Add 'third_party/nix/' from commit 'be66c7a6b24e3c3c6157fd37b86c7203d14acf10'

git-subtree-dir: third_party/nix
git-subtree-mainline: cf8cd640c1
git-subtree-split: be66c7a6b24e3c3c6157fd37b86c7203d14acf10

third_party/nix/src/libutil/config.hh

@@ -0,0 +1,261 @@
+#include <map>
+#include <set>
+
+#include "types.hh"
+
+#pragma once
+
+namespace nix {
+
+class Args;
+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:
+
+   class MyClass : private Config
+   {
+     Setting<int> foo{this, 123, "foo", "the number of foos to use"};
+     Setting<std::string> bar{this, "blabla", "bar", "the name of the bar"};
+
+     MyClass() : Config(readConfigFile("/etc/my-app.conf"))
+     {
+       std::cout << foo << "\n"; // will print 123 unless overriden
+     }
+   };
+*/
+
+class Config : public AbstractConfig
+{
+    friend class AbstractSetting;
+
+public:
+
+    struct SettingData
+    {
+        bool isAlias;
+        AbstractSetting * setting;
+        SettingData(bool isAlias, AbstractSetting * setting)
+            : isAlias(isAlias), setting(setting)
+        { }
+    };
+
+    typedef std::map<std::string, SettingData> Settings;
+
+private:
+
+    Settings _settings;
+
+public:
+
+    Config(const StringMap & initials = {})
+        : AbstractConfig(initials)
+    { }
+
+    bool set(const std::string & name, const std::string & value) override;
+
+    void addSetting(AbstractSetting * setting);
+
+    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;
+};
+
+class AbstractSetting
+{
+    friend class Config;
+
+public:
+
+    const std::string name;
+    const std::string description;
+    const std::set<std::string> aliases;
+
+    int created = 123;
+
+    bool overriden = false;
+
+protected:
+
+    AbstractSetting(
+        const std::string & name,
+        const std::string & description,
+        const std::set<std::string> & aliases);
+
+    virtual ~AbstractSetting()
+    {
+        // Check against a gcc miscompilation causing our constructor
+        // not to run (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80431).
+        assert(created == 123);
+    }
+
+    virtual void set(const std::string & value) = 0;
+
+    virtual std::string to_string() = 0;
+
+    virtual void toJSON(JSONPlaceholder & out);
+
+    virtual void convertToArg(Args & args, const std::string & category);
+
+    bool isOverriden() { return overriden; }
+};
+
+/* A setting of type T. */
+template<typename T>
+class BaseSetting : public AbstractSetting
+{
+protected:
+
+    T value;
+
+public:
+
+    BaseSetting(const T & def,
+        const std::string & name,
+        const std::string & description,
+        const std::set<std::string> & aliases = {})
+        : AbstractSetting(name, description, aliases)
+        , value(def)
+    { }
+
+    operator const T &() const { return value; }
+    operator T &() { return value; }
+    const T & get() const { return value; }
+    bool operator ==(const T & v2) const { return value == v2; }
+    bool operator !=(const T & v2) const { return value != v2; }
+    void operator =(const T & v) { assign(v); }
+    virtual void assign(const T & v) { value = v; }
+
+    void set(const std::string & str) override;
+
+    virtual void override(const T & v)
+    {
+        overriden = true;
+        value = v;
+    }
+
+    std::string to_string() override;
+
+    void convertToArg(Args & args, const std::string & category) override;
+
+    void toJSON(JSONPlaceholder & out) override;
+};
+
+template<typename T>
+std::ostream & operator <<(std::ostream & str, const BaseSetting<T> & opt)
+{
+    str << (const T &) opt;
+    return str;
+}
+
+template<typename T>
+bool operator ==(const T & v1, const BaseSetting<T> & v2) { return v1 == (const T &) v2; }
+
+template<typename T>
+class Setting : public BaseSetting<T>
+{
+public:
+    Setting(Config * options,
+        const T & def,
+        const std::string & name,
+        const std::string & description,
+        const std::set<std::string> & aliases = {})
+        : BaseSetting<T>(def, name, description, aliases)
+    {
+        options->addSetting(this);
+    }
+
+    void operator =(const T & v) { this->assign(v); }
+};
+
+/* A special setting for Paths. These are automatically canonicalised
+   (e.g. "/foo//bar/" becomes "/foo/bar"). */
+class PathSetting : public BaseSetting<Path>
+{
+    bool allowEmpty;
+
+public:
+
+    PathSetting(Config * options,
+        bool allowEmpty,
+        const Path & def,
+        const std::string & name,
+        const std::string & description,
+        const std::set<std::string> & aliases = {})
+        : BaseSetting<Path>(def, name, description, aliases)
+        , allowEmpty(allowEmpty)
+    {
+        options->addSetting(this);
+    }
+
+    void set(const std::string & str) override;
+
+    Path operator +(const char * p) const { return value + p; }
+
+    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;
+
+}