chore: get rid of dead code and unused variables where appropriate

Looks like some cruft has been left over from previous refactorings.
This removes dead variables, which should not have side effects in their
constructors. In cases where the variable initialization has a purpose
[[maybe_unused]] is inserted to silence compiler warnings.

src/libexpr/attr-path.cc

@@ -129,7 +129,6 @@ std::pair<SourcePath, uint32_t> findPackageFilename(EvalState & state, Value & v
     try {
         auto colon = fn.rfind(':');
         if (colon == std::string::npos) fail();
-        std::string filename(fn, 0, colon);
         auto lineno = std::stoi(std::string(fn, colon + 1, std::string::npos));
         return {SourcePath{path.accessor, CanonPath(fn.substr(0, colon))}, lineno};
     } catch (std::invalid_argument & e) {

src/libexpr/primops.cc

@@ -66,14 +66,12 @@ StringMap EvalState::realiseContext(const NixStringContext & context, StorePathS
                 ensureValid(b.drvPath->getBaseStorePath());
             },
             [&](const NixStringContextElem::Opaque & o) {
-                auto ctxS = store->printStorePath(o.path);
                 ensureValid(o.path);
                 if (maybePathsOut)
                     maybePathsOut->emplace(o.path);
             },
             [&](const NixStringContextElem::DrvDeep & d) {
                 /* Treat same as Opaque */
-                auto ctxS = store->printStorePath(d.drvPath);
                 ensureValid(d.drvPath);
                 if (maybePathsOut)
                     maybePathsOut->emplace(d.drvPath);

src/libfetchers/git.cc

@@ -514,8 +514,6 @@ struct GitInputScheme : InputScheme
 
         auto origRev = input.getRev();
 
-        std::string name = input.getName();
-
         auto originalRef = input.getRef();
         auto ref = originalRef ? *originalRef : getDefaultRef(repoInfo);
         input.attrs.insert_or_assign("ref", ref);

src/libflake/flake/flakeref.cc

@@ -257,8 +257,6 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
 {
     using namespace fetchers;
 
-    std::smatch match;
-
     if (auto res = parseFlakeIdRef(fetchSettings, url, isFlake)) {
         return *res;
     } else if (auto res = parseURLFlakeRef(fetchSettings, url, baseDir, isFlake)) {

src/libstore/build/derivation-goal.cc

@@ -1229,7 +1229,7 @@ HookReply DerivationGoal::tryBuildHook()
     hook->toHook.writeSide.close();
 
     /* Create the log file and pipe. */
-    Path logFile = openLogFile();
+    [[maybe_unused]] Path logFile = openLogFile();
 
     std::set<MuxablePipePollState::CommChannel> fds;
     fds.insert(hook->fromHook.readSide.get());

src/libstore/export-import.cc

@@ -13,14 +13,9 @@ void Store::exportPaths(const StorePathSet & paths, Sink & sink)
     auto sorted = topoSortPaths(paths);
     std::reverse(sorted.begin(), sorted.end());
 
-    std::string doneLabel("paths exported");
-    //logger->incExpected(doneLabel, sorted.size());
-
     for (auto & path : sorted) {
-        //Activity act(*logger, lvlInfo, "exporting path '%s'", path);
         sink << 1;
         exportPath(path, sink);
-        //logger->incProgress(doneLabel);
     }
 
     sink << 0;

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

@@ -883,7 +883,7 @@ void LocalDerivationGoal::startBuilder()
         printMsg(lvlVomit, "setting builder env variable '%1%'='%2%'", i.first, i.second);
 
     /* Create the log file. */
-    Path logFile = openLogFile();
+    [[maybe_unused]] Path logFile = openLogFile();
 
     /* Create a pseudoterminal to get the output of the builder. */
     builderOut = posix_openpt(O_RDWR | O_NOCTTY);

src/libutil-tests/nix_api_util.cc

@@ -136,7 +136,6 @@ TEST_F(nix_api_util_context, nix_err_name)
     // no error
     EXPECT_THROW(nix_err_name(NULL, ctx, OBSERVE_STRING(err_name)), nix::Error);
 
-    std::string err_msg_ref;
     try {
         throw nix::Error("testing error");
     } catch (...) {

src/libutil/serialise.cc

@@ -90,7 +90,6 @@ void Source::operator () (std::string_view data)
 
 void Source::drainInto(Sink & sink)
 {
-    std::string s;
     std::array<char, 8192> buf;
     while (true) {
         size_t n;
@@ -427,7 +426,7 @@ Error readError(Source & source)
     auto type = readString(source);
     assert(type == "Error");
     auto level = (Verbosity) readInt(source);
-    auto name = readString(source); // removed
+    [[maybe_unused]] auto name = readString(source); // removed
     auto msg = readString(source);
     ErrorInfo info {
         .level = level,

src/libutil/terminal.cc

@@ -26,7 +26,7 @@ bool isTTY()
 
 std::string filterANSIEscapes(std::string_view s, bool filterAll, unsigned int width)
 {
-    std::string t, e;
+    std::string t;
     size_t w = 0;
     auto i = s.begin();
 

src/nix/search.cc

@@ -161,7 +161,6 @@ struct CmdSearch : InstallableValueCommand, MixJSON
                                 {"description", description},
                             };
                         } else {
-                            auto name2 = hiliteMatches(name.name, nameMatches, ANSI_GREEN, "\e[0;2m");
                             if (results > 1) logger->cout("");
                             logger->cout(
                                 "* %s%s",

src/nix/sigs.cc

@@ -41,7 +41,6 @@ struct CmdCopySigs : StorePathsCommand
 
         ThreadPool pool;
 
-        std::string doneLabel = "done";
         std::atomic<size_t> added{0};
 
         //logger->setExpected(doneLabel, storePaths.size());