add werror=suggest-override

Improves code readability by making overrides explicit.
Inspired by lix code-base

Makefile

@@ -92,7 +92,7 @@ ifdef HOST_WINDOWS
   GLOBAL_LDFLAGS += -Wl,--export-all-symbols
 endif
 
-GLOBAL_CXXFLAGS += -g -Wall -Wdeprecated-copy -Wignored-qualifiers -Wimplicit-fallthrough -Werror=unused-result -include $(buildprefix)config.h -std=c++2a -I src
+GLOBAL_CXXFLAGS += -g -Wall -Wdeprecated-copy -Wignored-qualifiers -Wimplicit-fallthrough -Werror=unused-result -Werror=suggest-override -include $(buildprefix)config.h -std=c++2a -I src
 
 # Include the main lib, causing rules to be defined
 

build-utils-meson/diagnostics/meson.build

@@ -1,5 +1,6 @@
 add_project_arguments(
   '-Wdeprecated-copy',
+  '-Werror=suggest-override',
   '-Werror=switch',
   '-Werror=switch-enum',
   '-Werror=unused-result',

src/libexpr/json-to-value.cc

@@ -80,42 +80,42 @@ class JSONSax : nlohmann::json_sax<json> {
 public:
     JSONSax(EvalState & state, Value & v) : state(state), rs(new JSONState(&v)) {};
 
-    bool null()
+    bool null() override
     {
         rs->value(state).mkNull();
         rs->add();
         return true;
     }
 
-    bool boolean(bool val)
+    bool boolean(bool val) override
     {
         rs->value(state).mkBool(val);
         rs->add();
         return true;
     }
 
-    bool number_integer(number_integer_t val)
+    bool number_integer(number_integer_t val) override
     {
         rs->value(state).mkInt(val);
         rs->add();
         return true;
     }
 
-    bool number_unsigned(number_unsigned_t val)
+    bool number_unsigned(number_unsigned_t val) override
     {
         rs->value(state).mkInt(val);
         rs->add();
         return true;
     }
 
-    bool number_float(number_float_t val, const string_t & s)
+    bool number_float(number_float_t val, const string_t & s) override
     {
         rs->value(state).mkFloat(val);
         rs->add();
         return true;
     }
 
-    bool string(string_t & val)
+    bool string(string_t & val) override
     {
         rs->value(state).mkString(val);
         rs->add();
@@ -123,7 +123,7 @@ public:
     }
 
 #if NLOHMANN_JSON_VERSION_MAJOR >= 3 && NLOHMANN_JSON_VERSION_MINOR >= 8
-    bool binary(binary_t&)
+    bool binary(binary_t&) override
     {
         // This function ought to be unreachable
         assert(false);
@@ -131,35 +131,35 @@ public:
     }
 #endif
 
-    bool start_object(std::size_t len)
+    bool start_object(std::size_t len) override
     {
         rs = std::make_unique<JSONObjectState>(std::move(rs));
         return true;
     }
 
-    bool key(string_t & name)
+    bool key(string_t & name) override
     {
         dynamic_cast<JSONObjectState*>(rs.get())->key(name, state);
         return true;
     }
 
-    bool end_object() {
+    bool end_object() override {
         rs = rs->resolve(state);
         rs->add();
         return true;
     }
 
-    bool end_array() {
+    bool end_array() override {
         return end_object();
     }
 
-    bool start_array(size_t len) {
+    bool start_array(size_t len) override {
         rs = std::make_unique<JSONListState>(std::move(rs),
             len != std::numeric_limits<size_t>::max() ? len : 128);
         return true;
     }
 
-    bool parse_error(std::size_t, const std::string&, const nlohmann::detail::exception& ex) {
+    bool parse_error(std::size_t, const std::string&, const nlohmann::detail::exception& ex) override {
         throw JSONParseError("%s", ex.what());
     }
 };

src/libexpr/nixexpr.hh

@@ -186,7 +186,7 @@ struct ExprInheritFrom : ExprVar
         this->fromWith = nullptr;
     }
 
-    void bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env);
+    void bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env) override;
 };
 
 struct ExprSelect : Expr

src/libstore/daemon.cc

@@ -167,7 +167,7 @@ struct TunnelSink : Sink
 {
     Sink & to;
     TunnelSink(Sink & to) : to(to) { }
-    void operator () (std::string_view data)
+    void operator () (std::string_view data) override
     {
         to << STDERR_WRITE;
         writeString(data, to);

src/libstore/unix/build/local-derivation-goal.cc

@@ -1258,7 +1258,7 @@ bool LocalDerivationGoal::isAllowed(const DerivedPath & req)
 struct RestrictedStoreConfig : virtual LocalFSStoreConfig
 {
     using LocalFSStoreConfig::LocalFSStoreConfig;
-    const std::string name() { return "Restricted Store"; }
+    const std::string name() override { return "Restricted Store"; }
 };
 
 /* A wrapper around LocalStore that only allows building/querying of

src/libutil/serialise.cc

@@ -190,11 +190,11 @@ struct VirtualStackAllocator {
 class DefaultStackAllocator : public StackAllocator {
     boost::coroutines2::default_stack stack;
 
-    boost::context::stack_context allocate() {
+    boost::context::stack_context allocate() override {
         return stack.allocate();
     }
 
-    void deallocate(boost::context::stack_context sctx) {
+    void deallocate(boost::context::stack_context sctx) override {
         stack.deallocate(sctx);
     }
 };

src/libutil/serialise.hh

@@ -204,7 +204,7 @@ struct TeeSink : Sink
 {
     Sink & sink1, & sink2;
     TeeSink(Sink & sink1, Sink & sink2) : sink1(sink1), sink2(sink2) { }
-    virtual void operator () (std::string_view data)
+    virtual void operator () (std::string_view data) override
     {
         sink1(data);
         sink2(data);
@@ -221,7 +221,7 @@ struct TeeSource : Source
     Sink & sink;
     TeeSource(Source & orig, Sink & sink)
         : orig(orig), sink(sink) { }
-    size_t read(char * data, size_t len)
+    size_t read(char * data, size_t len) override
     {
         size_t n = orig.read(data, len);
         sink({data, n});
@@ -238,7 +238,7 @@ struct SizedSource : Source
     size_t remain;
     SizedSource(Source & orig, size_t size)
         : orig(orig), remain(size) { }
-    size_t read(char * data, size_t len)
+    size_t read(char * data, size_t len) override
     {
         if (this->remain <= 0) {
             throw EndOfFile("sized: unexpected end-of-file");

src/perl/meson.build

@@ -25,6 +25,7 @@ nix_perl_conf.set('PACKAGE_VERSION', meson.project_version())
 error_args = [
   '-Wdeprecated-copy',
   '-Wdeprecated-declarations',
+  '-Werror=suggest-override',
   '-Werror=unused-result',
   '-Wignored-qualifiers',
   '-Wno-duplicate-decl-specifier',