refactor: Introduce ChainType getters for ArgsManager

These are introduced for the next commit where the usage of the
ChainType is adopted throughout the code.

Co-authored-by: Russell Yanofsky <russ@yanofsky.org>
Co-authored-by: TheCharlatan <seb.kung@gmail.com>

Author: TheCharlatan

src/common/args.cpp

@@ -10,6 +10,7 @@
 #include <sync.h>
 #include <tinyformat.h>
 #include <univalue.h>
+#include <util/chaintype.h>
 #include <util/check.h>
 #include <util/fs.h>
 #include <util/fs_helpers.h>
@@ -33,6 +34,7 @@
 #include <stdexcept>
 #include <string>
 #include <utility>
+#include <variant>
 
 const char * const BITCOIN_CONF_FILENAME = "bitcoin.conf";
 const char * const BITCOIN_SETTINGS_FILENAME = "settings.json";
@@ -717,7 +719,21 @@ fs::path ArgsManager::GetConfigFilePath() const
     return GetConfigFile(*this, GetPathArg("-conf", BITCOIN_CONF_FILENAME));
 }
 
+ChainType ArgsManager::GetChainType() const
+{
+    std::variant<ChainType, std::string> arg = GetChainArg();
+    if (auto* parsed = std::get_if<ChainType>(&arg)) return *parsed;
+    throw std::runtime_error(strprintf("Unknown chain %s.", std::get<std::string>(arg)));
+}
+
 std::string ArgsManager::GetChainName() const
+{
+    auto arg = GetChainArg();
+    if (auto* parsed = std::get_if<ChainType>(&arg)) return ChainTypeToString(*parsed);
+    return std::get<std::string>(arg);
+}
+
+std::variant<ChainType, std::string> ArgsManager::GetChainArg() const
 {
     auto get_net = [&](const std::string& arg) {
         LOCK(cs_args);
@@ -731,20 +747,20 @@ std::string ArgsManager::GetChainName() const
     const bool fRegTest = get_net("-regtest");
     const bool fSigNet  = get_net("-signet");
     const bool fTestNet = get_net("-testnet");
-    const bool is_chain_arg_set = IsArgSet("-chain");
+    const auto chain_arg = GetArg("-chain");
 
-    if ((int)is_chain_arg_set + (int)fRegTest + (int)fSigNet + (int)fTestNet > 1) {
+    if ((int)chain_arg.has_value() + (int)fRegTest + (int)fSigNet + (int)fTestNet > 1) {
         throw std::runtime_error("Invalid combination of -regtest, -signet, -testnet and -chain. Can use at most one.");
     }
-    if (fRegTest)
-        return CBaseChainParams::REGTEST;
-    if (fSigNet) {
-        return CBaseChainParams::SIGNET;
+    if (chain_arg) {
+        if (auto parsed = ChainTypeFromString(*chain_arg)) return *parsed;
+        // Not a known string, so return original string
+        return *chain_arg;
     }
-    if (fTestNet)
-        return CBaseChainParams::TESTNET;
-
-    return GetArg("-chain", CBaseChainParams::MAIN);
+    if (fRegTest) return ChainType::REGTEST;
+    if (fSigNet) return ChainType::SIGNET;
+    if (fTestNet) return ChainType::TESTNET;
+    return ChainType::MAIN;
 }
 
 bool ArgsManager::UseDefaultSection(const std::string& arg) const

src/common/args.h

@@ -7,6 +7,7 @@
 
 #include <compat/compat.h>
 #include <sync.h>
+#include <util/chaintype.h>
 #include <util/fs.h>
 #include <util/settings.h>
 
@@ -17,6 +18,7 @@
 #include <set>
 #include <stdint.h>
 #include <string>
+#include <variant>
 #include <vector>
 
 class ArgsManager;
@@ -324,7 +326,15 @@ class ArgsManager
 
     /**
      * Returns the appropriate chain name from the program arguments.
-     * @return CBaseChainParams::MAIN by default; raises runtime error if an invalid combination is given.
+     * @return ChainType::MAIN by default; raises runtime error if an invalid
+     * combination, or unknown chain is given.
+     */
+    ChainType GetChainType() const;
+
+    /**
+     * Returns the appropriate chain name string from the program arguments.
+     * @return ChainType::MAIN string by default; raises runtime error if an
+     * invalid combination is given.
      */
     std::string GetChainName() const;
 
@@ -411,6 +421,14 @@ class ArgsManager
      */
     const fs::path& GetDataDir(bool net_specific) const;
 
+    /**
+     * Return -regtest/-signet/-testnet/-chain= setting as a ChainType enum if a
+     * recognized chain name was set, or as a string if an unrecognized chain
+     * name was set. Raise an exception if an invalid combination of flags was
+     * provided.
+     */
+    std::variant<ChainType, std::string> GetChainArg() const;
+
     // Helper function for LogArgs().
     void logArgsPrefix(
         const std::string& prefix,