Merge bitcoin/bitcoin#34684: refactor: Enable -Wswitch in exhaustive switch'es, Enable -Wcovered-switch-default

fa4ec13b44 build: Enable -Wcovered-switch-default (MarcoFalke)
fa2670bd4b refactor: Enable -Wswitch in exhaustive switch (MarcoFalke)

Pull request description:

  The compiler flag `-Wswitch` is enabled. However, it can not fire when a `default:` case exists. Fix that by removing the default case where a switch is already handling all cases exhaustively.

  Also, enable `-Wcovered-switch-default` to catch those cases at compile time in the future.

  Also, apply the comment according to the dev notes.

  Can be reviewed via `--ignore-all-space`

ACKs for top commit:
  stickies-v:
    re-ACK fa4ec13b44, no changes except for addressing silent merge conflict from d339884f1d
  l0rinc:
    ACK fa4ec13b44
  achow101:
    ACK fa4ec13b44
  sedited:
    ACK fa4ec13b44

Tree-SHA512: 8dd9e71a8cd338255f43448a59a1a4d40a9fc16e19a707cc10fb71442d4df9f82a0e5fae77868ef49cd0ea27fdd972687572c1a50b6aba7e08c6ce87576afc6a

src/bench/sign_transaction.cpp

@@ -42,12 +42,15 @@ static void SignTransactionSingleInput(benchmark::Bench& bench, InputType input_
         keystore.pubkeys.emplace(key_id, pubkey);
 
         // Create specified locking script type
-        CScript prev_spk;
-        switch (input_type) {
-        case InputType::P2WPKH: prev_spk = GetScriptForDestination(WitnessV0KeyHash(pubkey)); break;
-        case InputType::P2TR:   prev_spk = GetScriptForDestination(WitnessV1Taproot(XOnlyPubKey{pubkey})); break;
-        default: assert(false);
-        }
+        CScript prev_spk = [&]() {
+            switch (input_type) {
+            case InputType::P2WPKH:
+                return GetScriptForDestination(WitnessV0KeyHash(pubkey));
+            case InputType::P2TR:
+                return GetScriptForDestination(WitnessV1Taproot(XOnlyPubKey{pubkey}));
+            } // no default case, so the compiler can warn about missing cases
+            assert(false);
+        }();
         prev_spks.push_back(prev_spk);
     }
 

src/bench/verify_script.cpp

@@ -41,12 +41,13 @@ static void VerifyScriptBench(benchmark::Bench& bench, ScriptType script_type)
     keystore.pubkeys.emplace(key_id, pubkey);
 
     // Create crediting and spending transactions with provided input type
-    CTxDestination dest;
-    switch (script_type) {
-    case ScriptType::P2WPKH: dest = WitnessV0KeyHash(pubkey); break;
-    case ScriptType::P2TR:   dest = WitnessV1Taproot(XOnlyPubKey{pubkey}); break;
-    default: assert(false);
-    }
+    const auto dest{[&]() -> CTxDestination {
+        switch (script_type) {
+        case ScriptType::P2WPKH: return WitnessV0KeyHash(pubkey);
+        case ScriptType::P2TR: return WitnessV1Taproot(XOnlyPubKey{pubkey});
+        } // no default case, so the compiler can warn about missing cases
+        assert(false);
+    }()};
     const CMutableTransaction& txCredit = BuildCreditingTransaction(GetScriptForDestination(dest), 1);
     CMutableTransaction txSpend = BuildSpendingTransaction(/*scriptSig=*/{}, /*scriptWitness=*/{}, CTransaction(txCredit));