Modularize config settings

Allow global config settings to be defined in multiple Config
classes. For example, this means that libutil can have settings and
evaluator settings can be moved out of libstore. The Config classes
are registered in a new GlobalConfig class to which config files
etc. are applied.

Relevant to https://github.com/NixOS/nix/issues/2009 in that it
removes the need for ad hoc handling of useCaseHack, which was the
underlying cause of that issue.

1 files changed, 65 insertions, 16 deletions

diff --git a/src/libutil/config.hh b/src/libutil/config.hh
index d2e7faf174..d86c65ff03 100644
--- a/src/libutil/config.hh
+++ b/src/libutil/config.hh
@@ -12,6 +12,40 @@ class AbstractSetting;
 class JSONPlaceholder;
 class JSONObject;
 
+class AbstractConfig
+{
+protected:
+    StringMap unknownSettings;
+
+    AbstractConfig(const StringMap & initials = {})
+        : unknownSettings(initials)
+    { }
+
+public:
+
+    virtual bool set(const std::string & name, const std::string & value) = 0;
+
+    struct SettingInfo
+    {
+        std::string value;
+        std::string description;
+    };
+
+    virtual void getSettings(std::map<std::string, SettingInfo> & res, bool overridenOnly = false) = 0;
+
+    void applyConfigFile(const Path & path);
+
+    virtual void resetOverriden() = 0;
+
+    virtual void toJSON(JSONObject & out) = 0;
+
+    virtual void convertToArgs(Args & args, const std::string & category) = 0;
+
+    void warnUnknownSettings();
+
+    void reapplyUnknownSettings();
+};
+
 /* A class to simplify providing configuration settings. The typical
    use is to inherit Config and add Setting<T> members:
 
@@ -27,7 +61,7 @@ class JSONObject;
    };
 */
 
-class Config
+class Config : public AbstractConfig
 {
     friend class AbstractSetting;
 
@@ -48,31 +82,23 @@ private:
 
     Settings _settings;
 
-    StringMap extras;
-
 public:
 
-    Config(const StringMap & initials)
-        : extras(initials)
+    Config(const StringMap & initials = {})
+        : AbstractConfig(initials)
     { }
 
-    void set(const std::string & name, const std::string & value);
+    bool set(const std::string & name, const std::string & value) override;
 
     void addSetting(AbstractSetting * setting);
 
-    void handleUnknownSettings();
-
-    StringMap getSettings(bool overridenOnly = false);
+    void getSettings(std::map<std::string, SettingInfo> & res, bool overridenOnly = false) override;
 
-    const Settings & _getSettings() { return _settings; }
-
-    void applyConfigFile(const Path & path);
+    void resetOverriden() override;
 
-    void resetOverriden();
+    void toJSON(JSONObject & out) override;
 
-    void toJSON(JSONObject & out);
-
-    void convertToArgs(Args & args, const std::string & category);
+    void convertToArgs(Args & args, const std::string & category) override;
 };
 
 class AbstractSetting
@@ -209,4 +235,27 @@ public:
     void operator =(const Path & v) { this->assign(v); }
 };
 
+struct GlobalConfig : public AbstractConfig
+{
+    typedef std::vector<Config*> ConfigRegistrations;
+    static ConfigRegistrations * configRegistrations;
+
+    bool set(const std::string & name, const std::string & value) override;
+
+    void getSettings(std::map<std::string, SettingInfo> & res, bool overridenOnly = false) override;
+
+    void resetOverriden() override;
+
+    void toJSON(JSONObject & out) override;
+
+    void convertToArgs(Args & args, const std::string & category) override;
+
+    struct Register
+    {
+        Register(Config * config);
+    };
+};
+
+extern GlobalConfig globalConfig;
+
 }