Everything: Add -Wnon-virtual-dtor flag

This flag warns on classes which have `virtual` functions but do not
have a `virtual` destructor.

This patch adds both the flag and missing destructors. The access level
of the destructors was determined by a two rules of thumb:
1. A destructor should have a similar or lower access level to that of a
   constructor.
2. Having a `private` destructor implicitly deletes the default
   constructor, which is probably undesirable for "interface" types
   (classes with only virtual functions and no data).

In short, most of the added destructors are `protected`, unless the
compiler complained about access.

CMakeLists.txt

@@ -174,6 +174,7 @@ add_compile_options(-Wlogical-op)
 add_compile_options(-Wmisleading-indentation)
 add_compile_options(-Wmissing-declarations)
 add_compile_options(-Wno-nonnull-compare)
+add_compile_options(-Wnon-virtual-dtor)
 add_compile_options(-Wno-unknown-warning-option)
 add_compile_options(-Wundef)
 add_compile_options(-Wunused)

Kernel/ACPI/Parser.h

@@ -69,6 +69,7 @@ public:
 
 protected:
     explicit Parser(PhysicalAddress rsdp);
+    virtual ~Parser() = default;
 
 private:
     static void set_the(Parser&);

Kernel/Interrupts/InterruptManagement.h

@@ -83,6 +83,9 @@ public:
     void enumerate_interrupt_handlers(Function<void(GenericInterruptHandler&)>);
     IRQController& get_interrupt_controller(int index);
 
+protected:
+    virtual ~InterruptManagement() = default;
+
 private:
     InterruptManagement();
     PhysicalAddress search_for_madt();

Kernel/PCI/Access.h

@@ -66,6 +66,8 @@ protected:
     u16 early_read_type(Address address);
 
     Access();
+    virtual ~Access() = default;
+
     Vector<PhysicalID> m_physical_ids;
 };
 

Userland/Applications/PixelPaint/Image.h

@@ -49,6 +49,9 @@ public:
     virtual void image_did_modify_layer_stack() { }
     virtual void image_did_change() { }
     virtual void image_select_layer(Layer*) { }
+
+protected:
+    virtual ~ImageClient() = default;
 };
 
 class Image : public RefCounted<Image> {

Userland/Applications/SoundPlayer/Player.h

@@ -84,6 +84,8 @@ public:
     PlaybackManager& manager() { return m_player_state.manager; }
 
 protected:
+    virtual ~Player() = default;
+
     PlayerState m_player_state;
     RefPtr<PlaylistModel> m_playlist_model;
 };

Userland/Applications/SoundPlayer/VisualizationBase.h

@@ -32,4 +32,7 @@ class Visualization {
 public:
     virtual void set_buffer(RefPtr<Audio::Buffer> buffer) = 0;
     virtual void set_samplerate(int) { }
+
+protected:
+    virtual ~Visualization() = default;
 };

Userland/Applications/SpaceAnalyzer/TreeMapWidget.h

@@ -37,6 +37,9 @@ struct TreeMapNode {
     virtual size_t num_children() const = 0;
     virtual const TreeMapNode& child_at(size_t i) const = 0;
     virtual void sort_children_by_area() const = 0;
+
+protected:
+    virtual ~TreeMapNode() = default;
 };
 
 struct TreeMap : public RefCounted<TreeMap> {

Userland/Libraries/LibCrypto/Checksum/ChecksumFunction.h

@@ -35,6 +35,9 @@ class ChecksumFunction {
 public:
     virtual void update(ReadonlyBytes data) = 0;
     virtual ChecksumType digest() = 0;
+
+protected:
+    virtual ~ChecksumFunction() = default;
 };
 
 }

Userland/Libraries/LibCrypto/Cipher/Cipher.h

@@ -92,6 +92,9 @@ public:
         ptr[index] = (u8)value;
     }
 
+protected:
+    virtual ~CipherBlock() = default;
+
 private:
     virtual Bytes bytes() = 0;
     PaddingMode m_padding_mode;
@@ -132,6 +135,9 @@ public:
 
     virtual String class_name() const = 0;
 
+protected:
+    virtual ~Cipher() = default;
+
 private:
     PaddingMode m_padding_mode;
 };

Userland/Libraries/LibCrypto/Hash/HashFunction.h

@@ -57,6 +57,9 @@ public:
     virtual void reset() = 0;
 
     virtual String class_name() const = 0;
+
+protected:
+    virtual ~HashFunction() = default;
 };
 }
 }

Userland/Libraries/LibCrypto/PK/Code/Code.h

@@ -48,6 +48,8 @@ public:
     HashFunction& hasher() { return m_hasher; }
 
 protected:
+    virtual ~Code() = default;
+
     HashFunction m_hasher;
 };
 

Userland/Libraries/LibCrypto/PK/PK.h

@@ -60,6 +60,8 @@ public:
     virtual size_t output_size() const = 0;
 
 protected:
+    virtual ~PKSystem() = default;
+
     PublicKeyType m_public_key;
     PrivateKeyType m_private_key;
 };

Userland/Libraries/LibJS/Console.h

@@ -93,6 +93,8 @@ public:
     virtual Value count_reset() = 0;
 
 protected:
+    virtual ~ConsoleClient() = default;
+
     VM& vm();
 
     GlobalObject& global_object() { return m_console.global_object(); }

Userland/Libraries/LibJS/Runtime/Cell.h

@@ -58,6 +58,7 @@ public:
 
     protected:
         virtual void visit_impl(Cell*) = 0;
+        virtual ~Visitor() = default;
     };
 
     virtual void visit_edges(Visitor&) { }

Userland/Libraries/LibTextCodec/Decoder.h

@@ -33,6 +33,9 @@ namespace TextCodec {
 class Decoder {
 public:
     virtual String to_utf8(const StringView&) = 0;
+
+protected:
+    virtual ~Decoder() = default;
 };
 
 class UTF8Decoder final : public Decoder {

Userland/Libraries/LibWeb/Page/Page.h

@@ -113,6 +113,9 @@ public:
     virtual String page_did_request_prompt(const String&, const String&) { return {}; }
     virtual String page_did_request_cookie(const URL&, Cookie::Source) { return {}; }
     virtual void page_did_set_cookie(const URL&, const String&, Cookie::Source) { }
+
+protected:
+    virtual ~PageClient() = default;
 };
 
 }

Userland/Libraries/LibX86/Instruction.h

@@ -41,6 +41,9 @@ typedef void (Interpreter::*InstructionHandler)(const Instruction&);
 class SymbolProvider {
 public:
     virtual String symbolicate(FlatPtr, u32* offset = nullptr) const = 0;
+
+protected:
+    virtual ~SymbolProvider() = default;
 };
 
 template<typename T>
@@ -316,6 +319,9 @@ public:
     virtual u16 read16() = 0;
     virtual u32 read32() = 0;
     virtual u64 read64() = 0;
+
+protected:
+    virtual ~InstructionStream() = default;
 };
 
 class SimpleInstructionStream final : public InstructionStream {

Userland/Libraries/LibX86/Interpreter.h

@@ -622,6 +622,9 @@ public:
     virtual void wrap_0xD2(const Instruction&) = 0;
     virtual void wrap_0xD3_16(const Instruction&) = 0;
     virtual void wrap_0xD3_32(const Instruction&) = 0;
+
+protected:
+    virtual ~Interpreter() = default;
 };
 
 typedef void (Interpreter::*InstructionHandler)(const Instruction&);

Userland/Shell/NodeVisitor.h

@@ -75,6 +75,9 @@ public:
     virtual void visit(const AST::VariableDeclarations*);
     virtual void visit(const AST::WriteAppendRedirection*);
     virtual void visit(const AST::WriteRedirection*);
+
+protected:
+    virtual ~NodeVisitor() = default;
 };
 
 }

Userland/Utilities/test-js.cpp

@@ -99,6 +99,8 @@ public:
         s_the = this;
     }
 
+    virtual ~TestRunner() = default;
+
     void run();
 
     const Test::Counts& counts() const { return m_counts; }