{ "number": 36696, "repo": "bitcoin/bitcoin", "url": "https://github.com/bitcoin/bitcoin/pull/36696", "title": "CTransaction: Add constructor taking inputs and outputs", "author": "purpleKarrot", "author_association": "MEMBER", "created_at": "2026-10-29T16:13:13Z", "updated_at": "2026-10-30T09:27:20Z", "description_hash": "13cb59b10a9034d8", "age_days": 3, "draft": false, "labels": [], "milestone": null, "base": "master", "head_sha": "705d5d573774033b7cff5f45f602fdb40850866b", "head_ref": "declarative-test-data", "head_repo": "purpleKarrot/bitcoin", "head_history": [ { "t": "2026-10-29T16:43:54Z", "sha": "172feb035a76d292e75a81bf5d3b709e61796396" }, { "t": "2026-10-30T07:17:32Z", "sha": "705d5d573774033b7cff5f45f602fdb40850866b" } ], "additions": 87, "deletions": 59, "changed_files": 4, "commit_count": 3, "size_bucket": "M", "mergeable_state": "clean", "bot": { "drahtbot": { "present": true, "reviews": {}, "conflicts": [] } }, "acks_parsed": {}, "acks_tally": { "ack": 0, "stale_ack": 0, "concept_ack": 0, "approach_ack": 0, "nack": 0, "concept_nack": 0, "approach_nack": 0 }, "reviews": { "approved": 0, "changes_requested": 0, "distinct_reviewers": [ "alexanderwiederin", "maflcko" ] }, "signals": { "needs_rebase": false, "ci_failed": false, "mergeable_state": "clean", "last_author_activity": "2026-10-30T08:21:43Z", "last_reviewer_activity": "2026-10-30T09:27:20Z", "last_reviewer": "maflcko", "author_silent_days": 2, "waiting_on_author_days": 2, "days_since_update": 2 }, "refs": { "mentioned": [ 36606, 36692, 36694 ], "depends_on": [], "fixes": [], "linked_issues": [], "references": [ { "number": 36692, "type": "issue", "state": "open", "merged": false, "merged_at": null, "title": "Declarative construction of test data" }, { "number": 36606, "type": "pull", "state": "closed", "merged": true, "merged_at": "2026-10-29", "title": "test, bench: construct inputs/outputs declaratively in context-dependent cases" }, { "number": 36694, "type": "pull", "state": "open", "merged": false, "merged_at": null, "title": "test, bench: construct mempool inputs/outputs declaratively" } ], "conflicts": [] }, "stack": { "shares_commits_with": [], "based_on": [], "base_for": [] }, "review_paths": [ "src/primitives/transaction.h", "src/util/vector.h" ], "body": "Part of #36692. Please view this PR in context of changes like https://github.com/bitcoin/bitcoin/pull/36694.\n\n`CTransaction` gains a constructor that allows direct declarative construction as an alternative to building through `CMutableTransaction`. `CTxIn`'s constructors gain an optional argument to pass the script witness.\n\nIt is a conscious decision that `vin/vout` are passed as generic input ranges and that only *their elements* are copied/moved.\nPassing the `std::vector` by value and then moving the *container itself* into place would allow the following:\n\n```cpp\nstd::vector inputs = ...;\nCTxIn& backdoor = inputs.back();\n\nconst CTransaction tx{std::move(inputs), ...};\n\nbackdoor = ...; // <- modify `tx`, potentially breaking its invariant\n```", "commits": [ { "sha": "4dc7038b554182928b4cd0a47eee1dfb714195e3", "date": "2026-10-30T06:30:00Z", "message": "CTransaction: Add constructor that takes ranges of inputs and outputs" }, { "sha": "629b7da292e02910da3109b8ddb334c855149716", "date": "2026-10-30T06:30:10Z", "message": "CTxIn: Accept scriptWitness in constructor" }, { "sha": "705d5d573774033b7cff5f45f602fdb40850866b", "date": "2026-10-30T07:16:21Z", "message": "test: Demonstrate new CTransaction constructor in sigopcount_tests" } ], "timeline": [ { "t": "2026-10-29T16:28:07Z", "kind": "review_comment", "who": "maflcko", "assoc": "MEMBER", "path": "src/primitives/transaction.h", "commit": "7e66b30802bd8346bcbbb191eb3200c69ce5c8e0", "in_reply_to": null, "text": "nit: I'd still prefer the easier C++11 std::vector here (https://github.com/bitcoin/bitcoin/issues/36692#issuecomment-6501722895) but I'll leave it to other reviewers to decide.", "id": "rc:4415029088", "url": "https://github.com/bitcoin/bitcoin/pull/36696#discussion_r4415029088", "hash": "8a71febab27a826d", "edited": "2026-10-29T19:26:40Z" }, { "t": "2026-10-29T16:43:54Z", "kind": "force_push", "who": "purpleKarrot", "commit": "172feb035a76d292e75a81bf5d3b709e61796396", "id": "push:172feb035a76d292e75a81bf5d3b709e61796396" }, { "t": "2026-10-29T18:40:08Z", "kind": "review_comment", "who": "alexanderwiederin", "assoc": "MEMBER", "path": "src/util/vector.h", "commit": "4491755fdaed602c502b75c656c48fb2e966890a", "in_reply_to": null, "text": "```suggestion\n if constexpr (std::is_lvalue_reference_v || std::ranges::view>) {\n```\n\nI think `std::span{inputs}` would still move the elements out of `inputs`. Copying for views avoids that. What do you think?", "id": "rc:4416451512", "url": "https://github.com/bitcoin/bitcoin/pull/36696#discussion_r4416451512", "hash": "7b902f0693152791", "edited": "2026-10-29T18:49:08Z" }, { "t": "2026-10-29T18:43:46Z", "kind": "review_comment", "who": "alexanderwiederin", "assoc": "MEMBER", "path": "src/primitives/transaction.h", "commit": "705d5d573774033b7cff5f45f602fdb40850866b", "in_reply_to": null, "text": "```suggestion\n explicit CTransaction(In&& in, Out&& out, uint32_t ver = CURRENT_VERSION, uint32_t lt = 0)\n```\nShould this be explicit like the existing ones?", "id": "rc:4416488577", "url": "https://github.com/bitcoin/bitcoin/pull/36696#discussion_r4416488577", "hash": "8198edba2891d203", "edited": "2026-10-29T18:49:08Z" }, { "t": "2026-10-29T18:47:40Z", "kind": "review_comment", "who": "purpleKarrot", "assoc": "MEMBER", "path": "src/primitives/transaction.h", "commit": "7e66b30802bd8346bcbbb191eb3200c69ce5c8e0", "in_reply_to": 4415029088, "text": "I added a few cases to show the new constructor in action. If the constructor would accept `std::vector` arguments, a transaction without inputs could be constructed as:\n\n```cpp\nauto tx = CTransaction{{}, {\n CTxOut{nValues[0], CScript{} << ToByteVector(key[0].GetPubKey()) << OP_CHECKSIG},\n CTxOut{nValues[1], CScript{} << ToByteVector(key[1].GetPubKey()) << OP_CHECKSIG},\n}};\n```\n\nIt is certainly less verbose, but I don't think it does a service to readability.", "id": "rc:4416531182", "url": "https://github.com/bitcoin/bitcoin/pull/36696#discussion_r4416531182", "hash": "2763d9edafc0c3c4", "edited": "2026-10-29T18:49:53Z" }, { "t": "2026-10-29T18:49:08Z", "kind": "review", "who": "alexanderwiederin", "assoc": "MEMBER", "state": "COMMENTED", "commit": "4491755fdaed602c502b75c656c48fb2e966890a", "text": "The `CTxIn` witness argument is a nice addition. It would remove the \u201cassign the witness after replacing vin\u201d workaround I needed in several places in #36606 and #36694.", "id": "r:5703110328", "url": "https://github.com/bitcoin/bitcoin/pull/36696#pullrequestreview-5703110328", "hash": "66ce977a0dfdcf05", "edited": null }, { "t": "2026-10-29T19:21:54Z", "kind": "review_comment", "who": "purpleKarrot", "assoc": "MEMBER", "path": "src/util/vector.h", "commit": "4491755fdaed602c502b75c656c48fb2e966890a", "in_reply_to": 4416451512, "text": "That is a good point. I think we should just invoke `std::ranges::copy` unconditionally. In C++23, we can remove this helper and use tag dispatching with `std::from_range`. All as long as we actually want range support, so I will leave this open until https://github.com/bitcoin/bitcoin/pull/36696#discussion_r4415029088 is resolved.", "id": "rc:4416890613", "url": "https://github.com/bitcoin/bitcoin/pull/36696#discussion_r4416890613", "hash": "a77cc5827e08b613", "edited": null }, { "t": "2026-10-29T19:22:45Z", "kind": "review_comment", "who": "purpleKarrot", "assoc": "MEMBER", "path": "src/primitives/transaction.h", "commit": "705d5d573774033b7cff5f45f602fdb40850866b", "in_reply_to": 4416488577, "text": "Implicit conversion cannot happen because the constructor requires at least two arguments.", "id": "rc:4416898958", "url": "https://github.com/bitcoin/bitcoin/pull/36696#discussion_r4416898958", "hash": "58f55be21c61a307", "edited": "2026-10-29T19:22:46Z" }, { "t": "2026-10-30T07:17:32Z", "kind": "force_push", "who": "purpleKarrot", "commit": "705d5d573774033b7cff5f45f602fdb40850866b", "id": "push:705d5d573774033b7cff5f45f602fdb40850866b" }, { "t": "2026-10-30T07:42:41Z", "kind": "review_comment", "who": "purpleKarrot", "assoc": "MEMBER", "path": "src/util/vector.h", "commit": "4491755fdaed602c502b75c656c48fb2e966890a", "in_reply_to": 4416451512, "text": "Fixed it. Instead of moving when `R` is an rvalue, we want to move when R *yields* rvalues. `std::ranges::copy` already does that and so does `std::from_range`.", "id": "rc:4421462027", "url": "https://github.com/bitcoin/bitcoin/pull/36696#discussion_r4421462027", "hash": "1a8d116c40a482a1", "edited": "2026-10-30T07:42:42Z" }, { "t": "2026-10-30T08:21:43Z", "kind": "comment", "who": "purpleKarrot", "assoc": "MEMBER", "text": "I have replaced the commits that exemplify the constructor in action with one that shows multiple things in a single place:\n\n- It shows the new constructor of `CTransaction` in action.\n- It shows the new constructor of `CTxIn` in action.\n- It shows how `CMutableTransaction` is not necessary in many places, not just for building, but also as function argument.\n- It reveals `GetTxSigOpCost` as an example test that contains multiple blocks where each should become its own unit test.\n- It reveals potential test dependencies: Each test setup modifies the `CCoinsViewCache`. It is not clear whether a test might depend on the modifications of tests run earlier or not.\n- It shows that `CTransaction` could benefit from applying best practices (never use `const` data members, maintain immutability by not providing write access): In `return {std::move(creationTx), std::move(spendingTx)};`, the compiler provided move constructor of `CTransaction` invokes the move constructors of all its data members, which are `const`, so they fall back to copying (this does not fire `performance-move-const-arg`, because the individual data members fall back, not the tx object).\n- It reveals the annoyance that `CTransaction` does not provide regular semantics: It is not possible to replace the existing values with `std::tie(creationTx, spendingTx) = BuildTxs(...);`, because `CTransaction` is only sort-of copyable (due to not following ... I repeat myself. This is not a big deal here, as tests should be refactored for independence anyway).\n- It also provides an example where code could be much less verbose if the constructor accepted `std::vector` and explicit types were not required at the call site, and why I claim this to be less readable:\n\n```cpp\nCTransaction creationTx{{{{}}}, {{1, scriptPubKey}}, 1};\nCTransaction spendingTx{{{{creationTx.GetHash(), 0}, scriptSig, CTxIn::SEQUENCE_FINAL, witness}}, {{1, {}}}, 1};\n```", "id": "c:6518387886", "url": "https://github.com/bitcoin/bitcoin/pull/36696#issuecomment-6518387886", "hash": "2e97370f29e10a9e", "edited": "2026-10-30T08:32:16Z" }, { "t": "2026-10-30T09:27:20Z", "kind": "review_comment", "who": "maflcko", "assoc": "MEMBER", "path": "src/primitives/transaction.h", "commit": "7e66b30802bd8346bcbbb191eb3200c69ce5c8e0", "in_reply_to": 4415029088, "text": "Sure, but my thinking is that init-lists for CTransaction must always end in a trailing comma:\n\n```cpp\nauto tx = CTransaction{\n {},\n {\n CTxOut{nValues[0], CScript{} << ToByteVector(key[0].GetPubKey()) << OP_CHECKSIG},\n CTxOut{nValues[1], CScript{} << ToByteVector(key[1].GetPubKey()) << OP_CHECKSIG},\n },\n};\n```\n\nBut again, up to other reviewers to pick the side here :sweat_smile:", "id": "rc:4422197450", "url": "https://github.com/bitcoin/bitcoin/pull/36696#discussion_r4422197450", "hash": "099186395a19cfc0", "edited": null } ], "labels_log": [ { "t": "2026-10-29T16:44:27Z", "action": "labeled", "label": "CI failed", "who": "DrahtBot" }, { "t": "2026-10-29T17:57:23Z", "action": "unlabeled", "label": "CI failed", "who": "DrahtBot" } ], "state_log": [], "text_chars": 5135, "text_tokens_estimate": 1283, "changed_paths": [ "src/primitives/transaction.cpp", "src/primitives/transaction.h", "src/test/sigopcount_tests.cpp", "src/util/vector.h" ], "files": [ { "path": "src/primitives/transaction.cpp", "add": 17, "del": 4 }, { "path": "src/primitives/transaction.h", "add": 12, "del": 2 }, { "path": "src/test/sigopcount_tests.cpp", "add": 38, "del": 53 }, { "path": "src/util/vector.h", "add": 20, "del": 0 } ], "test_lines": 91, "git": { "head": "705d5d573774033b7cff5f45f602fdb40850866b", "head_matches_backup": true, "base": "6ed5aad06111177c39f9b9f07a52634476380ae1", "patch_id": "36df9383cf3e2e38", "commits": [ { "sha": "4dc7038b55", "subject": "CTransaction: Add constructor that takes ranges of inputs and outputs", "files": 3, "add": 43, "del": 2 }, { "sha": "629b7da292", "subject": "CTxIn: Accept scriptWitness in constructor", "files": 2, "add": 6, "del": 4 }, { "sha": "705d5d5737", "subject": "test: Demonstrate new CTransaction constructor in sigopcount_tests", "files": 1, "add": 38, "del": 53 } ], "patch_truncated": false }, "patch_id": "36df9383cf3e2e38", "input_hash": "c369eebf1cf90d94", "extracted_at": "2026-11-02T01:09:49+00:00" }