fix: prevent Constant Folding disconnecting linear outputs even if constant#1793
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acl-cqc
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Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #1793 +/- ##
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+ Coverage 85.57% 85.75% +0.18%
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Files 198 198
Lines 31087 31478 +391
Branches 29642 30033 +391
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+ Hits 26603 26995 +392
+ Misses 3210 3205 -5
- Partials 1274 1278 +4
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acl-cqc
commented
Jul 5, 2026
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aborgna-q
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aborgna-q
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maximilianruesch
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Note that this may be related / partially solving #1724 |
aborgna-q
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Jul 7, 2026
| // Overly conservative: see https://github.com/Quantinuum/tket2/issues/1794, | ||
| // https://github.com/Quantinuum/tket2/issues/1795, | ||
| // https://github.com/Quantinuum/tket2/issues/1796 | ||
| .flat_map(move |(outp, ty)| ty.copyable().then_some((n, outp))) |
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nit: It could also have been a .filter(...).map(...), but works that same anyways.
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Yeah, longer but clearer, so done
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I think so too, we should do some testing. |
acl-cqc
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For a Sum types where some variants are quantum but others are classical, we can deduce a constant value of the classical variant, but "breaking the wire" to insert the constant leads to an unconnected port of the sum type, which is linear...
Ideal solution in many cases is probably #1796, but that may not apply in all cases. Same problem could also happen for CustomConsts of linear type (BorrowArray?) if we constant-fold those.
For now the workaround is to avoid breaking any linear wire. This is overly conservative; we could insert consts and break such wires if the sources can also be removed, but that requires traversal done only in DCE.
First commit adds a test where the Hugr fails validation after constant-folding; second fixes.