Try to make Config a bit easier to use

- Use references, not pointers, to indicate Config must be initializd.

- Wrap cast to avoid the GCC bug in a helper function, so if we need to
  move it, it's not so bad.

src/libexpr/eval.cc

@@ -2522,7 +2522,7 @@ std::string EvalSettings::resolvePseudoUrl(std::string_view url)
 
 EvalSettings evalSettings;
 
-static GlobalConfig::Register rEvalSettings(&evalSettings);
+static GlobalConfig::Register rEvalSettings { evalSettings };
 
 
 }

src/libexpr/eval.hh

@@ -577,27 +577,27 @@ struct EvalSettings : Config
 
     static std::string resolvePseudoUrl(std::string_view url);
 
-    Setting<bool> enableNativeCode{this, false, "allow-unsafe-native-code-during-evaluation",
+    Setting<bool> enableNativeCode{*this, false, "allow-unsafe-native-code-during-evaluation",
         "Whether builtin functions that allow executing native code should be enabled."};
 
     Setting<Strings> nixPath{
-        this, getDefaultNixPath(), "nix-path",
+        *this, getDefaultNixPath(), "nix-path",
         "List of directories to be searched for `<...>` file references."};
 
     Setting<bool> restrictEval{
-        this, false, "restrict-eval",
+        *this, false, "restrict-eval",
         R"(
           If set to `true`, the Nix evaluator will not allow access to any
           files outside of the Nix search path (as set via the `NIX_PATH`
           environment variable or the `-I` option), or to URIs outside of
           `allowed-uri`. The default is `false`.
         )"};
 
-    Setting<bool> pureEval{this, false, "pure-eval",
+    Setting<bool> pureEval{*this, false, "pure-eval",
         "Whether to restrict file system and network access to files specified by cryptographic hash."};
 
     Setting<bool> enableImportFromDerivation{
-        this, true, "allow-import-from-derivation",
+        *this, true, "allow-import-from-derivation",
         R"(
           By default, Nix allows you to `import` from a derivation, allowing
           building at evaluation time. With this option set to false, Nix will
@@ -606,15 +606,15 @@ struct EvalSettings : Config
           builds to take place.
         )"};
 
-    Setting<Strings> allowedUris{this, {}, "allowed-uris",
+    Setting<Strings> allowedUris{*this, {}, "allowed-uris",
         R"(
           A list of URI prefixes to which access is allowed in restricted
           evaluation mode. For example, when set to
           `https://github.com/NixOS`, builtin functions such as `fetchGit` are
           allowed to access `https://github.com/NixOS/patchelf.git`.
         )"};
 
-    Setting<bool> traceFunctionCalls{this, false, "trace-function-calls",
+    Setting<bool> traceFunctionCalls{*this, false, "trace-function-calls",
         R"(
           If set to `true`, the Nix evaluator will trace every function call.
           Nix will print a log message at the "vomit" level for every function
@@ -632,16 +632,16 @@ struct EvalSettings : Config
           `flamegraph.pl`.
         )"};
 
-    Setting<bool> useEvalCache{this, true, "eval-cache",
+    Setting<bool> useEvalCache{*this, true, "eval-cache",
         "Whether to use the flake evaluation cache."};
 
-    Setting<bool> ignoreExceptionsDuringTry{this, false, "ignore-try",
+    Setting<bool> ignoreExceptionsDuringTry{*this, false, "ignore-try",
         R"(
           If set to true, ignore exceptions inside 'tryEval' calls when evaluating nix expressions in
           debug mode (using the --debugger flag). By default the debugger will pause on all exceptions.
         )"};
 
-    Setting<bool> traceVerbose{this, false, "trace-verbose",
+    Setting<bool> traceVerbose{*this, false, "trace-verbose",
         "Whether `builtins.traceVerbose` should trace its first argument when evaluated."};
 };
 

src/libfetchers/fetch-settings.cc

@@ -8,6 +8,6 @@ FetchSettings::FetchSettings()
 
 FetchSettings fetchSettings;
 
-static GlobalConfig::Register rFetchSettings(&fetchSettings);
+static GlobalConfig::Register rFetchSettings { fetchSettings };
 
 }

src/libfetchers/fetch-settings.hh

@@ -15,7 +15,7 @@ struct FetchSettings : public Config
 {
     FetchSettings();
 
-    Setting<StringMap> accessTokens{this, {}, "access-tokens",
+    Setting<StringMap> accessTokens{*this, {}, "access-tokens",
         R"(
           Access tokens used to access protected GitHub, GitLab, or
           other locations requiring token-based authentication.
@@ -64,28 +64,28 @@ struct FetchSettings : public Config
           value.
           )"};
 
-    Setting<bool> allowDirty{this, true, "allow-dirty",
+    Setting<bool> allowDirty{*this, true, "allow-dirty",
         "Whether to allow dirty Git/Mercurial trees."};
 
-    Setting<bool> warnDirty{this, true, "warn-dirty",
+    Setting<bool> warnDirty{*this, true, "warn-dirty",
         "Whether to warn about dirty Git/Mercurial trees."};
 
-    Setting<std::string> flakeRegistry{this, "https://channels.nixos.org/flake-registry.json", "flake-registry",
+    Setting<std::string> flakeRegistry{*this, "https://channels.nixos.org/flake-registry.json", "flake-registry",
         R"(
           Path or URI of the global flake registry.
 
           When empty, disables the global flake registry.
         )"};
 
 
-    Setting<bool> useRegistries{this, true, "use-registries",
+    Setting<bool> useRegistries{*this, true, "use-registries",
         "Whether to use flake registries to resolve flake references."};
 
-    Setting<bool> acceptFlakeConfig{this, false, "accept-flake-config",
+    Setting<bool> acceptFlakeConfig{*this, false, "accept-flake-config",
         "Whether to accept nix configuration from a flake without prompting."};
 
     Setting<std::string> commitLockFileSummary{
-        this, "", "commit-lockfile-summary",
+        *this, "", "commit-lockfile-summary",
         R"(
           The commit summary to use when committing changed flake lock files. If
           empty, the summary is generated based on the action performed.

src/libstore/binary-cache-store.hh

@@ -16,14 +16,14 @@ struct BinaryCacheStoreConfig : virtual StoreConfig
 {
     using StoreConfig::StoreConfig;
 
-    const Setting<std::string> compression{(StoreConfig*) this, "xz", "compression", "NAR compression method ('xz', 'bzip2', 'gzip', 'zstd', or 'none')"};
-    const Setting<bool> writeNARListing{(StoreConfig*) this, false, "write-nar-listing", "whether to write a JSON file listing the files in each NAR"};
-    const Setting<bool> writeDebugInfo{(StoreConfig*) this, false, "index-debug-info", "whether to index DWARF debug info files by build ID"};
-    const Setting<Path> secretKeyFile{(StoreConfig*) this, "", "secret-key", "path to secret key used to sign the binary cache"};
-    const Setting<Path> localNarCache{(StoreConfig*) this, "", "local-nar-cache", "path to a local cache of NARs"};
-    const Setting<bool> parallelCompression{(StoreConfig*) this, false, "parallel-compression",
+    const Setting<std::string> compression{this->dodgeGcc80431(), "xz", "compression", "NAR compression method ('xz', 'bzip2', 'gzip', 'zstd', or 'none')"};
+    const Setting<bool> writeNARListing{this->dodgeGcc80431(), false, "write-nar-listing", "whether to write a JSON file listing the files in each NAR"};
+    const Setting<bool> writeDebugInfo{this->dodgeGcc80431(), false, "index-debug-info", "whether to index DWARF debug info files by build ID"};
+    const Setting<Path> secretKeyFile{this->dodgeGcc80431(), "", "secret-key", "path to secret key used to sign the binary cache"};
+    const Setting<Path> localNarCache{this->dodgeGcc80431(), "", "local-nar-cache", "path to a local cache of NARs"};
+    const Setting<bool> parallelCompression{this->dodgeGcc80431(), false, "parallel-compression",
         "enable multi-threading compression for NARs, available for xz and zstd only currently"};
-    const Setting<int> compressionLevel{(StoreConfig*) this, -1, "compression-level",
+    const Setting<int> compressionLevel{this->dodgeGcc80431(), -1, "compression-level",
         "specify 'preset level' of compression to be used with NARs: "
         "meaning and accepted range of values depends on compression method selected, "
         "other than -1 which we reserve to indicate Nix defaults should be used"};

src/libstore/filetransfer.cc

@@ -31,7 +31,7 @@ namespace nix {
 
 FileTransferSettings fileTransferSettings;
 
-static GlobalConfig::Register rFileTransferSettings(&fileTransferSettings);
+static GlobalConfig::Register rFileTransferSettings {fileTransferSettings };
 
 struct curlFileTransfer : public FileTransfer
 {

src/libstore/filetransfer.hh

@@ -11,14 +11,14 @@ namespace nix {
 
 struct FileTransferSettings : Config
 {
-    Setting<bool> enableHttp2{this, true, "http2",
+    Setting<bool> enableHttp2{*this, true, "http2",
         "Whether to enable HTTP/2 support."};
 
-    Setting<std::string> userAgentSuffix{this, "", "user-agent-suffix",
+    Setting<std::string> userAgentSuffix{*this, "", "user-agent-suffix",
         "String appended to the user agent in HTTP requests."};
 
     Setting<size_t> httpConnections{
-        this, 25, "http-connections",
+        *this, 25, "http-connections",
         R"(
           The maximum number of parallel TCP connections used to fetch
           files from binary caches and by other downloads. It defaults
@@ -27,22 +27,22 @@ struct FileTransferSettings : Config
         {"binary-caches-parallel-connections"}};
 
     Setting<unsigned long> connectTimeout{
-        this, 0, "connect-timeout",
+        *this, 0, "connect-timeout",
         R"(
           The timeout (in seconds) for establishing connections in the
           binary cache substituter. It corresponds to `curl`’s
           `--connect-timeout` option. A value of 0 means no limit.
         )"};
 
     Setting<unsigned long> stalledDownloadTimeout{
-        this, 300, "stalled-download-timeout",
+        *this, 300, "stalled-download-timeout",
         R"(
           The timeout (in seconds) for receiving data from servers
           during download. Nix cancels idle downloads after this
           timeout's duration.
         )"};
 
-    Setting<unsigned int> tries{this, 5, "download-attempts",
+    Setting<unsigned int> tries{*this, 5, "download-attempts",
         "How often Nix will attempt to download a file before giving up."};
 };
 

src/libstore/globals.cc

@@ -26,7 +26,7 @@ namespace nix {
 
 Settings settings;
 
-static GlobalConfig::Register rSettings(&settings);
+static GlobalConfig::Register rSettings { settings };
 
 Settings::Settings()
     : nixPrefix(NIX_PREFIX)