From 1eff2adc93dacb6a647bc9701ffa7437e1eccde6 Mon Sep 17 00:00:00 2001
From: Mel Zuser <mel.zuser@arista.com>
Date: Wed, 15 May 2024 20:03:19 -0700
Subject: [PATCH] libexpr: abstract string members in Value

to allow multiple internal reps similar to how lists works

Change-Id: I94139aab28b04b73b055a3dc05d496758ee72538
---
 src/libcmd/repl.cc                          |  2 +-
 src/libexpr/eval-cache.cc                   |  8 +++---
 src/libexpr/eval.cc                         | 20 +++++++-------
 src/libexpr/flake/flake.cc                  |  8 +++---
 src/libexpr/get-drvs.cc                     | 12 ++++-----
 src/libexpr/primops.cc                      | 10 +++----
 src/libexpr/primops/fetchClosure.cc         |  2 +-
 src/libexpr/print-ambiguous.cc              |  2 +-
 src/libexpr/print.cc                        |  2 +-
 src/libexpr/value-to-json.cc                |  2 +-
 src/libexpr/value-to-xml.cc                 |  6 ++---
 src/libexpr/value.hh                        | 30 ++++++++++++++++++---
 src/nix-env/nix-env.cc                      |  6 ++---
 src/nix/eval.cc                             |  2 +-
 tests/unit/libexpr-support/tests/libexpr.hh |  4 +--
 tests/unit/libexpr/primops.cc               |  4 +--
 16 files changed, 72 insertions(+), 48 deletions(-)

diff --git a/src/libcmd/repl.cc b/src/libcmd/repl.cc
index 525c25560..35b802d89 100644
--- a/src/libcmd/repl.cc
+++ b/src/libcmd/repl.cc
@@ -674,7 +674,7 @@ ProcessLineResult NixRepl::processLine(std::string line)
         Value v;
         evalString(arg, v);
         if (v.type() == nString) {
-            std::cout << v.string.s;
+            std::cout << v.c_str();
         } else {
             printValue(std::cout, v);
         }
diff --git a/src/libexpr/eval-cache.cc b/src/libexpr/eval-cache.cc
index 5969ee449..ffe9e1bab 100644
--- a/src/libexpr/eval-cache.cc
+++ b/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.stringContext()),
+                           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(), {}}};
@@ -580,7 +580,7 @@ std::string AttrCursor::getString()
         root->state.error<TypeError>("'%s' is not a string but %s", getAttrPathStr(), v.type()).debugThrow();
     }
 
-    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()
@@ -622,7 +622,7 @@ 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(), {}};
     } else {
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 65f0a7938..d1f3e59d9 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -253,7 +253,7 @@ 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.string.s);
+        return state.symbols.create(nameValue.c_str());
     }
 }
 
@@ -1330,7 +1330,7 @@ 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.c_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();
@@ -2256,7 +2256,7 @@ std::string_view EvalState::forceString(Value & v, const PosIdx pos, std::string
                 showType(v),
                 ValuePrinter(*this, v, errorPrintOptions)
             ).atPos(pos).debugThrow();
-        return v.string.s;
+        return v.str();
     } catch (Error & e) {
         e.addTrace(positions[pos], errorCtx);
         throw;
@@ -2266,8 +2266,8 @@ std::string_view EvalState::forceString(Value & v, const PosIdx pos, std::string
 
 void copyContext(const Value & v, NixStringContext & context)
 {
-    if (v.string.context)
-        for (const char * * p = v.string.context; *p; ++p)
+    if (v.stringContext())
+        for (const char * * p = v.stringContext(); *p; ++p)
             context.insert(NixStringContextElem::parse(*p));
 }
 
@@ -2283,8 +2283,8 @@ 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<EvalError>("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();
+    if (v.stringContext()) {
+        error<EvalError>("the string '%1%' is not allowed to refer to a store path (such as '%2%')", v.c_str(), v.stringContext()[0]).withTrace(pos, errorCtx).debugThrow();
     }
     return s;
 }
@@ -2297,7 +2297,7 @@ 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 strcmp(i->value->c_str(), "derivation") == 0;
 }
 
 
@@ -2329,7 +2329,7 @@ BackedStringView EvalState::coerceToString(
 
     if (v.type() == nString) {
         copyContext(v, context);
-        return std::string_view(v.string.s);
+        return v.str();
     }
 
     if (v.type() == nPath) {
@@ -2534,7 +2534,7 @@ 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 strcmp(v1.c_str(), v2.c_str()) == 0;
 
         case nPath:
             return strcmp(v1._path, v2._path) == 0;
diff --git a/src/libexpr/flake/flake.cc b/src/libexpr/flake/flake.cc
index e13d1cb93..20bbd1898 100644
--- a/src/libexpr/flake/flake.cc
+++ b/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->c_str();
                 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, depth + 1);
             } 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 });
@@ -238,7 +238,7 @@ 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");
diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
index e686ffe8c..dadbc3aa3 100644
--- a/src/libexpr/get-drvs.cc
+++ b/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 (strcmp(v->c_str(), "true") == 0) return true;
+        if (strcmp(v->c_str(), "false") == 0) return false;
     }
     return def;
 }
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 33a2688f1..2d4eb9d33 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -594,7 +594,7 @@ struct CompareValues
                 case nFloat:
                     return v1->fpoint < v2->fpoint;
                 case nString:
-                    return strcmp(v1->string.s, v2->string.s) < 0;
+                    return strcmp(v1->c_str(), v2->c_str()) < 0;
                 case nPath:
                     return strcmp(v1->_path, v2->_path) < 0;
                 case nList:
@@ -977,7 +977,7 @@ 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]->c_str());
     else
         printError("trace: %1%", ValuePrinter(state, *args[0]));
     if (evalSettings.builtinsTraceDebugger && state.debugRepl && !state.debugTraces.empty()) {
@@ -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 strcmp(v1->c_str(), v2->c_str()) < 0; });
 }
 
 static RegisterPrimOp primop_attrNames({
@@ -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->string.s), nullptr);
+        names.emplace_back(state.symbols.create(elem->c_str()), nullptr);
     }
     std::sort(names.begin(), names.end());
 
@@ -3740,7 +3740,7 @@ static void prim_substring(EvalState & state, const PosIdx pos, Value * * args,
     if (len == 0) {
         state.forceValue(*args[2], pos);
         if (args[2]->type() == nString) {
-            v.mkString("", args[2]->string.context);
+            v.mkString("", args[2]->stringContext());
             return;
         }
     }
diff --git a/src/libexpr/primops/fetchClosure.cc b/src/libexpr/primops/fetchClosure.cc
index 3804db6eb..69de2b78b 100644
--- a/src/libexpr/primops/fetchClosure.cc
+++ b/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->c_str() == std::string("");
             if (isEmptyString) {
                 toPath = StorePathOrGap {};
             }
diff --git a/src/libexpr/print-ambiguous.cc b/src/libexpr/print-ambiguous.cc
index ec30f5073..022358053 100644
--- a/src/libexpr/print-ambiguous.cc
+++ b/src/libexpr/print-ambiguous.cc
@@ -28,7 +28,7 @@ void printAmbiguous(
         printLiteralBool(str, v.boolean);
         break;
     case nString:
-        escapeString(str, v.string.s);
+        escapeString(str, v.c_str());
         break;
     case nPath:
         str << v.path().to_string(); // !!! escaping?
diff --git a/src/libexpr/print.cc b/src/libexpr/print.cc
index 231bde0a0..6b91ed272 100644
--- a/src/libexpr/print.cc
+++ b/src/libexpr/print.cc
@@ -200,7 +200,7 @@ private:
     {
         escapeString(
             output,
-            v.string.s,
+            v.c_str(),
             {
                 .maxLength = options.maxStringLength,
                 .outputAnsiColors = options.ansiColors,
diff --git a/src/libexpr/value-to-json.cc b/src/libexpr/value-to-json.cc
index ebb3379a8..73a1bebf6 100644
--- a/src/libexpr/value-to-json.cc
+++ b/src/libexpr/value-to-json.cc
@@ -32,7 +32,7 @@ json printValueAsJSON(EvalState & state, bool strict,
 
         case nString:
             copyContext(v, context);
-            out = v.string.s;
+            out = v.c_str();
             break;
 
         case nPath:
diff --git a/src/libexpr/value-to-xml.cc b/src/libexpr/value-to-xml.cc
index 5d1fbd28d..2809aba43 100644
--- a/src/libexpr/value-to-xml.cc
+++ b/src/libexpr/value-to-xml.cc
@@ -75,7 +75,7 @@ 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:
@@ -97,14 +97,14 @@ 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);
diff --git a/src/libexpr/value.hh b/src/libexpr/value.hh
index 450216ec0..73981d869 100644
--- a/src/libexpr/value.hh
+++ b/src/libexpr/value.hh
@@ -437,11 +437,35 @@ public:
         return SourcePath{CanonPath(_path)};
     }
 
-    std::string_view str() const
+// Allow selecting a subset of enum values
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wswitch-enum"
+
+    const char * c_str() const
     {
-        assert(internalType == tString);
-        return std::string_view(string.s);
+        switch(internalType) {
+            case tString: return string.s;
+            default: abort();
+        }
     }
+
+    std::string_view str()
+    {
+        switch(internalType) {
+            case tString: return std::string_view(string.s);
+            default: abort();
+        }
+    }
+
+    const char * * stringContext() const
+    {
+        switch(internalType) {
+            case tString: return string.context;
+            default: abort();
+        }
+    }
+
+#pragma GCC diagnostic pop
 };
 
 
diff --git a/src/nix-env/nix-env.cc b/src/nix-env/nix-env.cc
index ad255a1e1..a8c1c250b 100644
--- a/src/nix-env/nix-env.cc
+++ b/src/nix-env/nix-env.cc
@@ -1233,7 +1233,7 @@ 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";
@@ -1253,7 +1253,7 @@ 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) {
@@ -1265,7 +1265,7 @@ 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);
                             }
                             }
diff --git a/src/nix/eval.cc b/src/nix/eval.cc
index 469ff7391..994a20004 100644
--- a/src/nix/eval.cc
+++ b/src/nix/eval.cc
@@ -86,7 +86,7 @@ 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.c_str());
                 else if (v.type() == nAttrs) {
                     if (mkdir(path.c_str(), 0777) == -1)
                         throw SysError("creating directory '%s'", path);
diff --git a/tests/unit/libexpr-support/tests/libexpr.hh b/tests/unit/libexpr-support/tests/libexpr.hh
index 4055784ca..3d93818d9 100644
--- a/tests/unit/libexpr-support/tests/libexpr.hh
+++ b/tests/unit/libexpr-support/tests/libexpr.hh
@@ -71,7 +71,7 @@ namespace nix {
         if (arg.type() != nString) {
             return false;
         }
-        return std::string_view(arg.string.s) == std::string_view(s);
+        return std::string_view(arg.c_str()) == std::string_view(s);
     }
 
     MATCHER_P(IsIntEq, v, fmt("The string is equal to \"%1%\"", v)) {
@@ -107,7 +107,7 @@ namespace nix {
                 *result_listener << "Expected a path got " << arg.type();
                 return false;
             } else if (std::string_view(arg._path) != p) {
-                *result_listener << "Expected a path that equals \"" << p << "\" but got: " << arg.string.s;
+                *result_listener << "Expected a path that equals \"" << p << "\" but got: " << arg.c_str();
                 return false;
             }
             return true;
diff --git a/tests/unit/libexpr/primops.cc b/tests/unit/libexpr/primops.cc
index bd174a6c0..ad1f6a260 100644
--- a/tests/unit/libexpr/primops.cc
+++ b/tests/unit/libexpr/primops.cc
@@ -713,14 +713,14 @@ 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.c_str(), std::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(std::string_view(v.c_str()), "foo%bar%baz");
     }
 
     TEST_F(PrimOpTest, split1) {