Fix gcc warning -Wmissing-field-initializers

The approach that was taken here was to add default values to the type
definitions rather than specify them whenever they are missing.

Now the only remaining warning is '-Wunused-parameter' which @jade said
is usually counterproductive and that we can just disable it:
lix-project/lix#456 (comment)

So this change adds the flags '-Wall', '-Wextra' and
'-Wno-unused-parameter', so that all warnings are enabled except for
'-Wunused-parameter'.

Change-Id: Ic223a964d67ab429e8da804c0721ba5e25d53012

meson.build

@@ -52,8 +52,7 @@ project('lix', 'cpp', 'rust',
   default_options : [
     'cpp_std=c++2a',
     'rust_std=2021',
-    # TODO(Qyriad): increase the warning level
+    'warning_level=2',
-    'warning_level=1',
     'debug=true',
     'optimization=2',
     'errorlogs=true', # Please print logs for tests that fail
@@ -485,7 +484,7 @@ add_project_arguments(
   # TODO(Qyriad): Yes this is how the autoconf+Make system did it.
   # It would be nice for our headers to be idempotent instead.
   '-include', 'config.h',
-  '-Wsign-compare',
+  '-Wno-unused-parameter',
   '-Wno-deprecated-declarations',
   '-Wimplicit-fallthrough',
   '-Werror=switch',

src/libexpr/parser/state.hh

@@ -9,7 +9,7 @@ namespace nix::parser {
 struct StringToken
 {
     std::string_view s;
-    bool hasIndentation;
+    bool hasIndentation = false;
     operator std::string_view() const { return s; }
 };
 

src/libstore/build-result.hh

@@ -47,7 +47,7 @@ struct BuildResult
      * @todo This should be an entire ErrorInfo object, not just a
      * string, for richer information.
      */
-    std::string errorMsg;
+    std::string errorMsg = {};
 
     std::string toString() const {
         auto strStatus = [&]() {
@@ -90,7 +90,7 @@ struct BuildResult
      * For derivations, a mapping from the names of the wanted outputs
      * to actual paths.
      */
-    SingleDrvOutputs builtOutputs;
+    SingleDrvOutputs builtOutputs = {};
 
     /**
      * The start/stop times of the build (or one of the rounds, if it

src/libstore/build/derivation-goal.hh

@@ -63,7 +63,7 @@ struct InitialOutputStatus {
 struct InitialOutput {
     bool wanted;
     Hash outputHash;
-    std::optional<InitialOutputStatus> known;
+    std::optional<InitialOutputStatus> known = {};
 };
 
 /**

src/libstore/build/goal.hh

@@ -88,8 +88,8 @@ protected:
 public:
     struct [[nodiscard]] WorkResult {
         ExitCode exitCode;
-        BuildResult result;
+        BuildResult result = {};
-        std::shared_ptr<Error> ex;
+        std::shared_ptr<Error> ex = {};
         bool permanentFailure = false;
         bool timedOut = false;
         bool hashMismatch = false;

src/libstore/nar-accessor.cc

@@ -20,10 +20,10 @@ struct NarMember
        file in the NAR. */
     uint64_t start = 0, size = 0;
 
-    std::string target;
+    std::string target = {};
 
     /* If this is a directory, all the children of the directory. */
-    std::map<std::string, NarMember> children;
+    std::map<std::string, NarMember> children = {};
 };
 
 struct NarAccessor : public FSAccessor

src/libstore/path-with-outputs.hh

@@ -17,7 +17,7 @@ namespace nix {
 struct StorePathWithOutputs
 {
     StorePath path;
-    std::set<std::string> outputs;
+    std::set<std::string> outputs = {};
 
     std::string to_string(const Store & store) const;
 

src/libstore/realisation.hh

@@ -50,7 +50,7 @@ struct Realisation {
     DrvOutput id;
     StorePath outPath;
 
-    StringSet signatures;
+    StringSet signatures = {};
 
     /**
      * The realisations that are required for the current one to be valid.
@@ -58,7 +58,7 @@ struct Realisation {
      * When importing this realisation, the store will first check that all its
      * dependencies exist, and map to the correct output path
      */
-    std::map<DrvOutput, StorePath> dependentRealisations;
+    std::map<DrvOutput, StorePath> dependentRealisations = {};
 
     nlohmann::json toJSON() const;
     static Realisation fromJSON(const nlohmann::json& json, const std::string& whence);

src/libstore/store-api.cc

@@ -829,7 +829,7 @@ StorePathSet Store::queryValidPaths(const StorePathSet & paths, SubstituteFlag m
     {
         size_t left;
         StorePathSet valid;
-        std::exception_ptr exc;
+        std::exception_ptr exc = {};
     };
 
     Sync<State> state_(State{paths.size(), StorePathSet()});

src/libutil/error.hh

@@ -70,17 +70,17 @@ inline bool operator<=(const Trace& lhs, const Trace& rhs);
 inline bool operator>=(const Trace& lhs, const Trace& rhs);
 
 struct ErrorInfo {
-    Verbosity level;
+    Verbosity level = Verbosity::lvlError;
     HintFmt msg;
     std::shared_ptr<Pos> pos;
-    std::list<Trace> traces;
+    std::list<Trace> traces = {};
 
     /**
      * Exit status.
      */
     unsigned int status = 1;
 
-    Suggestions suggestions;
+    Suggestions suggestions = {};
 
     static std::optional<std::string> programName;
 };

src/libutil/processes.hh

@@ -78,11 +78,11 @@ struct RunOptions
 {
     Path program;
     bool searchPath = true;
-    Strings args;
+    Strings args = {};
-    std::optional<uid_t> uid;
+    std::optional<uid_t> uid = {};
-    std::optional<uid_t> gid;
+    std::optional<uid_t> gid = {};
-    std::optional<Path> chdir;
+    std::optional<Path> chdir = {};
-    std::optional<std::map<std::string, std::string>> environment;
+    std::optional<std::map<std::string, std::string>> environment = {};
     bool captureStdout = false;
     bool mergeStderrToStdout = false;
     bool isInteractive = false;