descriptor: fix comments in descriptor.cpp::DescriptorImpl #33384

1. 
   pythcoiner commented at 12:40 pm on September 13, 2025: contributor

   P2TR was missing in m_pubkey_args description and it was a typo in doc/descriptors.md
2. descriptor: fix comments in descriptor.cpp::DescriptorImpl 768eeafbda
3. DrahtBot added the label Descriptors on Sep 13, 2025
4. 
   DrahtBot commented at 12:40 pm on September 13, 2025: contributor

   The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/33384.

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   LLM Linter (✨ experimental)

   Possible typos and grammar issues:

   • In doc/descriptors.md this is referred to as SCRIPT expressions sh(SCRIPT) -> In doc/descriptors.md, this is referred to as SCRIPT expressions: sh(SCRIPT) [Missing comma after the filename and missing colon before the example make the phrase harder to parse; adding them clarifies that sh(SCRIPT) is an example of “SCRIPT expressions”.]

   No other typos were found.

   drahtbot_id_5_m

5. fanquake requested review from Sjors on Sep 23, 2025
6. 
   Sjors commented at 9:57 am on September 26, 2025: member

   cc @achow101
7. in src/script/descriptor.cpp:796 in 768eeafbda

   792@@ -793,13 +793,13 @@ class MuSigPubkeyProvider final : public PubkeyProvider
   793 class DescriptorImpl : public Descriptor
   794 {
   795 protected:
   796-    //! Public key arguments for this descriptor (size 1 for PK, PKH, WPKH; any size for WSH and Multisig).
   797+    //! Public key arguments for this descriptor (size 1 for PK, PKH, WPKH; any size for WSH, P2TR, Multisig).
   

   ---

   ---

   

   rkrux commented at 3:06 pm on November 6, 2025:

   This doesn’t seem to be correct. I debugged the unit tests & the listdescriptors RPC, and found that m_pubkey_args.size() remains 1 for tr() descriptors as well. It’s the m_subdescriptor_args.size() that increases if script path(s) is(are) present. Following points support this:

   1. The TRDescriptor constructor accepts a single PubkeyProvider that’s treated as the Taproot internal key: https://github.com/bitcoin/bitcoin/blob/5c5704e730796c6f31e2d7891bf6334674a04219/src/script/descriptor.cpp#L1407-L1408
   2. The following older commit also hints at it https://github.com/bitcoin/bitcoin/commit/4441c6f3c046c0b28ce3f0ca6d938af71d797586:

   Make DescriptorImpl support multiple subscripts So far, no descriptor exists that supports more than one sub-script descriptor. This will change with taproot, so prepare for this by changing the m_subdescriptor_arg from a unique_ptr to a vector of unique_ptr’s.

   ---

   

   Dmenec commented at 7:10 pm on January 29, 2026:

   +1 to what @rkrux found.

   Checked the code as well and m_pubkey_args.size() remains 1 for TR descriptors. The internal key is passed via Vector(std::move(internal_key)), which constructs a single-element vector.

   I would suggest updating the comment to:

   0//! Public key arguments for this descriptor (size 1 for PK, PKH, WPKH, TR; any size for Multisig).
   

   Also, it looks like the only real “any size” case for m_pubkey_args is multisig, since it is the one that passes a vector of multiple providers directly into DescriptorImpl.

   0MultisigDescriptor(int threshold,
   1                   std::vector<std::unique_ptr<PubkeyProvider>> providers,
   2                   bool sorted = false)
   3  : DescriptorImpl(std::move(providers), sorted ? "sortedmulti" : "multi"),
   4    m_threshold(threshold), m_sorted(sorted) {}
   

   SHDescriptor don’t populate m_pubkey_args at all, it initializes it as an empty vector and stores the wrapped descriptor under m_subdescriptor_args:

   0SHDescriptor(std::unique_ptr<DescriptorImpl> desc) 
   1  : DescriptorImpl({}, std::move(desc), "sh") {}
   

   It might be worth updating the m_subdescriptor_args comment:

   https://github.com/bitcoin/bitcoin/blob/5c5704e730796c6f31e2d7891bf6334674a04219/src/script/descriptor.cpp#L795-L798

   As TRDescriptors are using m_subdescriptor_args.

8. 
   rkrux commented at 3:06 pm on November 6, 2025: contributor

   CR 768eeafbda3b36428d90239c92ddfb41402cfd0c

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pythcoiner DrahtBot Sjors rkrux Dmenec

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