Support validating some options values before setting them

Fixes #583

src/Makefile

@@ -60,7 +60,7 @@ endif
 # Picking the right name is done in the system detection switch above
 A2X ?= a2x
 
-CXXFLAGS += -std=gnu++11 -g -Wall -Wno-reorder -Wno-sign-compare
+CXXFLAGS += -std=gnu++11 -g -Wall -Wno-reorder -Wno-sign-compare -Wno-address
 
 kak : $(objects)
 	$(CXX) $(LDFLAGS) $(CXXFLAGS) $(objects) $(LIBS) -o $@

src/main.cc

@@ -178,15 +178,27 @@ void register_registers()
     register_manager.add_register('_', make_unique<NullRegister>());
 }
 
+static void check_positive(const int& val)
+{
+    if (val < 1)
+        throw runtime_error{"value should be strictly positive"};
+}
+
+static void check_scrolloff(const CharCoord& so)
+{
+    if (so.line < 0 or so.column < 0)
+        throw runtime_error{"scroll offset must be positive or zero"};
+}
+
 void register_options()
 {
     OptionsRegistry& reg = GlobalScope::instance().option_registry();
 
-    reg.declare_option("tabstop", "size of a tab character", 8);
+    reg.declare_option<int, check_positive>("tabstop", "size of a tab character", 8);
-    reg.declare_option("indentwidth", "indentation width", 4);
+    reg.declare_option<int, check_positive>("indentwidth", "indentation width", 4);
-    reg.declare_option("scrolloff",
+    reg.declare_option<CharCoord, check_scrolloff>(
-                       "number of lines and columns to keep visible main cursor when scrolling",
+        "scrolloff", "number of lines and columns to keep visible main cursor when scrolling",
-                       CharCoord{0,0});
+        {0,0});
     reg.declare_option("eolformat", "end of line format: crlf or lf", EolFormat::Lf);
     reg.declare_option("BOM", "insert a byte order mark when writing buffer (none or utf8)",
                        ByteOrderMark::None);

src/option_manager.hh

@@ -115,6 +115,7 @@ public:
 
     void set(T value, bool notify = true)
     {
+        validate(value);
         if (m_value != value)
         {
             m_value = std::move(value);
@@ -141,11 +142,6 @@ public:
             m_manager.on_option_changed(*this);
     }
 
-    Option* clone(OptionManager& manager) const override
-    {
-        return new TypedOption{manager, m_desc, m_value};
-    }
-
     using Alloc = Allocator<TypedOption, MemoryDomain::Options>;
     static void* operator new (std::size_t sz)
     {
@@ -158,9 +154,23 @@ public:
         return Alloc{}.deallocate(reinterpret_cast<TypedOption*>(ptr), 1);
     }
 private:
+    virtual void validate(const T& value) const {}
     T m_value;
 };
 
+template<typename T, void (*validator)(const T&)>
+class TypedCheckedOption : public TypedOption<T>
+{
+    using TypedOption<T>::TypedOption;
+
+    Option* clone(OptionManager& manager) const override
+    {
+        return new TypedCheckedOption{manager, this->m_desc, this->get()};
+    }
+
+    void validate(const T& value) const override { if (validator != nullptr) validator(value); }
+};
+
 template<typename T> const T& Option::get() const
 {
     auto* typed_opt = dynamic_cast<const TypedOption<T>*>(this);
@@ -199,7 +209,7 @@ class OptionsRegistry
 public:
     OptionsRegistry(OptionManager& global_manager) : m_global_manager(global_manager) {}
 
-    template<typename T>
+    template<typename T, void (*validator)(const T&) = nullptr>
     Option& declare_option(const String& name, const String& docstring,
                            const T& value,
                            OptionFlags flags = OptionFlags::None)
@@ -213,7 +223,7 @@ public:
             throw runtime_error(format("option '{}' already declared with different type or flags", name));
         }
         m_descs.emplace_back(new OptionDesc{name, docstring, flags});
-        opts.emplace_back(new TypedOption<T>{m_global_manager, *m_descs.back(), value});
+        opts.emplace_back(new TypedCheckedOption<T, validator>{m_global_manager, *m_descs.back(), value});
         return *opts.back();
     }