libexpr: prefer Value::str() over Value::c_str()

at call sites that already cast to string_view to take advantage of the
stored length

Change-Id: I525c68e83e1c71bdc5ad2c3ed0bd0863ad20aaf2

src/libexpr/eval.cc

@@ -264,7 +264,7 @@ static Symbol getName(const AttrName & name, EvalState & state, Env & env)
         Value nameValue;
         name.expr->eval(state, env, nameValue);
         state.forceStringNoCtx(nameValue, name.expr->getPos(), "while evaluating an attribute name");
-        return state.symbols.create(nameValue.c_str());
+        return state.symbols.create(nameValue.str());
     }
 }
 
@@ -1348,7 +1348,7 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
         if (nameVal.type() == nNull)
             continue;
         state.forceStringNoCtx(nameVal, i.pos, "while evaluating the name of a dynamic attribute");
-        auto nameSym = state.symbols.create(nameVal.c_str());
+        auto nameSym = state.symbols.create(nameVal.str());
         Bindings::iterator j = v.attrs->find(nameSym);
         if (j != v.attrs->end())
             state.error<EvalError>("dynamic attribute '%1%' already defined at %2%", state.symbols[nameSym], state.positions[j->pos]).atPos(i.pos).withFrame(env, *this).debugThrow();

src/libexpr/flake/flake.cc

@@ -122,7 +122,7 @@ static FlakeInput parseFlakeInput(EvalState & state,
                 input.overrides = parseFlakeInputs(state, attr.value, attr.pos, baseDir, lockRootPath, depth + 1);
             } else if (attr.name == sFollows) {
                 expectType(state, nString, *attr.value, attr.pos);
-                auto follows(parseInputPath(attr.value->c_str()));
+                auto follows(parseInputPath(attr.value->str()));
                 follows.insert(follows.begin(), lockRootPath.begin(), lockRootPath.end());
                 input.follows = follows;
             } else {

src/libexpr/primops.cc

@@ -2590,7 +2590,7 @@ static void prim_removeAttrs(EvalState & state, const PosIdx pos, Value * * args
     names.reserve(args[1]->listSize());
     for (auto elem : args[1]->listItems()) {
         state.forceStringNoCtx(*elem, pos, "while evaluating the values of the second argument passed to builtins.removeAttrs");
-        names.emplace_back(state.symbols.create(elem->c_str()), nullptr);
+        names.emplace_back(state.symbols.create(elem->str()), nullptr);
     }
     std::sort(names.begin(), names.end());
 

src/libexpr/print-ambiguous.cc

@@ -28,7 +28,7 @@ void printAmbiguous(
         printLiteralBool(str, v.boolean);
         break;
     case nString:
-        escapeString(str, v.c_str());
+        escapeString(str, v.str());
         break;
     case nPath:
         str << v.path().to_string(); // !!! escaping?

src/libexpr/print.cc

@@ -200,7 +200,7 @@ private:
     {
         escapeString(
             output,
-            v.c_str(),
+            v.str(),
             {
                 .maxLength = options.maxStringLength,
                 .outputAnsiColors = options.ansiColors,