fix(3p/nix): Compatibility with updated SymbolTable r/795

The functions in SymbolTable have been renamed to match the Google
Style guide, and some debug-only functions have been removed.

21 files changed, 141 insertions, 137 deletions

diff --git a/third_party/nix/src/libexpr/attr-path.cc b/third_party/nix/src/libexpr/attr-path.cc
index 485c240e3a..b9b9106be8 100644
--- a/third_party/nix/src/libexpr/attr-path.cc
+++ b/third_party/nix/src/libexpr/attr-path.cc
@@ -75,7 +75,7 @@ Value* findAlongAttrPath(EvalState& state, const string& attrPath,
                     attrPath);
       }
 
-      Bindings::iterator a = v->attrs->find(state.symbols.create(attr));
+      Bindings::iterator a = v->attrs->find(state.symbols.Create(attr));
       if (a == v->attrs->end()) {
         throw Error(
             format("attribute '%1%' in selection path '%2%' not found") % attr %
diff --git a/third_party/nix/src/libexpr/common-eval-args.cc b/third_party/nix/src/libexpr/common-eval-args.cc
index 33319cbabb..398d42b355 100644
--- a/third_party/nix/src/libexpr/common-eval-args.cc
+++ b/third_party/nix/src/libexpr/common-eval-args.cc
@@ -42,7 +42,7 @@ Bindings* MixEvalArgs::getAutoArgs(EvalState& state) {
     } else {
       mkString(*v, string(i.second, 1));
     }
-    res->push_back(Attr(state.symbols.create(i.first), v));
+    res->push_back(Attr(state.symbols.Create(i.first), v));
   }
   res->sort();
   return res;
diff --git a/third_party/nix/src/libexpr/eval.cc b/third_party/nix/src/libexpr/eval.cc
index 4053dffe51..5896bc96e3 100644
--- a/third_party/nix/src/libexpr/eval.cc
+++ b/third_party/nix/src/libexpr/eval.cc
@@ -198,7 +198,7 @@ static Symbol getName(const AttrName& name, EvalState& state, Env& env) {
   Value nameValue;
   name.expr->eval(state, env, nameValue);
   state.forceStringNoCtx(nameValue);
-  return state.symbols.create(nameValue.string.s);
+  return state.symbols.Create(nameValue.string.s);
 }
 
 static bool gcInitialised = false;
@@ -299,31 +299,31 @@ static Strings parseNixPath(const string& s) {
 }
 
 EvalState::EvalState(const Strings& _searchPath, const ref<Store>& store)
-    : sWith(symbols.create("<with>")),
-      sOutPath(symbols.create("outPath")),
-      sDrvPath(symbols.create("drvPath")),
-      sType(symbols.create("type")),
-      sMeta(symbols.create("meta")),
-      sName(symbols.create("name")),
-      sValue(symbols.create("value")),
-      sSystem(symbols.create("system")),
-      sOverrides(symbols.create("__overrides")),
-      sOutputs(symbols.create("outputs")),
-      sOutputName(symbols.create("outputName")),
-      sIgnoreNulls(symbols.create("__ignoreNulls")),
-      sFile(symbols.create("file")),
-      sLine(symbols.create("line")),
-      sColumn(symbols.create("column")),
-      sFunctor(symbols.create("__functor")),
-      sToString(symbols.create("__toString")),
-      sRight(symbols.create("right")),
-      sWrong(symbols.create("wrong")),
-      sStructuredAttrs(symbols.create("__structuredAttrs")),
-      sBuilder(symbols.create("builder")),
-      sArgs(symbols.create("args")),
-      sOutputHash(symbols.create("outputHash")),
-      sOutputHashAlgo(symbols.create("outputHashAlgo")),
-      sOutputHashMode(symbols.create("outputHashMode")),
+    : sWith(symbols.Create("<with>")),
+      sOutPath(symbols.Create("outPath")),
+      sDrvPath(symbols.Create("drvPath")),
+      sType(symbols.Create("type")),
+      sMeta(symbols.Create("meta")),
+      sName(symbols.Create("name")),
+      sValue(symbols.Create("value")),
+      sSystem(symbols.Create("system")),
+      sOverrides(symbols.Create("__overrides")),
+      sOutputs(symbols.Create("outputs")),
+      sOutputName(symbols.Create("outputName")),
+      sIgnoreNulls(symbols.Create("__ignoreNulls")),
+      sFile(symbols.Create("file")),
+      sLine(symbols.Create("line")),
+      sColumn(symbols.Create("column")),
+      sFunctor(symbols.Create("__functor")),
+      sToString(symbols.Create("__toString")),
+      sRight(symbols.Create("right")),
+      sWrong(symbols.Create("wrong")),
+      sStructuredAttrs(symbols.Create("__structuredAttrs")),
+      sBuilder(symbols.Create("builder")),
+      sArgs(symbols.Create("args")),
+      sOutputHash(symbols.Create("outputHash")),
+      sOutputHashAlgo(symbols.Create("outputHashAlgo")),
+      sOutputHashMode(symbols.Create("outputHashMode")),
       repair(NoRepair),
       store(store),
       baseEnv(allocEnv(128)),
@@ -467,10 +467,10 @@ Path EvalState::toRealPath(const Path& path, const PathSet& context) {
 Value* EvalState::addConstant(const string& name, Value& v) {
   Value* v2 = allocValue();
   *v2 = v;
-  staticBaseEnv.vars[symbols.create(name)] = baseEnvDispl;
+  staticBaseEnv.vars[symbols.Create(name)] = baseEnvDispl;
   baseEnv.values[baseEnvDispl++] = v2;
   string name2 = string(name, 0, 2) == "__" ? string(name, 2) : name;
-  baseEnv.values[0]->attrs->push_back(Attr(symbols.create(name2), v2));
+  baseEnv.values[0]->attrs->push_back(Attr(symbols.Create(name2), v2));
   return v2;
 }
 
@@ -483,17 +483,17 @@ Value* EvalState::addPrimOp(const string& name, size_t arity,
   }
   Value* v = allocValue();
   string name2 = string(name, 0, 2) == "__" ? string(name, 2) : name;
-  Symbol sym = symbols.create(name2);
+  Symbol sym = symbols.Create(name2);
   v->type = tPrimOp;
   v->primOp = new PrimOp(primOp, arity, sym);
-  staticBaseEnv.vars[symbols.create(name)] = baseEnvDispl;
+  staticBaseEnv.vars[symbols.Create(name)] = baseEnvDispl;
   baseEnv.values[baseEnvDispl++] = v;
   baseEnv.values[0]->attrs->push_back(Attr(sym, v));
   return v;
 }
 
 Value& EvalState::getBuiltin(const string& name) {
-  return *baseEnv.values[0]->attrs->find(symbols.create(name))->value;
+  return *baseEnv.values[0]->attrs->find(symbols.Create(name))->value;
 }
 
 /* Every "format" object (even temporary) takes up a few hundred bytes
@@ -885,7 +885,7 @@ void ExprAttrs::eval(EvalState& state, Env& env, Value& v) {
       continue;
     }
     state.forceStringNoCtx(nameVal);
-    Symbol nameSym = state.symbols.create(nameVal.string.s);
+    Symbol nameSym = state.symbols.Create(nameVal.string.s);
     Bindings::iterator j = v.attrs->find(nameSym);
     if (j != v.attrs->end()) {
       throwEvalError("dynamic attribute '%1%' at %2% already defined at %3%",
@@ -1828,8 +1828,8 @@ void EvalState::printStats() {
     }
     {
       auto syms = topObj.object("symbols");
-      syms.attr("number", symbols.size());
-      syms.attr("bytes", symbols.totalSize());
+      syms.attr("number", symbols.Size());
+      syms.attr("bytes", symbols.TotalSize());
     }
     {
       auto sets = topObj.object("sets");
@@ -1897,10 +1897,11 @@ void EvalState::printStats() {
       }
     }
 
-    if (getEnv("NIX_SHOW_SYMBOLS", "0") != "0") {
-      auto list = topObj.list("symbols");
-      symbols.dump([&](const std::string& s) { list.elem(s); });
-    }
+    // TODO(tazjin): what is this? commented out because .dump() is gone.
+    // if (getEnv("NIX_SHOW_SYMBOLS", "0") != "0") {
+    //   auto list = topObj.list("symbols");
+    //   symbols.dump([&](const std::string& s) { list.elem(s); });
+    // }
   }
 }
 
diff --git a/third_party/nix/src/libexpr/get-drvs.cc b/third_party/nix/src/libexpr/get-drvs.cc
index 39870abcbd..4d412a9c61 100644
--- a/third_party/nix/src/libexpr/get-drvs.cc
+++ b/third_party/nix/src/libexpr/get-drvs.cc
@@ -99,7 +99,7 @@ DrvInfo::Outputs DrvInfo::queryOutputs(bool onlyOutputsToInstall) {
         /* Evaluate the corresponding set. */
         string name =
             state->forceStringNoCtx(*i->value->listElems()[j], *i->pos);
-        Bindings::iterator out = attrs->find(state->symbols.create(name));
+        Bindings::iterator out = attrs->find(state->symbols.Create(name));
         if (out == attrs->end()) {
           continue;  // FIXME: throw error?
         }
@@ -213,7 +213,7 @@ Value* DrvInfo::queryMeta(const string& name) {
   if (getMeta() == nullptr) {
     return nullptr;
   }
-  Bindings::iterator a = meta->find(state->symbols.create(name));
+  Bindings::iterator a = meta->find(state->symbols.Create(name));
   if (a == meta->end() || !checkMeta(*a->value)) {
     return nullptr;
   }
@@ -291,7 +291,7 @@ void DrvInfo::setMeta(const string& name, Value* v) {
   getMeta();
   Bindings* old = meta;
   meta = state->allocBindings(1 + (old != nullptr ? old->size() : 0));
-  Symbol sym = state->symbols.create(name);
+  Symbol sym = state->symbols.Create(name);
   if (old != nullptr) {
     for (auto i : *old) {
       if (i.name != sym) {
@@ -377,7 +377,7 @@ static void getDerivations(EvalState& state, Value& vIn,
     /* !!! undocumented hackery to support combining channels in
        nix-env.cc. */
     bool combineChannels =
-        v.attrs->find(state.symbols.create("_combineChannels")) !=
+        v.attrs->find(state.symbols.Create("_combineChannels")) !=
         v.attrs->end();
 
     /* Consider the attributes in sorted order to get more
@@ -401,7 +401,7 @@ static void getDerivations(EvalState& state, Value& vIn,
            `recurseForDerivations = true' attribute. */
         if (i->value->type == tAttrs) {
           Bindings::iterator j = i->value->attrs->find(
-              state.symbols.create("recurseForDerivations"));
+              state.symbols.Create("recurseForDerivations"));
           if (j != i->value->attrs->end() &&
               state.forceBool(*j->value, *j->pos)) {
             getDerivations(state, *i->value, pathPrefix2, autoArgs, drvs, done,
diff --git a/third_party/nix/src/libexpr/json-to-value.cc b/third_party/nix/src/libexpr/json-to-value.cc
index 68f016904e..ea7d575aa9 100644
--- a/third_party/nix/src/libexpr/json-to-value.cc
+++ b/third_party/nix/src/libexpr/json-to-value.cc
@@ -105,7 +105,7 @@ static void parseJSON(EvalState& state, const char*& s, Value& v) {
       s++;
       Value* v2 = state.allocValue();
       parseJSON(state, s, *v2);
-      attrs[state.symbols.create(name)] = v2;
+      attrs[state.symbols.Create(name)] = v2;
       skipWhitespace(s);
       if (*s == '}') {
         break;
diff --git a/third_party/nix/src/libexpr/lexer.l b/third_party/nix/src/libexpr/lexer.l
index a0d6bd7e16..1f9e45a1cd 100644
--- a/third_party/nix/src/libexpr/lexer.l
+++ b/third_party/nix/src/libexpr/lexer.l
@@ -72,7 +72,7 @@ static Expr * unescapeStr(SymbolTable & symbols, const char * s, size_t length)
         }
         else t += c;
     }
-    return new ExprString(symbols.create(t));
+    return new ExprString(symbols.Create(t));
 }
 
 
diff --git a/third_party/nix/src/libexpr/meson.build b/third_party/nix/src/libexpr/meson.build
index 7ddd4cff4e..1bb311e999 100644
--- a/third_party/nix/src/libexpr/meson.build
+++ b/third_party/nix/src/libexpr/meson.build
@@ -16,6 +16,7 @@ libexpr_src = files(
     join_paths(meson.source_root(), 'src/libexpr/names.cc'),
     join_paths(meson.source_root(), 'src/libexpr/nixexpr.cc'),
     join_paths(meson.source_root(), 'src/libexpr/primops.cc'),
+    join_paths(meson.source_root(), 'src/libexpr/symbol-table.cc'),
     join_paths(meson.source_root(), 'src/libexpr/value-to-json.cc'),
     join_paths(meson.source_root(), 'src/libexpr/value-to-xml.cc'),
 )
@@ -42,18 +43,17 @@ libexpr_dep_list = [
     glog_dep,
     libdl_dep,
     libsodium_dep,
-]
-
-if sys_name == 'freebsd'
-    libexpr_dep_list += libdl_dep
-endif
+] + absl_deps
 
 libexpr_link_list = [
     libutil_lib,
     libstore_lib,
-    libmain_lib]
+    libmain_lib,
+]
 
-libexpr_link_args = []
+libexpr_link_args = [
+  '-lpthread',
+]
 
 libexpr_cxx_args = []
 
diff --git a/third_party/nix/src/libexpr/parser.y b/third_party/nix/src/libexpr/parser.y
index 5aa38bf2b8..f5a25d5934 100644
--- a/third_party/nix/src/libexpr/parser.y
+++ b/third_party/nix/src/libexpr/parser.y
@@ -35,7 +35,7 @@ namespace nix {
         ParseData(EvalState & state)
             : state(state)
             , symbols(state.symbols)
-            , sLetBody(symbols.create("<let-body>"))
+            , sLetBody(symbols.Create("<let-body>"))
             { };
     };
 
@@ -148,7 +148,7 @@ static void addFormal(const Pos & pos, Formals * formals, const Formal & formal)
 
 static Expr * stripIndentation(const Pos & pos, SymbolTable & symbols, vector<Expr *> & es)
 {
-    if (es.empty()) { return new ExprString(symbols.create("")); }
+    if (es.empty()) { return new ExprString(symbols.Create("")); }
 
     /* Figure out the minimum indentation.  Note that by design
        whitespace-only final lines are not taken into account.  (So
@@ -228,7 +228,7 @@ static Expr * stripIndentation(const Pos & pos, SymbolTable & symbols, vector<Ex
                 s2 = string(s2, 0, p + 1);
         }
 
-        es2->push_back(new ExprString(symbols.create(s2)));
+        es2->push_back(new ExprString(symbols.Create(s2)));
     }
 
     /* If this is a single string, then don't do a concatenation. */
@@ -314,13 +314,13 @@ expr: expr_function;
 
 expr_function
   : ID ':' expr_function
-    { $$ = new ExprLambda(CUR_POS, data->symbols.create($1), false, 0, $3); }
+    { $$ = new ExprLambda(CUR_POS, data->symbols.Create($1), false, 0, $3); }
   | '{' formals '}' ':' expr_function
-    { $$ = new ExprLambda(CUR_POS, data->symbols.create(""), true, $2, $5); }
+    { $$ = new ExprLambda(CUR_POS, data->symbols.Create(""), true, $2, $5); }
   | '{' formals '}' '@' ID ':' expr_function
-    { $$ = new ExprLambda(CUR_POS, data->symbols.create($5), true, $2, $7); }
+    { $$ = new ExprLambda(CUR_POS, data->symbols.Create($5), true, $2, $7); }
   | ID '@' '{' formals '}' ':' expr_function
-    { $$ = new ExprLambda(CUR_POS, data->symbols.create($1), true, $4, $7); }
+    { $$ = new ExprLambda(CUR_POS, data->symbols.Create($1), true, $4, $7); }
   | ASSERT expr ';' expr_function
     { $$ = new ExprAssert(CUR_POS, $2, $4); }
   | WITH expr ';' expr_function
@@ -341,13 +341,13 @@ expr_if
 
 expr_op
   : '!' expr_op %prec NOT { $$ = new ExprOpNot($2); }
-  | '-' expr_op %prec NEGATE { $$ = new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.create("__sub")), new ExprInt(0)), $2); }
+  | '-' expr_op %prec NEGATE { $$ = new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.Create("__sub")), new ExprInt(0)), $2); }
   | expr_op EQ expr_op { $$ = new ExprOpEq($1, $3); }
   | expr_op NEQ expr_op { $$ = new ExprOpNEq($1, $3); }
-  | expr_op '<' expr_op { $$ = new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.create("__lessThan")), $1), $3); }
-  | expr_op LEQ expr_op { $$ = new ExprOpNot(new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.create("__lessThan")), $3), $1)); }
-  | expr_op '>' expr_op { $$ = new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.create("__lessThan")), $3), $1); }
-  | expr_op GEQ expr_op { $$ = new ExprOpNot(new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.create("__lessThan")), $1), $3)); }
+  | expr_op '<' expr_op { $$ = new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.Create("__lessThan")), $1), $3); }
+  | expr_op LEQ expr_op { $$ = new ExprOpNot(new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.Create("__lessThan")), $3), $1)); }
+  | expr_op '>' expr_op { $$ = new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.Create("__lessThan")), $3), $1); }
+  | expr_op GEQ expr_op { $$ = new ExprOpNot(new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.Create("__lessThan")), $1), $3)); }
   | expr_op AND expr_op { $$ = new ExprOpAnd(CUR_POS, $1, $3); }
   | expr_op OR expr_op { $$ = new ExprOpOr(CUR_POS, $1, $3); }
   | expr_op IMPL expr_op { $$ = new ExprOpImpl(CUR_POS, $1, $3); }
@@ -355,9 +355,9 @@ expr_op
   | expr_op '?' attrpath { $$ = new ExprOpHasAttr($1, *$3); }
   | expr_op '+' expr_op
     { $$ = new ExprConcatStrings(CUR_POS, false, new vector<Expr *>({$1, $3})); }
-  | expr_op '-' expr_op { $$ = new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.create("__sub")), $1), $3); }
-  | expr_op '*' expr_op { $$ = new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.create("__mul")), $1), $3); }
-  | expr_op '/' expr_op { $$ = new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.create("__div")), $1), $3); }
+  | expr_op '-' expr_op { $$ = new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.Create("__sub")), $1), $3); }
+  | expr_op '*' expr_op { $$ = new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.Create("__mul")), $1), $3); }
+  | expr_op '/' expr_op { $$ = new ExprApp(CUR_POS, new ExprApp(new ExprVar(data->symbols.Create("__div")), $1), $3); }
   | expr_op CONCAT expr_op { $$ = new ExprOpConcatLists(CUR_POS, $1, $3); }
   | expr_app
   ;
@@ -376,7 +376,7 @@ expr_select
   | /* Backwards compatibility: because Nixpkgs has a rarely used
        function named ‘or’, allow stuff like ‘map or [...]’. */
     expr_simple OR_KW
-    { $$ = new ExprApp(CUR_POS, $1, new ExprVar(CUR_POS, data->symbols.create("or"))); }
+    { $$ = new ExprApp(CUR_POS, $1, new ExprVar(CUR_POS, data->symbols.Create("or"))); }
   | expr_simple { $$ = $1; }
   ;
 
@@ -385,7 +385,7 @@ expr_simple
       if (strcmp($1, "__curPos") == 0)
           $$ = new ExprPos(CUR_POS);
       else
-          $$ = new ExprVar(CUR_POS, data->symbols.create($1));
+          $$ = new ExprVar(CUR_POS, data->symbols.Create($1));
   }
   | INT { $$ = new ExprInt($1); }
   | FLOAT { $$ = new ExprFloat($1); }
@@ -398,16 +398,16 @@ expr_simple
   | SPATH {
       string path($1 + 1, strlen($1) - 2);
       $$ = new ExprApp(CUR_POS,
-          new ExprApp(new ExprVar(data->symbols.create("__findFile")),
-              new ExprVar(data->symbols.create("__nixPath"))),
-          new ExprString(data->symbols.create(path)));
+          new ExprApp(new ExprVar(data->symbols.Create("__findFile")),
+              new ExprVar(data->symbols.Create("__nixPath"))),
+          new ExprString(data->symbols.Create(path)));
   }
-  | URI { $$ = new ExprString(data->symbols.create($1)); }
+  | URI { $$ = new ExprString(data->symbols.Create($1)); }
   | '(' expr ')' { $$ = $2; }
   /* Let expressions `let {..., body = ...}' are just desugared
      into `(rec {..., body = ...}).body'. */
   | LET '{' binds '}'
-    { $3->recursive = true; $$ = new ExprSelect(noPos, $3, data->symbols.create("body")); }
+    { $3->recursive = true; $$ = new ExprSelect(noPos, $3, data->symbols.Create("body")); }
   | REC '{' binds '}'
     { $3->recursive = true; $$ = $3; }
   | '{' binds '}'
@@ -418,7 +418,7 @@ expr_simple
 string_parts
   : STR
   | string_parts_interpolated { $$ = new ExprConcatStrings(CUR_POS, true, $1); }
-  | { $$ = new ExprString(data->symbols.create("")); }
+  | { $$ = new ExprString(data->symbols.Create("")); }
   ;
 
 string_parts_interpolated
@@ -462,7 +462,7 @@ binds
   ;
 
 attrs
-  : attrs attr { $$ = $1; $1->push_back(AttrName(data->symbols.create($2))); }
+  : attrs attr { $$ = $1; $1->push_back(AttrName(data->symbols.Create($2))); }
   | attrs string_attr
     { $$ = $1;
       ExprString * str = dynamic_cast<ExprString *>($2);
@@ -477,7 +477,7 @@ attrs
   ;
 
 attrpath
-  : attrpath '.' attr { $$ = $1; $1->push_back(AttrName(data->symbols.create($3))); }
+  : attrpath '.' attr { $$ = $1; $1->push_back(AttrName(data->symbols.Create($3))); }
   | attrpath '.' string_attr
     { $$ = $1;
       ExprString * str = dynamic_cast<ExprString *>($3);
@@ -487,7 +487,7 @@ attrpath
       } else
           $$->push_back(AttrName($3));
     }
-  | attr { $$ = new vector<AttrName>; $$->push_back(AttrName(data->symbols.create($1))); }
+  | attr { $$ = new vector<AttrName>; $$->push_back(AttrName(data->symbols.Create($1))); }
   | string_attr
     { $$ = new vector<AttrName>;
       ExprString *str = dynamic_cast<ExprString *>($1);
@@ -526,8 +526,8 @@ formals
   ;
 
 formal
-  : ID { $$ = new Formal(data->symbols.create($1), 0); }
-  | ID '?' expr { $$ = new Formal(data->symbols.create($1), $3); }
+  : ID { $$ = new Formal(data->symbols.Create($1), 0); }
+  | ID '?' expr { $$ = new Formal(data->symbols.Create($1), $3); }
   ;
 
 %%
@@ -552,7 +552,7 @@ Expr * EvalState::parse(const char * text,
     yyscan_t scanner;
     ParseData data(*this);
     data.basePath = basePath;
-    data.path = data.symbols.create(path);
+    data.path = data.symbols.Create(path);
 
     yylex_init(&scanner);
     yy_scan_string(text, scanner);
diff --git a/third_party/nix/src/libexpr/primops.cc b/third_party/nix/src/libexpr/primops.cc
index 307459396e..50a745624d 100644
--- a/third_party/nix/src/libexpr/primops.cc
+++ b/third_party/nix/src/libexpr/primops.cc
@@ -118,12 +118,12 @@ static void prim_scopedImport(EvalState& state, const Pos& pos, Value** args,
     mkString(*v2, path, {"=" + path});
     v2 = state.allocAttr(w, state.sName);
     mkString(*v2, drv.env["name"]);
-    Value* outputsVal = state.allocAttr(w, state.symbols.create("outputs"));
+    Value* outputsVal = state.allocAttr(w, state.symbols.Create("outputs"));
     state.mkList(*outputsVal, drv.outputs.size());
     unsigned int outputs_index = 0;
 
     for (const auto& o : drv.outputs) {
-      v2 = state.allocAttr(w, state.symbols.create(o.first));
+      v2 = state.allocAttr(w, state.symbols.Create(o.first));
       mkString(*v2, o.second.path, {"!" + o.first + "!" + path});
       outputsVal->listElems()[outputs_index] = state.allocValue();
       mkString(*(outputsVal->listElems()[outputs_index++]), o.first);
@@ -291,7 +291,7 @@ static void prim_typeOf(EvalState& state, const Pos& pos, Value** args,
     default:
       abort();
   }
-  mkString(v, state.symbols.create(t));
+  mkString(v, state.symbols.Create(t));
 }
 
 /* Determine whether the argument is the null value. */
@@ -394,7 +394,7 @@ static void prim_genericClosure(EvalState& state, const Pos& pos, Value** args,
 
   /* Get the start set. */
   Bindings::iterator startSet =
-      args[0]->attrs->find(state.symbols.create("startSet"));
+      args[0]->attrs->find(state.symbols.Create("startSet"));
   if (startSet == args[0]->attrs->end()) {
     throw EvalError(format("attribute 'startSet' required, at %1%") % pos);
   }
@@ -407,7 +407,7 @@ static void prim_genericClosure(EvalState& state, const Pos& pos, Value** args,
 
   /* Get the operator. */
   Bindings::iterator op =
-      args[0]->attrs->find(state.symbols.create("operator"));
+      args[0]->attrs->find(state.symbols.Create("operator"));
   if (op == args[0]->attrs->end()) {
     throw EvalError(format("attribute 'operator' required, at %1%") % pos);
   }
@@ -426,7 +426,7 @@ static void prim_genericClosure(EvalState& state, const Pos& pos, Value** args,
 
     state.forceAttrs(*e, pos);
 
-    Bindings::iterator key = e->attrs->find(state.symbols.create("key"));
+    Bindings::iterator key = e->attrs->find(state.symbols.Create("key"));
     if (key == e->attrs->end()) {
       throw EvalError(format("attribute 'key' required, at %1%") % pos);
     }
@@ -493,10 +493,10 @@ static void prim_tryEval(EvalState& state, const Pos& pos, Value** args,
   try {
     state.forceValue(*args[0]);
     v.attrs->push_back(Attr(state.sValue, args[0]));
-    mkBool(*state.allocAttr(v, state.symbols.create("success")), true);
+    mkBool(*state.allocAttr(v, state.symbols.Create("success")), true);
   } catch (AssertionError& e) {
     mkBool(*state.allocAttr(v, state.sValue), false);
-    mkBool(*state.allocAttr(v, state.symbols.create("success")), false);
+    mkBool(*state.allocAttr(v, state.symbols.Create("success")), false);
   }
   v.attrs->sort();
 }
@@ -846,7 +846,7 @@ static void prim_derivationStrict(EvalState& state, const Pos& pos,
   state.mkAttrs(v, 1 + drv.outputs.size());
   mkString(*state.allocAttr(v, state.sDrvPath), drvPath, {"=" + drvPath});
   for (auto& i : drv.outputs) {
-    mkString(*state.allocAttr(v, state.symbols.create(i.first)), i.second.path,
+    mkString(*state.allocAttr(v, state.symbols.Create(i.first)), i.second.path,
              {"!" + i.first + "!" + drvPath});
   }
   v.attrs->sort();
@@ -987,12 +987,12 @@ static void prim_findFile(EvalState& state, const Pos& pos, Value** args,
     state.forceAttrs(v2, pos);
 
     string prefix;
-    Bindings::iterator i = v2.attrs->find(state.symbols.create("prefix"));
+    Bindings::iterator i = v2.attrs->find(state.symbols.Create("prefix"));
     if (i != v2.attrs->end()) {
       prefix = state.forceStringNoCtx(*i->value, pos);
     }
 
-    i = v2.attrs->find(state.symbols.create("path"));
+    i = v2.attrs->find(state.symbols.Create("path"));
     if (i == v2.attrs->end()) {
       throw EvalError(format("attribute 'path' missing, at %1%") % pos);
     }
@@ -1050,7 +1050,7 @@ static void prim_readDir(EvalState& state, const Pos& pos, Value** args,
   state.mkAttrs(v, entries.size());
 
   for (auto& ent : entries) {
-    Value* ent_val = state.allocAttr(v, state.symbols.create(ent.name));
+    Value* ent_val = state.allocAttr(v, state.symbols.Create(ent.name));
     if (ent.type == DT_UNKNOWN) {
       ent.type = getFileType(path + "/" + ent.name);
     }
@@ -1301,7 +1301,7 @@ void prim_getAttr(EvalState& state, const Pos& pos, Value** args, Value& v) {
   string attr = state.forceStringNoCtx(*args[0], pos);
   state.forceAttrs(*args[1], pos);
   // !!! Should we create a symbol here or just do a lookup?
-  Bindings::iterator i = args[1]->attrs->find(state.symbols.create(attr));
+  Bindings::iterator i = args[1]->attrs->find(state.symbols.Create(attr));
   if (i == args[1]->attrs->end()) {
     throw EvalError(format("attribute '%1%' missing, at %2%") % attr % pos);
   }
@@ -1318,7 +1318,7 @@ void prim_unsafeGetAttrPos(EvalState& state, const Pos& pos, Value** args,
                            Value& v) {
   string attr = state.forceStringNoCtx(*args[0], pos);
   state.forceAttrs(*args[1], pos);
-  Bindings::iterator i = args[1]->attrs->find(state.symbols.create(attr));
+  Bindings::iterator i = args[1]->attrs->find(state.symbols.Create(attr));
   if (i == args[1]->attrs->end()) {
     mkNull(v);
   } else {
@@ -1331,7 +1331,7 @@ static void prim_hasAttr(EvalState& state, const Pos& pos, Value** args,
                          Value& v) {
   string attr = state.forceStringNoCtx(*args[0], pos);
   state.forceAttrs(*args[1], pos);
-  mkBool(v, args[1]->attrs->find(state.symbols.create(attr)) !=
+  mkBool(v, args[1]->attrs->find(state.symbols.Create(attr)) !=
                 args[1]->attrs->end());
 }
 
@@ -1351,7 +1351,7 @@ static void prim_removeAttrs(EvalState& state, const Pos& pos, Value** args,
   std::set<Symbol> names;
   for (unsigned int i = 0; i < args[1]->listSize(); ++i) {
     state.forceStringNoCtx(*args[1]->listElems()[i], pos);
-    names.insert(state.symbols.create(args[1]->listElems()[i]->string.s));
+    names.insert(state.symbols.Create(args[1]->listElems()[i]->string.s));
   }
 
   /* Copy all attributes not in that set.  Note that we don't need
@@ -1391,10 +1391,13 @@ static void prim_listToAttrs(EvalState& state, const Pos& pos, Value** args,
     }
     string name = state.forceStringNoCtx(*j->value, pos);
 
-    Symbol sym = state.symbols.create(name);
+    Symbol sym = state.symbols.Create(name);
     if (seen.find(sym) == seen.end()) {
       Bindings::iterator j2 =
-          v2.attrs->find(state.symbols.create(state.sValue));
+          // TODO(tazjin): this line used to construct the symbol again:
+          // state.symbols.Create(state.sValue));
+          // Why?
+          v2.attrs->find(state.sValue);
       if (j2 == v2.attrs->end()) {
         throw TypeError(format("'value' attribute missing in a call to "
                                "'listToAttrs', at %1%") %
@@ -1436,7 +1439,7 @@ static void prim_intersectAttrs(EvalState& state, const Pos& pos, Value** args,
 */
 static void prim_catAttrs(EvalState& state, const Pos& pos, Value** args,
                           Value& v) {
-  Symbol attrName = state.symbols.create(state.forceStringNoCtx(*args[0], pos));
+  Symbol attrName = state.symbols.Create(state.forceStringNoCtx(*args[0], pos));
   state.forceList(*args[1], pos);
 
   Value* res[args[1]->listSize()];
@@ -2144,7 +2147,7 @@ static void prim_parseDrvName(EvalState& state, const Pos& pos, Value** args,
   DrvName parsed(name);
   state.mkAttrs(v, 2);
   mkString(*state.allocAttr(v, state.sName), parsed.name);
-  mkString(*state.allocAttr(v, state.symbols.create("version")),
+  mkString(*state.allocAttr(v, state.symbols.Create("version")),
            parsed.version);
   v.attrs->sort();
 }
@@ -2430,7 +2433,7 @@ void EvalState::createBaseEnv() {
      `drvPath' and `outPath' attributes lazily. */
   string path =
       canonPath(settings.nixDataDir + "/nix/corepkgs/derivation.nix", true);
-  sDerivationNix = symbols.create(path);
+  sDerivationNix = symbols.Create(path);
   evalFile(path, v);
   addConstant("derivation", v);
 
@@ -2440,8 +2443,8 @@ void EvalState::createBaseEnv() {
   for (auto& i : searchPath) {
     v2 = v.listElems()[n++] = allocValue();
     mkAttrs(*v2, 2);
-    mkString(*allocAttr(*v2, symbols.create("path")), i.second);
-    mkString(*allocAttr(*v2, symbols.create("prefix")), i.first);
+    mkString(*allocAttr(*v2, symbols.Create("path")), i.second);
+    mkString(*allocAttr(*v2, symbols.Create("prefix")), i.first);
     v2->attrs->sort();
   }
   addConstant("__nixPath", v);
diff --git a/third_party/nix/src/libexpr/primops/context.cc b/third_party/nix/src/libexpr/primops/context.cc
index 347b7a0a52..7fa33bd87f 100644
--- a/third_party/nix/src/libexpr/primops/context.cc
+++ b/third_party/nix/src/libexpr/primops/context.cc
@@ -108,10 +108,10 @@ static void prim_getContext(EvalState& state, const Pos& pos, Value** args,
 
   state.mkAttrs(v, contextInfos.size());
 
-  auto sPath = state.symbols.create("path");
-  auto sAllOutputs = state.symbols.create("allOutputs");
+  auto sPath = state.symbols.Create("path");
+  auto sAllOutputs = state.symbols.Create("allOutputs");
   for (const auto& info : contextInfos) {
-    auto& infoVal = *state.allocAttr(v, state.symbols.create(info.first));
+    auto& infoVal = *state.allocAttr(v, state.symbols.Create(info.first));
     state.mkAttrs(infoVal, 3);
     if (info.second.path) {
       mkBool(*state.allocAttr(infoVal, sPath), true);
@@ -145,8 +145,8 @@ static void prim_appendContext(EvalState& state, const Pos& pos, Value** args,
 
   state.forceAttrs(*args[1], pos);
 
-  auto sPath = state.symbols.create("path");
-  auto sAllOutputs = state.symbols.create("allOutputs");
+  auto sPath = state.symbols.Create("path");
+  auto sAllOutputs = state.symbols.Create("allOutputs");
   for (auto& i : *args[1]->attrs) {
     if (!state.store->isStorePath(i.name))
       throw EvalError("Context key '%s' is not a store path, at %s", i.name,
diff --git a/third_party/nix/src/libexpr/primops/fetchGit.cc b/third_party/nix/src/libexpr/primops/fetchGit.cc
index 818a475f5e..374f075a91 100644
--- a/third_party/nix/src/libexpr/primops/fetchGit.cc
+++ b/third_party/nix/src/libexpr/primops/fetchGit.cc
@@ -246,10 +246,10 @@ static void prim_fetchGit(EvalState& state, const Pos& pos, Value** args,
   state.mkAttrs(v, 8);
   mkString(*state.allocAttr(v, state.sOutPath), gitInfo.storePath,
            PathSet({gitInfo.storePath}));
-  mkString(*state.allocAttr(v, state.symbols.create("rev")), gitInfo.rev);
-  mkString(*state.allocAttr(v, state.symbols.create("shortRev")),
+  mkString(*state.allocAttr(v, state.symbols.Create("rev")), gitInfo.rev);
+  mkString(*state.allocAttr(v, state.symbols.Create("shortRev")),
            gitInfo.shortRev);
-  mkInt(*state.allocAttr(v, state.symbols.create("revCount")),
+  mkInt(*state.allocAttr(v, state.symbols.Create("revCount")),
         gitInfo.revCount);
   v.attrs->sort();
 
diff --git a/third_party/nix/src/libexpr/primops/fetchMercurial.cc b/third_party/nix/src/libexpr/primops/fetchMercurial.cc
index 392dbcb008..67ecf4f498 100644
--- a/third_party/nix/src/libexpr/primops/fetchMercurial.cc
+++ b/third_party/nix/src/libexpr/primops/fetchMercurial.cc
@@ -220,11 +220,11 @@ static void prim_fetchMercurial(EvalState& state, const Pos& pos, Value** args,
   state.mkAttrs(v, 8);
   mkString(*state.allocAttr(v, state.sOutPath), hgInfo.storePath,
            PathSet({hgInfo.storePath}));
-  mkString(*state.allocAttr(v, state.symbols.create("branch")), hgInfo.branch);
-  mkString(*state.allocAttr(v, state.symbols.create("rev")), hgInfo.rev);
-  mkString(*state.allocAttr(v, state.symbols.create("shortRev")),
+  mkString(*state.allocAttr(v, state.symbols.Create("branch")), hgInfo.branch);
+  mkString(*state.allocAttr(v, state.symbols.Create("rev")), hgInfo.rev);
+  mkString(*state.allocAttr(v, state.symbols.Create("shortRev")),
            std::string(hgInfo.rev, 0, 12));
-  mkInt(*state.allocAttr(v, state.symbols.create("revCount")), hgInfo.revCount);
+  mkInt(*state.allocAttr(v, state.symbols.Create("revCount")), hgInfo.revCount);
   v.attrs->sort();
 
   if (state.allowedPaths)
diff --git a/third_party/nix/src/libexpr/primops/fromTOML.cc b/third_party/nix/src/libexpr/primops/fromTOML.cc
index 4b652b379a..320b6120e7 100644
--- a/third_party/nix/src/libexpr/primops/fromTOML.cc
+++ b/third_party/nix/src/libexpr/primops/fromTOML.cc
@@ -25,7 +25,7 @@ static void prim_fromTOML(EvalState& state, const Pos& pos, Value** args,
       state.mkAttrs(v, size);
 
       for (auto& i : *t2) {
-        auto& v2 = *state.allocAttr(v, state.symbols.create(i.first));
+        auto& v2 = *state.allocAttr(v, state.symbols.Create(i.first));
 
         if (auto i2 = i.second->as_table_array()) {
           size_t size2 = i2->get().size();
diff --git a/third_party/nix/src/libexpr/value-to-json.cc b/third_party/nix/src/libexpr/value-to-json.cc
index eaf0fca3d3..52ab44083b 100644
--- a/third_party/nix/src/libexpr/value-to-json.cc
+++ b/third_party/nix/src/libexpr/value-to-json.cc
@@ -54,7 +54,7 @@ void printValueAsJSON(EvalState& state, bool strict, Value& v,
           names.insert(j.name);
         }
         for (auto& j : names) {
-          Attr& a(*v.attrs->find(state.symbols.create(j)));
+          Attr& a(*v.attrs->find(state.symbols.Create(j)));
           auto placeholder(obj.placeholder(j));
           printValueAsJSON(state, strict, *a.value, placeholder, context);
         }
diff --git a/third_party/nix/src/libexpr/value-to-xml.cc b/third_party/nix/src/libexpr/value-to-xml.cc
index 7fab6e2ffe..160c6eba33 100644
--- a/third_party/nix/src/libexpr/value-to-xml.cc
+++ b/third_party/nix/src/libexpr/value-to-xml.cc
@@ -34,7 +34,7 @@ static void showAttrs(EvalState& state, bool strict, bool location,
   }
 
   for (auto& i : names) {
-    Attr& a(*attrs.find(state.symbols.create(i)));
+    Attr& a(*attrs.find(state.symbols.Create(i)));
 
     XMLAttrs xmlAttrs;
     xmlAttrs["name"] = i;
@@ -86,7 +86,7 @@ static void printValueAsXML(EvalState& state, bool strict, bool location,
         XMLAttrs xmlAttrs;
 
         Bindings::iterator a =
-            v.attrs->find(state.symbols.create("derivation"));
+            v.attrs->find(state.symbols.Create("derivation"));
 
         Path drvPath;
         a = v.attrs->find(state.sDrvPath);
diff --git a/third_party/nix/src/nix-env/nix-env.cc b/third_party/nix/src/nix-env/nix-env.cc
index 95a395a96f..93a8e4c1ec 100644
--- a/third_party/nix/src/nix-env/nix-env.cc
+++ b/third_party/nix/src/nix-env/nix-env.cc
@@ -132,7 +132,7 @@ static void getAllExprs(EvalState& state, const Path& path, StringSet& attrs,
         throw Error(format("too many Nix expressions in directory '%1%'") %
                     path);
       }
-      mkApp(*state.allocAttr(v, state.symbols.create(attrName)), vFun, vArg);
+      mkApp(*state.allocAttr(v, state.symbols.Create(attrName)), vFun, vArg);
     } else if (S_ISDIR(st.st_mode)) {
       /* `path2' is a directory (with no default.nix in it);
          recurse into it. */
@@ -159,7 +159,7 @@ static void loadSourceExpr(EvalState& state, const Path& path, Value& v) {
      directory). */
   else if (S_ISDIR(st.st_mode)) {
     state.mkAttrs(v, 1024);
-    state.mkList(*state.allocAttr(v, state.symbols.create("_combineChannels")),
+    state.mkList(*state.allocAttr(v, state.symbols.Create("_combineChannels")),
                  0);
     StringSet attrs;
     getAllExprs(state, path, attrs, v);
diff --git a/third_party/nix/src/nix-env/user-env.cc b/third_party/nix/src/nix-env/user-env.cc
index bf15543c3f..adff263ff4 100644
--- a/third_party/nix/src/nix-env/user-env.cc
+++ b/third_party/nix/src/nix-env/user-env.cc
@@ -73,7 +73,7 @@ bool createUserEnv(EvalState& state, DrvInfos& elems, const Path& profile,
     unsigned int m = 0;
     for (auto& j : outputs) {
       mkString(*(vOutputs.listElems()[m++] = state.allocValue()), j.first);
-      Value& vOutputs = *state.allocAttr(v, state.symbols.create(j.first));
+      Value& vOutputs = *state.allocAttr(v, state.symbols.Create(j.first));
       state.mkAttrs(vOutputs, 2);
       mkString(*state.allocAttr(vOutputs, state.sOutPath), j.second);
 
@@ -94,7 +94,7 @@ bool createUserEnv(EvalState& state, DrvInfos& elems, const Path& profile,
       if (v == nullptr) {
         continue;
       }
-      vMeta.attrs->push_back(Attr(state.symbols.create(j), v));
+      vMeta.attrs->push_back(Attr(state.symbols.Create(j), v));
     }
     vMeta.attrs->sort();
     v.attrs->sort();
@@ -119,9 +119,9 @@ bool createUserEnv(EvalState& state, DrvInfos& elems, const Path& profile,
   Value args;
   Value topLevel;
   state.mkAttrs(args, 3);
-  mkString(*state.allocAttr(args, state.symbols.create("manifest")),
+  mkString(*state.allocAttr(args, state.symbols.Create("manifest")),
            manifestFile, {manifestFile});
-  args.attrs->push_back(Attr(state.symbols.create("derivations"), &manifest));
+  args.attrs->push_back(Attr(state.symbols.Create("derivations"), &manifest));
   args.attrs->sort();
   mkApp(topLevel, envBuilder, args);
 
diff --git a/third_party/nix/src/nix-prefetch-url/nix-prefetch-url.cc b/third_party/nix/src/nix-prefetch-url/nix-prefetch-url.cc
index 5a9b81103d..17341e382d 100644
--- a/third_party/nix/src/nix-prefetch-url/nix-prefetch-url.cc
+++ b/third_party/nix/src/nix-prefetch-url/nix-prefetch-url.cc
@@ -39,7 +39,7 @@ string resolveMirrorUri(EvalState& state, string uri) {
       vMirrors);
   state.forceAttrs(vMirrors);
 
-  auto mirrorList = vMirrors.attrs->find(state.symbols.create(mirrorName));
+  auto mirrorList = vMirrors.attrs->find(state.symbols.Create(mirrorName));
   if (mirrorList == vMirrors.attrs->end()) {
     throw Error(format("unknown mirror name '%1%'") % mirrorName);
   }
@@ -126,7 +126,7 @@ static int _main(int argc, char** argv) {
       state->forceAttrs(v);
 
       /* Extract the URI. */
-      auto attr = v.attrs->find(state->symbols.create("urls"));
+      auto attr = v.attrs->find(state->symbols.Create("urls"));
       if (attr == v.attrs->end()) {
         throw Error("attribute set does not contain a 'urls' attribute");
       }
@@ -137,7 +137,7 @@ static int _main(int argc, char** argv) {
       uri = state->forceString(*attr->value->listElems()[0]);
 
       /* Extract the hash mode. */
-      attr = v.attrs->find(state->symbols.create("outputHashMode"));
+      attr = v.attrs->find(state->symbols.Create("outputHashMode"));
       if (attr == v.attrs->end()) {
         LOG(WARNING) << "this does not look like a fetchurl call";
       } else {
@@ -146,7 +146,7 @@ static int _main(int argc, char** argv) {
 
       /* Extract the name. */
       if (name.empty()) {
-        attr = v.attrs->find(state->symbols.create("name"));
+        attr = v.attrs->find(state->symbols.Create("name"));
         if (attr != v.attrs->end()) {
           name = state->forceString(*attr->value);
         }
diff --git a/third_party/nix/src/nix/installables.cc b/third_party/nix/src/nix/installables.cc
index 8d2f932568..59dfc1b1ac 100644
--- a/third_party/nix/src/nix/installables.cc
+++ b/third_party/nix/src/nix/installables.cc
@@ -27,7 +27,7 @@ Value* SourceExprCommand::getSourceExpr(EvalState& state) {
     return vSourceExpr;
   }
 
-  auto sToplevel = state.symbols.create("_toplevel");
+  auto sToplevel = state.symbols.Create("_toplevel");
 
   vSourceExpr = state.allocValue();
 
@@ -57,7 +57,7 @@ Value* SourceExprCommand::getSourceExpr(EvalState& state) {
                   state.getBuiltin("nixPath"));
       Value* v2 = state.allocValue();
       mkApp(*v2, *v1, mkString(*state.allocValue(), name));
-      mkApp(*state.allocAttr(*vSourceExpr, state.symbols.create(name)),
+      mkApp(*state.allocAttr(*vSourceExpr, state.symbols.Create(name)),
             state.getBuiltin("import"), *v2);
     };
 
diff --git a/third_party/nix/src/nix/repl.cc b/third_party/nix/src/nix/repl.cc
index 78991645ac..e60ef89652 100644
--- a/third_party/nix/src/nix/repl.cc
+++ b/third_party/nix/src/nix/repl.cc
@@ -574,7 +574,7 @@ bool NixRepl::processLine(string line) {
       v.type = tThunk;
       v.thunk.env = env;
       v.thunk.expr = e;
-      addVarToScope(state.symbols.create(name), v);
+      addVarToScope(state.symbols.Create(name), v);
     } else {
       Value v;
       evalString(line, v);
diff --git a/third_party/nix/src/nix/search.cc b/third_party/nix/src/nix/search.cc
index 7fe81adb69..169daf7a32 100644
--- a/third_party/nix/src/nix/search.cc
+++ b/third_party/nix/src/nix/search.cc
@@ -90,8 +90,8 @@ struct CmdSearch : SourceExprCommand, MixJSON {
 
     auto jsonOut = json ? std::make_unique<JSONObject>(std::cout) : nullptr;
 
-    auto sToplevel = state->symbols.create("_toplevel");
-    auto sRecurse = state->symbols.create("recurseForDerivations");
+    auto sToplevel = state->symbols.Create("_toplevel");
+    auto sRecurse = state->symbols.Create("recurseForDerivations");
 
     bool fromCache = false;