Trace the eval.cc functions with Tracy

We're leveraging the ZoneTransientN macro to send dynamic strings
containing the expression type, file and position in that file of the
expression Nix is currently evaluating.

We had to add a new showExprType method to the Expr class to get a
const string containing the name of an expression.

src/libexpr/eval.cc

@@ -55,6 +55,11 @@
 
 #endif
 
+#define TRACY_TRACE(evalstate, expr) \
+    std::ostringstream tracyss; \
+    tracyss << evalstate.positions[(expr)->getPos()] << " " << (expr)->showExprType(); \
+    ZoneTransientN(nix, tracyss.str().c_str(), true);
+
 using json = nlohmann::json;
 
 namespace nix {
@@ -1204,29 +1209,34 @@ void Expr::eval(EvalState & state, Env & env, Value & v)
 
 void ExprInt::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     v = this->v;
 }
 
 
 void ExprFloat::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     v = this->v;
 }
 
 void ExprString::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     v = this->v;
 }
 
 
 void ExprPath::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     v = this->v;
 }
 
 
 void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     v.mkAttrs(state.buildBindings(attrs.size() + dynamicAttrs.size()).finish());
     auto dynamicEnv = &env;
 
@@ -1311,6 +1321,7 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
 
 void ExprLet::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     /* Create a new environment that contains the attributes in this
        `let'. */
     Env & env2(state.allocEnv(attrs->attrs.size()));
@@ -1329,6 +1340,7 @@ void ExprLet::eval(EvalState & state, Env & env, Value & v)
 
 void ExprList::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     state.mkList(v, elems.size());
     for (auto [n, v2] : enumerate(v.listItems()))
         const_cast<Value * &>(v2) = elems[n]->maybeThunk(state, env);
@@ -1337,6 +1349,7 @@ void ExprList::eval(EvalState & state, Env & env, Value & v)
 
 Value * ExprList::maybeThunk(EvalState & state, Env & env)
 {
+    TRACY_TRACE(state, this);
     if (elems.empty()) {
         return &state.vEmptyList;
     }
@@ -1346,6 +1359,7 @@ Value * ExprList::maybeThunk(EvalState & state, Env & env)
 
 void ExprVar::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     Value * v2 = state.lookupVar(&env, *this, false);
     state.forceValue(*v2, pos);
     v = *v2;
@@ -1373,7 +1387,7 @@ static std::string showAttrPath(EvalState & state, Env & env, const AttrPath & a
 
 void ExprSelect::eval(EvalState & state, Env & env, Value & v)
 {
-    ZoneScopedN("select");
+    TRACY_TRACE(state, this)
     Value vTmp;
     PosIdx pos2;
     Value * vAttrs = &vTmp;
@@ -1438,6 +1452,7 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
 
 void ExprOpHasAttr::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this)
     Value vTmp;
     Value * vAttrs = &vTmp;
 
@@ -1463,6 +1478,7 @@ void ExprOpHasAttr::eval(EvalState & state, Env & env, Value & v)
 
 void ExprLambda::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this)
     v.mkLambda(&env, this);
 }
 
@@ -1720,6 +1736,7 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
 
 void ExprCall::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     Value vFun;
     fun->eval(state, env, vFun);
 
@@ -1797,6 +1814,7 @@ https://nixos.org/manual/nix/stable/language/constructs.html#functions.)", symbo
 
 void ExprWith::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     Env & env2(state.allocEnv(1));
     env2.up = &env;
     env2.values[0] = attrs->maybeThunk(state, env);
@@ -1807,6 +1825,7 @@ void ExprWith::eval(EvalState & state, Env & env, Value & v)
 
 void ExprIf::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     // We cheat in the parser, and pass the position of the condition as the position of the if itself.
     (state.evalBool(env, cond, pos, "while evaluating a branch condition") ? then : else_)->eval(state, env, v);
 }
@@ -1814,6 +1833,7 @@ void ExprIf::eval(EvalState & state, Env & env, Value & v)
 
 void ExprAssert::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     if (!state.evalBool(env, cond, pos, "in the condition of the assert statement")) {
         std::ostringstream out;
         cond->show(state.symbols, out);
@@ -1825,12 +1845,14 @@ void ExprAssert::eval(EvalState & state, Env & env, Value & v)
 
 void ExprOpNot::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     v.mkBool(!state.evalBool(env, e, getPos(), "in the argument of the not operator")); // XXX: FIXME: !
 }
 
 
 void ExprOpEq::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     Value v1; e1->eval(state, env, v1);
     Value v2; e2->eval(state, env, v2);
     v.mkBool(state.eqValues(v1, v2, pos, "while testing two values for equality"));
@@ -1839,6 +1861,7 @@ void ExprOpEq::eval(EvalState & state, Env & env, Value & v)
 
 void ExprOpNEq::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     Value v1; e1->eval(state, env, v1);
     Value v2; e2->eval(state, env, v2);
     v.mkBool(!state.eqValues(v1, v2, pos, "while testing two values for inequality"));
@@ -1847,6 +1870,7 @@ void ExprOpNEq::eval(EvalState & state, Env & env, Value & v)
 
 void ExprOpAnd::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     v.mkBool(state.evalBool(env, e1, pos, "in the left operand of the AND (&&) operator") && state.evalBool(env, e2, pos, "in the right operand of the AND (&&) operator"));
 }
 
@@ -1859,12 +1883,14 @@ void ExprOpOr::eval(EvalState & state, Env & env, Value & v)
 
 void ExprOpImpl::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     v.mkBool(!state.evalBool(env, e1, pos, "in the left operand of the IMPL (->) operator") || state.evalBool(env, e2, pos, "in the right operand of the IMPL (->) operator"));
 }
 
 
 void ExprOpUpdate::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     Value v1, v2;
     state.evalAttrs(env, e1, v1, pos, "in the left operand of the update (//) operator");
     state.evalAttrs(env, e2, v2, pos, "in the right operand of the update (//) operator");
@@ -1903,6 +1929,7 @@ void ExprOpUpdate::eval(EvalState & state, Env & env, Value & v)
 
 void ExprOpConcatLists::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     Value v1; e1->eval(state, env, v1);
     Value v2; e2->eval(state, env, v2);
     Value * lists[2] = { &v1, &v2 };
@@ -1941,6 +1968,7 @@ void EvalState::concatLists(Value & v, size_t nrLists, Value * * lists, const Po
 
 void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     NixStringContext context;
     std::vector<BackedStringView> s;
     size_t sSize = 0;
@@ -2033,12 +2061,14 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
 
 void ExprPos::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     state.mkPos(v, pos);
 }
 
 
 void ExprBlackHole::eval(EvalState & state, Env & env, Value & v)
 {
+    TRACY_TRACE(state, this);
     state.error("infinite recursion encountered")
         .debugThrow<InfiniteRecursionError>();
 }

src/libexpr/local.mk

@@ -13,7 +13,7 @@ libexpr_SOURCES := \
   $(d)/parser-tab.cc \
   $(d)/tracy/public/TracyClient.cpp
 
-libexpr_CXXFLAGS += -I src/libutil -I src/libstore -I src/libfetchers -I src/libmain -I src/libexpr -I src/libexpr/tracy/public
+libexpr_CXXFLAGS += -I src/libutil -I src/libstore -I src/libfetchers -I src/libmain -I src/libexpr -I src/libexpr/tracy/public -DTRACY_ENABLE=1
 
 libexpr_LIBS = libutil libstore libfetchers
 
@@ -49,3 +49,4 @@ $(d)/primops.cc: $(d)/imported-drv-to-derivation.nix.gen.hh
 $(d)/eval.cc: $(d)/primops/derivation.nix.gen.hh $(d)/fetchurl.nix.gen.hh $(d)/flake/call-flake.nix.gen.hh
 
 $(buildprefix)src/libexpr/primops/fromTOML.o:	ERROR_SWITCH_ENUM =
+$(buildprefix)src/libexpr/tracy/public/TracyClient.o: ERROR_SWITCH_ENUM =

src/libexpr/nixexpr.hh

@@ -156,6 +156,7 @@ struct Expr
     virtual Value * maybeThunk(EvalState & state, Env & env);
     virtual void setName(Symbol name);
     virtual PosIdx getPos() const { return noPos; }
+    virtual const char* showExprType() const { return "undefined"; }
 };
 
 #define COMMON_METHODS \
@@ -168,6 +169,7 @@ struct ExprInt : Expr
     Value v;
     ExprInt(NixInt n) { v.mkInt(n); };
     Value * maybeThunk(EvalState & state, Env & env) override;
+    const char* showExprType() const { return "int"; }
     COMMON_METHODS
 };
 
@@ -176,6 +178,7 @@ struct ExprFloat : Expr
     Value v;
     ExprFloat(NixFloat nf) { v.mkFloat(nf); };
     Value * maybeThunk(EvalState & state, Env & env) override;
+    const char* showExprType() const { return "float"; }
     COMMON_METHODS
 };
 
@@ -185,6 +188,7 @@ struct ExprString : Expr
     Value v;
     ExprString(std::string &&s) : s(std::move(s)) { v.mkString(this->s.data()); };
     Value * maybeThunk(EvalState & state, Env & env) override;
+    const char* showExprType() const { return "string"; }
     COMMON_METHODS
 };
 
@@ -198,6 +202,7 @@ struct ExprPath : Expr
         v.mkPath(&*accessor, this->s.c_str());
     }
     Value * maybeThunk(EvalState & state, Env & env) override;
+    const char* showExprType() const { return "path"; }
     COMMON_METHODS
 };
 
@@ -229,6 +234,7 @@ struct ExprVar : Expr
     ExprVar(const PosIdx & pos, Symbol name) : pos(pos), name(name) { };
     Value * maybeThunk(EvalState & state, Env & env) override;
     PosIdx getPos() const override { return pos; }
+    const char* showExprType() const { return "var"; }
     COMMON_METHODS
 };
 
@@ -240,6 +246,7 @@ struct ExprSelect : Expr
     ExprSelect(const PosIdx & pos, Expr * e, AttrPath attrPath, Expr * def) : pos(pos), e(e), def(def), attrPath(std::move(attrPath)) { };
     ExprSelect(const PosIdx & pos, Expr * e, Symbol name) : pos(pos), e(e), def(0) { attrPath.push_back(AttrName(name)); };
     PosIdx getPos() const override { return pos; }
+    const char* showExprType() const { return "select"; }
     COMMON_METHODS
 };
 
@@ -249,6 +256,7 @@ struct ExprOpHasAttr : Expr
     AttrPath attrPath;
     ExprOpHasAttr(Expr * e, AttrPath attrPath) : e(e), attrPath(std::move(attrPath)) { };
     PosIdx getPos() const override { return e->getPos(); }
+    const char* showExprType() const { return "op_has_attr"; }
     COMMON_METHODS
 };
 
@@ -278,6 +286,7 @@ struct ExprAttrs : Expr
     ExprAttrs(const PosIdx &pos) : recursive(false), pos(pos) { };
     ExprAttrs() : recursive(false) { };
     PosIdx getPos() const override { return pos; }
+    const char* showExprType() const { return "attrs"; }
     COMMON_METHODS
 };
 
@@ -285,6 +294,7 @@ struct ExprList : Expr
 {
     std::vector<Expr *> elems;
     ExprList() { };
+    const char* showExprType() const { return "list"; }
     COMMON_METHODS
     Value * maybeThunk(EvalState & state, Env & env) override;
 
@@ -345,6 +355,7 @@ struct ExprLambda : Expr
     std::string showNamePos(const EvalState & state) const;
     inline bool hasFormals() const { return formals != nullptr; }
     PosIdx getPos() const override { return pos; }
+    const char* showExprType() const { return "lambda"; }
     COMMON_METHODS
 };
 
@@ -357,6 +368,7 @@ struct ExprCall : Expr
         : fun(fun), args(args), pos(pos)
     { }
     PosIdx getPos() const override { return pos; }
+    const char* showExprType() const { return "call"; }
     COMMON_METHODS
 };
 
@@ -365,6 +377,7 @@ struct ExprLet : Expr
     ExprAttrs * attrs;
     Expr * body;
     ExprLet(ExprAttrs * attrs, Expr * body) : attrs(attrs), body(body) { };
+    const char* showExprType() const { return "let"; }
     COMMON_METHODS
 };
 
@@ -376,6 +389,7 @@ struct ExprWith : Expr
     ExprWith * parentWith;
     ExprWith(const PosIdx & pos, Expr * attrs, Expr * body) : pos(pos), attrs(attrs), body(body) { };
     PosIdx getPos() const override { return pos; }
+    const char* showExprType() const { return "with"; }
     COMMON_METHODS
 };
 
@@ -385,6 +399,7 @@ struct ExprIf : Expr
     Expr * cond, * then, * else_;
     ExprIf(const PosIdx & pos, Expr * cond, Expr * then, Expr * else_) : pos(pos), cond(cond), then(then), else_(else_) { };
     PosIdx getPos() const override { return pos; }
+    const char* showExprType() const { return "if"; }
     COMMON_METHODS
 };
 
@@ -394,6 +409,7 @@ struct ExprAssert : Expr
     Expr * cond, * body;
     ExprAssert(const PosIdx & pos, Expr * cond, Expr * body) : pos(pos), cond(cond), body(body) { };
     PosIdx getPos() const override { return pos; }
+    const char* showExprType() const { return "assert"; }
     COMMON_METHODS
 };
 
@@ -422,6 +438,7 @@ struct ExprOpNot : Expr
         } \
         void eval(EvalState & state, Env & env, Value & v) override; \
         PosIdx getPos() const override { return pos; } \
+        const char* showExprType() const { return #name; } \
     };
 
 MakeBinOp(ExprOpEq, "==")
@@ -440,6 +457,7 @@ struct ExprConcatStrings : Expr
     ExprConcatStrings(const PosIdx & pos, bool forceString, std::vector<std::pair<PosIdx, Expr *>> * es)
         : pos(pos), forceString(forceString), es(es) { };
     PosIdx getPos() const override { return pos; }
+    const char* showExprType() const { return "concat_strings"; }
     COMMON_METHODS
 };
 
@@ -448,6 +466,7 @@ struct ExprPos : Expr
     PosIdx pos;
     ExprPos(const PosIdx & pos) : pos(pos) { };
     PosIdx getPos() const override { return pos; }
+    const char* showExprType() const { return "pos"; }
     COMMON_METHODS
 };
 
@@ -457,6 +476,7 @@ struct ExprBlackHole : Expr
     void show(const SymbolTable & symbols, std::ostream & str) const override {}
     void eval(EvalState & state, Env & env, Value & v) override;
     void bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env) override {}
+    const char* showExprType() const { return "blackhole"; }
 };
 
 extern ExprBlackHole eBlackHole;