as it was also directly loading symengine expressions. The code handling the workaround is extracted to a standalone function which is used in both spots now instead of calling symengine directly. * Remove unused imports * Gracefully handle failure to parse historical symengine files During the discovery on the fix in this PR we discovered that setting the ``use_symengine`` flag from Qiskit 0.45.x and 0.46.x would result in newer versions of Qiskit being unable to parse the QPY file for the same issue as being addressed here. This commit expands the logic to account for this and raise a useful warning. It also updates the release notes and documentation to document these limitations. * Cap upper version of symengine in requirements list Out of an abundance of caution this commit places a cap on the allowed version of symengine users can install to be compatible with Qiskit. Due to the symengine version dependence discovered in QPY around serializing ParameterExpressions, we'll likely have a similar issue when symengine 0.14.0 releases. Pre-emptively capping this means we aren't going to be in this situation until we can confirm compatibility with QPY serialization. The real solution for this will come in #13252, although as this behavior is embedded in QPY formats 10, 11, and 12 at this point we'll have to handle this edge case moving forward regardless of whether we introduce a better solution in 1.3.0 or not. Although realistically in that case we will likely need to just document this as a limitation when exporting QPY payloads with Qiskit 0.45.0 through 1.2.3 (and with the ``version`` flag set to >= 10 and < 13) and have explicit error checking around the symengine version (which this PR adds) when in that code path. * Fix release note upgrade section label * Rewrite support documentation * Fix mistakes in release note Co-authored-by: Matthew Treinish <[email protected]> --------- Co-authored-by: Jake Lishman <[email protected]> Co-authored-by: Jake Lishman <[email protected]> (cherry picked from commit fee9f77) * Fix symengine typo --------- Co-authored-by: Matthew Treinish <[email protected]> Co-authored-by: Jake Lishman <[email protected]>
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This commit fixes a bug that slipped into the sole fix that made up the now yanked 1.2.3 release, Qiskit#13251. The fix logic had a typo/mistake when evaluating the major version in the symengine payload that meant if you were trying to load a QPY payload generated with a different symengine release it would always error. This only got through CI because there was no test coverage of the edge case we were trying to fix. This commit addresses both issues. It first fixes the typo in the QPY parsing (which is a 2 character change) and then updates the QPY compat tests to explicitly test using multiple symengine versions with QPY to make sure we're exercising this code path moving forward (and validating this fix).
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This commit fixes a bug that slipped into the sole fix that made up the now yanked 1.2.3 release, #13251. The fix logic had a typo/mistake when evaluating the major version in the symengine payload that meant if you were trying to load a QPY payload generated with a different symengine release it would always error. This only got through CI because there was no test coverage of the edge case we were trying to fix. This commit addresses both issues. It first fixes the typo in the QPY parsing (which is a 2 character change) and then updates the QPY compat tests to explicitly test using multiple symengine versions with QPY to make sure we're exercising this code path moving forward (and validating this fix).
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This commit fixes a bug that slipped into the sole fix that made up the now yanked 1.2.3 release, #13251. The fix logic had a typo/mistake when evaluating the major version in the symengine payload that meant if you were trying to load a QPY payload generated with a different symengine release it would always error. This only got through CI because there was no test coverage of the edge case we were trying to fix. This commit addresses both issues. It first fixes the typo in the QPY parsing (which is a 2 character change) and then updates the QPY compat tests to explicitly test using multiple symengine versions with QPY to make sure we're exercising this code path moving forward (and validating this fix). (cherry picked from commit e5ec413) # Conflicts: # qiskit/qpy/__init__.py
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) * Workaround symengine serialization payload incompatibility In QPY we rely on symengine's internal serialization to represent the internal symbolic expression stored inside a ParameterExpression object. However, this format is nominally symengine version specific and will raise an error if there is a mismatch between the version used to generate the payload and what is trying to read it. This became an issue in the recent symengine 0.13 release which started to raise an error when people installed it and tried to load QPY payloads across the versions. This makes the symengine serialization unsuitable for use in QPY because it's supposed to be independent of these kind of concerns, especially when QPY is used in a server-client model where you don't necessarily control the installed environment of symengine. To correctly address this issue we'll need a new version of the QPY format that owns the serialization format of ParameterExpressions directly instead of relying on symengine which doesn't offer a compatibility guarantee on the format. However this won't be quick solution and users are encountering issues since the release of 0.13. This commit introduces a workaround for this specific instance of the mismatch. It turns out the payload format between 0.11 and 0.13 is completely unchanged except for the version number. So before passing the parameter expression payload to symengine for deserialization this commit checks the versions numbers are the same, if they're not it checks that we're dealing with 0.11 or 0.13, and if so it changes the version number in the payloads header appropriately. If the version number is outside those bounds it raises an exception because while this hack is known to be safe for translating between symengine 0.11 and 0.13, it's not possible to know for a future version whether the payload format changed or not. Longer term we will need a proper fix in qpy version 13 that introduces a qiskit native serialization format for parameter expression instead of relying on symengine or sympy to do it for us. * Handle schedules too This commit updates the schedule serialization path too, as it was also directly loading symengine expressions. The code handling the workaround is extracted to a standalone function which is used in both spots now instead of calling symengine directly. * Remove unused imports * Gracefully handle failure to parse historical symengine files During the discovery on the fix in this PR we discovered that setting the ``use_symengine`` flag from Qiskit 0.45.x and 0.46.x would result in newer versions of Qiskit being unable to parse the QPY file for the same issue as being addressed here. This commit expands the logic to account for this and raise a useful warning. It also updates the release notes and documentation to document these limitations. * Cap upper version of symengine in requirements list Out of an abundance of caution this commit places a cap on the allowed version of symengine users can install to be compatible with Qiskit. Due to the symengine version dependence discovered in QPY around serializing ParameterExpressions, we'll likely have a similar issue when symengine 0.14.0 releases. Pre-emptively capping this means we aren't going to be in this situation until we can confirm compatibility with QPY serialization. The real solution for this will come in Qiskit#13252, although as this behavior is embedded in QPY formats 10, 11, and 12 at this point we'll have to handle this edge case moving forward regardless of whether we introduce a better solution in 1.3.0 or not. Although realistically in that case we will likely need to just document this as a limitation when exporting QPY payloads with Qiskit 0.45.0 through 1.2.3 (and with the ``version`` flag set to >= 10 and < 13) and have explicit error checking around the symengine version (which this PR adds) when in that code path. * Fix release note upgrade section label * Rewrite support documentation * Fix mistakes in release note Co-authored-by: Matthew Treinish <[email protected]> --------- Co-authored-by: Jake Lishman <[email protected]> Co-authored-by: Jake Lishman <[email protected]>
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This commit fixes a bug that slipped into the sole fix that made up the now yanked 1.2.3 release, Qiskit#13251. The fix logic had a typo/mistake when evaluating the major version in the symengine payload that meant if you were trying to load a QPY payload generated with a different symengine release it would always error. This only got through CI because there was no test coverage of the edge case we were trying to fix. This commit addresses both issues. It first fixes the typo in the QPY parsing (which is a 2 character change) and then updates the QPY compat tests to explicitly test using multiple symengine versions with QPY to make sure we're exercising this code path moving forward (and validating this fix).
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…13260) * Fix bug in QPY symengine payload version handling (#13259) This commit fixes a bug that slipped into the sole fix that made up the now yanked 1.2.3 release, #13251. The fix logic had a typo/mistake when evaluating the major version in the symengine payload that meant if you were trying to load a QPY payload generated with a different symengine release it would always error. This only got through CI because there was no test coverage of the edge case we were trying to fix. This commit addresses both issues. It first fixes the typo in the QPY parsing (which is a 2 character change) and then updates the QPY compat tests to explicitly test using multiple symengine versions with QPY to make sure we're exercising this code path moving forward (and validating this fix). (cherry picked from commit e5ec413) # Conflicts: # qiskit/qpy/__init__.py * Fix merge artifact --------- Co-authored-by: Matthew Treinish <[email protected]> Co-authored-by: Julien Gacon <[email protected]>
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) * Workaround symengine serialization payload incompatibility In QPY we rely on symengine's internal serialization to represent the internal symbolic expression stored inside a ParameterExpression object. However, this format is nominally symengine version specific and will raise an error if there is a mismatch between the version used to generate the payload and what is trying to read it. This became an issue in the recent symengine 0.13 release which started to raise an error when people installed it and tried to load QPY payloads across the versions. This makes the symengine serialization unsuitable for use in QPY because it's supposed to be independent of these kind of concerns, especially when QPY is used in a server-client model where you don't necessarily control the installed environment of symengine. To correctly address this issue we'll need a new version of the QPY format that owns the serialization format of ParameterExpressions directly instead of relying on symengine which doesn't offer a compatibility guarantee on the format. However this won't be quick solution and users are encountering issues since the release of 0.13. This commit introduces a workaround for this specific instance of the mismatch. It turns out the payload format between 0.11 and 0.13 is completely unchanged except for the version number. So before passing the parameter expression payload to symengine for deserialization this commit checks the versions numbers are the same, if they're not it checks that we're dealing with 0.11 or 0.13, and if so it changes the version number in the payloads header appropriately. If the version number is outside those bounds it raises an exception because while this hack is known to be safe for translating between symengine 0.11 and 0.13, it's not possible to know for a future version whether the payload format changed or not. Longer term we will need a proper fix in qpy version 13 that introduces a qiskit native serialization format for parameter expression instead of relying on symengine or sympy to do it for us. * Handle schedules too This commit updates the schedule serialization path too, as it was also directly loading symengine expressions. The code handling the workaround is extracted to a standalone function which is used in both spots now instead of calling symengine directly. * Remove unused imports * Gracefully handle failure to parse historical symengine files During the discovery on the fix in this PR we discovered that setting the ``use_symengine`` flag from Qiskit 0.45.x and 0.46.x would result in newer versions of Qiskit being unable to parse the QPY file for the same issue as being addressed here. This commit expands the logic to account for this and raise a useful warning. It also updates the release notes and documentation to document these limitations. * Cap upper version of symengine in requirements list Out of an abundance of caution this commit places a cap on the allowed version of symengine users can install to be compatible with Qiskit. Due to the symengine version dependence discovered in QPY around serializing ParameterExpressions, we'll likely have a similar issue when symengine 0.14.0 releases. Pre-emptively capping this means we aren't going to be in this situation until we can confirm compatibility with QPY serialization. The real solution for this will come in Qiskit#13252, although as this behavior is embedded in QPY formats 10, 11, and 12 at this point we'll have to handle this edge case moving forward regardless of whether we introduce a better solution in 1.3.0 or not. Although realistically in that case we will likely need to just document this as a limitation when exporting QPY payloads with Qiskit 0.45.0 through 1.2.3 (and with the ``version`` flag set to >= 10 and < 13) and have explicit error checking around the symengine version (which this PR adds) when in that code path. * Fix release note upgrade section label * Rewrite support documentation * Fix mistakes in release note Co-authored-by: Matthew Treinish <[email protected]> --------- Co-authored-by: Jake Lishman <[email protected]> Co-authored-by: Jake Lishman <[email protected]>
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This commit fixes a bug that slipped into the sole fix that made up the now yanked 1.2.3 release, Qiskit#13251. The fix logic had a typo/mistake when evaluating the major version in the symengine payload that meant if you were trying to load a QPY payload generated with a different symengine release it would always error. This only got through CI because there was no test coverage of the edge case we were trying to fix. This commit addresses both issues. It first fixes the typo in the QPY parsing (which is a 2 character change) and then updates the QPY compat tests to explicitly test using multiple symengine versions with QPY to make sure we're exercising this code path moving forward (and validating this fix).
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With the release of symengine 0.13.0 we discovered a version dependence on the payload format used for serializing symengine expressions. This was worked around in Qiskit#13251 but this is not a sustainable solution and only works for symengine 0.11.0 and 0.13.0 (there was no 0.12.0). While there was always the option to use sympy to serialize the underlying symbolic expression (there is a `use_symengine` flag on `qpy.dumps` you can set to `False` to do this) the sympy serialzation has several tradeoffs most importantly is much higher runtime overhead. To solve the issue moving forward a qiskit native representation of the parameter expression object is necessary for serialization. This commit bumps the QPY format version to 13 and adds a new serialization format for ParameterExpression objects. This new format is a serialization of the API calls made to ParameterExpression that resulted in the creation of the underlying object. To facilitate this the ParameterExpression class is expanded to store an internal "replay" record of the API calls used to construct the ParameterExpression object. This internal list is what gets serialized by QPY and then on deserialization the "replay" is replayed to reconstruct the expression object. This is a different approach to the previous QPY representations of the ParameterExpression objects which instead represented the internal state stored in the ParameterExpression object with the symbolic expression from symengine (or a sympy copy of the expression). Doing this directly in Qiskit isn't viable though because symengine's internal expression tree is not exposed to Python directly. There isn't any method (private or public) to walk the expression tree to construct a serialization format based off of it. Converting symengine to a sympy expression and then using sympy's API to walk the expression tree is a possibility but that would tie us to sympy which would be problematic for Qiskit#13267 and Qiskit#13131, have significant runtime overhead, and it would be just easier to rely on sympy's native serialization tools. The tradeoff with this approach is that it does increase the memory overhead of the `ParameterExpression` class because for each element in the expression we have to store a record of it. Depending on the depth of the expression tree this also could be a lot larger than symengine's internal representation as we store the raw api calls made to create the ParameterExpression but symengine is likely simplifying it's internal representation as it builds it out. But I personally think this tradeoff is worthwhile as it ties the serialization format to the Qiskit objects instead of relying on a 3rd party library. This also gives us the flexibility of changing the internal symbolic expression library internally in the future if we decide to stop using symengine at any point. Fixes Qiskit#13252
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* Add Qiskit native QPY ParameterExpression serialization With the release of symengine 0.13.0 we discovered a version dependence on the payload format used for serializing symengine expressions. This was worked around in #13251 but this is not a sustainable solution and only works for symengine 0.11.0 and 0.13.0 (there was no 0.12.0). While there was always the option to use sympy to serialize the underlying symbolic expression (there is a `use_symengine` flag on `qpy.dumps` you can set to `False` to do this) the sympy serialzation has several tradeoffs most importantly is much higher runtime overhead. To solve the issue moving forward a qiskit native representation of the parameter expression object is necessary for serialization. This commit bumps the QPY format version to 13 and adds a new serialization format for ParameterExpression objects. This new format is a serialization of the API calls made to ParameterExpression that resulted in the creation of the underlying object. To facilitate this the ParameterExpression class is expanded to store an internal "replay" record of the API calls used to construct the ParameterExpression object. This internal list is what gets serialized by QPY and then on deserialization the "replay" is replayed to reconstruct the expression object. This is a different approach to the previous QPY representations of the ParameterExpression objects which instead represented the internal state stored in the ParameterExpression object with the symbolic expression from symengine (or a sympy copy of the expression). Doing this directly in Qiskit isn't viable though because symengine's internal expression tree is not exposed to Python directly. There isn't any method (private or public) to walk the expression tree to construct a serialization format based off of it. Converting symengine to a sympy expression and then using sympy's API to walk the expression tree is a possibility but that would tie us to sympy which would be problematic for #13267 and #13131, have significant runtime overhead, and it would be just easier to rely on sympy's native serialization tools. The tradeoff with this approach is that it does increase the memory overhead of the `ParameterExpression` class because for each element in the expression we have to store a record of it. Depending on the depth of the expression tree this also could be a lot larger than symengine's internal representation as we store the raw api calls made to create the ParameterExpression but symengine is likely simplifying it's internal representation as it builds it out. But I personally think this tradeoff is worthwhile as it ties the serialization format to the Qiskit objects instead of relying on a 3rd party library. This also gives us the flexibility of changing the internal symbolic expression library internally in the future if we decide to stop using symengine at any point. Fixes #13252 * Remove stray comment * Add format documentation * Add release note * Add test and fix some issues with recursive expressions * Add int type for operands * Add dedicated subs test * Pivot to stack based postfix/rpn deserialization This commit changes how the deserialization works to use a postfix stack based approach. Operands are push on the stack and then popped off based on the operation being run. The result of the operation is then pushed on the stack. This handles nested objects much more cleanly than the recursion based approach because we just keep pushing on the stack instead of recursing, making the accounting much simpler. After the expression payload is finished being processed there will be a single value on the stack and that is returned as the final expression. * Apply suggestions from code review Co-authored-by: Elena Peña Tapia <[email protected]> * Change DERIV to GRAD * Change side kwarg to r_side * Change all the v4s to v13s * Correctly handle non-commutative operations This commit fixes a bug with handling the operand order of subtraction, division, and exponentiation. These operations are not commutative but the qpy deserialization code was treating them as such. So in cases where the argument order was reversed qpy was trying to flip the operands around for code simplicity and this would result in incorrect behavior. This commit fixes this by adding explicit op codes for the reversed sub, div, and pow and preserving the operand order correctly in these cases. * Fix lint --------- Co-authored-by: Elena Peña Tapia <[email protected]>
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Summary
In QPY we rely on symengine's internal serialization to represent the internal symbolic expression stored inside a ParameterExpression object. However, this format is nominally symengine version specific and will raise an error if there is a mismatch between the version used to generate the payload and what is trying to read it. This became an issue in the recent symengine 0.13 release which started to raise an error when people installed it and tried to load QPY payloads across the versions. This makes the symengine serialization unsuitable for use in QPY because it's supposed to be independent of these kind of concerns, especially when QPY is used in a server-client model where you don't necessarily control the installed environment of symengine.
To correctly address this issue we'll need a new version of the QPY format that owns the serialization format of ParameterExpressions directly instead of relying on symengine which doesn't offer a compatibility guarantee on the format. However this won't be quick solution and users are encountering issues since the release of 0.13. This commit introduces a workaround for this specific instance of the mismatch. It turns out the payload format between 0.11 and 0.13 is completely unchanged except for the version number. So before passing the parameter expression payload to symengine for deserialization this commit checks the versions numbers are the same, if they're not it checks that we're dealing with 0.11 or 0.13, and if so it changes the version number in the payloads header appropriately. If the version number is outside those bounds it raises an exception because while this hack is known to be safe for translating between symengine 0.11 and 0.13, it's not possible to know for a future version whether the payload format changed or not.
Longer term we will need a proper fix in qpy version 13 that introduces a qiskit native serialization format for parameter expression instead of relying on symengine or sympy to do it for us.
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