refactor: use string accessors

Create context, string_view, and c_str, accessors throughout in order to
better support improvements to the underlying string representation.

src/libcmd/repl.cc

@@ -922,7 +922,7 @@ std::ostream & NixRepl::printValue(std::ostream & str, Value & v, unsigned int m
 
     case nString:
         str << ANSI_WARNING;
-        printLiteralString(str, v.string.s);
+        printLiteralString(str, v.string_view());
         str << ANSI_NORMAL;
         break;
 

src/libexpr/eval-cache.cc

@@ -440,8 +440,8 @@ Value & AttrCursor::forceValue()
 
     if (root->db && (!cachedValue || std::get_if<placeholder_t>(&cachedValue->second))) {
         if (v.type() == nString)
-            cachedValue = {root->db->setString(getKey(), v.string.s, v.string.context),
-                           string_t{v.string.s, {}}};
+            cachedValue = {root->db->setString(getKey(), v.c_str(), v.context()),
+                           string_t{v.c_str(), {}}};
         else if (v.type() == nPath) {
             auto path = v.path().path;
             cachedValue = {root->db->setString(getKey(), path.abs()), string_t{path.abs(), {}}};
@@ -582,7 +582,7 @@ std::string AttrCursor::getString()
     if (v.type() != nString && v.type() != nPath)
         root->state.error("'%s' is not a string but %s", getAttrPathStr()).debugThrow<TypeError>();
 
-    return v.type() == nString ? v.string.s : v.path().to_string();
+    return v.type() == nString ? v.c_str() : v.path().to_string();
 }
 
 string_t AttrCursor::getStringWithContext()
@@ -624,7 +624,7 @@ string_t AttrCursor::getStringWithContext()
     if (v.type() == nString) {
         NixStringContext context;
         copyContext(v, context);
-        return {v.string.s, std::move(context)};
+        return {v.c_str(), std::move(context)};
     }
     else if (v.type() == nPath)
         return {v.path().to_string(), {}};

src/libexpr/eval.cc

@@ -114,7 +114,7 @@ void Value::print(const SymbolTable &symbols, std::ostream &str,
         printLiteralBool(str, boolean);
         break;
     case tString:
-        printLiteralString(str, string.s);
+        printLiteralString(str, string_view());
         break;
     case tPath:
         str << path().to_string(); // !!! escaping?
@@ -339,7 +339,7 @@ static Symbol getName(const AttrName & name, EvalState & state, Env & env)
         Value nameValue;
         name.expr->eval(state, env, nameValue);
         state.forceStringNoCtx(nameValue, noPos, "while evaluating an attribute name");
-        return state.symbols.create(nameValue.string.s);
+        return state.symbols.create(nameValue.string_view());
     }
 }
 
@@ -1343,7 +1343,7 @@ 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.string.s);
+        auto nameSym = state.symbols.create(nameVal.string_view());
         Bindings::iterator j = v.attrs->find(nameSym);
         if (j != v.attrs->end())
             state.error("dynamic attribute '%1%' already defined at %2%", state.symbols[nameSym], state.positions[j->pos]).atPos(i.pos).withFrame(env, *this).debugThrow<EvalError>();
@@ -2155,7 +2155,7 @@ std::string_view EvalState::forceString(Value & v, const PosIdx pos, std::string
         forceValue(v, pos);
         if (v.type() != nString)
             error("value is %1% while a string was expected", showType(v)).debugThrow<TypeError>();
-        return v.string.s;
+        return v.string_view();
     } catch (Error & e) {
         e.addTrace(positions[pos], errorCtx);
         throw;
@@ -2182,8 +2182,8 @@ std::string_view EvalState::forceString(Value & v, NixStringContext & context, c
 std::string_view EvalState::forceStringNoCtx(Value & v, const PosIdx pos, std::string_view errorCtx)
 {
     auto s = forceString(v, pos, errorCtx);
-    if (v.string.context) {
-        error("the string '%1%' is not allowed to refer to a store path (such as '%2%')", v.string.s, v.string.context[0]).withTrace(pos, errorCtx).debugThrow<EvalError>();
+    if (v.context()) {
+        error("the string '%1%' is not allowed to refer to a store path (such as '%2%')", v.string_view(), v.context()[0]).withTrace(pos, errorCtx).debugThrow<EvalError>();
     }
     return s;
 }
@@ -2196,7 +2196,7 @@ bool EvalState::isDerivation(Value & v)
     if (i == v.attrs->end()) return false;
     forceValue(*i->value, i->pos);
     if (i->value->type() != nString) return false;
-    return strcmp(i->value->string.s, "derivation") == 0;
+    return i->value->string_view().compare("derivation") == 0;
 }
 
 
@@ -2228,7 +2228,7 @@ BackedStringView EvalState::coerceToString(
 
     if (v.type() == nString) {
         copyContext(v, context);
-        return std::string_view(v.string.s);
+        return v.string_view();
     }
 
     if (v.type() == nPath) {
@@ -2426,7 +2426,7 @@ bool EvalState::eqValues(Value & v1, Value & v2, const PosIdx pos, std::string_v
             return v1.boolean == v2.boolean;
 
         case nString:
-            return strcmp(v1.string.s, v2.string.s) == 0;
+            return v1.string_view().compare(v2.string_view()) == 0;
 
         case nPath:
             return strcmp(v1._path, v2._path) == 0;

src/libexpr/flake/flake.cc

@@ -113,7 +113,7 @@ static FlakeInput parseFlakeInput(EvalState & state,
         try {
             if (attr.name == sUrl) {
                 expectType(state, nString, *attr.value, attr.pos);
-                url = attr.value->string.s;
+                url = attr.value->string_view();
                 attrs.emplace("url", *url);
             } else if (attr.name == sFlake) {
                 expectType(state, nBool, *attr.value, attr.pos);
@@ -122,7 +122,7 @@ static FlakeInput parseFlakeInput(EvalState & state,
                 input.overrides = parseFlakeInputs(state, attr.value, attr.pos, baseDir, lockRootPath);
             } else if (attr.name == sFollows) {
                 expectType(state, nString, *attr.value, attr.pos);
-                auto follows(parseInputPath(attr.value->string.s));
+                auto follows(parseInputPath(attr.value->c_str()));
                 follows.insert(follows.begin(), lockRootPath.begin(), lockRootPath.end());
                 input.follows = follows;
             } else {
@@ -131,7 +131,7 @@ static FlakeInput parseFlakeInput(EvalState & state,
                 #pragma GCC diagnostic ignored "-Wswitch-enum"
                 switch (attr.value->type()) {
                     case nString:
-                        attrs.emplace(state.symbols[attr.name], attr.value->string.s);
+                        attrs.emplace(state.symbols[attr.name], attr.value->c_str());
                         break;
                     case nBool:
                         attrs.emplace(state.symbols[attr.name], Explicit<bool> { attr.value->boolean });
@@ -229,7 +229,7 @@ static Flake getFlake(
 
     if (auto description = vInfo.attrs->get(state.sDescription)) {
         expectType(state, nString, *description->value, description->pos);
-        flake.description = description->value->string.s;
+        flake.description = description->value->c_str();
     }
 
     auto sInputs = state.symbols.create("inputs");
@@ -850,7 +850,7 @@ static void prim_flakeRefToString(
                           Explicit<bool> { attr.value->boolean });
         } else if (t == nString) {
             attrs.emplace(state.symbols[attr.name],
-                          std::string(attr.value->str()));
+                          std::string(attr.value->string_view()));
         } else {
             state.error(
                 "flake reference attribute sets may only contain integers, Booleans, "

src/libexpr/get-drvs.cc

@@ -156,7 +156,7 @@ DrvInfo::Outputs DrvInfo::queryOutputs(bool withPaths, bool onlyOutputsToInstall
         Outputs result;
         for (auto elem : outTI->listItems()) {
             if (elem->type() != nString) throw errMsg;
-            auto out = outputs.find(elem->string.s);
+            auto out = outputs.find(elem->c_str());
             if (out == outputs.end()) throw errMsg;
             result.insert(*out);
         }
@@ -230,7 +230,7 @@ std::string DrvInfo::queryMetaString(const std::string & name)
 {
     Value * v = queryMeta(name);
     if (!v || v->type() != nString) return "";
-    return v->string.s;
+    return v->c_str();
 }
 
 
@@ -242,7 +242,7 @@ NixInt DrvInfo::queryMetaInt(const std::string & name, NixInt def)
     if (v->type() == nString) {
         /* Backwards compatibility with before we had support for
            integer meta fields. */
-        if (auto n = string2Int<NixInt>(v->string.s))
+        if (auto n = string2Int<NixInt>(v->c_str()))
             return *n;
     }
     return def;
@@ -256,7 +256,7 @@ NixFloat DrvInfo::queryMetaFloat(const std::string & name, NixFloat def)
     if (v->type() == nString) {
         /* Backwards compatibility with before we had support for
            float meta fields. */
-        if (auto n = string2Float<NixFloat>(v->string.s))
+        if (auto n = string2Float<NixFloat>(v->c_str()))
             return *n;
     }
     return def;
@@ -271,8 +271,8 @@ bool DrvInfo::queryMetaBool(const std::string & name, bool def)
     if (v->type() == nString) {
         /* Backwards compatibility with before we had support for
            Boolean meta fields. */
-        if (strcmp(v->string.s, "true") == 0) return true;
-        if (strcmp(v->string.s, "false") == 0) return false;
+        if (v->string_view() == "true") return true;
+        if (v->string_view() == "false") return false;
     }
     return def;
 }

src/libexpr/primops.cc

@@ -590,7 +590,7 @@ struct CompareValues
                 case nFloat:
                     return v1->fpoint < v2->fpoint;
                 case nString:
-                    return strcmp(v1->string.s, v2->string.s) < 0;
+                    return v1->string_view().compare(v2->string_view()) < 0;
                 case nPath:
                     return strcmp(v1->_path, v2->_path) < 0;
                 case nList:
@@ -982,7 +982,7 @@ static void prim_trace(EvalState & state, const PosIdx pos, Value * * args, Valu
 {
     state.forceValue(*args[0], pos);
     if (args[0]->type() == nString)
-        printError("trace: %1%", args[0]->string.s);
+        printError("trace: %1%", args[0]->string_view());
     else
         printError("trace: %1%", printValue(state, *args[0]));
     state.forceValue(*args[1], pos);
@@ -1528,7 +1528,7 @@ static void prim_pathExists(EvalState & state, const PosIdx pos, Value * * args,
     auto path = realisePath(state, pos, arg, { .checkForPureEval = false });
 
     /* SourcePath doesn't know about trailing slash. */
-    auto mustBeDir = arg.type() == nString && arg.str().ends_with("/");
+    auto mustBeDir = arg.type() == nString && arg.string_view().ends_with("/");
 
     try {
         auto checked = state.checkSourcePath(path);
@@ -2400,7 +2400,7 @@ static void prim_attrNames(EvalState & state, const PosIdx pos, Value * * args,
         (v.listElems()[n++] = state.allocValue())->mkString(state.symbols[i.name]);
 
     std::sort(v.listElems(), v.listElems() + n,
-              [](Value * v1, Value * v2) { return strcmp(v1->string.s, v2->string.s) < 0; });
+              [](Value * v1, Value * v2) { return v1->string_view().compare(v2->string_view()) < 0; });
 }
 
 static RegisterPrimOp primop_attrNames({
@@ -2541,7 +2541,7 @@ 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->string.s), nullptr);
+        names.emplace_back(state.symbols.create(elem->string_view()), nullptr);
     }
     std::sort(names.begin(), names.end());
 

src/libexpr/primops/fetchClosure.cc

@@ -133,7 +133,7 @@ static void prim_fetchClosure(EvalState & state, const PosIdx pos, Value * * arg
 
         else if (attrName == "toPath") {
             state.forceValue(*attr.value, attr.pos);
-            bool isEmptyString = attr.value->type() == nString && attr.value->string.s == std::string("");
+            bool isEmptyString = attr.value->type() == nString && attr.value->string_view() == "";
             if (isEmptyString) {
                 toPath = StorePathOrGap {};
             }

src/libexpr/tests/primops.cc

@@ -711,14 +711,14 @@ namespace nix {
         // FIXME: add a test that verifies the string context is as expected
         auto v = eval("builtins.replaceStrings [\"oo\" \"a\"] [\"a\" \"i\"] \"foobar\"");
         ASSERT_EQ(v.type(), nString);
-        ASSERT_EQ(v.string.s, std::string_view("fabir"));
+        ASSERT_EQ(v.string_view(), "fabir");
     }
 
     TEST_F(PrimOpTest, concatStringsSep) {
         // FIXME: add a test that verifies the string context is as expected
         auto v = eval("builtins.concatStringsSep \"%\" [\"foo\" \"bar\" \"baz\"]");
         ASSERT_EQ(v.type(), nString);
-        ASSERT_EQ(std::string_view(v.string.s), "foo%bar%baz");
+        ASSERT_EQ(v.string_view(), "foo%bar%baz");
     }
 
     TEST_F(PrimOpTest, split1) {

src/libexpr/value-to-json.cc

@@ -31,7 +31,7 @@ json printValueAsJSON(EvalState & state, bool strict,
 
         case nString:
             copyContext(v, context);
-            out = v.string.s;
+            out = v.c_str();
             break;
 
         case nPath:

src/libexpr/value-to-xml.cc

@@ -74,7 +74,7 @@ static void printValueAsXML(EvalState & state, bool strict, bool location,
         case nString:
             /* !!! show the context? */
             copyContext(v, context);
-            doc.writeEmptyElement("string", singletonAttrs("value", v.string.s));
+            doc.writeEmptyElement("string", singletonAttrs("value", v.c_str()));
             break;
 
         case nPath:
@@ -96,14 +96,14 @@ static void printValueAsXML(EvalState & state, bool strict, bool location,
                 if (a != v.attrs->end()) {
                     if (strict) state.forceValue(*a->value, a->pos);
                     if (a->value->type() == nString)
-                        xmlAttrs["drvPath"] = drvPath = a->value->string.s;
+                        xmlAttrs["drvPath"] = drvPath = a->value->c_str();
                 }
 
                 a = v.attrs->find(state.sOutPath);
                 if (a != v.attrs->end()) {
                     if (strict) state.forceValue(*a->value, a->pos);
                     if (a->value->type() == nString)
-                        xmlAttrs["outPath"] = a->value->string.s;
+                        xmlAttrs["outPath"] = a->value->c_str();
                 }
 
                 XMLOpenElement _(doc, "derivation", xmlAttrs);

src/libexpr/value.hh

@@ -186,10 +186,9 @@ public:
          * For canonicity, the store paths should be in sorted order.
          */
         struct {
-            const char * s;
+            const char * c_str;
             const char * * context; // must be in sorted order
         } string;
-
         const char * _path;
         Bindings * attrs;
         struct {
@@ -270,7 +269,7 @@ public:
     inline void mkString(const char * s, const char * * context = 0)
     {
         internalType = tString;
-        string.s = s;
+        string.c_str = s;
         string.context = context;
     }
 
@@ -441,10 +440,21 @@ public:
         return SourcePath{CanonPath(_path)};
     }
 
-    std::string_view str() const
+    std::string_view string_view() const
+    {
+        assert(internalType == tString);
+        return std::string_view(string.c_str);
+    }
+
+    const char * const c_str() const
     {
         assert(internalType == tString);
-        return std::string_view(string.s);
+        return string.c_str;
+    }
+
+    const char * * context() const
+    {
+        return string.context;
     }
 };
 

src/nix-env/nix-env.cc

@@ -1228,7 +1228,7 @@ static void opQuery(Globals & globals, Strings opFlags, Strings opArgs)
                         else {
                             if (v->type() == nString) {
                                 attrs2["type"] = "string";
-                                attrs2["value"] = v->string.s;
+                                attrs2["value"] = v->c_str();
                                 xml.writeEmptyElement("meta", attrs2);
                             } else if (v->type() == nInt) {
                                 attrs2["type"] = "int";
@@ -1248,7 +1248,7 @@ static void opQuery(Globals & globals, Strings opFlags, Strings opArgs)
                                 for (auto elem : v->listItems()) {
                                     if (elem->type() != nString) continue;
                                     XMLAttrs attrs3;
-                                    attrs3["value"] = elem->string.s;
+                                    attrs3["value"] = elem->c_str();
                                     xml.writeEmptyElement("string", attrs3);
                                 }
                             } else if (v->type() == nAttrs) {
@@ -1260,7 +1260,7 @@ static void opQuery(Globals & globals, Strings opFlags, Strings opArgs)
                                     if(a.value->type() != nString) continue;
                                     XMLAttrs attrs3;
                                     attrs3["type"] = globals.state->symbols[i.name];
-                                    attrs3["value"] = a.value->string.s;
+                                    attrs3["value"] = a.value->c_str();
                                     xml.writeEmptyElement("string", attrs3);
                             }
                             }

src/nix/eval.cc

@@ -85,7 +85,7 @@ struct CmdEval : MixJSON, InstallableValueCommand, MixReadOnlyOption
                 state->forceValue(v, pos);
                 if (v.type() == nString)
                     // FIXME: disallow strings with contexts?
-                    writeFile(path, v.string.s);
+                    writeFile(path, v.string_view());
                 else if (v.type() == nAttrs) {
                     if (mkdir(path.c_str(), 0777) == -1)
                         throw SysError("creating directory '%s'", path);