Merge bitcoin/bitcoin#25748: refactor: Avoid copies in FlatSigningProvider Merge

fa3f15f2dd94ae597a66037f5928fe4e90fe099d refactor: Avoid copies in FlatSigningProvider Merge (MacroFake)

Pull request description:

  `Merge` will create several copies unconditionally:
  * To initialize the args `a`, and `b`
  * `ret`, which is the merge of the two args

  So change the code to let the caller decide how many copies they need/want:
  * `a`, and `b` must be explicitly moved or copied by the caller
  * `ret` is no longer needed, as `a` can be used for it in place "for free"

ACKs for top commit:
  achow101:
    ACK fa3f15f2dd94ae597a66037f5928fe4e90fe099d
  furszy:
    looks good, ACK fa3f15f2
  ryanofsky:
    Code review ACK fa3f15f2dd94ae597a66037f5928fe4e90fe099d. Confirmed that all the places `std::move` was added the argument actually did seem safe to move from. Compiler enforces that temporary copies are explicitly created in non-move cases.

Tree-SHA512: 7c027ccdea1549cd9f37403344ecbb76e008adf545f6ce52996bf95e89eb7dc89af6cb31435a9289d6f2eea1c416961b2fb96348bc8a211d550728f1d99ac49c

1 files changed, 8 insertions, 14 deletions

diff --git a/src/script/signingprovider.cpp b/src/script/signingprovider.cpp
index c624a17628..a82a8b252a 100644
--- a/src/script/signingprovider.cpp
+++ b/src/script/signingprovider.cpp
@@ -77,20 +77,14 @@ bool FlatSigningProvider::GetTaprootBuilder(const XOnlyPubKey& output_key, Tapro
     return LookupHelper(tr_trees, output_key, builder);
 }
 
-FlatSigningProvider Merge(const FlatSigningProvider& a, const FlatSigningProvider& b)
-{
-    FlatSigningProvider ret;
-    ret.scripts = a.scripts;
-    ret.scripts.insert(b.scripts.begin(), b.scripts.end());
-    ret.pubkeys = a.pubkeys;
-    ret.pubkeys.insert(b.pubkeys.begin(), b.pubkeys.end());
-    ret.keys = a.keys;
-    ret.keys.insert(b.keys.begin(), b.keys.end());
-    ret.origins = a.origins;
-    ret.origins.insert(b.origins.begin(), b.origins.end());
-    ret.tr_trees = a.tr_trees;
-    ret.tr_trees.insert(b.tr_trees.begin(), b.tr_trees.end());
-    return ret;
+FlatSigningProvider& FlatSigningProvider::Merge(FlatSigningProvider&& b)
+{
+    scripts.merge(b.scripts);
+    pubkeys.merge(b.pubkeys);
+    keys.merge(b.keys);
+    origins.merge(b.origins);
+    tr_trees.merge(b.tr_trees);
+    return *this;
 }
 
 void FillableSigningProvider::ImplicitlyLearnRelatedKeyScripts(const CPubKey& pubkey)